'use strict';

const express = require('express');
const { Transform } = require('stream');

const app = express();
const PORT = process.env.PORT || 3200;
const LOKI_URL = process.env.LOKI_URL || 'http://loki:3100';
const API_KEY = process.env.LOG_EXPORTER_API_KEY;

// ─── Helpers ─────────────────────────────────────────────────────────────────

/**
 * Simple API key middleware (optional, enabled when LOG_EXPORTER_API_KEY is set).
 */
function authMiddleware(req, res, next) {
  if (!API_KEY) return next();
  const key = req.headers['x-api-key'] || req.query.apiKey;
  if (key !== API_KEY) {
    return res.status(401).json({ error: 'Unauthorized' });
  }
  next();
}

/**
 * Build a Loki LogQL query from request params.
 * Supports: service, level, search (free text filter)
 */
function buildLogQLQuery({ service, level, search }) {
  const labelFilters = [];

  if (service && service !== 'all') {
    const services = service.split(',').map((s) => s.trim()).filter(Boolean);
    if (services.length === 1) {
      labelFilters.push(`service="${services[0]}"`);
    } else {
      labelFilters.push(`service=~"${services.join('|')}"`);
    }
  }

  if (level && level !== 'all') {
    const levels = level.split(',').map((l) => l.trim()).filter(Boolean);
    if (levels.length === 1) {
      labelFilters.push(`level="${levels[0]}"`);
    } else {
      labelFilters.push(`level=~"${levels.join('|')}"`);
    }
  }

  const streamSelector = labelFilters.length > 0
    ? `{${labelFilters.join(', ')}}`
    : `{service=~".+"}`;

  const lineFilters = search ? ` |= \`${search}\`` : '';

  return `${streamSelector}${lineFilters}`;
}

/**
 * Query Loki's query_range endpoint and return flattened log entries.
 */
async function queryLoki({ query, start, end, limit = 5000 }) {
  const params = new URLSearchParams({
    query,
    start: String(start),
    end: String(end),
    limit: String(Math.min(limit, 5000)),
    direction: 'BACKWARD',
  });

  const url = `${LOKI_URL}/loki/api/v1/query_range?${params}`;

  const response = await fetch(url, {
    headers: { 'Accept': 'application/json' },
    signal: AbortSignal.timeout(30000),
  });

  if (!response.ok) {
    const body = await response.text();
    throw new Error(`Loki query failed (${response.status}): ${body}`);
  }

  const data = await response.json();

  if (data.status !== 'success') {
    throw new Error(`Loki returned status: ${data.status}`);
  }

  // Flatten streams → individual log entries
  const entries = [];
  for (const stream of data.data.result || []) {
    const labels = stream.stream || {};
    for (const [tsNano, line] of stream.values || []) {
      let parsed = {};
      try {
        parsed = JSON.parse(line);
      } catch {
        parsed = { msg: line };
      }

      entries.push({
        timestamp: new Date(Math.floor(Number(tsNano) / 1e6)).toISOString(),
        service: labels.service || labels.container || 'unknown',
        level: labels.level || parsed.level || 'info',
        context: labels.context || parsed.context || '',
        message: parsed.msg || parsed.message || line,
        reqId: parsed.reqId || '',
        req_method: parsed.req?.method || '',
        req_url: parsed.req?.url || '',
        res_status: parsed.res?.statusCode || '',
        response_time_ms: parsed.responseTime || '',
        error: parsed.err?.message || '',
        raw: line,
      });
    }
  }

  // Sort by timestamp ascending
  entries.sort((a, b) => new Date(a.timestamp) - new Date(b.timestamp));
  return entries;
}

/**
 * Convert array of objects to CSV string.
 */
function toCSV(entries) {
  if (entries.length === 0) return '';

  const headers = [
    'timestamp', 'service', 'level', 'context',
    'message', 'reqId', 'req_method', 'req_url',
    'res_status', 'response_time_ms', 'error',
  ];

  const escape = (val) => {
    if (val === null || val === undefined) return '';
    const str = String(val);
    if (str.includes(',') || str.includes('"') || str.includes('\n')) {
      return `"${str.replace(/"/g, '""')}"`;
    }
    return str;
  };

  const rows = [headers.join(',')];
  for (const entry of entries) {
    rows.push(headers.map((h) => escape(entry[h])).join(','));
  }
  return rows.join('\n');
}

// ─── Routes ──────────────────────────────────────────────────────────────────

app.use(express.json());

// Rate limiting (basic — 60 requests/min per IP)
const requestCounts = new Map();
setInterval(() => requestCounts.clear(), 60000);

app.use((req, res, next) => {
  const ip = req.ip;
  const count = (requestCounts.get(ip) || 0) + 1;
  requestCounts.set(ip, count);
  if (count > 60) {
    return res.status(429).json({ error: 'Too Many Requests' });
  }
  next();
});

