export interface CachedPolicy {
  defaultLightThemeUri: string | null;
  defaultDarkThemeUri: string | null;
  allowUserChoice: boolean;
  availableThemes: Array<{
    uri: string;
    /**
     * Present for pinned refs (locked to an exact version).
     * Absent for live refs (e.g. canonical atbb.space presets) — those
     * resolve to the current record at the URI without CID verification.
     */
    cid?: string;
  }>;
}

export interface CachedTheme {
  cid: string;
  /** All token values are CSS strings at the cache boundary. */
  tokens: Record<string, string>;
  cssOverrides: string | null;
  fontUrls: string[] | null;
}

interface CacheEntry<T> {
  data: T;
  expiresAt: number;
}

/**
 * In-memory TTL cache for resolved theme data on the web server.
 *
 * Themes change rarely. A single instance is created per server startup
 * (inside createThemeMiddleware) and shared across all requests.
 *
 * Policy: single entry, keyed to the forum.
 * Themes: map keyed by `${at-uri}:${colorScheme}` — colorScheme in the key
 * ensures light and dark cached entries are never confused, even if the same
 * AT-URI is used for both defaults.
 */
export class ThemeCache {
  private policy: CacheEntry<CachedPolicy> | null = null;
  private themes = new Map<string, CacheEntry<CachedTheme>>();

  constructor(readonly ttlMs: number) {}

  getPolicy(): Readonly<CachedPolicy> | null {
    if (!this.policy || Date.now() > this.policy.expiresAt) {
      this.policy = null;
      return null;
    }
    return this.policy.data;
  }

  setPolicy(data: CachedPolicy): void {
    this.policy = { data, expiresAt: Date.now() + this.ttlMs };
  }

  getTheme(uri: string, colorScheme: "light" | "dark"): Readonly<CachedTheme> | null {
    const key = `${uri}:${colorScheme}`;
    const entry = this.themes.get(key);
    if (!entry || Date.now() > entry.expiresAt) {
      this.themes.delete(key);
      return null;
    }
    return entry.data;
  }

  setTheme(uri: string, colorScheme: "light" | "dark", data: CachedTheme): void {
    const key = `${uri}:${colorScheme}`;
    this.themes.set(key, { data, expiresAt: Date.now() + this.ttlMs });
  }

  /** Evict a stale theme entry so the next request fetches fresh data. */
  deleteTheme(uri: string, colorScheme: "light" | "dark"): void {
    this.themes.delete(`${uri}:${colorScheme}`);
  }
}