/**
 * Unit tests for src/observability/metrics.ts
 *
 * Covers:
 *  - serializeMetrics() returns valid Prometheus exposition format with the
 *    full metric inventory present (some at zero)
 *  - counter increments are reflected in the serialized output
 *  - teltonika_unknown_codec_total{codec_id="0xff"} appears after an unknown-codec event
 *  - startMetricsServer responds correctly to /metrics, /healthz, and /readyz
 *  - /readyz returns 503 when Redis is not ready or TCP is not listening
 */

import { describe, it, expect, afterEach } from 'vitest';
import * as http from 'node:http';
import { createMetrics, startMetricsServer } from '../src/observability/metrics.js';
import type { ReadyzDeps } from '../src/observability/metrics.js';

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

/**
 * Makes an HTTP GET request and resolves with { statusCode, body }.
 * Uses the raw node:http module to match the server's implementation.
 */
function get(port: number, path: string): Promise<{ statusCode: number; body: string }> {
  return new Promise((resolve, reject) => {
    const req = http.get(`http://localhost:${port}${path}`, (res) => {
      let body = '';
      res.on('data', (chunk: Buffer) => {
        body += chunk.toString();
      });
      res.on('end', () => {
        resolve({ statusCode: res.statusCode ?? 0, body });
      });
    });
    req.on('error', reject);
  });
}

/**
 * Waits for a server to be listening, then runs `fn`, then closes the server.
 * Returns after the server is fully closed.
 */
function withServer(
  server: http.Server,
  fn: (port: number) => Promise<void>,
): Promise<void> {
  return new Promise((resolve, reject) => {
    server.once('listening', () => {
      const addr = server.address();
      const port = typeof addr === 'object' && addr !== null ? addr.port : 0;

      fn(port)
        .then(() => {
          server.close((err) => {
            if (err) reject(err);
            else resolve();
          });
        })
        .catch((err: unknown) => {
          server.close(() => reject(err));
        });
    });
    server.once('error', reject);
  });
}

// ---------------------------------------------------------------------------
// 1. serializeMetrics — Prometheus exposition format
// ---------------------------------------------------------------------------

describe('createMetrics — serializeMetrics', () => {
  it('returns a non-empty string', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();
    expect(typeof text).toBe('string');
    expect(text.length).toBeGreaterThan(0);
  });

  it('contains every teltonika_* metric in the Phase 1 inventory', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();

    const expectedMetrics = [
      'teltonika_connections_active',
      'teltonika_handshake_total',
      'teltonika_device_authority_failures_total',
      'teltonika_frames_total',
      'teltonika_records_published_total',
      'teltonika_parse_duration_seconds',
      'teltonika_unknown_codec_total',
      'teltonika_publish_queue_depth',
      'teltonika_publish_overflow_total',
      'teltonika_publish_duration_seconds',
    ];

    for (const name of expectedMetrics) {
      expect(text, `expected "${name}" in metrics output`).toContain(name);
    }
  });

  it('contains nodejs_* default process metrics', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();
    // prom-client collectDefaultMetrics registers nodejs_version_info at minimum
    expect(text).toContain('nodejs_');
  });

  it('exposition format contains HELP and TYPE lines', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();
    expect(text).toContain('# HELP teltonika_handshake_total');
    expect(text).toContain('# TYPE teltonika_handshake_total counter');
    expect(text).toContain('# HELP teltonika_frames_total');
    expect(text).toContain('# TYPE teltonika_frames_total counter');
  });
});

// ---------------------------------------------------------------------------
// 2. Counter increments
// ---------------------------------------------------------------------------

describe('createMetrics — counter increments', () => {
  it('increments teltonika_frames_total and teltonika_records_published_total', async () => {
    const metrics = createMetrics();

    // Simulate a successful Codec 8E frame
    metrics.inc('teltonika_frames_total', { codec: '8E', result: 'ok' });
    metrics.inc('teltonika_records_published_total', { codec: '8E' });

    const text = await metrics.serializeMetrics();

    // The exposition format for a counter with labels looks like:
    // teltonika_frames_total{codec="8E",result="ok"} 1
    expect(text).toMatch(/teltonika_frames_total\{[^}]*codec="8E"[^}]*result="ok"[^}]*\}\s+1/);
    expect(text).toMatch(/teltonika_records_published_total\{[^}]*codec="8E"[^}]*\}\s+1/);
  });

  it('accumulates multiple increments on the same label set', async () => {
    const metrics = createMetrics();

    metrics.inc('teltonika_frames_total', { codec: '8', result: 'ok' });
    metrics.inc('teltonika_frames_total', { codec: '8', result: 'ok' });
    metrics.inc('teltonika_frames_total', { codec: '8', result: 'ok' });

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/teltonika_frames_total\{[^}]*codec="8"[^}]*result="ok"[^}]*\}\s+3/);
  });

  it('tracks crc_fail result separately from ok', async () => {
    const metrics = createMetrics();

    metrics.inc('teltonika_frames_total', { codec: '8', result: 'ok' });
    metrics.inc('teltonika_frames_total', { codec: '8', result: 'crc_fail' });

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/teltonika_frames_total\{[^}]*codec="8"[^}]*result="ok"[^}]*\}\s+1/);
    expect(text).toMatch(/teltonika_frames_total\{[^}]*codec="8"[^}]*result="crc_fail"[^}]*\}\s+1/);
  });
});

