/***********************************************************************************************************************************************************************
 * File Name: health.service.js
 * Type of Program: Service
 * Description: Health check registry — runs all dependency checks and builds two response formats.
 *
 *   runDashboard()  → rich human-readable payload  (for GET /api/health)
 *   runReadiness()  → compact machine payload       (for GET /api/health/ready)
 *
 *   Both call runChecks() internally and share the same check results.
 *
 *   Check registry (CHECKS array):
 *     Each entry is self-contained — name, criticality, enable condition, metadata, and runner.
 *     To add a new infrastructure check: push one entry here. Nothing else changes.
 *
 *   Criticality model:
 *     critical: true  → failure → overall "unhealthy" → HTTP 503
 *     critical: false → failure → overall "degraded"  → HTTP 200
 *
 *   Checks included:
 *     ✓ database  — PostgreSQL via Sequelize            (CRITICAL)
 *     ✓ cache     — Redis PING; skipped in memory mode  (optional)
 *     ✓ storage   — S3/Garage HeadBucket                (optional)
 *     ✓ email     — Gmail API profile fetch (OAuth2)     (optional)
 *
 *   Checks intentionally excluded:
 *     ✗ chibisafe — third-party CDN; not owned infrastructure
 *     ✗ paypal    — third-party payment gateway; not owned infrastructure
 *
 * Author: Kenneth Obsequio (@lash0000)
 * Date Created: Jun. 20, 2026
 ***********************************************************************************************************************************************************************/
"use strict";

const os = require('os');

const sequelize          = require('../config/db.config');
const redis              = require('../config/redis.config');
const { ping: pingS3 }    = require('./s3.service');
const { ping: pingEmail } = require('./email.service');

const PKG        = require('../package.json');
const TIMEOUT_MS = 3000;

// ─── Connection status labels (internal status → human label) ─────────────────

const CONNECTION_LABEL = {
  healthy:   'established',
  unhealthy: 'unavailable',
  timeout:   'timeout',
  skipped:   'not configured',
};

// ─── Check registry ───────────────────────────────────────────────────────────
//
// Fields:
//   name      {string}   — key used in response JSON
//   critical  {boolean}  — true: 503 on failure; false: degraded (200)
//   enabled   {boolean}  — false: skipped entirely
//   skipNote  {string}   — shown in dashboard when enabled = false
//   meta      {object}   — extra context shown in the dashboard (provider, host, port, etc.)
//   run       {async fn} — throws on failure, resolves on success

const CHECKS = [
  {
    name:     'database',
    critical: true,
    enabled:  true,
    meta:     { dialect: 'postgresql', host: process.env.DB_HOST, port: Number(process.env.DB_PORT) || 5432 },
    run:      () => sequelize.authenticate(),
  },
  {
    name:     'cache',
    critical: false,
    enabled:  !!redis,
    skipNote: 'CACHE_DRIVER=memory — Redis is not used in this environment',
    meta:     { driver: 'redis', url: process.env.REDIS_URL || 'redis://127.0.0.1:6379' },
    run:      () => redis.ping(),
  },
  {
    name:     'storage',
    critical: false,
    enabled:  !!(process.env.S3_ENDPOINT || process.env.S3_PUBLIC_URL),
    skipNote: 'S3_ENDPOINT is not configured',
    meta:     { provider: 's3', endpoint: process.env.S3_PUBLIC_URL ?? process.env.S3_ENDPOINT, bucket: process.env.S3_BUCKET },
    run:      pingS3,
  },
  {
    name:     'email',
    critical: false,
    enabled:  !!(process.env.GOOGLE_CLIENT_ID && process.env.GMAIL_REFRESH_TOKEN),
    skipNote: 'GMAIL_REFRESH_TOKEN is not configured',
    meta:     { provider: 'gmail-api', account: process.env.EMAIL_FROM },
    run:      pingEmail,
  },
];

