/**
 * Main replication orchestrator.
 * Publishes manifest records, syncs remote repos to IPFS.
 * Optionally driven by a PolicyEngine for per-DID intervals, priority, and filtering.
 */

import type Database from "better-sqlite3";
import type { Config } from "../config.js";
import type { RepoManager } from "../repo-manager.js";
import { extractBlobCids } from "../repo-manager.js";
import { create as createCid, CODEC_RAW, toString as cidToString } from "@atcute/cid";
import type { BlockStore, NetworkService, CommitNotification, IdentityNotification } from "../ipfs.js";
import type { DidResolver } from "../did-resolver.js";
import { readCarWithRoot } from "@atproto/repo";
import { decode as cborDecode } from "../cbor-compat.js";
import type { ReplicatedRepoReader } from "./replicated-repo-reader.js";
import type { PolicyEngine } from "../policy/engine.js";

import {
	MANIFEST_NSID,
	didToRkey,
	type ManifestRecord,
	type SyncState,
	type SyncTrigger,
	type VerificationConfig,
	type LayeredVerificationResult,
	DEFAULT_VERIFICATION_CONFIG,
} from "./types.js";
import { SyncStorage } from "./sync-storage.js";
import { RepoFetcher } from "./repo-fetcher.js";
import { PeerDiscovery } from "./peer-discovery.js";
import { BlockVerifier, RemoteVerifier } from "./verification.js";
import { extractAllRecordPaths, extractAllCids } from "./mst-proof.js";
import {
	FirehoseSubscription,
	type FirehoseCommitEvent,
	type FirehoseAccountEvent,
} from "./firehose-subscription.js";
import { ChallengeScheduler } from "./challenge-response/challenge-scheduler.js";
import { ChallengeStorage, type ChallengeHistoryRow, type PeerReliabilityRow } from "./challenge-response/challenge-storage.js";
import type { ChallengeTransport } from "./challenge-response/transport.js";
import { OfferManager, type RecordWriter } from "./offer-manager.js";
import { fetchRepoFromPeer } from "./libp2p-sync.js";
import type { Libp2p } from "@libp2p/interface";

/** Progress event emitted during sync operations for live UI updates. */
export interface SyncProgressEvent {
	type: string;
	did: string;
	sourceType?: string;
	carBytes?: number;
	blocksStored?: number;
	blocksSizeKb?: number;
	blobsFetched?: number;
	blobsTotal?: number;
	blobBytes?: number;
	durationMs?: number;
	error?: string;
	missingBlocks?: number;
}

/** Extract unique NSIDs from record paths (collection/rkey format). */
function extractNsids(paths: string[]): string[] {
	const nsids = new Set<string>();
	for (const p of paths) {
		const slash = p.indexOf("/");
		if (slash > 0) nsids.add(p.slice(0, slash));
	}
	return [...nsids];
}

/** How old cached peer info can be before re-fetching (1 hour). */
const PEER_INFO_TTL_MS = 60 * 60 * 1000;

/** Default sync interval when no policy engine is present (5 minutes). */
const DEFAULT_SYNC_INTERVAL_MS = 5 * 60 * 1000;

/** Minimum tick interval to prevent excessive polling (10 seconds). */
const MIN_TICK_INTERVAL_MS = 10 * 1000;

export class ReplicationManager {
	private syncStorage: SyncStorage;
	private repoFetcher: RepoFetcher;
	private peerDiscovery: PeerDiscovery;
	private verifier: BlockVerifier;
	private remoteVerifier: RemoteVerifier;
	private syncTimer: ReturnType<typeof setInterval> | null = null;
	private verificationTimer: ReturnType<typeof setInterval> | null = null;
	private verificationConfig: VerificationConfig;
	private lastVerificationResults: Map<string, LayeredVerificationResult> =
		new Map();
	private firehoseSubscription: FirehoseSubscription | null = null;
	private firehoseCursorSaveTimer: ReturnType<typeof setInterval> | null = null;
	private challengeStorage: ChallengeStorage;
	private challengeScheduler: ChallengeScheduler | null = null;
	private stopped = false;
	private policyEngine: PolicyEngine | null = null;
	private offerManager: OfferManager | null = null;
	/** Per-DID last-sync timestamps (epoch ms) for policy-driven interval tracking. */
	private lastSyncTimestamps: Map<string, number> = new Map();
	/** Dedup set for gossipsub notifications, keyed by `${did}:${rev}`. */
	private recentNotifications: Set<string> = new Set();
	private notificationCleanupTimer: ReturnType<typeof setInterval> | null = null;
	/** libp2p node for peer-first repo sync. Set via setLibp2p(). */
	private libp2p: Libp2p | null = null;
	/** Cached multiaddrs from last peer record publish, for change detection. */
	private lastPublishedAddrs: Set<string> = new Set();
	/** Callback to republish peer record when multiaddrs change. */
	private publishPeerRecordFn?: () => Promise<void>;
	/** Sync progress event subscribers for live UI updates via SSE. */
	private progressCallbacks: Set<(event: SyncProgressEvent) => void> = new Set();
	/** Timer for periodic PLC mirror refresh (6 hours). */
	private plcRefreshTimer: ReturnType<typeof setInterval> | null = null;

	constructor(
		private db: Database.Database,
		private config: Config,
		private repoManager: RepoManager | undefined,
		private blockStore: BlockStore,
		private networkService: NetworkService,
		private didResolver: DidResolver,
		verificationConfig?: Partial<VerificationConfig>,
		private replicatedRepoReader?: ReplicatedRepoReader,
		policyEngine?: PolicyEngine,
		pdsClient?: RecordWriter,
	) {
		this.syncStorage = new SyncStorage(db);
		this.syncStorage.initSchema();
		this.challengeStorage = new ChallengeStorage(db);
		this.challengeStorage.initSchema();
		this.repoFetcher = new RepoFetcher(didResolver);
		this.peerDiscovery = new PeerDiscovery(this.repoFetcher);
		this.verifier = new BlockVerifier(blockStore);
		this.verificationConfig = {
			...DEFAULT_VERIFICATION_CONFIG,
			...verificationConfig,
		};
		this.remoteVerifier = new RemoteVerifier(
			blockStore,
			this.verificationConfig,
		);
		if (policyEngine) {
			this.policyEngine = policyEngine;
			// Prefer remote PDS client for offer records; fall back to local repo
			const recordWriter: RecordWriter | undefined = pdsClient ?? repoManager;
			if (recordWriter) {
				this.offerManager = new OfferManager(
					recordWriter,
					this.peerDiscovery,
					policyEngine,
					config.DID ?? "",
				);
			}
		}
	}

	/**
	 * Get the PolicyEngine, if one is configured.
	 */
	getPolicyEngine(): PolicyEngine | null {
		return this.policyEngine;
	}

	/**
	 * Get the OfferManager, if one is configured (requires PolicyEngine).
	 */
	getOfferManager(): OfferManager | null {
		return this.offerManager;
	}

	/**
	 * Late-bind a PdsClient (or any RecordWriter) after construction.
	 * Called when OAuth login completes after the server has already started.
	 * Creates the OfferManager if a PolicyEngine is present but OfferManager
	 * wasn't created at construction time (because no RecordWriter was available).
	 */
	setPdsClient(client: RecordWriter, did: string): void {
		if (this.policyEngine && !this.offerManager) {
			this.offerManager = new OfferManager(
				client,
				this.peerDiscovery,
				this.policyEngine,
				did,
			);
		}
	}

	/**
	 * Set the libp2p node for peer-first repo sync.
	 * Called from start.ts after IPFS is started.
	 */
	setLibp2p(libp2p: Libp2p): void {
		this.libp2p = libp2p;
	}

	/**
	 * Set a callback to republish the peer record when multiaddrs change.
	 * Called from start.ts after IPFS and replication are ready.
	 */
	setPublishPeerRecordFn(fn: () => Promise<void>): void {
		this.publishPeerRecordFn = fn;
		// Seed the cache with current addrs so the first check doesn't spuriously trigger
		this.lastPublishedAddrs = new Set(this.networkService.getMultiaddrs());
	}

	/** Subscribe to sync progress events (for SSE streaming). */
	onSyncProgress(cb: (event: SyncProgressEvent) => void): void {
		this.progressCallbacks.add(cb);
	}

	/** Unsubscribe from sync progress events. */
	offSyncProgress(cb: (event: SyncProgressEvent) => void): void {
		this.progressCallbacks.delete(cb);
	}

	/** Emit a progress event to all subscribers. */
	private emitProgress(event: SyncProgressEvent): void {
		for (const cb of this.progressCallbacks) {
			try { cb(event); } catch { /* non-fatal */ }
		}
	}

	/**
	 * Check if multiaddrs have changed since last peer record publish.
	 * If changed, republish the peer record and update the cache.
	 */
	private async _checkMultiaddrsChanged(): Promise<void> {
		if (!this.publishPeerRecordFn) return;

		const current = new Set(this.networkService.getMultiaddrs());
		if (current.size === 0) return;

		// Compare sets
		if (
			current.size === this.lastPublishedAddrs.size &&
			[...current].every((a) => this.lastPublishedAddrs.has(a))
		) {
			return;
		}

		this.lastPublishedAddrs = current;
		try {
			await this.publishPeerRecordFn();
			console.log("[replication] Multiaddrs changed, republished peer record");
		} catch (err) {
			console.warn(
				"[replication] Failed to republish peer record:",
				err instanceof Error ? err.message : String(err),
			);
		}
	}

	/**
	 * Initialize replication: create tables, sync manifests.
	 */
	async init(): Promise<void> {
		this.syncStorage.initSchema();
		this.challengeStorage.initSchema();
		await this.syncManifests();
		await this.discoverPeerEndpoints();
		await this.runOfferDiscovery();
		this.setupGossipsubSubscription();
	}

	/**
	 * Get the list of DIDs to replicate.
	 *
	 * When a PolicyEngine is present, uses getActiveDids() as the single source of truth.
	 * Falls back to legacy three-source merge when no PolicyEngine is configured.
	 */
	getReplicateDids(): string[] {
		if (this.policyEngine) {
			return this.policyEngine.getActiveDids();
		}

		// Legacy fallback: merge config + admin DIDs (no policy engine)
		const allDids = new Set(this.config.REPLICATE_DIDS);
		for (const did of this.syncStorage.getAdminDids()) {
			allDids.add(did);
		}
		return [...allDids];
	}

	/**
	 * Determine the source of a tracked DID by looking up its policy.
	 */
	getDidSource(did: string): "config" | "user" | "policy" | null {
		if (this.policyEngine) {
			const configPolicy = this.policyEngine.getStoredPolicy(`config:${did}`);
			if (configPolicy) return "config";
			const archivePolicy = this.policyEngine.getStoredPolicy(`archive:${did}`);
			if (archivePolicy) return "user";
			const p2pPolicy = this.policyEngine.getStoredPolicy(`p2p:${did}`);
			if (p2pPolicy) return "policy";
			// Check if any other policy covers this DID
			if (this.policyEngine.shouldReplicate(did)) return "policy";
		}
		// Legacy fallback
		if (this.config.REPLICATE_DIDS.includes(did)) return "config";
		if (this.syncStorage.isAdminDid(did)) return "user";
		return null;
	}

