use std::path::PathBuf;
use std::sync::Arc;
use std::time::Instant;

use anyhow::{Context, Result};
use onis_common::metrics::PrometheusHandle;
use sqlx::SqlitePool;
use tokio::sync::RwLock;

use onis_common::config::DatabaseConfig;
use onis_common::db;

use crate::tap::{RecordAction, TapEvent, TapRecordEvent};

pub struct AppState {
    /// Reverse index: domain → DID, verification status
    pub index: SqlitePool,
    /// Base directory for per-DID SQLite databases
    pub db_dir: PathBuf,
    /// Database pool configuration
    pub db_config: DatabaseConfig,
    /// Cache of open per-DID database pools
    pub user_dbs: RwLock<std::collections::HashMap<String, SqlitePool>>,
    /// Prometheus metrics handle for /metrics endpoint
    pub metrics_handle: PrometheusHandle,
}

impl AppState {
    pub async fn new(
        index_path: &std::path::Path,
        db_dir: PathBuf,
        db_config: DatabaseConfig,
        metrics_handle: PrometheusHandle,
    ) -> Result<Self> {
        let index = db::open_index_db(index_path, &db_config).await?;
        Ok(Self {
            index,
            db_dir,
            db_config,
            user_dbs: RwLock::new(std::collections::HashMap::new()),
            metrics_handle,
        })
    }

    /// Get or create a per-DID database pool.
    pub async fn get_user_db(&self, did: &str) -> Result<SqlitePool> {
        {
            let dbs = self.user_dbs.read().await;
            if let Some(pool) = dbs.get(did) {
                return Ok(pool.clone());
            }
        }

        let path = db::did_to_db_path(&self.db_dir, did);
        let pool = db::open_user_db(&path, &self.db_config).await?;

        let mut dbs = self.user_dbs.write().await;
        dbs.insert(did.to_string(), pool.clone());
        Ok(pool)
    }
}

/// Look up the domain for a record by rkey, then delete the row.
/// Returns the domain if the record existed.
async fn delete_by_rkey(pool: &SqlitePool, table: &str, rkey: &str) -> Result<Option<String>> {
    let select = format!("SELECT domain FROM {table} WHERE rkey = ?");
    let domain: Option<(String,)> = sqlx::query_as(&select)
        .bind(rkey)
        .fetch_optional(pool)
        .await?;

    let delete = format!("DELETE FROM {table} WHERE rkey = ?");
    sqlx::query(&delete)
        .bind(rkey)
        .execute(pool)
        .await
        .with_context(|| format!("failed to delete from {table}"))?;

    Ok(domain.map(|(d,)| d))
}

/// Yield each candidate zone for a domain by walking up the tree.
/// e.g. "a.b.example.com" → ["a.b.example.com", "b.example.com", "example.com"]
pub(crate) fn domain_ancestors(domain: &str) -> impl Iterator<Item = String> + '_ {
    let parts: Vec<&str> = domain.split('.').collect();
    (0..parts.len().saturating_sub(1)).map(move |i| parts[i..].join("."))
}

/// Check if the user has a declared zone that covers the given domain.
async fn has_zone_for(pool: &SqlitePool, domain: &str) -> Result<bool> {
    for candidate in domain_ancestors(domain) {
        let found: Option<(i64,)> =
            sqlx::query_as("SELECT 1 FROM zones WHERE domain = ?")
                .bind(&candidate)
                .fetch_optional(pool)
                .await?;
        if found.is_some() {
            return Ok(true);
        }
    }
    Ok(false)
}

pub async fn handle_event(state: Arc<AppState>, event: TapEvent) -> Result<()> {
    match event.event_type.as_str() {
        "record" => {
            let rec = event.record.context("record event missing record field")?;
            let collection = match rec.collection.as_str() {
                "systems.kiri.zone" => "zone",
                "systems.kiri.dns" => "dns",
                _ => return Ok(()),
            };
            let action = match rec.action {
                RecordAction::Create => "create",
                RecordAction::Update => "update",
                RecordAction::Delete => "delete",
            };

            let result = match collection {
                "zone" => handle_zone_event(state, rec).await,
                _ => handle_record_event(state, rec).await,
            };

            let status = if result.is_ok() { "success" } else { "error" };
            metrics::counter!(
                "appview_firehose_events_total",
                "collection" => collection,
                "action" => action,
                "status" => status,
            )
            .increment(1);

            result
        }
        "identity" => {
            if let Some(ident) = event.identity {
                tracing::debug!(
                    did = %ident.did,
                    handle = %ident.handle,
                    active = ident.is_active,
                    "identity event"
                );
            }
            Ok(())
        }
        other => {
            tracing::debug!("ignoring tap event type: {other}");
            Ok(())
        }
    }
}

async fn handle_record_event(state: Arc<AppState>, event: TapRecordEvent) -> Result<()> {
    let did = &event.did;
    let rkey = &event.rkey;

    match event.action {
        RecordAction::Create | RecordAction::Update => {
            let record_value = event
                .record
                .context("create/update event missing record payload")?;