// ─── Internal helpers ─────────────────────────────────────────────────────────

const mb = (bytes) => Math.round(bytes / 1024 / 1024 * 10) / 10;

function formatUptime(seconds) {
  if (seconds < 60)        return `${seconds} secs`;
  if (seconds < 3600)      return `${Math.floor(seconds / 60)} mins`;
  if (seconds < 86400)     return `${Math.floor(seconds / 3600)} hours`;
  if (seconds < 2592000)   return `${Math.floor(seconds / 86400)} days`;
  if (seconds < 31536000)  return `${Math.floor(seconds / 2592000)} months`;
  return `${Math.floor(seconds / 31536000)} years`;
}

function memoryInfo() {
  const m = process.memoryUsage();
  return {
    heap_used_mb:  mb(m.heapUsed),
    heap_total_mb: mb(m.heapTotal),
    rss_mb:        mb(m.rss),
    external_mb:   mb(m.external),
  };
}

function systemInfo() {
  const load = os.loadavg();
  return {
    platform: process.platform,
    arch:     process.arch,
    cpus:     os.cpus().length,
    load_avg: {
      '1m':  Math.round(load[0] * 100) / 100,
      '5m':  Math.round(load[1] * 100) / 100,
      '15m': Math.round(load[2] * 100) / 100,
    },
    memory:   memoryInfo(),
  };
}

function appInfo() {
  return {
    name:         PKG.name,
    version:      PKG.version,
    environment:  process.env.NODE_ENV || 'development',
    node_version: process.version,
    pid:          process.pid,
  };
}

// ─── Check runner ─────────────────────────────────────────────────────────────

async function runCheck(check) {
  const { name, critical, enabled, skipNote, run } = check;

  if (!enabled) {
    return [name, { status: 'skipped', note: skipNote, critical }];
  }

  const start = Date.now();
  try {
    await Promise.race([
      run(),
      new Promise((_, reject) =>
        setTimeout(() => reject(new Error('timeout')), TIMEOUT_MS)
      ),
    ]);
    return [name, { status: 'healthy', latency_ms: Date.now() - start, critical }];
  } catch (err) {
    return [name, {
      status:     err.message === 'timeout' ? 'timeout' : 'unhealthy',
      latency_ms: Date.now() - start,
      critical,
    }];
  }
}

async function runChecks() {
  const results = await Promise.all(CHECKS.map(runCheck));
  const checks  = Object.fromEntries(results);

  const criticalFailed = results.some(
    ([, r]) => r.critical && r.status !== 'healthy' && r.status !== 'skipped'
  );
  const anyDegraded = results.some(
    ([, r]) => !r.critical && r.status !== 'healthy' && r.status !== 'skipped'
  );

  const overallStatus = criticalFailed ? 'unhealthy'
                      : anyDegraded    ? 'degraded'
                      :                  'healthy';

  return { checks, criticalFailed, overallStatus };
}

// ─── Dashboard payload (GET /api/health) ─────────────────────────────────────
//
// Human-readable — full context: app info, system info, service connection details.
// Uses "established / unavailable / timeout / not configured" language.

async function runDashboard() {
  const { checks, criticalFailed, overallStatus } = await runChecks();

  const services = {};
  for (const check of CHECKS) {
    const result = checks[check.name];
    services[check.name] = {
      connection: CONNECTION_LABEL[result.status] ?? result.status,
      ...(result.latency_ms !== undefined && { latency_ms: result.latency_ms }),
      ...(result.note       !== undefined && { note:       result.note }),
      ...(check.meta        !== undefined && check.meta),
      critical: result.critical,
    };
  }

  return {
    httpStatus: criticalFailed ? 503 : 200,
    body: {
      status:    overallStatus,
      app:       appInfo(),
      uptime:    formatUptime(Math.floor(process.uptime())),
      timestamp: new Date().toISOString(),
      system:    systemInfo(),
      services,
    },
  };
}

// ─── Readiness payload (GET /api/health/ready) ───────────────────────────────
//
// Compact — intended for machines (Kubernetes probe, deployment scripts, CI gates).
// Uses "healthy / unhealthy / timeout / skipped" language.

async function runReadiness() {
  const { checks, criticalFailed, overallStatus } = await runChecks();

  return {
    httpStatus: criticalFailed ? 503 : 200,
    body: {
      status:    overallStatus,
      version:   PKG.version,
      uptime:    formatUptime(Math.floor(process.uptime())),
      timestamp: new Date().toISOString(),
      checks,
      memory:    memoryInfo(),
    },
  };
}

module.exports = { runDashboard, runReadiness };