	/**
	 * Add a DID via the admin interface.
	 * Creates an archive policy (+ dual-write to admin_tracked_dids for rollback safety),
	 * creates manifest + sync state, subscribes gossipsub, updates firehose.
	 * Returns the status and source if already tracked.
	 */
	async addDid(did: string): Promise<{ status: "added" | "already_tracked"; source?: string }> {
		const existingSource = this.getDidSource(did);
		if (existingSource) {
			return { status: "already_tracked", source: existingSource };
		}

		// Check if already tracked via getReplicateDids (covers pattern/all policies)
		if (this.getReplicateDids().includes(did)) {
			return { status: "already_tracked", source: "policy" };
		}

		// Create archive policy in PolicyEngine (auto-persists to DB)
		if (this.policyEngine) {
			const policyId = `archive:${did}`;
			if (!this.policyEngine.getPolicies().some((p) => p.id === policyId)) {
				const { archive } = await import("../policy/presets.js");
				this.policyEngine.addPolicy(archive(did));
			}
		}

		// Dual-write to admin_tracked_dids for rollback safety
		this.syncStorage.addAdminDid(did);

		await this.syncManifestForDid(did);
		this.networkService.subscribeCommitTopics([did]);
		this.networkService.subscribeIdentityTopics([did]);
		this.updateFirehoseDids();

		// Trigger initial sync in background (fire-and-forget)
		this.syncDid(did, "manual").catch((err) => {
			console.error(`[replication] Initial sync for admin-added ${did} failed:`, err);
		});

		// Fetch PLC log in background (fire-and-forget)
		if (did.startsWith("did:plc:")) {
			this.fetchPlcLog(did).catch((err) => {
				console.warn(`[replication] PLC log fetch for ${did} failed:`, err instanceof Error ? err.message : String(err));
			});
		}

		return { status: "added" };
	}

	/**
	 * Offer to replicate a DID (consent-gated).
	 * Publishes an offer record and stores in offered_dids, but does NOT sync.
	 * Replication begins only when mutual consent is detected during offer discovery.
	 */
	async offerDid(did: string): Promise<{ status: "offered" | "already_tracked" | "already_offered"; source?: string }> {
		// Already fully tracked?
		const existingSource = this.getDidSource(did);
		if (existingSource) {
			return { status: "already_tracked", source: existingSource };
		}

		// Already offered?
		if (this.syncStorage.isOfferedDid(did)) {
			return { status: "already_offered" };
		}

		// Require active session to publish offer record
		if (!this.offerManager) {
			throw new Error("No active session — log in first to publish offers");
		}

		// Resolve PDS endpoint
		const pdsEndpoint = await this.repoFetcher.resolvePds(did);

		// Publish offer record to user's PDS
		await this.offerManager.publishOffer(did);

		// Store in offered_dids (does NOT create replication_state or trigger sync)
		this.syncStorage.addOfferedDid(did, pdsEndpoint ?? null);

		// Push notification: tell the target node about this offer (fire-and-forget)
		// Small delay to ensure PDS has committed the record before the peer verifies it
		setTimeout(() => {
			this.pushOfferNotification(did).catch((err) => {
				console.warn(
					`[replication] Failed to push offer notification to ${did}:`,
					err instanceof Error ? err.message : String(err),
				);
			});
		}, 2000);

		return { status: "offered" };
	}

	/**
	 * Remove an offered DID: revoke the offer, notify the peer, and remove from offered_dids.
	 */
	async removeOfferedDid(did: string): Promise<{ status: "removed" | "not_found" }> {
		if (!this.syncStorage.isOfferedDid(did)) {
			return { status: "not_found" };
		}

		// Revoke offer record if OfferManager is available
		if (this.offerManager) {
			await this.offerManager.revokeOffer(did);
		}

		this.syncStorage.removeOfferedDid(did);

		// Notify peer that the offer was revoked (fire-and-forget)
		this.pushRevokeNotification(did).catch((err) => {
			console.warn(`[replication] Failed to push revoke notification to ${did}:`, err instanceof Error ? err.message : String(err));
		});

		return { status: "removed" };
	}

	/**
	 * Revoke consent and remove a DID that was promoted to active replication via mutual offer.
	 * Revokes the offer record, purges all data, and notifies the peer.
	 */
	async revokeReplication(did: string): Promise<{ status: "revoked" | "not_found" | "error"; error?: string }> {
		// Must be an actively tracked DID
		const source = this.getDidSource(did);
		const hasState = this.syncStorage.getAllStates().some((s) => s.did === did);
		if (!source && !hasState) {
			return { status: "not_found" };
		}

		// Revoke offer record on PDS
		if (this.offerManager) {
			try {
				await this.offerManager.revokeOffer(did);
			} catch {
				// Non-fatal: offer record may not exist
			}
		}

		// Transition P2P policy to terminated
		if (this.policyEngine) {
			const policyId = `p2p:${did}`;
			this.policyEngine.transitionPolicy(policyId, "terminated");
		}

		// Remove from offered_dids if present
		if (this.syncStorage.isOfferedDid(did)) {
			this.syncStorage.removeOfferedDid(did);
		}

		// Notify peer BEFORE purging (purge clears peer endpoints needed for notification)
		try {
			await this.pushRevokeNotification(did);
		} catch (err) {
			console.warn(`[replication] Failed to push revoke notification to ${did}:`, err instanceof Error ? err.message : String(err));
		}

		// Remove from replication with full data purge
		const result = await this.removeDid(did, true);
		if (result.status === "error") {
			return { status: "error", error: result.error };
		}

		return { status: "revoked" };
	}

	/**
	 * Handle a revocation from a remote peer: stop replicating their DID and purge data.
	 */
	async handleRemoteRevocation(revokerDid: string): Promise<void> {
		// Remove from incoming offers if present
		const incomingOffers = this.syncStorage.getIncomingOffers();
		for (const offer of incomingOffers) {
			if (offer.offererDid === revokerDid) {
				this.syncStorage.removeIncomingOffer(revokerDid, offer.subjectDid);
			}
		}

		// Remove from offered_dids if present
		if (this.syncStorage.isOfferedDid(revokerDid)) {
			if (this.offerManager) {
				try { await this.offerManager.revokeOffer(revokerDid); } catch { /* non-fatal */ }
			}
			this.syncStorage.removeOfferedDid(revokerDid);
		}

		// Transition P2P policy to terminated
		if (this.policyEngine) {
			const policyId = `p2p:${revokerDid}`;
			if (this.policyEngine.transitionPolicy(policyId, "terminated")) {
				console.log(`[replication] Terminated P2P policy ${policyId}`);
			}
		}

		// Remove from active replication with data purge
		const isTracked = this.getDidSource(revokerDid) !== null
			|| this.syncStorage.getAllStates().some((s) => s.did === revokerDid);
		if (isTracked) {
			console.log(`[replication] Remote revocation from ${revokerDid} — removing DID and purging data`);
			await this.removeDid(revokerDid, true);
		}
	}

	/**
	 * Push an offer notification to the target node's p2pds endpoint.
	 * Resolves the target's org.p2pds.peer record to find their endpoint URL,
	 * then POSTs to their notifyOffer XRPC method.
	 */
	private async pushOfferNotification(targetDid: string): Promise<void> {
		const peerInfo = await this.peerDiscovery.discoverPeer(targetDid);
		if (!peerInfo?.endpoint) {
			console.log(`[replication] No p2pds endpoint found for ${targetDid}, skipping push notification`);
			return;
		}

		const url = `${peerInfo.endpoint}/xrpc/org.p2pds.replication.notifyOffer`;
		const body = {
			offererDid: this.config.DID,
			subjectDid: targetDid,
			offererPdsEndpoint: await this.repoFetcher.resolvePds(this.config.DID ?? ""),
			params: {
				minCopies: 2,
				intervalSec: 600,
				priority: 50,
			},
		};

		const res = await fetch(url, {
			method: "POST",
			headers: { "Content-Type": "application/json" },
			body: JSON.stringify(body),
		});

		if (!res.ok) {
			const text = await res.text().catch(() => "");
			console.warn(`[replication] Push notification to ${targetDid} failed (${res.status}): ${text}`);
		} else {
			console.log(`[replication] Push notification sent to ${targetDid} at ${peerInfo.endpoint}`);
		}
	}

	/**
	 * Push a revocation notification to the target node's p2pds endpoint.
	 */
	private async pushRevokeNotification(targetDid: string): Promise<void> {
		const peerInfo = await this.peerDiscovery.discoverPeer(targetDid);
		if (!peerInfo?.endpoint) {
			console.log(`[replication] No p2pds endpoint found for ${targetDid}, skipping revoke notification`);
			return;
		}

		const url = `${peerInfo.endpoint}/xrpc/org.p2pds.replication.notifyRevoke`;
		const body = {
			revokerDid: this.config.DID,
			subjectDid: targetDid,
		};

		const res = await fetch(url, {
			method: "POST",
			headers: { "Content-Type": "application/json" },
			body: JSON.stringify(body),
		});

		if (!res.ok) {
			const text = await res.text().catch(() => "");
			console.warn(`[replication] Revoke notification to ${targetDid} failed (${res.status}): ${text}`);
		} else {
			console.log(`[replication] Revoke notification sent to ${targetDid} at ${peerInfo.endpoint}`);
		}
	}

	/**
	 * Accept an incoming offer: create a reciprocal offer and remove from incoming_offers.
	 */
	async acceptOffer(offererDid: string): Promise<{ status: "accepted" | "not_found" | "error"; error?: string }> {
		// Find the incoming offer to get the subject DID
		const offers = this.syncStorage.getIncomingOffers();
		const offer = offers.find((o) => o.offererDid === offererDid);
		if (!offer) {
			return { status: "not_found" };
		}

		// Create reciprocal offer (which also push-notifies back)
		try {
			await this.offerDid(offererDid);
		} catch (err) {
			return {
				status: "error",
				error: `Failed to create reciprocal offer: ${err instanceof Error ? err.message : String(err)}`,
			};
		}

		// Remove from incoming_offers
		this.syncStorage.removeIncomingOffer(offererDid, offer.subjectDid);

		// Run offer discovery immediately to detect mutual agreement and start replication
		this.triggerOfferDiscovery();

		return { status: "accepted" };
	}

	/**
	 * Reject an incoming offer: remove from incoming_offers without creating a reciprocal offer.
	 */
	rejectOffer(offererDid: string): { status: "rejected" | "not_found" } {
		const offers = this.syncStorage.getIncomingOffers();
		const offer = offers.find((o) => o.offererDid === offererDid);
		if (!offer) {
			return { status: "not_found" };
		}

		this.syncStorage.removeIncomingOffer(offererDid, offer.subjectDid);
		return { status: "rejected" };
	}