// ---------------------------------------------------------------------------
// 3. Unknown codec canary
// ---------------------------------------------------------------------------

describe('createMetrics — unknown codec canary', () => {
  it('records teltonika_unknown_codec_total{codec_id="0xff"} after an unknown-codec event', async () => {
    const metrics = createMetrics();

    metrics.inc('teltonika_unknown_codec_total', { codec_id: '0xff' });

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/teltonika_unknown_codec_total\{[^}]*codec_id="0xff"[^}]*\}\s+1/);
  });

  it('distinguishes different codec_id values', async () => {
    const metrics = createMetrics();

    metrics.inc('teltonika_unknown_codec_total', { codec_id: '0x0f' });
    metrics.inc('teltonika_unknown_codec_total', { codec_id: '0x0f' });
    metrics.inc('teltonika_unknown_codec_total', { codec_id: '0x20' });

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/teltonika_unknown_codec_total\{[^}]*codec_id="0x0f"[^}]*\}\s+2/);
    expect(text).toMatch(/teltonika_unknown_codec_total\{[^}]*codec_id="0x20"[^}]*\}\s+1/);
  });
});

// ---------------------------------------------------------------------------
// 4. observe() — gauge and histogram
// ---------------------------------------------------------------------------

describe('createMetrics — observe', () => {
  it('sets teltonika_publish_queue_depth gauge', async () => {
    const metrics = createMetrics();

    metrics.observe('teltonika_publish_queue_depth', 42);

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/teltonika_publish_queue_depth\s+42/);
  });

  it('records teltonika_parse_duration_seconds histogram observation', async () => {
    const metrics = createMetrics();

    metrics.observe('teltonika_parse_duration_seconds', 0.0003, { codec: '8E' });

    const text = await metrics.serializeMetrics();
    // The histogram sum should contain the observed value
    expect(text).toMatch(/teltonika_parse_duration_seconds_sum\{[^}]*codec="8E"[^}]*\}\s+0\.0003/);
  });

  it('ignores unknown metric names without throwing', () => {
    const metrics = createMetrics();
    // Must not throw — the Metrics interface contract is never-throw
    expect(() => metrics.inc('teltonika_nonexistent_metric')).not.toThrow();
    expect(() => metrics.observe('teltonika_nonexistent_metric', 1.0)).not.toThrow();
  });
});

// ---------------------------------------------------------------------------
// 5. startMetricsServer — HTTP endpoint behaviour
// ---------------------------------------------------------------------------

describe('startMetricsServer', () => {
  // Track servers for cleanup in case of test failure
  const openServers: http.Server[] = [];

  afterEach(() => {
    for (const s of openServers) {
      if (s.listening) s.close();
    }
    openServers.length = 0;
  });

  it('GET /metrics returns 200 with Prometheus text', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => true,
      isTcpListening: () => true,
    };

    // port=0 → OS picks a free port
    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode, body } = await get(port, '/metrics');
      expect(statusCode).toBe(200);
      expect(body).toContain('teltonika_');
      expect(body).toContain('nodejs_');
    });
  });

  it('GET /healthz returns 200 regardless of Redis/TCP state', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => false, // deliberately unhealthy
      isTcpListening: () => false,
    };

    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode, body } = await get(port, '/healthz');
      expect(statusCode).toBe(200);
      expect(JSON.parse(body)).toEqual({ status: 'ok' });
    });
  });

  it('GET /readyz returns 200 when Redis is ready and TCP is listening', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => true,
      isTcpListening: () => true,
    };

    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode, body } = await get(port, '/readyz');
      expect(statusCode).toBe(200);
      expect(JSON.parse(body)).toEqual({ status: 'ok' });
    });
  });

  it('GET /readyz returns 503 when Redis is not ready', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => false,
      isTcpListening: () => true,
    };

    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode, body } = await get(port, '/readyz');
      expect(statusCode).toBe(503);
      const parsed = JSON.parse(body) as { status: string; redis: boolean; tcp: boolean };
      expect(parsed.status).toBe('not ready');
      expect(parsed.redis).toBe(false);
      expect(parsed.tcp).toBe(true);
    });
  });

  it('GET /readyz returns 503 when TCP server is not listening', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => true,
      isTcpListening: () => false,
    };

    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode } = await get(port, '/readyz');
      expect(statusCode).toBe(503);
    });
  });

  it('GET /readyz returns 503 when both Redis and TCP are down', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => false,
      isTcpListening: () => false,
    };

    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode, body } = await get(port, '/readyz');
      expect(statusCode).toBe(503);
      const parsed = JSON.parse(body) as { status: string; redis: boolean; tcp: boolean };
      expect(parsed.redis).toBe(false);
      expect(parsed.tcp).toBe(false);
    });
  });

  it('GET /unknown-path returns 404', async () => {
    const metrics = createMetrics();
    const readyzDeps: ReadyzDeps = {
      isRedisReady: () => true,
      isTcpListening: () => true,
    };

    const server = startMetricsServer(0, metrics.serializeMetrics, readyzDeps);
    openServers.push(server);

    await withServer(server, async (port) => {
      const { statusCode } = await get(port, '/not-a-real-endpoint');
      expect(statusCode).toBe(404);
    });
  });
});