import type * as http from 'node:http';
import type { Redis } from 'ioredis';
import type pg from 'pg';
import { loadConfig } from './config/load.js';
import type { Config } from './config/load.js';
import { createLogger } from './observability/logger.js';
import {
  createMetrics,
  startMetricsServer,
  createPostgresHealthCheck,
  createConsumerLagSampler,
} from './observability/metrics.js';
import { createPool, connectWithRetry } from './db/pool.js';
import { runMigrations } from './db/migrate.js';
import { connectRedis, createConsumer } from './core/consumer.js';
import type { ConsumedRecord } from './core/consumer.js';
import { createDeviceStateStore } from './core/state.js';
import { createWriter } from './core/writer.js';

// -------------------------------------------------------------------------
// Startup: validate config (fail fast on bad env), build logger
// -------------------------------------------------------------------------

let config: Config;
try {
  config = loadConfig();
} catch (err) {
  // Config validation failures print a human-readable message and exit 1.
  // Logger is not available yet — process.stderr is the only output channel.
  process.stderr.write(`${err instanceof Error ? err.message : String(err)}\n`);
  process.exit(1);
}

const logger = createLogger({
  level: config.LOG_LEVEL,
  nodeEnv: config.NODE_ENV,
  instanceId: config.INSTANCE_ID,
});

logger.info('processor starting');

// -------------------------------------------------------------------------
// Wire up the pipeline
// -------------------------------------------------------------------------

async function main(): Promise<void> {
  // 1. Build real prom-client metrics (replaces the trace-log shim from
  //    pre-1.9 main.ts). Metrics are wired before any I/O so that counters
  //    start at zero from the moment the process starts.
  const metrics = createMetrics();

  // 2. Connect Postgres with exponential-backoff retry
  const pool = createPool(config.POSTGRES_URL);
  await connectWithRetry(pool, logger);

  // 3. Run migrations before any consumer activity.
  //    Phase 1 limitation: multiple instances starting simultaneously both try
  //    to migrate. Postgres advisory locks would solve this — deferred to Phase 3
  //    (production hardening), which is acceptable for the Phase 1 single-instance
  //    pilot.
  await runMigrations(pool, logger);
  logger.info('migrations applied');

  // 4. Connect Redis with exponential-backoff retry
  const redis: Redis = await connectRedis(config.REDIS_URL, logger);

  // 5. Build pipeline components
  const state = createDeviceStateStore(config, logger, metrics);
  const writer = createWriter(pool, config, logger, metrics);

  // 6. Postgres health check — background cached SELECT 1 for /readyz.
  //    The check starts probing immediately so /readyz is accurate from the
  //    first request after the metrics server starts listening.
  const pgHealth = createPostgresHealthCheck(pool);

  // 7. Start metrics HTTP server.
  //    Bound before the consumer starts so /healthz responds even during the
  //    brief window between metrics-server start and first stream read.
  const metricsServer: http.Server = startMetricsServer(
    config.METRICS_PORT,
    () => metrics.serializeMetrics(),
    {
      isRedisReady: () => redis.status === 'ready',
      isPostgresReady: pgHealth.isReady,
    },
  );
  logger.info({ port: config.METRICS_PORT }, 'metrics server listening');

  // 8. Start consumer lag sampler (background interval, every 10 s).
  const lagSampler = createConsumerLagSampler(
    redis,
    config.REDIS_TELEMETRY_STREAM,
    config.REDIS_CONSUMER_GROUP,
    metrics,
    (msg) => logger.debug(msg),
  );

  // 9. Define the sink: central decision point for state update and Postgres write.
  //    State is updated BEFORE the write so that in-memory state is consistent with
  //    what has been seen, even if the Postgres write subsequently fails. If the write
  //    fails the record stays pending (not ACKed) and will be re-delivered — applying
  //    the same position twice to state is idempotent for last_position and last_seen;
  //    only position_count_session is double-counted, which is a session counter that
  //    resets on restart and is not a correctness concern.
  const sink = async (records: ConsumedRecord[]): Promise<string[]> => {
    // 9a. Update in-memory state for every record (cheap, synchronous-like, cannot
    //     fail meaningfully — Map operations do not throw).
    for (const record of records) {
      state.update(record.position);
    }