	/**
	 * Trigger offer discovery asynchronously (fire-and-forget).
	 * Used after accepting an offer or receiving a push notification
	 * to immediately detect mutual agreements.
	 */
	triggerOfferDiscovery(): void {
		this.runOfferDiscovery().catch((err) => {
			console.warn("[replication] Triggered offer discovery failed:", err instanceof Error ? err.message : String(err));
		});
	}

	/**
	 * Get all incoming offers (from other nodes wanting to replicate our data).
	 */
	getIncomingOffers(): Array<{
		offererDid: string;
		subjectDid: string;
		offererPdsEndpoint: string | null;
		offererEndpoint: string | null;
		minCopies: number;
		intervalSec: number;
		priority: number;
		receivedAt: string;
	}> {
		return this.syncStorage.getIncomingOffers();
	}

	/**
	 * Get the PeerDiscovery instance (for verifying incoming offers).
	 */
	getPeerDiscovery(): PeerDiscovery {
		return this.peerDiscovery;
	}

	/**
	 * Get the RepoFetcher instance (for resolving PDS endpoints).
	 */
	getRepoFetcher(): RepoFetcher {
		return this.repoFetcher;
	}

	/**
	 * Remove an admin-added DID.
	 * Returns error info if the DID cannot be removed (config/policy origin).
	 * If purgeData is true, deletes all associated data. Otherwise pauses.
	 */
	async removeDid(did: string, purgeData: boolean = false): Promise<{
		status: "removed" | "error";
		purged: boolean;
		error?: string;
	}> {
		// Check if it's a config-origin DID (not removable via UI)
		const configPolicyId = `config:${did}`;
		if (this.policyEngine?.getStoredPolicy(configPolicyId) || this.config.REPLICATE_DIDS.includes(did)) {
			return { status: "error", purged: false, error: "Cannot remove config-origin DID. Remove from REPLICATE_DIDS env var." };
		}

		// Transition archive/p2p policies to purged state
		if (this.policyEngine) {
			const archivePolicyId = `archive:${did}`;
			this.policyEngine.transitionPolicy(archivePolicyId, "purged");
			const p2pPolicyId = `p2p:${did}`;
			this.policyEngine.transitionPolicy(p2pPolicyId, "purged");
		}

		// Dual-write: also remove from legacy table
		this.syncStorage.removeAdminDid(did);
		this.networkService.unsubscribeCommitTopics([did]);
		this.networkService.unsubscribeIdentityTopics([did]);
		this.updateFirehoseDids();

		if (purgeData) {
			this.syncStorage.clearBlocks(did);
			this.syncStorage.clearBlobs(did);
			this.syncStorage.clearRecordPaths(did);
			this.syncStorage.clearPeerEndpoints(did);
			this.syncStorage.deleteState(did);

			// Remove manifest record
			if (this.repoManager) {
				const rkey = didToRkey(did);
				try {
					await this.repoManager.deleteRecord(MANIFEST_NSID, rkey);
				} catch {
					// Non-fatal: manifest may not exist
				}
			}
		} else {
			// Pause: update manifest status but keep data
			if (this.repoManager) {
				const rkey = didToRkey(did);
				const existing = await this.repoManager.getRecord(MANIFEST_NSID, rkey);
				if (existing) {
					const manifest: ManifestRecord = {
						...(existing.record as ManifestRecord),
						status: "paused",
					};
					await this.repoManager.putRecord(MANIFEST_NSID, rkey, manifest);
				}
			}
		}

		return { status: "removed", purged: purgeData };
	}

	/**
	 * Update firehose subscription with the current set of tracked DIDs.
	 */
	private updateFirehoseDids(): void {
		if (this.firehoseSubscription) {
			this.firehoseSubscription.updateDids(new Set(this.getReplicateDids()));
		}
	}

	/**
	 * Ensure a manifest record and sync state exist for a single DID.
	 * Extracted from syncManifests() for use by addDid().
	 */
	private async syncManifestForDid(did: string): Promise<void> {
		if (this.repoManager) {
			const rkey = didToRkey(did);
			const existing = await this.repoManager.getRecord(MANIFEST_NSID, rkey);

			if (!existing) {
				const manifest: ManifestRecord = {
					$type: MANIFEST_NSID,
					subject: did,
					status: "active",
					lastSyncRev: null,
					lastSyncAt: null,
					createdAt: new Date().toISOString(),
				};
				await this.repoManager.putRecord(MANIFEST_NSID, rkey, manifest);
			}
		}

		const pdsEndpoint = await this.repoFetcher.resolvePds(did);
		if (pdsEndpoint) {
			this.syncStorage.upsertState({ did, pdsEndpoint });
		}
	}

	/**
	 * Ensure a manifest record exists for each configured DID.
	 * Creates new manifests or updates existing ones.
	 */
	async syncManifests(): Promise<void> {
		for (const did of this.getReplicateDids()) {
			await this.syncManifestForDid(did);
		}
	}

	/**
	 * Run offer discovery: gather peers from sync state AND offered_dids,
	 * then discover mutual agreements.
	 * When a mutual agreement is detected for an offered DID,
	 * promotes it to full replication via addDid() and removes from offered_dids.
	 * Non-fatal: errors are logged but don't block sync.
	 */
	private async runOfferDiscovery(): Promise<void> {
		if (!this.offerManager) return;

		try {
			// Existing: peers from replication_state
			const states = this.syncStorage.getAllStates();
			const syncPeers = states
				.filter((s) => s.pdsEndpoint)
				.map((s) => ({ did: s.did, pdsEndpoint: s.pdsEndpoint }));

			// New: peers from offered_dids
			const offeredDids = this.syncStorage.getOfferedDids();
			const offeredPeers = offeredDids
				.filter((o) => o.pdsEndpoint)
				.map((o) => ({ did: o.did, pdsEndpoint: o.pdsEndpoint! }));

			// Merge and deduplicate by DID
			const seenDids = new Set<string>();
			const allPeers: Array<{ did: string; pdsEndpoint: string }> = [];
			for (const peer of [...syncPeers, ...offeredPeers]) {
				if (!seenDids.has(peer.did)) {
					seenDids.add(peer.did);
					allPeers.push(peer);
				}
			}

			if (allPeers.length > 0) {
				const agreements = await this.offerManager.discoverAgreements(allPeers);

				// Check if any offered DIDs now have mutual agreements
				for (const offered of offeredDids) {
					const hasAgreement = agreements.some(
						(a) => a.localOffer.subject === offered.did || a.remoteOffer.subject === offered.did,
					);
					if (hasAgreement) {
						console.log(`[replication] Mutual agreement detected for offered DID ${offered.did} — promoting to replication`);
						try {
							await this.addDid(offered.did);
							this.syncStorage.removeOfferedDid(offered.did);
						} catch (err) {
							console.error(
								`[replication] Failed to promote offered DID ${offered.did}:`,
								err instanceof Error ? err.message : String(err),
							);
						}
					}
				}

				// Detect broken agreements: P2P-origin DIDs whose remote offer was revoked
				const activePeerDids = new Set(agreements.map((a) => a.counterpartyDid));
				for (const state of states) {
					// Only check P2P-origin DIDs (those that were promoted from offers)
					const policyId = `p2p:${state.did}`;
					const hasP2pPolicy = this.policyEngine?.getPolicies().some((p) => p.id === policyId);
					if (hasP2pPolicy && !activePeerDids.has(state.did)) {
						console.log(`[replication] Agreement broken for ${state.did} (remote offer revoked) — removing and purging data`);
						try {
							await this.removeDid(state.did, true);
						} catch (err) {
							console.error(`[replication] Failed to remove broken-agreement DID ${state.did}:`, err instanceof Error ? err.message : String(err));
						}
					}
				}

				// Still run full discoverAndSync for sync-state peers
				await this.offerManager.discoverAndSync(syncPeers);
			}
		} catch (err) {
			console.error(
				"[replication] Offer discovery error:",
				err instanceof Error ? err.message : String(err),
			);
		}
	}

	/**
	 * Discover peer endpoints by scanning manifests of known peers.
	 * For each peer whose manifest includes a DID we're tracking, record
	 * that peer as a potential fallback source for that DID.
	 */
	private async discoverPeerEndpoints(): Promise<void> {
		const trackedDids = new Set(this.getReplicateDids());
		const states = this.syncStorage.getAllStates();

		for (const state of states) {
			if (!state.pdsEndpoint) continue;

			try {
				const manifests = await this.peerDiscovery.discoverManifests(
					state.did,
					state.pdsEndpoint,
				);

				for (const manifest of manifests) {
					if (
						manifest.subject &&
						trackedDids.has(manifest.subject) &&
						manifest.status === "active"
					) {
						this.syncStorage.upsertPeerEndpoint(
							manifest.subject,
							state.did,
							state.pdsEndpoint,
							manifest.lastSyncRev ?? null,
						);
					}
				}
			} catch {
				// Non-fatal: peer endpoint discovery is best-effort
			}
		}
	}

	/**
	 * Fetch a repo from known peer endpoints when the source PDS is unavailable.
	 * Tries peers in order of freshest data (highest lastSyncRev).
	 * Throws the original error if no peers succeed.
	 */
	private async fetchFromPeersOrThrow(
		did: string,
		since: string | undefined,
		originalError: Error,
	): Promise<Uint8Array> {
		const peers = this.syncStorage.getPeerEndpoints(did);
		if (peers.length === 0) throw originalError;

		// Sort by lastSyncRev descending (prefer freshest data)
		peers.sort((a, b) => {
			if (!a.lastSyncRev && !b.lastSyncRev) return 0;
			if (!a.lastSyncRev) return 1;
			if (!b.lastSyncRev) return -1;
			return b.lastSyncRev.localeCompare(a.lastSyncRev);
		});

		for (const peer of peers) {
			try {
				return await this.repoFetcher.fetchRepo(
					peer.pdsEndpoint,
					did,
					since,
				);
			} catch {
				// Try next peer
			}
		}

		throw originalError;
	}

	/**
	 * Sync all configured DIDs.
	 *
	 * When a PolicyEngine is present:
	 * - Merges config DIDs with policy explicit DIDs
	 * - Filters out DIDs where shouldReplicate is false
	 * - Sorts by priority (highest first)
	 * - Respects per-DID sync intervals (skips DIDs not yet due)
	 */
	async syncAll(): Promise<void> {
		const dids = this.getReplicateDids();

		// Sort by priority (highest first) when policy engine is present
		const sortedDids = this.policyEngine
			? this.sortDidsByPriority(dids)
			: dids;

		this.emitProgress({ type: "sync-cycle:start", did: "*" });

		for (const did of sortedDids) {
			if (this.stopped) break;

			// Skip tombstoned DIDs (handled separately by cleanupTombstonedDids)
			const currentState = this.syncStorage.getState(did);
			if (currentState?.status === "tombstoned") continue;

