// IndexedDB persistence: the Signal protocol store + app data (contacts, chats).
// Private keys live ONLY here, in the browser. They are never sent to the server.

const DB_NAME = "cipher";
const DB_VERSION = 1;

function openDB() {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, DB_VERSION);
    req.onupgradeneeded = () => {
      const db = req.result;
      // Signal protocol material (identity keypair, prekeys, sessions, peer identities).
      if (!db.objectStoreNames.contains("signal")) db.createObjectStore("signal");
      // App metadata (my account, settings).
      if (!db.objectStoreNames.contains("meta")) db.createObjectStore("meta");
      // Known contacts, keyed by userId.
      if (!db.objectStoreNames.contains("contacts")) db.createObjectStore("contacts", { keyPath: "userId" });
      // Message history, keyed by autoincrement, indexed by conversation.
      if (!db.objectStoreNames.contains("messages")) {
        const s = db.createObjectStore("messages", { keyPath: "id", autoIncrement: true });
        s.createIndex("convo", "convo");
      }
    };
    req.onsuccess = () => resolve(req.result);
    req.onerror = () => reject(req.error);
  });
}

let _db;
async function db() {
  if (!_db) _db = await openDB();
  return _db;
}

function tx(store, mode = "readonly") {
  return db().then((d) => d.transaction(store, mode).objectStore(store));
}

function reqP(request) {
  return new Promise((resolve, reject) => {
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

// ---- generic KV helpers over the "signal" and "meta" stores ----
async function kvGet(store, key) {
  return reqP((await tx(store)).get(key));
}
async function kvPut(store, key, val) {
  return reqP((await tx(store, "readwrite")).put(val, key));
}
async function kvDel(store, key) {
  return reqP((await tx(store, "readwrite")).delete(key));
}

export const meta = {
  get: (k) => kvGet("meta", k),
  set: (k, v) => kvPut("meta", k, v),
  del: (k) => kvDel("meta", k),
};

// ---- contacts ----
export const contacts = {
  async put(contact) {
    return reqP((await tx("contacts", "readwrite")).put(contact));
  },
  async get(userId) {
    return reqP((await tx("contacts")).get(userId));
  },
  async all() {
    return reqP((await tx("contacts")).getAll());
  },
};

// ---- messages ----
export const messages = {
  async add(msg) {
    return reqP((await tx("messages", "readwrite")).add(msg));
  },
  async forConvo(convo) {
    const idx = (await tx("messages")).index("convo");
    return reqP(idx.getAll(convo));
  },
};

// ---- Signal protocol store ----
// Implements the StorageType interface libsignal expects. Keys are strings;
// ArrayBuffers and records are stored directly (IndexedDB structured-clones them).
export class SignalStore {
  Direction = { SENDING: 1, RECEIVING: 2 };

  async getIdentityKeyPair() {
    return kvGet("signal", "identityKey");
  }
  async getLocalRegistrationId() {
    return kvGet("signal", "registrationId");
  }
  async setIdentity(keyPair, registrationId) {
    await kvPut("signal", "identityKey", keyPair);
    await kvPut("signal", "registrationId", registrationId);
  }

  // Trust-on-first-use: trust a new peer identity; reject if it silently changes.
  async isTrustedIdentity(identifier, identityKey /*, direction */) {
    const existing = await kvGet("signal", "identity/" + identifier);
    if (!existing) return true;
    return buffersEqual(existing, identityKey);
  }
  async saveIdentity(identifier, identityKey) {
    const addr = identifier.split(".")[0];
    const existing = await kvGet("signal", "identity/" + addr);
    await kvPut("signal", "identity/" + addr, identityKey);
    return !!existing && !buffersEqual(existing, identityKey); // true = identity changed
  }
  async loadIdentityKey(identifier) {
    return kvGet("signal", "identity/" + identifier.split(".")[0]);
  }

  async loadPreKey(keyId) {
    return kvGet("signal", "prekey/" + keyId);
  }
  async storePreKey(keyId, keyPair) {
    return kvPut("signal", "prekey/" + keyId, keyPair);
  }
  async removePreKey(keyId) {
    return kvDel("signal", "prekey/" + keyId);
  }

  async loadSignedPreKey(keyId) {
    return kvGet("signal", "signedprekey/" + keyId);
  }
  async storeSignedPreKey(keyId, keyPair) {
    return kvPut("signal", "signedprekey/" + keyId, keyPair);
  }
  async removeSignedPreKey(keyId) {
    return kvDel("signal", "signedprekey/" + keyId);
  }

  async loadSession(identifier) {
    return kvGet("signal", "session/" + identifier);
  }
  async storeSession(identifier, record) {
    return kvPut("signal", "session/" + identifier, record);
  }
  async removeSession(identifier) {
    return kvDel("signal", "session/" + identifier);
  }
  async removeAllSessions() {
    /* not needed for MVP */
  }
}

function buffersEqual(a, b) {
  const ua = new Uint8Array(a);
  const ub = new Uint8Array(b);
  if (ua.length !== ub.length) return false;
  let diff = 0;
  for (let i = 0; i < ua.length; i++) diff |= ua[i] ^ ub[i];
  return diff === 0;
}