    // 9b. Emit device-state gauges (sampled per-batch; cheap).
    metrics.observe('processor_device_state_size', state.size());

    // 9c. Write to Postgres
    const results = await writer.write(records);

    // 9d. ACK only the IDs that succeeded or were already present.
    //     'failed' records are deliberately left pending for retry.
    const ackIds = results
      .filter((r) => r.status === 'inserted' || r.status === 'duplicate')
      .map((r) => r.id);

    if (ackIds.length > 0) {
      metrics.inc('processor_acks_total', undefined, ackIds.length);
    }

    return ackIds;
  };

  // 10. Build and start the consumer
  const consumer = createConsumer(redis, config, logger, metrics, sink);
  await consumer.start();

  // 11. Install graceful shutdown.
  //     Full Phase 3 hardening: explicit consumer-group commit on SIGTERM,
  //     uncaught-exception handler, multi-instance drain mode.
  installGracefulShutdown({
    redis,
    pool,
    consumer,
    metricsServer,
    pgHealth,
    lagSampler,
    logger,
  });

  logger.info(
    {
      stream: config.REDIS_TELEMETRY_STREAM,
      group: config.REDIS_CONSUMER_GROUP,
      consumer: config.REDIS_CONSUMER_NAME,
      metricsPort: config.METRICS_PORT,
    },
    'processor ready',
  );
}

// -------------------------------------------------------------------------
// Graceful shutdown — Phase 3 finalizes this
// -------------------------------------------------------------------------

type ShutdownDeps = {
  readonly redis: Redis;
  readonly pool: pg.Pool;
  readonly consumer: { stop: () => Promise<void> };
  readonly metricsServer: http.Server;
  readonly pgHealth: { stop: () => void };
  readonly lagSampler: { stop: () => void };
  readonly logger: ReturnType<typeof createLogger>;
};

function installGracefulShutdown(deps: ShutdownDeps): void {
  const { redis, pool, consumer, metricsServer, pgHealth, lagSampler, logger: log } = deps;

  let shuttingDown = false;

  function shutdown(signal: string): void {
    if (shuttingDown) return;
    shuttingDown = true;

    log.info({ signal }, 'shutdown signal received');

    // Cancel background intervals first — they hold no resources that need
    // draining, and stopping them early prevents spurious log noise during
    // the shutdown sequence.
    lagSampler.stop();
    pgHealth.stop();

    consumer
      .stop()
      .then(() => {
        log.info('consumer stopped');
        return new Promise<void>((resolve, reject) =>
          metricsServer.close((err) => (err ? reject(err) : resolve())),
        );
      })
      .then(() => {
        log.info('metrics server closed');
        return redis.quit();
      })
      .then(() => {
        log.info('Redis disconnected');
        return pool.end();
      })
      .then(() => {
        log.info('graceful shutdown complete');
        process.exit(0);
      })
      .catch((err: unknown) => {
        log.error({ err }, 'error during shutdown');
        process.exit(1);
      });

    // Force exit after 15s if the graceful path stalls (e.g. a hung Postgres write).
    setTimeout(() => {
      log.warn('forced exit after shutdown timeout');
      process.exit(1);
    }, 15_000).unref();
  }

  process.on('SIGTERM', () => shutdown('SIGTERM'));
  process.on('SIGINT', () => shutdown('SIGINT'));
}

// -------------------------------------------------------------------------
// Entry point
// -------------------------------------------------------------------------

main().catch((err: unknown) => {
  process.stderr.write(
    `Fatal startup error: ${err instanceof Error ? err.message : String(err)}\n`,
  );
  process.exit(1);
});