			// Check per-DID interval when policy engine is present
			if (this.policyEngine && !this.isDidDueForSync(did)) {
				continue;
			}

			try {
				await this.syncDid(did, "periodic");
				// Record successful sync timestamp
				this.lastSyncTimestamps.set(did, Date.now());
			} catch (err) {
				const message =
					err instanceof Error ? err.message : String(err);
				this.syncStorage.updateStatus(did, "error", message);
			}
		}

		// Run deferred GC for DIDs flagged by firehose delete/update ops
		await this.runDeferredGc();

		// Clean up tombstoned DIDs after grace period
		await this.cleanupTombstonedDids();

		// Discover peer endpoints for P2P fallback
		await this.discoverPeerEndpoints();

		// Re-run offer discovery to pick up new/revoked offers
		await this.runOfferDiscovery();

		// Check if multiaddrs changed and republish peer record if needed
		await this._checkMultiaddrsChanged();

		this.emitProgress({ type: "sync-cycle:complete", did: "*" });
	}

	/**
	 * Sort DIDs by their effective policy priority (highest first).
	 * DIDs without a matching policy get priority 0.
	 */
	private sortDidsByPriority(dids: string[]): string[] {
		if (!this.policyEngine) return dids;
		return [...dids].sort((a, b) => {
			const pa = this.policyEngine!.evaluate(a).priority;
			const pb = this.policyEngine!.evaluate(b).priority;
			return pb - pa;
		});
	}

	/**
	 * Check whether a DID is due for sync based on its policy interval.
	 * DIDs that have never been synced are always due.
	 */
	private isDidDueForSync(did: string): boolean {
		if (!this.policyEngine) return true;

		const lastSync = this.lastSyncTimestamps.get(did);
		if (lastSync === undefined) return true; // never synced

		const config = this.policyEngine.getReplicationConfig(did);
		// Config DIDs without a matching policy use the default interval
		const intervalMs = config
			? config.sync.intervalSec * 1000
			: DEFAULT_SYNC_INTERVAL_MS;

		return Date.now() - lastSync >= intervalMs;
	}

	/**
	 * Get the effective sync interval for a DID in milliseconds.
	 * Returns the policy-driven interval if a policy engine is present,
	 * otherwise returns the default 5-minute interval.
	 */
	getEffectiveSyncIntervalMs(did: string): number {
		if (!this.policyEngine) return DEFAULT_SYNC_INTERVAL_MS;

		const config = this.policyEngine.getReplicationConfig(did);
		return config
			? config.sync.intervalSec * 1000
			: DEFAULT_SYNC_INTERVAL_MS;
	}

	/**
	 * Sync a single DID: fetch repo, store blocks in IPFS, verify, update state.
	 */
	async syncDid(did: string, trigger: SyncTrigger = "unknown"): Promise<void> {
		this.syncStorage.updateStatus(did, "syncing");
		const syncStart = Date.now();
		let sourceType = "pds";

		// 1. Resolve PDS endpoint
		let state = this.syncStorage.getState(did);
		let pdsEndpoint = await this.repoFetcher.resolvePds(did);

		if (!pdsEndpoint) {
			// If previously had a PDS endpoint, this may be a tombstoned/deleted account
			if (state?.pdsEndpoint) {
				this.syncStorage.markTombstoned(did);
				console.warn(`[replication] DID ${did} no longer resolvable — marked as tombstoned`);
			} else {
				this.syncStorage.updateStatus(did, "error", "Could not resolve PDS endpoint");
			}
			return;
		}

		// Update PDS endpoint if it changed
		this.syncStorage.upsertState({ did, pdsEndpoint });
		state = this.syncStorage.getState(did);

		// 2. Optionally refresh peer info (peerId + multiaddrs)
		if (state && this.shouldRefreshPeerInfo(state)) {
			try {
				const peerInfo = await this.peerDiscovery.discoverPeer(did);
				if (peerInfo) {
					// Detect PeerID changes (peer restarted with new identity)
					if (state.peerId && peerInfo.peerId && state.peerId !== peerInfo.peerId) {
						console.warn(
							`[replication] PeerID changed for ${did}: ${state.peerId} → ${peerInfo.peerId}`,
						);
					}
					this.syncStorage.updatePeerInfo(did, peerInfo.peerId, peerInfo.multiaddrs);
					// Merge observed multiaddrs from active libp2p connections
					if (peerInfo.peerId) {
						const observed = this.networkService.getRemoteAddrs(peerInfo.peerId);
						if (observed.length > 0) {
							const merged = [...new Set([...peerInfo.multiaddrs, ...observed])];
							if (merged.length > peerInfo.multiaddrs.length) {
								this.syncStorage.updatePeerInfo(did, peerInfo.peerId, merged);
							}
						}
					}
				}
			} catch {
				// Non-fatal: peer discovery is optional
			}
		}

		// 3. Fetch repo (with incremental sync if we have a previous rev)
		const since = state?.lastSyncRev ?? undefined;

		// 3a. Try libp2p peer-first sync if we have peer info
		let carBytes: Uint8Array | null = null;
		state = this.syncStorage.getState(did); // re-read for fresh peer info
		if (this.libp2p && state?.peerId && state.peerMultiaddrs && state.peerMultiaddrs.length > 0) {
			try {
				console.log(`[sync] ${did} — fetching repo from peer ${state.peerId.slice(0, 12)}… via libp2p`);
				carBytes = await fetchRepoFromPeer(
					this.libp2p,
					state.peerMultiaddrs,
					did,
					since,
				);
				sourceType = "libp2p";
				console.log(`[sync] ${did} — received ${(carBytes.length / 1024).toFixed(1)} KB from peer via libp2p`);
			} catch (err) {
				console.log(
					`[sync] ${did} — libp2p sync failed, falling back to HTTP: ${err instanceof Error ? err.message : String(err)}`,
				);
				carBytes = null;
			}
		}

		// 3b. Fall back to HTTP PDS fetch
		if (!carBytes) {
			sourceType = "pds";
			console.log(`[sync] ${did} — fetching repo from ${pdsEndpoint}${since ? ` (since: ${since.slice(0, 8)}…)` : ""}`);
			try {
				carBytes = await this.repoFetcher.fetchRepo(
					pdsEndpoint,
					did,
					since,
				);
			} catch (sourceErr) {
				// On failure, clear cached peer info and trigger re-discovery
				this.syncStorage.clearPeerInfo(did);
				this.peerDiscovery.discoverPeer(did).then((peerInfo) => {
					if (peerInfo) {
						this.syncStorage.updatePeerInfo(did, peerInfo.peerId, peerInfo.multiaddrs);
					}
				}).catch(() => {});
				const err = sourceErr instanceof Error ? sourceErr : new Error(String(sourceErr));
				if (since) {
					// Retry full sync from source, then fall back to peers
					try {
						carBytes = await this.repoFetcher.fetchRepo(pdsEndpoint, did);
					} catch {
						sourceType = "peer_fallback";
						carBytes = await this.fetchFromPeersOrThrow(did, since, err);
					}
				} else {
					sourceType = "peer_fallback";
					carBytes = await this.fetchFromPeersOrThrow(did, undefined, err);
				}
			}
		}

		// Start sync event after source is determined
		this.emitProgress({ type: "sync:start", did, sourceType });
		const syncEventId = this.syncStorage.startSyncEvent(did, sourceType, trigger);

		try {
			// 4. Parse CAR and store blocks
			const carSizeKb = (carBytes.length / 1024).toFixed(1);
			console.log(`[sync] ${did} — CAR received: ${carSizeKb} KB, parsing...`);
			this.emitProgress({ type: "sync:car-received", did, carBytes: carBytes.length });
			const { root, blocks } = await readCarWithRoot(carBytes);

			await this.blockStore.putBlocks(blocks);

			// 5. Collect CID strings + sizes for DHT announcement + verification
			const cidStrs: string[] = [];
			const blockEntries: Array<{ cid: string; sizeBytes: number }> = [];
			const internalMap = (
				blocks as unknown as { map: Map<string, Uint8Array> }
			).map;
			if (internalMap) {
				for (const [cidStr, blockBytes] of internalMap.entries()) {
					cidStrs.push(cidStr);
					blockEntries.push({ cid: cidStr, sizeBytes: blockBytes.length });
				}
			}

			console.log(`[sync] ${did} — stored ${blockEntries.length} blocks, verifying...`);

			// 5b. Track block CIDs with sizes for remote verification
			if (blockEntries.length > 0) {
				this.syncStorage.trackBlocksWithSize(did, blockEntries);
			}

			const totalBlockSizeKb = blockEntries.reduce((s, b) => s + b.sizeBytes, 0) / 1024;
			this.emitProgress({ type: "sync:blocks-stored", did, blocksStored: blockEntries.length, blocksSizeKb: Math.round(totalBlockSizeKb) });

			// 6. Announce to DHT (fire-and-forget)
			this.networkService.provideBlocks(cidStrs).catch(() => {});

			// 7. Verify local block availability
			const verification =
				await this.verifier.verifyBlockAvailability(cidStrs);
			if (verification.missing.length > 0) {
				console.warn(
					`Local verification: ${verification.missing.length}/${verification.checked} blocks missing for ${did}`,
				);
			}
			this.syncStorage.updateVerifiedAt(did);
			this.emitProgress({ type: "sync:verified", did, missingBlocks: verification.missing.length });

			// 8. Extract actual rev from the commit block
			const rootCidStr = root.toString();
			let rev = rootCidStr; // fallback
			const commitBytes = internalMap?.get(rootCidStr);
			if (commitBytes) {
				try {
					const commitObj = cborDecode(commitBytes) as Record<string, unknown>;
					if (typeof commitObj.rev === "string") {
						rev = commitObj.rev;
					}
				} catch {
					// If CBOR decode fails, fall back to root CID as rev
				}
			}

			// 9. Update sync state with both rev and root CID
			this.syncStorage.updateSyncProgress(did, rev, rootCidStr);

			// 9a. Publish gossipsub notification (fire-and-forget)
			this.networkService.publishCommitNotification(did, rootCidStr, rev).catch(() => {});

			// 9b. Invalidate cached ReadableRepo so it reloads with new root
			this.replicatedRepoReader?.invalidateCache(did);

			// 9c. Track record paths for challenge generation (full MST walk)
			try {
				const recordPaths = await extractAllRecordPaths(
					this.blockStore,
					rootCidStr,
				);
				this.syncStorage.clearRecordPaths(did);
				this.syncStorage.trackRecordPaths(did, recordPaths);
				// Update lexicon index with NSIDs from these paths
				const nsids = extractNsids(recordPaths);
				if (nsids.length > 0) {
					this.syncStorage.updateLexiconIndex(nsids);
				}
			} catch {
				// Non-fatal: path extraction is best-effort
			}

			// 9d. Reconcile blocks: remove orphaned blocks from this DID's tracking
			try {
				const liveCids = await extractAllCids(this.blockStore, rootCidStr);
				const trackedCids = this.syncStorage.getBlockCidSet(did);

