// Disposable caches (profiles, reports, previews, …) in IndexedDB instead of
// localStorage, behind the same getItem/setItem/removeItem shape.
//
// Why: localStorage is about five million characters per site, whatever the
// device, and a phone that follows a few hundred people filled it — every
// cache then had to be squeezed (a 150-row profile cache churned through in
// twenty minutes, and a reload painted punks and npubs). IndexedDB shares the
// site's disk allowance instead: gigabytes.
//
// The values stay the strings localStorage held, so callers keep their
// JSON.parse/stringify and nothing about a cache's shape changes. Reads are
// synchronous from memory; writes are coalesced and land in IndexedDB in the
// background, flushed at once when the page hides.
//
// Before the store has opened (a few ms into boot) reads fall back to
// localStorage and writes go there only if the key still lives there — a
// write built from an early, empty read must never replace the full copy in
// IndexedDB. Boot waits for `cacheReady()` before restoring the wallet, so
// wallet-scoped caches never see that window; caches read at construction
// re-merge from `onCacheReady`. localStorage copies migrate on open (they're
// newer: written by this device before the move, or by an older build still
// open in another tab) and are removed once the IndexedDB write completed.
// If IndexedDB is unavailable everything stays in localStorage, as before.

const DB = 'coinos-cache';
const STORE = 'kv';
const DEBOUNCE_MS = 1000;
const OPEN_WAIT_MS = 3000;

// What lives here: rebuildable caches only. State a user would miss (read
// markers, drafts, the follow list, sync outboxes) stays in localStorage,
// where every tab sees every other tab's writes at once.
const WALLET_CACHES = ['profiles', 'profilesFaceless', 'reports', 'followPacks', 'profPages', 'relayLists'];
const WALLET_RE = new RegExp('^btc-wallet-cache:[0-9a-f]+:(' + WALLET_CACHES.join('|') + ')$');
const GLOBAL_KEYS = new Set([
  // (btc-wallet-note-threads stays: a server-rendered note page seeds it
  // before boot has waited for anything)
  'coinos-mod-baseline', 'coinos-community-directory-v1',
  'coinos-link-previews', 'coinos-video-info', 'coinos-video-dims', 'btc-wallet-search-profiles',
]);
export const isCacheKey = (k) => typeof k === 'string' && (GLOBAL_KEYS.has(k) || WALLET_RE.test(k));

function idbBackend() {
  if (typeof indexedDB === 'undefined') return null;
  let dbp = null;
  const open = () => dbp || (dbp = new Promise((resolve, reject) => {
    const req = indexedDB.open(DB, 1);
    req.onupgradeneeded = () => { if (!req.result.objectStoreNames.contains(STORE)) req.result.createObjectStore(STORE); };
    req.onsuccess = () => {
      const db = req.result;
      db.onversionchange = () => { try { db.close(); } catch {} dbp = null; };
      db.onclose = () => { dbp = null; };
      resolve(db);
    };
    req.onerror = () => { dbp = null; reject(req.error); };
    req.onblocked = () => { dbp = null; reject(new Error('IndexedDB blocked')); };
  }));
  return {
    async list() {
      const db = await open();
      return new Promise((resolve, reject) => {
        const t = db.transaction(STORE, 'readonly');
        const s = t.objectStore(STORE);
        const keys = s.getAllKeys(), vals = s.getAll();
        t.oncomplete = () => resolve(keys.result.map((k, i) => [k, vals.result[i]]));
        t.onerror = () => reject(t.error);
      });
    },
    async write(puts, dels) {
      if (!puts.length && !dels.length) return;
      const db = await open();
      return new Promise((resolve, reject) => {
        const t = db.transaction(STORE, 'readwrite');
        const s = t.objectStore(STORE);
        for (const [k, v] of puts) s.put(v, k);
        for (const k of dels) s.delete(k);
        t.oncomplete = () => resolve();
        t.onerror = () => reject(t.error);
        t.onabort = () => reject(t.error || new Error('aborted'));
      });
    },
  };
}

export class CacheStore {
  constructor({ backend = idbBackend(), ls = () => globalThis.localStorage, listen = true } = {}) {
    this.backend = backend;
    this.ls = ls;
    this.mem = new Map();
    this.dirty = new Set();
    this.ready = !backend;
    this.timer = 0;
    this.opening = null;
    this._flushing = null;
    this._onReady = [];
    if (listen && typeof document !== 'undefined') {
      document.addEventListener('visibilitychange', () => { if (document.visibilityState === 'hidden') this.flush(); });
      addEventListener('pagehide', () => this.flush());
    }
  }
  get lsMode() { return !this.backend; }
  _ls() { try { return this.ls(); } catch { return null; } }