            let domain = record_value
                .get("domain")
                .and_then(|v| v.as_str())
                .context("record missing domain field")?
                .to_lowercase();

            let record_type = record_value
                .get("record")
                .and_then(|v| v.get("$type"))
                .and_then(|v| v.as_str())
                .context("record missing $type")?;

            let type_name = record_type
                .strip_prefix("systems.kiri.dns#")
                .context("unexpected $type prefix")?
                .trim_end_matches("Record");

            let user_db = state.get_user_db(did).await?;

            if !has_zone_for(&user_db, &domain).await? {
                tracing::warn!(
                    did = %did,
                    domain = %domain,
                    "record for {domain} has no matching zone, skipping"
                );
                metrics::counter!("appview_records_skipped_no_zone_total").increment(1);
                return Ok(());
            }

            let data = serde_json::to_string(&record_value)?;
            let now = chrono::Utc::now().timestamp();

            let write_start = Instant::now();
            sqlx::query(
                "INSERT INTO records (rkey, domain, record_type, data, created_at, updated_at)
                 VALUES (?, ?, ?, ?, ?, ?)
                 ON CONFLICT(rkey) DO UPDATE SET
                     domain = excluded.domain,
                     record_type = excluded.record_type,
                     data = excluded.data,
                     updated_at = excluded.updated_at",
            )
            .bind(rkey)
            .bind(&domain)
            .bind(type_name)
            .bind(&data)
            .bind(now)
            .bind(now)
            .execute(&user_db)
            .await
            .context("failed to upsert record")?;
            metrics::histogram!("appview_sqlite_write_duration_seconds")
                .record(write_start.elapsed().as_secs_f64());

            tracing::info!(
                did = %did,
                rkey = %rkey,
                domain = %domain,
                record_type = %type_name,
                live = event.live,
                "record upserted"
            );
        }

        RecordAction::Delete => {
            let Ok(user_db) = state.get_user_db(did).await else {
                tracing::debug!(did = %did, rkey = %rkey, "delete for unknown DID, skipping");
                return Ok(());
            };

            let write_start = Instant::now();
            let domain = delete_by_rkey(&user_db, "records", rkey).await?;
            metrics::histogram!("appview_sqlite_write_duration_seconds")
                .record(write_start.elapsed().as_secs_f64());

            if let Some(domain) = domain {
                tracing::info!(
                    did = %did,
                    rkey = %rkey,
                    domain = %domain,
                    live = event.live,
                    "record deleted"
                );
            }
        }
    }

    Ok(())
}

async fn handle_zone_event(state: Arc<AppState>, event: TapRecordEvent) -> Result<()> {
    let did = &event.did;
    let rkey = &event.rkey;

    match event.action {
        RecordAction::Create | RecordAction::Update => {
            let record_value = event
                .record
                .context("create/update zone event missing record payload")?;

            let domain = record_value
                .get("domain")
                .and_then(|v| v.as_str())
                .context("zone record missing domain field")?
                .to_lowercase();

            let now = chrono::Utc::now().timestamp();
            let user_db = state.get_user_db(did).await?;

            let write_start = Instant::now();
            sqlx::query(
                "INSERT INTO zones (rkey, domain, created_at)
                 VALUES (?, ?, ?)
                 ON CONFLICT(rkey) DO UPDATE SET domain = excluded.domain",
            )
            .bind(rkey)
            .bind(&domain)
            .bind(now)
            .execute(&user_db)
            .await
            .context("failed to upsert zone")?;

            sqlx::query(
                "INSERT INTO zone_index (zone, did, first_seen)
                 VALUES (?, ?, ?)
                 ON CONFLICT(zone, did) DO NOTHING",
            )
            .bind(&domain)
            .bind(did)
            .bind(now)
            .execute(&state.index)
            .await
            .context("failed to update zone index")?;
            metrics::histogram!("appview_sqlite_write_duration_seconds")
                .record(write_start.elapsed().as_secs_f64());

            tracing::info!(
                did = %did,
                rkey = %rkey,
                domain = %domain,
                live = event.live,
                "zone upserted"
            );
        }

        RecordAction::Delete => {
            let Ok(user_db) = state.get_user_db(did).await else {
                tracing::debug!(did = %did, rkey = %rkey, "zone delete for unknown DID, skipping");
                return Ok(());
            };

            let write_start = Instant::now();
            let domain = delete_by_rkey(&user_db, "zones", rkey).await?;

            if let Some(domain) = domain {
                sqlx::query("DELETE FROM zone_index WHERE zone = ? AND did = ?")
                    .bind(&domain)
                    .bind(did)
                    .execute(&state.index)
                    .await
                    .context("failed to delete from zone index")?;
                metrics::histogram!("appview_sqlite_write_duration_seconds")
                    .record(write_start.elapsed().as_secs_f64());

                tracing::info!(
                    did = %did,
                    rkey = %rkey,
                    domain = %domain,
                    live = event.live,
                    "zone deleted"
                );
            }
        }
    }

    Ok(())
}