				// Find CIDs that are tracked but no longer live
				const orphanedFromDid: string[] = [];
				for (const cid of trackedCids) {
					if (!liveCids.has(cid)) {
						orphanedFromDid.push(cid);
					}
				}

				if (orphanedFromDid.length > 0) {
					// Remove from this DID's tracking
					this.syncStorage.removeBlocks(did, orphanedFromDid);

					// Find which are truly orphaned (no other DID references them)
					const trulyOrphaned = this.syncStorage.findOrphanedCids(orphanedFromDid);

					// Delete from blockstore
					for (const cid of trulyOrphaned) {
						await this.blockStore.deleteBlock(cid);
					}
				}

				// Clear the needs_gc flag since we just did a full reconciliation
				this.syncStorage.clearNeedsGc(did);
			} catch {
				// Non-fatal: GC is best-effort
			}

			// 9e. Reconcile blobs: remove blobs for deleted records
			try {
				const currentBlobCids = new Set<string>();
				if (this.replicatedRepoReader) {
					const repo = await this.replicatedRepoReader.getRepo(did);
					if (repo) {
						for await (const entry of repo.walkRecords()) {
							const cids = extractBlobCids(entry.record);
							for (const cid of cids) {
								currentBlobCids.add(cid);
							}
						}
					}
				}

				const trackedBlobCids = this.syncStorage.getBlobCids(did);
				const orphanedBlobs = trackedBlobCids.filter(cid => !currentBlobCids.has(cid));

				if (orphanedBlobs.length > 0) {
					this.syncStorage.removeBlobs(did, orphanedBlobs);
					const trulyOrphanedBlobs = this.syncStorage.findOrphanedBlobCids(orphanedBlobs);
					for (const cid of trulyOrphanedBlobs) {
						await this.blockStore.deleteBlock(cid);
					}
				}
			} catch {
				// Non-fatal: blob GC is best-effort
			}

			// 10. Update manifest record
			if (this.repoManager) {
				const rkey = didToRkey(did);
				const existingManifest = await this.repoManager.getRecord(
					MANIFEST_NSID,
					rkey,
				);
				if (existingManifest) {
					const manifest: ManifestRecord = {
						$type: MANIFEST_NSID,
						subject: did,
						status: "active",
						lastSyncRev: rev,
						lastSyncAt: new Date().toISOString(),
						createdAt:
							(existingManifest.record as Record<string, unknown>)
								?.createdAt as string ?? new Date().toISOString(),
					};
					await this.repoManager.putRecord(MANIFEST_NSID, rkey, manifest);
				}
			}

			// 11. Sync blobs and capture result
			console.log(`[sync] ${did} — syncing blobs...`);
			const blobResult = await this.syncBlobs(did);

			// 12. Complete sync event with metrics
			const totalDuration = ((Date.now() - syncStart) / 1000).toFixed(1);
			const totalBlobKb = (blobResult.totalBytes / 1024).toFixed(1);
			console.log(
				`[sync] ${did} — complete: ${blockEntries.length} blocks, ${blobResult.fetched} blobs (${totalBlobKb} KB), ${totalDuration}s`,
			);
			this.syncStorage.completeSyncEvent(syncEventId, {
				status: "success",
				blocksAdded: blockEntries.length,
				blobsAdded: blobResult.fetched,
				carBytes: carBytes.length,
				blobBytes: blobResult.totalBytes,
				durationMs: Date.now() - syncStart,
				rev,
				rootCid: rootCidStr,
				incremental: !!since,
			});
			this.emitProgress({
				type: "sync:complete",
				did,
				blocksStored: blockEntries.length,
				blobsFetched: blobResult.fetched,
				blobBytes: blobResult.totalBytes,
				durationMs: Date.now() - syncStart,
			});
		} catch (err) {
			this.syncStorage.completeSyncEvent(syncEventId, {
				status: "error",
				errorMessage: err instanceof Error ? err.message : String(err),
				durationMs: Date.now() - syncStart,
				incremental: !!since,
			});
			this.emitProgress({
				type: "sync:error",
				did,
				error: err instanceof Error ? err.message : String(err),
			});
			throw err;
		}
	}

	/** Grace period before purging tombstoned DID data (24 hours). */
	private static readonly TOMBSTONE_GRACE_MS = 24 * 60 * 60 * 1000;

	/**
	 * Clean up tombstoned DIDs: re-verify resolution, purge if still dead.
	 * Only purges after a grace period (24 hours) to avoid premature deletion
	 * from transient DID resolution failures.
	 */
	private async cleanupTombstonedDids(): Promise<void> {
		const states = this.syncStorage.getAllStates();
		const tombstoned = states.filter((s) => s.status === "tombstoned");

		for (const state of tombstoned) {
			if (this.stopped) break;

			// Check grace period: only purge if tombstoned for > 24 hours
			const lastSyncAt = state.lastSyncAt ? new Date(state.lastSyncAt).getTime() : 0;
			const timeSinceLastSync = Date.now() - lastSyncAt;
			if (timeSinceLastSync < ReplicationManager.TOMBSTONE_GRACE_MS) {
				continue;
			}

			// Re-verify: try to resolve the DID again
			try {
				const pdsEndpoint = await this.repoFetcher.resolvePds(state.did);
				if (pdsEndpoint) {
					// DID is alive again! Un-tombstone and resume.
					this.syncStorage.updateStatus(state.did, "pending");
					this.syncStorage.upsertState({ did: state.did, pdsEndpoint });
					console.log(`[replication] Tombstoned DID ${state.did} is alive again, resuming`);
					this.syncDid(state.did, "tombstone-recovery").catch((err) => {
						const message = err instanceof Error ? err.message : String(err);
						this.syncStorage.updateStatus(state.did, "error", message);
					});
					continue;
				}
			} catch {
				// Resolution failed, proceed with purge
			}

			// Still dead — purge data
			console.warn(`[replication] Purging data for tombstoned DID ${state.did}`);
			const { blocksRemoved, blobsRemoved } = this.syncStorage.purgeDidData(state.did);

			// Delete truly orphaned blocks/blobs from blockstore
			if (blocksRemoved.length > 0) {
				const orphanedBlocks = this.syncStorage.findOrphanedCids(blocksRemoved);
				for (const cid of orphanedBlocks) {
					await this.blockStore.deleteBlock(cid);
				}
			}
			if (blobsRemoved.length > 0) {
				const orphanedBlobs = this.syncStorage.findOrphanedBlobCids(blobsRemoved);
				for (const cid of orphanedBlobs) {
					await this.blockStore.deleteBlock(cid);
				}
			}

			// Remove manifest record
			if (this.repoManager) {
				const rkey = didToRkey(state.did);
				try {
					await this.repoManager.deleteRecord(MANIFEST_NSID, rkey);
				} catch {
					// Non-fatal
				}
			}
		}
	}

	/**
	 * Run deferred GC for DIDs that were flagged by firehose delete/update ops.
	 * Triggers a full sync for each flagged DID, which includes block/blob reconciliation.
	 */
	private async runDeferredGc(): Promise<void> {
		const didsNeedingGc = this.syncStorage.getDidsNeedingGc();
		for (const did of didsNeedingGc) {
			if (this.stopped) break;
			try {
				await this.syncDid(did, "gc");
				this.lastSyncTimestamps.set(did, Date.now());
			} catch (err) {
				const message = err instanceof Error ? err.message : String(err);
				this.syncStorage.updateStatus(did, "error", message);
			}
		}
	}

	/**
	 * Compute the tick interval for periodic sync.
	 *
	 * When a PolicyEngine is present, uses the minimum sync interval
	 * across all DIDs so that no DID misses its window. Each DID's
	 * individual interval is checked inside syncAll().
	 *
	 * Falls back to the provided intervalMs (default 5 minutes).
	 */
	private computeTickIntervalMs(fallbackMs: number): number {
		if (!this.policyEngine) return fallbackMs;

		const dids = this.getReplicateDids();
		if (dids.length === 0) return fallbackMs;

		let minInterval = Infinity;
		for (const did of dids) {
			const config = this.policyEngine.getReplicationConfig(did);
			const intervalMs = config
				? config.sync.intervalSec * 1000
				: DEFAULT_SYNC_INTERVAL_MS;
			if (intervalMs < minInterval) {
				minInterval = intervalMs;
			}
		}

		// Clamp to minimum tick interval to prevent excessive polling
		return Math.max(
			minInterval === Infinity ? fallbackMs : minInterval,
			MIN_TICK_INTERVAL_MS,
		);
	}

	/**
	 * Start periodic sync and verification at their respective intervals.
	 *
	 * When a PolicyEngine is present, the tick rate is derived from the
	 * minimum sync interval across all DIDs. Each tick, syncAll() checks
	 * which DIDs are actually due for sync based on their individual intervals.
	 */
	startPeriodicSync(intervalMs: number = 5 * 60 * 1000): void {
		if (this.syncTimer) return;
		this.stopped = false;

		const tickMs = this.computeTickIntervalMs(intervalMs);

		// Run first sync after a short delay to let startup complete
		setTimeout(() => {
			if (!this.stopped) {
				this.syncAll().catch((err) => {
					console.error("Periodic sync error:", err);
				});
			}
		}, 5000);

		this.syncTimer = setInterval(() => {
			if (!this.stopped) {
				this.syncAll().catch((err) => {
					console.error("Periodic sync error:", err);
				});
			}
		}, tickMs);

		// Start periodic PLC mirror refresh (6 hours)
		const PLC_REFRESH_MS = 6 * 60 * 60 * 1000;
		this.plcRefreshTimer = setInterval(() => {
			if (!this.stopped) {
				this.refreshAllPlcLogs().catch((err) => {
					console.error("[replication] PLC mirror refresh error:", err);
				});
			}
		}, PLC_REFRESH_MS);

		// Initial PLC log fetch for all tracked did:plc DIDs (fire-and-forget)
		this.refreshAllPlcLogs().catch((err) => {
			console.error("[replication] Initial PLC mirror fetch error:", err);
		});

		// Build lexicon index from existing record paths
		try {
			this.syncStorage.rebuildLexiconIndex();
		} catch (err) {
			console.error("[replication] Lexicon index rebuild error:", err);
		}

		// Run verification once on startup, then on a timer
		this.runVerification().catch((err) => {
			console.error("Initial verification error:", err);
		});
		this.verificationTimer = setInterval(() => {
			if (!this.stopped) {
				this.runVerification().catch((err) => {
					console.error("Periodic verification error:", err);
				});
			}
		}, this.verificationConfig.verificationIntervalMs);
	}

	/**
	 * Start the firehose subscription for real-time updates.
	 * The firehose provides streaming updates for serviced DIDs,
	 * complementing the periodic polling sync.
	 */
	startFirehose(): void {
		if (this.firehoseSubscription) return;
		if (!this.config.FIREHOSE_ENABLED) return;

		const replicateDids = this.getReplicateDids();
		if (replicateDids.length === 0) return;

		this.firehoseSubscription = new FirehoseSubscription({
			firehoseUrl: this.config.FIREHOSE_URL,
		});

