const axios = require('axios');
const crypto = require('crypto');
const db    = require('../config/db');

const SEND_INTERVAL_MS = Number(process.env.SMS_SEND_INTERVAL_MS || 5000);
const MAX_ATTEMPTS = Number(process.env.SMS_MAX_ATTEMPTS || 4);
const RATE_LIMIT_BACKOFF_MS = Number(process.env.SMS_RATE_LIMIT_BACKOFF_MS || 60000);
const MAX_BACKOFF_MS = Number(process.env.SMS_MAX_BACKOFF_MS || 180000);
const DEFAULT_TTL_SECONDS = 24 * 60 * 60;
const DEFAULT_PRIORITY = 0;
const HIGH_PRIORITY = 100;

let sendQueue = Promise.resolve();
let lastSendAt = 0;
let rateLimitUntil = 0;

function normalizePhone(phone) {
  const d = phone.replace(/\D/g, '');
  if (d.startsWith('255')) return '+' + d;
  if (d.startsWith('0'))   return '+255' + d.slice(1);
  return '+255' + d;
}

function delay(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

function errorDetails(err) {
  const statusCode = err.response?.status;
  const body = err.response?.data;
  const bodyText = body
    ? ` body=${typeof body === 'string' ? body : JSON.stringify(body).slice(0, 180)}`
    : '';
  return `${err.message}${statusCode ? ` status=${statusCode}` : ''}${bodyText}`.slice(0, 255);
}

function retryAfterMs(err) {
  const retryAfter = err.response?.headers?.['retry-after'];
  if (!retryAfter) return null;

  const seconds = Number(retryAfter);
  if (Number.isFinite(seconds)) return Math.max(0, seconds * 1000);

  const dateMs = Date.parse(retryAfter);
  if (Number.isFinite(dateMs)) return Math.max(0, dateMs - Date.now());
  return null;
}

async function waitForTurn() {
  const cooldownMs = Math.max(0, rateLimitUntil - Date.now());
  if (cooldownMs > 0) await delay(cooldownMs);

  const elapsed = Date.now() - lastSendAt;
  const waitMs = Math.max(0, SEND_INTERVAL_MS - elapsed);
  if (waitMs > 0) await delay(waitMs);
  lastSendAt = Date.now();
}

function boundedNumber(value, fallback, min, max) {
  const number = Number(value);
  if (!Number.isFinite(number)) return fallback;
  return Math.min(max, Math.max(min, Math.trunc(number)));
}

function buildPayload(to, message, options = {}) {
  const ttl = boundedNumber(options.ttl, DEFAULT_TTL_SECONDS, 60, 7 * 24 * 60 * 60);
  const priority = boundedNumber(options.priority, DEFAULT_PRIORITY, -128, 127);
  const payload = {
    id: options.id || crypto.randomUUID(),
    textMessage: { text: message },
    phoneNumbers: [to],
    ttl,
    priority,
    withDeliveryReport: options.withDeliveryReport === true,
  };

  if (options.deviceId) payload.deviceId = options.deviceId;
  if (options.simNumber !== undefined) {
    payload.simNumber = boundedNumber(options.simNumber, 1, 1, 3);
  }

  return payload;
}

async function postSMS(payload) {
  await waitForTurn();

  const res = await axios.post(
    process.env.SMS_GATEWAY_URL,
    payload,
    {
      auth: {
        username: process.env.SMS_GATEWAY_USER,
        password: process.env.SMS_GATEWAY_PASS,
      },
      timeout: 10000,
    }
  );

  return res.data?.id || payload.id || null;
}

async function sendWithRetry(to, message, options) {
  let lastError = null;
  const payload = buildPayload(to, message, options);

  for (let attempt = 1; attempt <= MAX_ATTEMPTS; attempt += 1) {
    try {
      return { sent: true, gatewayId: await postSMS(payload), error: null };
    } catch (err) {
      lastError = err;
      const statusCode = err.response?.status;
      const isRateLimited = statusCode === 429;
      const canRetry = isRateLimited && attempt < MAX_ATTEMPTS;
      const gatewayWait = retryAfterMs(err);
      const backoffMs = Math.min(gatewayWait || RATE_LIMIT_BACKOFF_MS * attempt, MAX_BACKOFF_MS);

      if (isRateLimited) {
        rateLimitUntil = Math.max(rateLimitUntil, Date.now() + backoffMs);
      }

      if (!canRetry) break;

      console.warn(`[SMS] Rate limited for ${to}; retrying attempt ${attempt + 1}/${MAX_ATTEMPTS} in ${backoffMs}ms`);
      await delay(backoffMs);
    }
  }

  return { sent: false, gatewayId: null, error: errorDetails(lastError) };
}

async function sendNow(phone, message, options = {}) {
  const to = normalizePhone(phone);
  const result = await sendWithRetry(to, message, options);
  const status = result.sent ? 'sent' : 'failed';

  if (result.sent) {
    console.log(`[SMS] Sent to ${to}: "${message.slice(0, 40)}..."`);
  } else {
    console.error(`[SMS] Failed to ${to}:`, result.error);
  }

  db.query(
    'INSERT INTO sms_log (phone, message, status, gateway_id, error) VALUES (?, ?, ?, ?, ?)',
    [to, message, status, result.gatewayId, result.error]
  ).catch(() => {});

  return result.sent;
}

async function sendSMS(phone, message, options = {}) {
  const queued = sendQueue.then(() => sendNow(phone, message, options));
  sendQueue = queued.catch(() => {});
  return queued;
}

module.exports = {
  sendSMS,
  priorities: {
    high: HIGH_PRIORITY,
    normal: DEFAULT_PRIORITY,
    low: -50,
  },
};