  open() {
    if (this.ready) return Promise.resolve();
    if (this.opening) return this.opening;
    this.opening = (async () => {
      let rows;
      try { rows = await this.backend.list(); } catch {
        this.backend = null; // IndexedDB refused (private mode, quota): stay on localStorage
        this._becomeReady();
        return;
      }
      for (const [k, v] of rows) if (typeof v === 'string') this.mem.set(k, v);
      const migrated = [];
      const ls = this._ls();
      if (ls) {
        for (let i = 0; i < ls.length; i++) {
          const k = ls.key(i);
          if (!isCacheKey(k)) continue;
          const v = ls.getItem(k);
          if (v != null) { this.mem.set(k, v); this.dirty.add(k); }
          migrated.push(k);
        }
      }
      this._becomeReady();
      if (migrated.length) {
        this.flush().then(() => {
          for (const k of migrated) { try { ls.removeItem(k); } catch {} }
        }).catch(() => {});
      }
    })();
    return this.opening;
  }
  _becomeReady() {
    this.ready = true;
    for (const fn of this._onReady.splice(0)) { try { fn(); } catch (e) { console.warn('cache ready hook:', e); } }
  }
  // Runs once the store has opened (at once if it already has).
  onReady(fn) { if (this.ready) { try { fn(); } catch {} } else this._onReady.push(fn); }

  getItem(key) {
    if (this.ready && !this.lsMode && isCacheKey(key)) {
      if (this.mem.has(key)) return this.mem.get(key);
      // a copy that reached localStorage after we opened (an older build in
      // another tab) moves in on first ask
      let v = null;
      try { v = this._ls().getItem(key); } catch {}
      if (v != null) this._adopt(key, v);
      return v;
    }
    try { return this._ls().getItem(key); } catch { return null; }
  }
  _adopt(key, v) {
    this.mem.set(key, v);
    this.dirty.add(key);
    this._schedule();
    const ls = this._ls();
    Promise.resolve(this._flushing || this.flush()).then(() => this.flush())
      .then(() => { try { if (ls.getItem(key) === v) ls.removeItem(key); } catch {} }).catch(() => {});
  }
  setItem(key, value) {
    value = String(value);
    if (!isCacheKey(key) || this.lsMode) { this._ls()?.setItem(key, value); return; }
    if (!this.ready) {
      // early: only a key that hasn't migrated yet may be written (see above)
      const ls = this._ls();
      try { if (ls && ls.getItem(key) != null) ls.setItem(key, value); } catch {}
      return;
    }
    if (this.mem.get(key) === value) return;
    this.mem.set(key, value);
    this.dirty.add(key);
    this._schedule();
  }
  removeItem(key) {
    try { this._ls()?.removeItem(key); } catch {}
    if (!isCacheKey(key) || this.lsMode || !this.ready) return;
    if (!this.mem.has(key)) return;
    this.mem.delete(key);
    this.dirty.add(key);
    this._schedule();
  }
  // Every cache key held, wherever it lives right now.
  keys() {
    const out = new Set(this.ready && !this.lsMode ? this.mem.keys() : []);
    const ls = this._ls();
    try { for (let i = 0; i < ls.length; i++) { const k = ls.key(i); if (isCacheKey(k)) out.add(k); } } catch {}
    return [...out];
  }
  // Wallet wipe: every cache under the wallet's key prefix.
  removePrefix(prefix) {
    for (const k of [...this.mem.keys()]) if (k.startsWith(prefix)) this.removeItem(k);
  }

  _schedule() {
    if (typeof document !== 'undefined' && document.visibilityState === 'hidden') { this.flush(); return; }
    if (this.timer) return;
    this.timer = setTimeout(() => { this.timer = 0; this.flush(); }, DEBOUNCE_MS);
  }
  flush() {
    if (this.timer) { clearTimeout(this.timer); this.timer = 0; }
    if (!this.ready || this.lsMode || !this.dirty.size) return this._flushing || Promise.resolve();
    if (this._flushing) return this._flushing.then(() => this.flush());
    const keys = [...this.dirty]; this.dirty.clear();
    const puts = [], dels = [];
    for (const k of keys) { if (this.mem.has(k)) puts.push([k, this.mem.get(k)]); else dels.push(k); }
    this._flushing = this.backend.write(puts, dels)
      .catch(() => { for (const k of keys) if (!this.dirty.has(k)) this.dirty.add(k); })
      .finally(() => { this._flushing = null; });
    return this._flushing;
  }
}

let shared = null;
export function cacheStore() {
  if (!shared) {
    shared = new CacheStore();
    shared.open().catch(() => {});
  }
  return shared;
}
// A Storage-shaped handle for code that used localStorage directly.
export const cacheStorage = {
  getItem: (k) => cacheStore().getItem(k),
  setItem: (k, v) => cacheStore().setItem(k, v),
  removeItem: (k) => cacheStore().removeItem(k),
  keys: () => cacheStore().keys(),
  flush: () => cacheStore().flush(),
};
export const onCacheReady = (fn) => cacheStore().onReady(fn);
// for tests and the console: what a cache holds, wherever it lives
try { globalThis.coinosCache = cacheStorage; } catch {}
// Boot waits for this, but never long: a wedged IndexedDB must not hold the
// wallet closed — the caches just start out empty.
export function cacheReady() {
  const s = cacheStore();
  if (s.ready) return Promise.resolve();
  return Promise.race([s.open(), new Promise((r) => setTimeout(r, OPEN_WAIT_MS))]);
}
export const cacheIsReady = () => cacheStore().ready;