		// Register handler for commit events
		this.firehoseSubscription.onCommit((event) => {
			this.handleFirehoseCommit(event).catch((err) => {
				console.error(`[replication] Firehose commit handler error for ${event.repo}:`, err);
			});
		});

		// Register handler for account status events (tombstone/deactivation)
		this.firehoseSubscription.onAccount((event) => {
			this.handleFirehoseAccount(event).catch((err) => {
				console.error(`[replication] Firehose account handler error for ${event.did}:`, err);
			});
		});

		// Load saved cursor for resumption
		const savedCursor = this.syncStorage.getFirehoseCursor();

		// Start with the merged set of DIDs
		const dids = new Set(replicateDids);
		this.firehoseSubscription.start(dids, savedCursor);

		// Periodically save the cursor to SQLite (every 30 seconds)
		this.firehoseCursorSaveTimer = setInterval(() => {
			this.saveFirehoseCursor();
		}, 30_000);

		console.log(
			`[replication] Firehose subscription started` +
			(savedCursor !== null ? ` (resuming from cursor ${savedCursor})` : "") +
			` — tracking ${dids.size} DIDs`,
		);
	}

	/**
	 * Handle a commit event from the firehose.
	 *
	 * Optimization: the firehose event already contains the blocks (as CAR bytes)
	 * and the commit rev/CID. We apply them directly to our blockstore, avoiding
	 * an HTTP round-trip to the source PDS.
	 *
	 * Falls back to full syncDid() if incremental apply fails (e.g., tooBig event,
	 * empty blocks, gap in sequence, or CAR parsing error).
	 */
	private async handleFirehoseCommit(event: FirehoseCommitEvent): Promise<void> {
		const did = event.repo;

		// Only process if this DID is one we are tracking
		const replicateDids = this.getReplicateDids();
		if (!replicateDids.includes(did)) return;

		// Determine if we should attempt incremental apply or fall back to full sync.
		// Fall back when:
		// - tooBig is set (blocks were too large to include in the event)
		// - rebase occurred (repo structure changed, need full sync)
		// - blocks are empty (nothing to apply)
		if (event.tooBig || event.rebase || event.blocks.length === 0) {
			try {
				await this.syncDid(did, "firehose-resync");
				this.lastSyncTimestamps.set(did, Date.now());
			} catch (err) {
				const message = err instanceof Error ? err.message : String(err);
				this.syncStorage.updateStatus(did, "error", message);
			}
			return;
		}

		// Check for sequence gaps: if we have a `since` (previous rev) in the event
		// and it doesn't match our last sync rev, we may have missed events.
		const state = this.syncStorage.getState(did);
		if (event.since !== null && state !== null && state.lastSyncRev !== null) {
			if (state.lastSyncRev !== event.since) {
				// Gap detected: our last known rev doesn't match the event's `since`.
				// Fall back to full sync to catch up.
				console.warn(
					`[replication] Gap detected for ${did}: local rev=${state.lastSyncRev}, event.since=${event.since}. Falling back to full sync.`,
				);
				try {
					await this.syncDid(did, "firehose-resync");
					this.lastSyncTimestamps.set(did, Date.now());
				} catch (err) {
					const message = err instanceof Error ? err.message : String(err);
					this.syncStorage.updateStatus(did, "error", message);
				}
				return;
			}
		}

		// Attempt incremental block application from firehose event
		try {
			await this.applyFirehoseBlocks(did, event);
			this.lastSyncTimestamps.set(did, Date.now());
		} catch (err) {
			// Incremental apply failed — fall back to full sync
			console.warn(
				`[replication] Incremental apply failed for ${did}, falling back to full sync:`,
				err instanceof Error ? err.message : String(err),
			);
			try {
				await this.syncDid(did, "firehose-resync");
				this.lastSyncTimestamps.set(did, Date.now());
			} catch (syncErr) {
				const message = syncErr instanceof Error ? syncErr.message : String(syncErr);
				this.syncStorage.updateStatus(did, "error", message);
			}
		}
	}

	/**
	 * Handle an account status event from the firehose.
	 * Detects tombstoned/deactivated accounts and marks them accordingly.
	 * Handles re-activation by clearing tombstone and triggering sync.
	 */
	private async handleFirehoseAccount(event: FirehoseAccountEvent): Promise<void> {
		const did = event.did;

		// Only process DIDs we are tracking
		const replicateDids = this.getReplicateDids();
		if (!replicateDids.includes(did)) return;

		if (!event.active || event.status === "deleted" || event.status === "takendown") {
			// Refresh PLC log to capture tombstone operation
			if (did.startsWith("did:plc:")) {
				this.fetchPlcLog(did).catch((err) => {
					console.warn(`[replication] PLC log refresh on tombstone for ${did} failed:`, err instanceof Error ? err.message : String(err));
				});
			}

			// Mark as tombstoned
			this.syncStorage.markTombstoned(did);

			// Update manifest to paused
			if (this.repoManager) {
				const rkey = didToRkey(did);
				const existing = await this.repoManager.getRecord(MANIFEST_NSID, rkey);
				if (existing) {
					const manifest: ManifestRecord = {
						...(existing.record as ManifestRecord),
						status: "paused",
					};
					await this.repoManager.putRecord(MANIFEST_NSID, rkey, manifest);
				}
			}

			console.warn(
				`[replication] Account ${did} deactivated/tombstoned (status=${event.status}, active=${event.active})`,
			);
		} else if (event.active) {
			// Re-activated: clear tombstone and trigger full sync
			const state = this.syncStorage.getState(did);
			if (state?.status === "tombstoned") {
				this.syncStorage.updateStatus(did, "pending");
				console.log(`[replication] Account ${did} re-activated, triggering sync`);
				this.syncDid(did, "tombstone-recovery").catch((err) => {
					const message = err instanceof Error ? err.message : String(err);
					this.syncStorage.updateStatus(did, "error", message);
				});
				// Refresh PLC log on reactivation
				if (did.startsWith("did:plc:")) {
					this.fetchPlcLog(did).catch((err) => {
						console.warn(`[replication] PLC log refresh on reactivation for ${did} failed:`, err instanceof Error ? err.message : String(err));
					});
				}
			}
		}
	}

	/**
	 * Apply blocks from a firehose commit event directly to the blockstore.
	 * The event's `blocks` field contains CAR-encoded bytes that can be parsed
	 * and stored without fetching from the source PDS.
	 */
	private async applyFirehoseBlocks(
		did: string,
		event: FirehoseCommitEvent,
	): Promise<void> {
		const syncStart = Date.now();
		const syncEventId = this.syncStorage.startSyncEvent(did, "firehose", "firehose");

		try {
			// 1. Parse the CAR bytes from the firehose event
			const { root, blocks } = await readCarWithRoot(event.blocks);

			// 2. Store blocks in our blockstore
			await this.blockStore.putBlocks(blocks);

			// 3. Collect CID strings + sizes for DHT announcement + block tracking
			const cidStrs: string[] = [];
			const blockEntries: Array<{ cid: string; sizeBytes: number }> = [];
			const internalMap = (
				blocks as unknown as { map: Map<string, Uint8Array> }
			).map;
			if (internalMap) {
				for (const [cidStr, blockBytes] of internalMap.entries()) {
					cidStrs.push(cidStr);
					blockEntries.push({ cid: cidStr, sizeBytes: blockBytes.length });
				}
			}

			// 4. Track block CIDs with sizes
			if (blockEntries.length > 0) {
				this.syncStorage.trackBlocksWithSize(did, blockEntries);
			}

			const fhBlockSizeKb = blockEntries.reduce((s, b) => s + b.sizeBytes, 0) / 1024;
			this.emitProgress({ type: "sync:blocks-stored", did, blocksStored: blockEntries.length, blocksSizeKb: Math.round(fhBlockSizeKb) });

			// 5. Announce to DHT (fire-and-forget)
			this.networkService.provideBlocks(cidStrs).catch(() => {});

			// 6. Determine rev and root CID
			const rootCidStr = root.toString();
			let rev = event.rev; // Use the rev directly from the firehose event

			// If no rev in the event, try to extract from commit block
			if (!rev) {
				const commitBytes = internalMap?.get(rootCidStr);
				if (commitBytes) {
					try {
						const commitObj = cborDecode(commitBytes) as Record<string, unknown>;
						if (typeof commitObj.rev === "string") {
							rev = commitObj.rev;
						}
					} catch {
						// Fall back to root CID as rev
						rev = rootCidStr;
					}
				} else {
					rev = rootCidStr;
				}
			}

			// 7. Update sync state
			this.syncStorage.updateSyncProgress(did, rev, rootCidStr);

			// 7a. Publish gossipsub notification (fire-and-forget)
			this.networkService.publishCommitNotification(did, rootCidStr, rev).catch(() => {});

			// 8. Invalidate cached ReadableRepo so it reloads with new root
			this.replicatedRepoReader?.invalidateCache(did);

			// 8b. Track record paths incrementally from firehose ops
			try {
				const createdPaths = event.ops
					.filter((op) => op.action === "create" || op.action === "update")
					.map((op) => op.path);
				const deletedPaths = event.ops
					.filter((op) => op.action === "delete")
					.map((op) => op.path);
				if (createdPaths.length > 0) {
					this.syncStorage.trackRecordPaths(did, createdPaths);
					// Update lexicon index with NSIDs from created paths
					const nsids = extractNsids(createdPaths);
					if (nsids.length > 0) {
						this.syncStorage.updateLexiconIndex(nsids);
					}
				}
				if (deletedPaths.length > 0) {
					this.syncStorage.removeRecordPaths(did, deletedPaths);
				}

				// Flag for deferred GC if deletes or updates occurred
				// (updates may orphan old MST nodes/record blocks)
				const hasDeletesOrUpdates = event.ops.some(
					(op) => op.action === "delete" || op.action === "update",
				);
				if (hasDeletesOrUpdates) {
					this.syncStorage.setNeedsGc(did);
				}
			} catch {
				// Non-fatal: path tracking is best-effort
			}

			// 9. Update manifest record
			if (this.repoManager) {
				const rkey = didToRkey(did);
				const existingManifest = await this.repoManager.getRecord(
					MANIFEST_NSID,
					rkey,
				);
				if (existingManifest) {
					const manifest: ManifestRecord = {
						$type: MANIFEST_NSID,
						subject: did,
						status: "active",
						lastSyncRev: rev,
						lastSyncAt: new Date().toISOString(),
						createdAt:
							(existingManifest.record as Record<string, unknown>)
								?.createdAt as string ?? new Date().toISOString(),
					};
					await this.repoManager.putRecord(MANIFEST_NSID, rkey, manifest);
				}
			}

			// 10. Sync blobs for firehose ops (fire-and-forget)
			const pdsEndpoint = this.syncStorage.getState(did)?.pdsEndpoint;
			if (pdsEndpoint) {
				this.syncBlobsForOps(did, pdsEndpoint, event.ops).catch((err) => {
					console.warn(
						`[replication] Blob sync error for firehose ops (${did}):`,
						err instanceof Error ? err.message : String(err),
					);
				});
			}

