/**
 * Unit tests for src/observability/metrics.ts
 *
 * Covers:
 *  - createMetrics(): Prometheus exposition format contains all Phase 1 metrics
 *  - Counter increments via metrics.inc()
 *  - Histogram observation via metrics.observe()
 *  - Gauge set via metrics.observe() for processor_consumer_lag and processor_device_state_size
 *  - Unknown metric name is silently ignored (no throw)
 *  - startMetricsServer(): GET /metrics returns 200 with text/plain
 *  - startMetricsServer(): GET /healthz returns 200 {"status":"ok"}
 *  - startMetricsServer(): GET /readyz returns 200 when both deps are ready
 *  - startMetricsServer(): GET /readyz returns 503 when Redis is not ready
 *  - startMetricsServer(): GET /readyz returns 503 when Postgres is not ready
 *  - startMetricsServer(): GET /readyz returns 503 when neither dep is ready
 *  - startMetricsServer(): non-GET method returns 405
 *  - startMetricsServer(): unknown path returns 404
 *  - nodejs_* default metrics are present in the exposition output
 */

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

// ---------------------------------------------------------------------------
// HTTP helper — makes a simple GET (or other method) against the test server
// ---------------------------------------------------------------------------

function httpGet(
  port: number,
  path: string,
  method = 'GET',
): Promise<{ statusCode: number; body: string; contentType: string }> {
  return new Promise((resolve, reject) => {
    const req = http.request({ hostname: '127.0.0.1', port, path, method }, (res) => {
      let body = '';
      res.on('data', (chunk: Buffer) => {
        body += chunk.toString();
      });
      res.on('end', () => {
        resolve({
          statusCode: res.statusCode ?? 0,
          body,
          contentType: (res.headers['content-type'] as string | undefined) ?? '',
        });
      });
    });
    req.on('error', reject);
    req.end();
  });
}

// ---------------------------------------------------------------------------
// createMetrics tests
// ---------------------------------------------------------------------------

describe('createMetrics — exposition format', () => {
  it('returns valid Prometheus text format containing all Phase 1 metrics', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();

    // Every metric from the task 1.9 inventory must appear in the output.
    expect(text).toContain('processor_consumer_reads_total');
    expect(text).toContain('processor_consumer_records_total');
    expect(text).toContain('processor_consumer_lag');
    expect(text).toContain('processor_decode_errors_total');
    expect(text).toContain('processor_position_writes_total');
    expect(text).toContain('processor_position_write_duration_seconds');
    expect(text).toContain('processor_acks_total');
    expect(text).toContain('processor_device_state_size');
    expect(text).toContain('processor_device_state_evictions_total');

    // Default Node.js process metrics must be present.
    expect(text).toContain('nodejs_');
  });

  it('label-less counters appear in the exposition at 0 before any inc() call', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();

    // prom-client emits label-less counters at 0 from the start.
    // Counters with label dims only appear once .inc() is called with a label value.
    expect(text).toMatch(/processor_consumer_records_total\s+0/);
    expect(text).toMatch(/processor_decode_errors_total\s+0/);
    expect(text).toMatch(/processor_acks_total\s+0/);
    expect(text).toMatch(/processor_device_state_evictions_total\s+0/);
  });
});

describe('createMetrics — counter increments', () => {
  it('increments processor_consumer_reads_total with label', async () => {
    const metrics = createMetrics();
    metrics.inc('processor_consumer_reads_total', { result: 'ok' });
    metrics.inc('processor_consumer_reads_total', { result: 'ok' });
    metrics.inc('processor_consumer_reads_total', { result: 'empty' });

    const text = await metrics.serializeMetrics();
    // result="ok" incremented twice
    expect(text).toMatch(/processor_consumer_reads_total\{result="ok"\} 2/);
    // result="empty" incremented once
    expect(text).toMatch(/processor_consumer_reads_total\{result="empty"\} 1/);
  });

  it('increments processor_consumer_records_total', async () => {
    const metrics = createMetrics();
    metrics.inc('processor_consumer_records_total');
    metrics.inc('processor_consumer_records_total');
    metrics.inc('processor_consumer_records_total');

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/processor_consumer_records_total\s+3/);
  });

  it('increments processor_decode_errors_total', async () => {
    const metrics = createMetrics();
    metrics.inc('processor_decode_errors_total');

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/processor_decode_errors_total\s+1/);
  });

  it('increments processor_position_writes_total with status label', async () => {
    const metrics = createMetrics();
    metrics.inc('processor_position_writes_total', { status: 'inserted' });
    metrics.inc('processor_position_writes_total', { status: 'duplicate' });
    metrics.inc('processor_position_writes_total', { status: 'failed' });

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/processor_position_writes_total\{status="inserted"\} 1/);
    expect(text).toMatch(/processor_position_writes_total\{status="duplicate"\} 1/);
    expect(text).toMatch(/processor_position_writes_total\{status="failed"\} 1/);
  });

  it('increments processor_acks_total', async () => {
    const metrics = createMetrics();
    metrics.inc('processor_acks_total');
    metrics.inc('processor_acks_total');

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/processor_acks_total\s+2/);
  });

  it('increments processor_device_state_evictions_total', async () => {
    const metrics = createMetrics();
    metrics.inc('processor_device_state_evictions_total');

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/processor_device_state_evictions_total\s+1/);
  });

  it('silently ignores unknown metric names', () => {
    const metrics = createMetrics();
    // Must not throw
    expect(() => metrics.inc('no_such_metric_total')).not.toThrow();
    expect(() => metrics.observe('no_such_metric', 42)).not.toThrow();
  });
});

describe('createMetrics — gauge and histogram', () => {
  it('sets processor_consumer_lag via observe()', async () => {
    const metrics = createMetrics();
    metrics.observe('processor_consumer_lag', 42);

