const queue = require('./queue');
const client = require('./client');
const logger = require('../utils/logger');
const config = require('../../config/app');

let running = false;
let workerPromise;

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

const transientCodes = new Set(['ECONNRESET', 'ETIMEDOUT', 'ECONNREFUSED', 'EAI_AGAIN', 'ENETUNREACH']);

function buildNextAttempt(attempts) {
  const schedule = config.retries.schedule;
  const index = Math.min(attempts - 1, schedule.length - 1);
  const delaySeconds = schedule[index] || schedule[schedule.length - 1] || 60;
  return Math.floor(Date.now() / 1000) + delaySeconds;
}

function isTransientError(err) {
  if (!err) return true;
  if (err.code && transientCodes.has(err.code)) return true;
  if (err.message && err.message.toLowerCase().includes('timeout')) return true;
  return false;
}

async function handleEntry(entry) {
  const payload = JSON.parse(entry.canonical_payload);
  const attemptNumber = entry.attempts + 1;
  let response;
  let attemptStatus = 'failure';

  try {
    response = await client.deliver(payload);
    attemptStatus = response.code >= 200 && response.code < 300 ? 'success' : 'failure';
    await queue.recordDeliveryAttempt({
      outboxId: entry.id,
      attempt: attemptNumber,
      status: attemptStatus,
      responseCode: response.code,
      responseBody: response.body,
      latency: response.latency
    });

    if (attemptStatus === 'success') {
      await queue.markOutboxStatus(entry.id, 'processed', {
        attempts: attemptNumber,
        lastError: null,
        nextAttemptAt: Math.floor(Date.now() / 1000)
      });
      return;
    }

    if (response.code === 400 || response.code === 422) {
      await queue.markOutboxStatus(entry.id, 'dead_letter', {
        attempts: attemptNumber,
        lastError: `HTTP ${response.code}`,
        nextAttemptAt: Math.floor(Date.now() / 1000)
      });
      await queue.moveToDeadLetter(payload, `HTTP ${response.code}`);
      return;
    }

    if (attemptNumber >= config.retries.maxAttempts) {
      await queue.markOutboxStatus(entry.id, 'dead_letter', {
        attempts: attemptNumber,
        lastError: response.body,
        nextAttemptAt: Math.floor(Date.now() / 1000)
      });
      await queue.moveToDeadLetter(payload, response.body);
      return;
    }

    const nextAttemptAt = buildNextAttempt(attemptNumber);
    await queue.markOutboxStatus(entry.id, 'retrying', {
      attempts: attemptNumber,
      lastError: `HTTP ${response.code}`,
      nextAttemptAt
    });
  } catch (error) {
    await queue.recordDeliveryAttempt({
      outboxId: entry.id,
      attempt: attemptNumber,
      status: 'failure',
      responseCode: null,
      responseBody: error.message,
      latency: null
    });

    const shouldDeadLetter = attemptNumber >= config.retries.maxAttempts || !isTransientError(error);
    if (shouldDeadLetter) {
      await queue.markOutboxStatus(entry.id, 'dead_letter', {
        attempts: attemptNumber,
        lastError: error.message,
        nextAttemptAt: Math.floor(Date.now() / 1000)
      });
      await queue.moveToDeadLetter(payload, error.message);
      return;
    }
    const nextAttemptAt = buildNextAttempt(attemptNumber);
    await queue.markOutboxStatus(entry.id, 'retrying', {
      attempts: attemptNumber,
      lastError: error.message,
      nextAttemptAt
    });
  }
}

async function loop() {
  while (running) {
    try {
      const batch = await queue.claimPending(config.worker.batchSize, config.worker.workerId);
      if (!batch.length) {
        await sleep(config.worker.pollInterval);
        continue;
      }
      for (const entry of batch) {
        await handleEntry(entry);
      }
    } catch (err) {
      logger.error({ err: err.message }, 'delivery worker error');
      await sleep(config.worker.pollInterval);
    }
  }
}

async function startWorker() {
  if (running) return;
  running = true;
  workerPromise = loop();
}

async function stopWorker() {
  running = false;
  if (workerPromise) {
    await workerPromise;
  }
}

module.exports = { startWorker, stopWorker };