			// 11. Complete sync event
			this.syncStorage.completeSyncEvent(syncEventId, {
				status: "success",
				blocksAdded: blockEntries.length,
				carBytes: event.blocks.length,
				durationMs: Date.now() - syncStart,
				rev,
				rootCid: rootCidStr,
				incremental: true,
			});
			this.emitProgress({
				type: "sync:complete",
				did,
				blocksStored: blockEntries.length,
				durationMs: Date.now() - syncStart,
			});
		} catch (err) {
			this.syncStorage.completeSyncEvent(syncEventId, {
				status: "error",
				errorMessage: err instanceof Error ? err.message : String(err),
				durationMs: Date.now() - syncStart,
				incremental: true,
			});
			this.emitProgress({
				type: "sync:error",
				did,
				error: err instanceof Error ? err.message : String(err),
			});
			throw err;
		}
	}

	/**
	 * Save the current firehose cursor to persistent storage.
	 */
	private saveFirehoseCursor(): void {
		if (!this.firehoseSubscription) return;
		const cursor = this.firehoseSubscription.getCursor();
		if (cursor !== null) {
			this.syncStorage.saveFirehoseCursor(cursor);
		}
	}

	/**
	 * Get firehose subscription statistics.
	 */
	getFirehoseStats(): {
		connected: boolean;
		cursor: number | null;
		eventsReceived: number;
		eventsProcessed: number;
		trackedDids: number;
	} | null {
		if (!this.firehoseSubscription) return null;
		return this.firehoseSubscription.getStats();
	}

	/**
	 * Set up gossipsub subscription for commit notifications.
	 * Subscribes to topics for all tracked DIDs and registers a handler
	 * that triggers syncDid() when a newer rev is received.
	 */
	private setupGossipsubSubscription(): void {
		const dids = this.getReplicateDids();
		if (dids.length === 0) return;

		this.networkService.onCommitNotification((notification) => {
			this.handleGossipsubNotification(notification).catch((err) => {
				console.error(
					`[replication] Gossipsub notification handler error for ${notification.did}:`,
					err instanceof Error ? err.message : String(err),
				);
			});
		});

		this.networkService.onIdentityNotification((notification) => {
			this.handleIdentityNotification(notification);
		});

		this.networkService.subscribeCommitTopics(dids);
		this.networkService.subscribeIdentityTopics(dids);

		// Periodically clear the dedup set to prevent unbounded growth
		this.notificationCleanupTimer = setInterval(() => {
			this.recentNotifications.clear();
		}, 60_000);
	}

	/**
	 * Handle an incoming gossipsub commit notification.
	 * Deduplicates by did:rev, skips if local state is already current,
	 * and triggers syncDid() if the notification represents a newer commit.
	 */
	private async handleGossipsubNotification(notification: CommitNotification): Promise<void> {
		const did = notification.did;

		// Only process DIDs we are tracking
		const trackedDids = this.getReplicateDids();
		if (!trackedDids.includes(did)) return;

		// Dedup: skip if we've already processed this did:rev
		const dedupKey = `${did}:${notification.rev}`;
		if (this.recentNotifications.has(dedupKey)) return;
		this.recentNotifications.add(dedupKey);

		// Skip if local state already matches this rev
		const state = this.syncStorage.getState(did);
		if (state?.lastSyncRev === notification.rev) return;

		try {
			await this.syncDid(did, "gossipsub");
			this.lastSyncTimestamps.set(did, Date.now());
		} catch (err) {
			const message = err instanceof Error ? err.message : String(err);
			this.syncStorage.updateStatus(did, "error", message);
		}
	}

	/**
	 * Handle an incoming gossipsub identity notification.
	 * Updates peer info immediately if the DID is tracked.
	 */
	private handleIdentityNotification(notification: IdentityNotification): void {
		const did = notification.did;

		// Only process DIDs we are tracking
		const trackedDids = this.getReplicateDids();
		if (!trackedDids.includes(did)) return;

		// Log PeerID changes
		const state = this.syncStorage.getState(did);
		if (state?.peerId && state.peerId !== notification.peerId) {
			console.warn(
				`[replication] Identity notification: PeerID changed for ${did}: ${state.peerId} → ${notification.peerId}`,
			);
		}

		// Update peer info immediately
		this.syncStorage.updatePeerInfo(did, notification.peerId, notification.multiaddrs);

		// Refresh PLC log on identity change (key rotation, PDS migration, etc.)
		if (did.startsWith("did:plc:")) {
			this.fetchPlcLog(did).catch((err) => {
				console.warn(`[replication] PLC log refresh on identity change for ${did} failed:`, err instanceof Error ? err.message : String(err));
			});
		}
	}

	/**
	 * Stop periodic sync, verification, and firehose subscription.
	 */
	stop(): void {
		this.stopped = true;
		if (this.syncTimer) {
			clearInterval(this.syncTimer);
			this.syncTimer = null;
		}
		if (this.verificationTimer) {
			clearInterval(this.verificationTimer);
			this.verificationTimer = null;
		}
		// Save cursor and stop firehose
		if (this.firehoseCursorSaveTimer) {
			clearInterval(this.firehoseCursorSaveTimer);
			this.firehoseCursorSaveTimer = null;
		}
		if (this.firehoseSubscription) {
			this.saveFirehoseCursor();
			this.firehoseSubscription.stop();
			this.firehoseSubscription = null;
		}
		// Stop PLC mirror refresh
		if (this.plcRefreshTimer) {
			clearInterval(this.plcRefreshTimer);
			this.plcRefreshTimer = null;
		}
		// Stop challenge scheduler
		if (this.challengeScheduler) {
			this.challengeScheduler.stop();
			this.challengeScheduler = null;
		}
		// Stop gossipsub notification cleanup and unsubscribe identity topics
		if (this.notificationCleanupTimer) {
			clearInterval(this.notificationCleanupTimer);
			this.notificationCleanupTimer = null;
		}
		try {
			this.networkService.unsubscribeIdentityTopics(this.getReplicateDids());
		} catch {
			// Gossipsub streams may already be closed during shutdown
		}
	}

	/**
	 * Run remote verification for all synced DIDs.
	 */
	async runVerification(): Promise<LayeredVerificationResult[]> {
		const results: LayeredVerificationResult[] = [];

		for (const did of this.getReplicateDids()) {
			if (this.stopped) break;
			try {
				const result = await this.verifyDid(did);
				if (result) {
					results.push(result);
					this.lastVerificationResults.set(did, result);
				}
			} catch (err) {
				console.error(`Verification error for ${did}:`, err);
			}
		}

		return results;
	}

	/**
	 * Run layered verification for a single DID against its source PDS.
	 */
	async verifyDid(did: string): Promise<LayeredVerificationResult | null> {
		const state = this.syncStorage.getState(did);
		if (!state || !state.pdsEndpoint) return null;

		// Get tracked block CIDs for this DID
		const blockCids = this.syncStorage.getBlockCids(did);

		// Use the root CID (commit root) for verification
		const rootCid = state.rootCid ?? state.lastSyncRev ?? null;

		// Get tracked record paths for challenge generation
		const recordPaths = this.syncStorage.getRecordPaths(did);

		const result = await this.remoteVerifier.verifyPeer(
			did,
			state.pdsEndpoint,
			rootCid,
			blockCids,
			recordPaths,
		);

		if (result.overallPassed) {
			this.syncStorage.updateVerifiedAt(did);
		}

		return result;
	}

	/**
	 * Get the underlying SyncStorage instance.
	 */
	getSyncStorage(): SyncStorage {
		return this.syncStorage;
	}

	/**
	 * Get the underlying ChallengeStorage instance.
	 */
	getChallengeStorage(): ChallengeStorage {
		return this.challengeStorage;
	}

	/**
	 * Set the replicated repo reader for cache invalidation after sync.
	 */
	setReplicatedRepoReader(reader: ReplicatedRepoReader): void {
		this.replicatedRepoReader = reader;
	}

	/**
	 * Get sync states for all tracked DIDs.
	 */
	getSyncStates(): SyncState[] {
		return this.syncStorage.getAllStates();
	}

	/**
	 * Query the lexicon index with optional prefix filter.
	 */
	getLexiconIndex(prefix?: string, limit?: number) {
		return this.syncStorage.getLexiconIndex(prefix, limit);
	}

	/**
	 * Get aggregate lexicon stats.
	 */
	getLexiconStats() {
		return this.syncStorage.getLexiconStats();
	}

	/**
	 * Get all offered DIDs (awaiting mutual consent).
	 */
	getOfferedDids(): Array<{ did: string; pdsEndpoint: string | null; offeredAt: string }> {
		return this.syncStorage.getOfferedDids();
	}

	/**
	 * Get the most recent verification results.
	 */
	getVerificationResults(): Map<string, LayeredVerificationResult> {
		return this.lastVerificationResults;
	}

	// ============================================
	// Blob replication
	// ============================================

	/**
	 * Sync blobs for a DID: walk all records, extract blob CIDs, fetch new ones.
	 */
	async syncBlobs(did: string): Promise<{ fetched: number; skipped: number; errors: number; totalBytes: number }> {
		const state = this.syncStorage.getState(did);
		if (!state?.pdsEndpoint || !state.rootCid) {
			return { fetched: 0, skipped: 0, errors: 0, totalBytes: 0 };
		}

		if (!this.replicatedRepoReader) {
			return { fetched: 0, skipped: 0, errors: 0, totalBytes: 0 };
		}

		// Walk all records and collect blob CIDs
		const allBlobCids = new Set<string>();
		const repo = await this.replicatedRepoReader.getRepo(did);
		if (!repo) {
			return { fetched: 0, skipped: 0, errors: 0, totalBytes: 0 };
		}

		for await (const entry of repo.walkRecords()) {
			const cids = extractBlobCids(entry.record);
			for (const cid of cids) {
				allBlobCids.add(cid);
			}
		}