// CORS for Grafana / frontend
app.use((req, res, next) => {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, x-api-key');
  res.setHeader('Access-Control-Allow-Methods', 'GET, OPTIONS');
  if (req.method === 'OPTIONS') return res.sendStatus(204);
  next();
});

/**
 * GET /health
 */
app.get('/health', (req, res) => {
  res.json({ status: 'ok', loki: LOKI_URL });
});

/**
 * GET /api/logs/services
 * Returns the list of services currently emitting logs.
 */
app.get('/api/logs/services', authMiddleware, async (req, res) => {
  try {
    const response = await fetch(`${LOKI_URL}/loki/api/v1/label/service/values`, {
      signal: AbortSignal.timeout(5000),
    });
    if (!response.ok) throw new Error(`Loki error: ${response.status}`);
    const data = await response.json();
    res.json({ services: data.data || [] });
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

/**
 * GET /api/logs/labels
 * Returns all available label names.
 */
app.get('/api/logs/labels', authMiddleware, async (req, res) => {
  try {
    const response = await fetch(`${LOKI_URL}/loki/api/v1/labels`, {
      signal: AbortSignal.timeout(5000),
    });
    if (!response.ok) throw new Error(`Loki error: ${response.status}`);
    const data = await response.json();
    res.json({ labels: data.data || [] });
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

/**
 * GET /api/logs/export
 *
 * Query params:
 *   - start     : ISO date or Unix timestamp in ns (default: 1h ago)
 *   - end       : ISO date or Unix timestamp in ns (default: now)
 *   - service   : comma-separated service names (default: all)
 *   - level     : comma-separated levels: error,warn,info,debug (default: all)
 *   - search    : free-text search string
 *   - limit     : max number of log lines (default: 5000, max: 5000)
 *   - format    : "json" | "csv" (default: json)
 *
 * Examples:
 *   GET /api/logs/export?service=backend&level=error&format=csv
 *   GET /api/logs/export?start=2024-01-01T00:00:00Z&end=2024-01-02T00:00:00Z&format=json
 */
app.get('/api/logs/export', authMiddleware, async (req, res) => {
  try {
    const now = Date.now();
    const ONE_HOUR_NS = 3600 * 1e9;
    const nowNs = BigInt(now) * 1000000n;
    const oneHourAgoNs = nowNs - BigInt(ONE_HOUR_NS);

    // Parse time range
    const parseTime = (val, defaultNs) => {
      if (!val) return defaultNs;
      // Already in nanoseconds (large number)
      if (/^\d{18,}$/.test(val)) return BigInt(val);
      // Unix timestamp in seconds or ms
      const n = Number(val);
      if (!isNaN(n)) {
        // seconds → ns
        if (n < 1e12) return BigInt(Math.floor(n * 1e9));
        // ms → ns
        if (n < 1e15) return BigInt(n) * 1000000n;
        return BigInt(n);
      }
      // ISO date string
      const ms = Date.parse(val);
      if (isNaN(ms)) throw new Error(`Invalid time value: ${val}`);
      return BigInt(ms) * 1000000n;
    };

    const startNs = parseTime(req.query.start, oneHourAgoNs);
    const endNs = parseTime(req.query.end, nowNs);

    if (endNs <= startNs) {
      return res.status(400).json({ error: '"end" must be after "start"' });
    }

    const format = (req.query.format || 'json').toLowerCase();
    if (!['json', 'csv'].includes(format)) {
      return res.status(400).json({ error: 'format must be "json" or "csv"' });
    }

    const limit = Math.min(parseInt(req.query.limit, 10) || 5000, 5000);

    const query = buildLogQLQuery({
      service: req.query.service,
      level: req.query.level,
      search: req.query.search,
    });

    const entries = await queryLoki({
      query,
      start: startNs.toString(),
      end: endNs.toString(),
      limit,
    });

    if (format === 'csv') {
      const csv = toCSV(entries);
      const filename = `xpeditis-logs-${new Date().toISOString().slice(0, 10)}.csv`;
      res.setHeader('Content-Type', 'text/csv; charset=utf-8');
      res.setHeader('Content-Disposition', `attachment; filename="${filename}"`);
      return res.send(csv);
    }

    // JSON response
    res.json({
      total: entries.length,
      query,
      range: {
        from: new Date(Number(startNs / 1000000n)).toISOString(),
        to: new Date(Number(endNs / 1000000n)).toISOString(),
      },
      logs: entries,
    });
  } catch (err) {
    console.error('[log-exporter] Export error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// ─── Start ────────────────────────────────────────────────────────────────────

app.listen(PORT, () => {
  console.log(`[log-exporter] Listening on port ${PORT}`);
  console.log(`[log-exporter] Loki URL: ${LOKI_URL}`);
  console.log(`[log-exporter] API key protection: ${API_KEY ? 'enabled' : 'disabled'}`);
});