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

  it('sets processor_device_state_size via observe()', async () => {
    const metrics = createMetrics();
    metrics.observe('processor_device_state_size', 7);

    const text = await metrics.serializeMetrics();
    expect(text).toMatch(/processor_device_state_size\s+7/);
  });

  it('records processor_position_write_duration_seconds histogram observation', async () => {
    const metrics = createMetrics();
    metrics.observe('processor_position_write_duration_seconds', 0.007);

    const text = await metrics.serializeMetrics();
    // Histogram emits _bucket, _sum, _count lines.
    expect(text).toContain('processor_position_write_duration_seconds_sum');
    expect(text).toContain('processor_position_write_duration_seconds_count 1');
  });

  it('histogram buckets include all spec-defined breakpoints', async () => {
    const metrics = createMetrics();
    const text = await metrics.serializeMetrics();

    // Spec buckets: [0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 5]
    const expectedBuckets = ['0.001', '0.005', '0.01', '0.05', '0.1', '0.5', '1', '5'];
    for (const bucket of expectedBuckets) {
      expect(text).toContain(`le="${bucket}"`);
    }
  });
});

// ---------------------------------------------------------------------------
// startMetricsServer tests
// ---------------------------------------------------------------------------

describe('startMetricsServer — HTTP endpoints', () => {
  let server: http.Server;
  let port: number;
  let isRedisReady = true;
  let isPostgresReady = true;

  const readyzDeps: ReadyzDeps = {
    isRedisReady: () => isRedisReady,
    isPostgresReady: () => isPostgresReady,
  };

  beforeAll(async () => {
    const metrics = createMetrics();
    server = startMetricsServer(0, () => metrics.serializeMetrics(), readyzDeps);
    // Wait for the server to bind a port (port=0 lets OS pick)
    await new Promise<void>((resolve) => {
      if (server.listening) {
        resolve();
      } else {
        server.once('listening', () => resolve());
      }
    });
    const addr = server.address();
    port = typeof addr === 'object' && addr !== null ? addr.port : 0;
  });

  afterAll(async () => {
    await new Promise<void>((resolve, reject) =>
      server.close((err) => (err ? reject(err) : resolve())),
    );
  });

  it('GET /metrics returns 200 with Prometheus content-type', async () => {
    const res = await httpGet(port, '/metrics');
    expect(res.statusCode).toBe(200);
    expect(res.contentType).toMatch('text/plain');
    expect(res.body).toContain('processor_consumer_reads_total');
  });

  it('GET /healthz returns 200 with {"status":"ok"}', async () => {
    const res = await httpGet(port, '/healthz');
    expect(res.statusCode).toBe(200);
    expect(JSON.parse(res.body)).toEqual({ status: 'ok' });
  });

  it('GET /readyz returns 200 when both Redis and Postgres are ready', async () => {
    isRedisReady = true;
    isPostgresReady = true;
    const res = await httpGet(port, '/readyz');
    expect(res.statusCode).toBe(200);
    expect(JSON.parse(res.body)).toEqual({ status: 'ok' });
  });

  it('GET /readyz returns 503 when Redis is not ready', async () => {
    isRedisReady = false;
    isPostgresReady = true;
    const res = await httpGet(port, '/readyz');
    expect(res.statusCode).toBe(503);
    const body = JSON.parse(res.body) as { status: string; redis: boolean; postgres: boolean };
    expect(body.status).toBe('not ready');
    expect(body.redis).toBe(false);
    expect(body.postgres).toBe(true);
    isRedisReady = true;
  });

  it('GET /readyz returns 503 when Postgres is not ready', async () => {
    isRedisReady = true;
    isPostgresReady = false;
    const res = await httpGet(port, '/readyz');
    expect(res.statusCode).toBe(503);
    const body = JSON.parse(res.body) as { status: string; redis: boolean; postgres: boolean };
    expect(body.status).toBe('not ready');
    expect(body.redis).toBe(true);
    expect(body.postgres).toBe(false);
    isPostgresReady = true;
  });

  it('GET /readyz returns 503 when both Redis and Postgres are not ready', async () => {
    isRedisReady = false;
    isPostgresReady = false;
    const res = await httpGet(port, '/readyz');
    expect(res.statusCode).toBe(503);
    const body = JSON.parse(res.body) as { status: string; redis: boolean; postgres: boolean };
    expect(body.redis).toBe(false);
    expect(body.postgres).toBe(false);
    isRedisReady = true;
    isPostgresReady = true;
  });

  it('non-GET request returns 405', async () => {
    const res = await httpGet(port, '/metrics', 'POST');
    expect(res.statusCode).toBe(405);
  });

  it('unknown path returns 404', async () => {
    const res = await httpGet(port, '/not-found');
    expect(res.statusCode).toBe(404);
  });
});

describe('startMetricsServer — /metrics error path', () => {
  it('returns 500 when serializeMetrics rejects', async () => {
    const serializeMetrics = vi.fn().mockRejectedValue(new Error('prom-client exploded'));
    const server = startMetricsServer(
      0,
      serializeMetrics,
      { isRedisReady: () => true, isPostgresReady: () => true },
    );

    await new Promise<void>((resolve) => {
      if (server.listening) resolve();
      else server.once('listening', () => resolve());
    });

    const addr = server.address();
    const port = typeof addr === 'object' && addr !== null ? addr.port : 0;

    const res = await httpGet(port, '/metrics');
    expect(res.statusCode).toBe(500);
    expect(res.body).toContain('prom-client exploded');

    await new Promise<void>((resolve, reject) =>
      server.close((err) => (err ? reject(err) : resolve())),
    );
  });
});