		// Filter to blobs not already fetched
		let fetched = 0;
		let skipped = 0;
		let errors = 0;
		let totalBytes = 0;
		const total = allBlobCids.size;

		for (const blobCid of allBlobCids) {
			if (this.syncStorage.hasBlobCid(did, blobCid)) {
				skipped++;
				continue;
			}

			try {
				const bytes = await this.repoFetcher.fetchBlob(
					state.pdsEndpoint,
					did,
					blobCid,
				);
				if (!bytes) {
					skipped++; // 404 — blob deleted upstream
					continue;
				}

				if (!await this.verifyBlobCid(blobCid, bytes)) {
					console.warn(`[replication] Blob CID mismatch for ${blobCid} (${did})`);
					errors++;
					continue;
				}

				await this.blockStore.putBlock(blobCid, bytes);
				this.syncStorage.trackBlobsWithSize(did, [{ cid: blobCid, sizeBytes: bytes.length }]);
				this.networkService.provideBlocks([blobCid]).catch(() => {});
				fetched++;
				totalBytes += bytes.length;
				this.emitProgress({ type: "sync:blob-progress", did, blobsFetched: fetched, blobsTotal: total, blobBytes: totalBytes });
			} catch (err) {
				console.warn(
					`[replication] Failed to fetch blob ${blobCid} for ${did}:`,
					err instanceof Error ? err.message : String(err),
				);
				errors++;
			}
		}

		return { fetched, skipped, errors, totalBytes };
	}

	/**
	 * Sync blobs for specific firehose ops (create/update only).
	 */
	private async syncBlobsForOps(
		did: string,
		pdsEndpoint: string,
		ops: Array<{ action: string; path: string }>,
	): Promise<void> {
		if (!this.replicatedRepoReader) return;

		for (const op of ops) {
			if (op.action !== "create" && op.action !== "update") continue;

			const parts = op.path.split("/");
			if (parts.length < 2) continue;
			const collection = parts.slice(0, -1).join("/");
			const rkey = parts[parts.length - 1]!;

			try {
				const record = await this.replicatedRepoReader.getRecord(did, collection, rkey);
				if (!record) continue;

				const blobCids = extractBlobCids(record.value);
				for (const blobCid of blobCids) {
					if (this.syncStorage.hasBlobCid(did, blobCid)) continue;

					const bytes = await this.repoFetcher.fetchBlob(pdsEndpoint, did, blobCid);
					if (!bytes) continue;

					if (!await this.verifyBlobCid(blobCid, bytes)) {
						console.warn(`[replication] Blob CID mismatch for ${blobCid} (${did})`);
						continue;
					}

					await this.blockStore.putBlock(blobCid, bytes);
					this.syncStorage.trackBlobs(did, [blobCid]);
					this.networkService.provideBlocks([blobCid]).catch(() => {});
				}
			} catch (err) {
				console.warn(
					`[replication] Failed to sync blobs for op ${op.path} (${did}):`,
					err instanceof Error ? err.message : String(err),
				);
			}
		}
	}

	/**
	 * Verify that blob bytes match the expected CID.
	 */
	private async verifyBlobCid(expectedCid: string, bytes: Uint8Array): Promise<boolean> {
		const actualCid = await createCid(CODEC_RAW, bytes);
		return cidToString(actualCid) === expectedCid;
	}

	// ============================================
	// Challenge-response verification
	// ============================================

	/**
	 * Start the challenge scheduler for periodic proof-of-storage verification.
	 * Requires a ChallengeTransport to communicate with peers.
	 */
	startChallengeScheduler(transport: ChallengeTransport): void {
		if (this.challengeScheduler) return;

		this.challengeScheduler = new ChallengeScheduler(
			this.config.DID ?? "",
			this.policyEngine,
			this.syncStorage,
			this.challengeStorage,
			this.blockStore,
			transport,
		);
		this.challengeScheduler.start();
	}

	/**
	 * Get challenge history for a target peer.
	 */
	getChallengeResults(
		targetDid: string,
		subjectDid?: string,
	): ChallengeHistoryRow[] {
		return this.challengeStorage.getHistory(targetDid, subjectDid);
	}

	/**
	 * Get peer reliability scores.
	 * If peerDid is provided, returns reliability for that specific peer.
	 * Otherwise, returns all peer reliability scores.
	 */
	getPeerReliability(peerDid?: string): PeerReliabilityRow[] {
		if (peerDid) {
			return this.challengeStorage.getReliability(peerDid);
		}
		return this.challengeStorage.getAllReliability();
	}

	/**
	 * Refresh peer info for all DIDs associated with a PDS endpoint.
	 * Called when a connection to that endpoint fails (e.g. challenge transport fallback).
	 * Fire-and-forget: clears stale cache and triggers re-discovery.
	 */
	refreshPeerInfoForEndpoint(pdsEndpoint: string): void {
		const states = this.syncStorage.getAllStates();
		for (const state of states) {
			if (state.pdsEndpoint === pdsEndpoint) {
				this.syncStorage.clearPeerInfo(state.did);
				this.peerDiscovery.discoverPeer(state.did).then((peerInfo) => {
					if (peerInfo) {
						this.syncStorage.updatePeerInfo(state.did, peerInfo.peerId, peerInfo.multiaddrs);
					}
				}).catch(() => {});
			}
		}
	}

	// ============================================
	// PLC mirror
	// ============================================

	/**
	 * Fetch and validate the PLC audit log for a single DID.
	 */
	private async fetchPlcLog(did: string): Promise<void> {
		const { fetchAndValidateLog } = await import("../identity/plc-mirror.js");
		await fetchAndValidateLog(this.db, did);
		// Announce via DHT that we hold this DID's PLC log
		this.networkService.provideForDid(did).catch(() => {});
	}

	/**
	 * Refresh PLC logs for all tracked did:plc DIDs.
	 */
	private async refreshAllPlcLogs(): Promise<void> {
		const { getAllPlcMirrorDids, fetchAndValidateLog, publishPlcProviders } = await import("../identity/plc-mirror.js");

		// Refresh existing mirrored DIDs
		const mirroredDids = getAllPlcMirrorDids(this.db);
		for (const did of mirroredDids) {
			if (this.stopped) break;
			try {
				await fetchAndValidateLog(this.db, did);
			} catch (err) {
				console.warn(
					`[replication] PLC log refresh for ${did} failed:`,
					err instanceof Error ? err.message : String(err),
				);
				// Fallback: try discovering PLC log from DHT peers
				await this.fetchPlcLogFromPeers(did).catch(() => {});
			}
		}

		// Also fetch for any tracked did:plc DIDs that don't have a mirror entry yet
		const trackedDids = this.getReplicateDids().filter((d) => d.startsWith("did:plc:"));
		const mirroredSet = new Set(mirroredDids);
		for (const did of trackedDids) {
			if (this.stopped) break;
			if (mirroredSet.has(did)) continue;
			try {
				await fetchAndValidateLog(this.db, did);
			} catch (err) {
				console.warn(
					`[replication] PLC log fetch for ${did} failed:`,
					err instanceof Error ? err.message : String(err),
				);
				// Fallback: try discovering PLC log from DHT peers
				await this.fetchPlcLogFromPeers(did).catch(() => {});
			}
		}

		// Re-announce all mirrored DIDs to the DHT
		const allMirrored = getAllPlcMirrorDids(this.db);
		if (allMirrored.length > 0) {
			const helia = this.networkService as unknown as { getLibp2p?(): unknown };
			if (typeof helia.getLibp2p === "function" && helia.getLibp2p()) {
				// Use the IpfsService routing directly via provideForDid
				for (const did of allMirrored) {
					this.networkService.provideForDid(did).catch(() => {});
				}
			}
		}
	}

	/**
	 * Fallback: discover PLC log providers via DHT and fetch from a peer.
	 * Used when plc.directory is unavailable.
	 */
	private async fetchPlcLogFromPeers(did: string): Promise<void> {
		const providers = await this.networkService.findProvidersForDid(did);
		if (providers.length === 0) return;

		const { validateOperationChain, getStoredLog } = await import("../identity/plc-mirror.js");

		for (const multiaddr of providers) {
			try {
				// Extract the host:port from the multiaddr for an HTTP fetch
				const hostMatch = multiaddr.match(/\/ip[46]\/([^/]+)\/tcp\/(\d+)/);
				if (!hostMatch) continue;
				const [, host, port] = hostMatch;

				const url = `http://${host}:${port}/xrpc/org.p2pds.plc.getLog?did=${encodeURIComponent(did)}`;
				const res = await fetch(url, { signal: AbortSignal.timeout(10000) });
				if (!res.ok) continue;

				const data = await res.json() as { operations?: unknown[]; status?: { validated?: boolean } };
				if (!data.operations || !Array.isArray(data.operations)) continue;

				// Validate the returned chain independently
				const validation = await validateOperationChain(data.operations as any, did);
				if (!validation.valid) continue;

				// Store it — we verified it ourselves
				const existingLog = getStoredLog(this.db, did);
				const newOpCount = data.operations.length;

				// Accept if we don't have it yet, or if the new chain is longer
				if (!existingLog || newOpCount > existingLog.status.opCount) {
					const isTombstoned = (data.operations as any[]).some(
						(op: any) => !op.nullified && op.operation?.type === "plc_tombstone",
					);
					const lastOpCreatedAt = newOpCount > 0
						? (data.operations as any[])[newOpCount - 1]!.createdAt ?? null
						: null;

					this.db.prepare(
						`INSERT INTO plc_mirror (did, operations_json, op_count, last_fetched_at, last_op_created_at, validated, is_tombstoned)
						 VALUES (?, ?, ?, ?, ?, ?, ?)
						 ON CONFLICT(did) DO UPDATE SET
							operations_json = excluded.operations_json,
							op_count = excluded.op_count,
							last_fetched_at = excluded.last_fetched_at,
							last_op_created_at = excluded.last_op_created_at,
							validated = excluded.validated,
							is_tombstoned = excluded.is_tombstoned`,
					).run(
						did,
						JSON.stringify(data.operations),
						newOpCount,
						new Date().toISOString(),
						lastOpCreatedAt,
						validation.valid ? 1 : 0,
						isTombstoned ? 1 : 0,
					);
					console.log(`[replication] PLC log for ${did} fetched from peer (${newOpCount} ops)`);
					return;
				}
			} catch {
				// Try next provider
			}
		}
	}

	/**
	 * Get PLC log status for a single DID.
	 */
	getPlcLogStatus(did: string): { opCount: number; lastFetchedAt: string; lastOpCreatedAt: string | null; validated: boolean; isTombstoned: boolean } | null {
		const row = this.db
			.prepare("SELECT * FROM plc_mirror WHERE did = ?")
			.get(did) as Record<string, unknown> | undefined;
		if (!row) return null;
		return {
			opCount: row.op_count as number,
			lastFetchedAt: row.last_fetched_at as string,
			lastOpCreatedAt: (row.last_op_created_at as string) ?? null,
			validated: (row.validated as number) === 1,
			isTombstoned: (row.is_tombstoned as number) === 1,
		};
	}

	/**
	 * Get aggregate PLC mirror stats.
	 */
	getPlcMirrorStatus(): { mirroredDids: number; totalOps: number; lastRefresh: string | null } {
		const countRow = this.db
			.prepare("SELECT COUNT(*) as count, COALESCE(SUM(op_count), 0) as total_ops FROM plc_mirror")
			.get() as { count: number; total_ops: number };
		const lastRow = this.db
			.prepare("SELECT MAX(last_fetched_at) as last_refresh FROM plc_mirror")
			.get() as { last_refresh: string | null };
		return {
			mirroredDids: countRow.count,
			totalOps: countRow.total_ops,
			lastRefresh: lastRow.last_refresh,
		};
	}

	/**
	 * Check if peer info should be refreshed based on TTL.
	 */
	private shouldRefreshPeerInfo(state: SyncState): boolean {
		if (!state.peerInfoFetchedAt) return true;
		const fetchedAt = new Date(state.peerInfoFetchedAt).getTime();
		return Date.now() - fetchedAt > PEER_INFO_TTL_MS;
	}
}