const fs = require('node:fs/promises');
const { assertExternalSessionFile } = require('../config/telegram');

class TelegramSource {
  constructor(config) { this.config = config; this.client = null; this.channel = null; }

  async connect() {
    if (this.client?.connected && this.channel) return;
    if (this.client) await this.close();
    const file = await assertExternalSessionFile(this.config.sessionFile);
    const session = (await fs.readFile(file, 'utf8')).trim();
    if (!session) throw new Error('SESSION_MISSING');
    const { TelegramClient } = require('teleproto');
    const { StringSession } = require('teleproto/sessions');
    const { Logger } = require('teleproto/extensions/Logger');
    const client = new TelegramClient(new StringSession(session), this.config.apiId, this.config.apiHash, {
      connectionRetries: 2, requestRetries: 2, floodSleepThreshold: 0, baseLogger: new Logger('none')
    });
    this.client = client;
    await client.connect();
    if (!await client.checkAuthorization()) throw new Error('AUTH_REQUIRED');
    if ((await client.getMe()).bot) throw new Error('USER_ACCOUNT_REQUIRED');
    const channel = await client.getEntity(this.config.channel);
    if (channel.className !== 'Channel' || !channel.broadcast || channel.username?.toLowerCase() !== this.config.channel.toLowerCase()) {
      throw new Error('CHANNEL_INVALID');
    }
    this.channel = channel;
  }

  async fetchMessages(since) {
    await this.connect();
    const messages = [];
    // Pagination revisits recent messages so edits are detected after restarts.
    // The bound prevents an accidental full-history import of a busy channel.
    for await (const message of this.client.iterMessages(this.channel, { limit: 1000, waitTime: 1 })) {
      if (message.date && message.date * 1000 < since.getTime()) return messages.reverse();
      if (message.className !== 'Message' || !message.date) continue;
      messages.push({
        channelId: this.channel.id.toString(), channelUsername: this.channel.username,
        messageId: message.id, text: message.message || '', hasMedia: Boolean(message.media && message.media.className !== 'MessageMediaWebPage'),
        publishedAt: new Date(message.date * 1000).toISOString(),
        editedAt: message.editDate ? new Date(message.editDate * 1000).toISOString() : null
      });
    }
    if (messages.length >= 1000) throw new Error('HISTORY_LIMIT');
    return messages.reverse();
  }

  async close() {
    const client = this.client;
    this.client = null;
    this.channel = null;
    if (client) await client.destroy();
  }
}

module.exports = { TelegramSource };