import postgres from 'postgres';
import { GBrainError, type EngineConfig } from './types.ts';
import { SCHEMA_SQL } from './schema-embedded.ts';
import type { BrainEngine } from './engine.ts';
import { verifySchema } from './schema-verify.ts';

let sql: ReturnType<typeof postgres> | null = null;
let connectedUrl: string | null = null;

/**
 * Default pool size for Postgres connections. Users on the Supabase transaction
 * pooler (port 6543) or any multi-tenant pooler can lower this to avoid
 * MaxClients errors when `gbrain upgrade` spawns subprocesses that each open
 * their own pool. Set `GBRAIN_POOL_SIZE=2` (or similar) before the command.
 */
const DEFAULT_POOL_SIZE_FALLBACK = 10;

/**
 * Supabase PgBouncer transaction-mode convention: port 6543 routes through
 * PgBouncer, which recycles the backend connection between queries and
 * invalidates per-client prepared-statement caches. On that port postgres.js
 * defaults (prepare=true) surface as `prepared statement "..." does not exist`
 * under sustained load and silently drop rows during sync.
 *
 * This is a heuristic, not a protocol guarantee. A direct-Postgres server
 * deliberately bound to 6543 will also get `prepare: false`; the
 * `GBRAIN_PREPARE=true` env var (or `?prepare=true` on the URL) is the
 * documented escape hatch.
 */
const AUTO_DETECT_PORTS = new Set(['6543']);

/**
 * Decide whether to force `prepare: true`/`false` on the postgres.js client.
 *
 * Precedence:
 *   1. `GBRAIN_PREPARE` env var (`true`/`1` or `false`/`0`)
 *   2. `?prepare=true|false` query param on the URL
 *   3. Auto-detect: port 6543 → `false`
 *   4. Default: `undefined` (caller omits the option; postgres.js default stands)
 *
 * Returns `boolean | undefined`. `undefined` is meaningful — callers MUST
 * omit the `prepare` key entirely in that case rather than passing
 * `undefined` through to `postgres(url, {prepare: undefined})`.
 */
export function resolvePrepare(url: string): boolean | undefined {
  const envPrepare = process.env.GBRAIN_PREPARE;
  if (envPrepare === 'false' || envPrepare === '0') return false;
  if (envPrepare === 'true' || envPrepare === '1') return true;

  try {
    const parsed = new URL(url.replace(/^postgres(ql)?:\/\//, 'http://'));
    const urlPrepare = parsed.searchParams.get('prepare');
    if (urlPrepare === 'false') return false;
    if (urlPrepare === 'true') return true;

    if (AUTO_DETECT_PORTS.has(parsed.port)) {
      return false;
    }
  } catch {
    // URL parse failure — fall through to default
  }

  return undefined;
}

export function resolvePoolSize(explicit?: number): number {
  if (typeof explicit === 'number' && explicit > 0) return explicit;
  const raw = process.env.GBRAIN_POOL_SIZE;
  if (raw) {
    const parsed = parseInt(raw, 10);
    if (Number.isFinite(parsed) && parsed > 0) return parsed;
  }
  return DEFAULT_POOL_SIZE_FALLBACK;
}

/**
 * Session-level GUCs applied to every new backend connection. Prevents
 * orphan pgbouncer sessions from holding locks or running queries
 * indefinitely when the postgres.js client disconnects mid-transaction
 * (typical cause: autopilot SIGKILL'd by launchd, worker crash-loop,
 * or transient network drop).
 *
 * Observed failure mode these prevent: a single autopilot UPDATE on
 * `minion_jobs.lock_until` left a pooler backend in `state='active'`
 * / `wait_event='ClientRead'` for 24h+, holding a RowExclusiveLock
 * that blocked every subsequent `ALTER TABLE minion_jobs ...`.
 *
 * Defaults are conservative (chosen not to interfere with bulk work
 * like long-running embed passes or CREATE INDEX on large tables):
 *   - statement_timeout = '5min'
 *   - idle_in_transaction_session_timeout = '5min' (matches v0.18.0
 *     posture; #363's original 2min default was tightened to 5min on
 *     merge with v0.21.0's setSessionDefaults to avoid regressing
 *     long-running embed passes)
 *
 * Override per-GUC with env vars:
 *   - GBRAIN_STATEMENT_TIMEOUT
 *   - GBRAIN_IDLE_TX_TIMEOUT
 *   - GBRAIN_CLIENT_CHECK_INTERVAL (Postgres 14+; empty default - opt-in
 *     only since older self-hosted Postgres rejects this startup param)
 *
 * Set any env var to '0' or 'off' to disable that GUC entirely.
 *
 * Delivered via postgres.js's `connection` option, which sends these as
 * startup parameters in the initial connection packet. Works correctly
 * with PgBouncer session mode AND transaction mode: startup parameters
 * pass through to the backend on connection creation and persist for the
 * backend's lifetime (unlike `SET` commands which transaction-mode
 * PgBouncer strips between transactions).
 *
 * Supersedes the v0.21.0 `setSessionDefaults(sql)` helper, which used
 * a post-pool `SET` command. That approach is unreliable in PgBouncer
 * transaction mode (transaction-mode poolers strip session-state SETs
 * between transactions); startup parameters are durable.
 */
const DEFAULT_STATEMENT_TIMEOUT = '5min';
const DEFAULT_IDLE_TX_TIMEOUT = '5min';

export function resolveSessionTimeouts(): Record<string, string> {
  const out: Record<string, string> = {};
  const add = (envKey: string, gucKey: string, defaultVal: string) => {
    const raw = process.env[envKey];
    if (raw === '0' || raw === 'off') return; // explicitly disabled
    const val = raw ?? defaultVal;
    if (val) out[gucKey] = val;
  };
  add('GBRAIN_STATEMENT_TIMEOUT', 'statement_timeout', DEFAULT_STATEMENT_TIMEOUT);
  add('GBRAIN_IDLE_TX_TIMEOUT', 'idle_in_transaction_session_timeout', DEFAULT_IDLE_TX_TIMEOUT);
  // client_connection_check_interval is opt-in: Postgres 14+ only, and some
  // managed pooler tiers reject unknown startup parameters. Users can enable
  // it explicitly once they know their Postgres version supports it.
  add('GBRAIN_CLIENT_CHECK_INTERVAL', 'client_connection_check_interval', '');
  return out;
}

/**
 * Backward-compat shim for v0.21.0's `setSessionDefaults` callers.
 * The current implementation no-ops because session timeouts are now
 * applied at connection-startup time via `resolveSessionTimeouts()` +
 * postgres.js's `connection` option (more durable across PgBouncer
 * transaction mode).
 *
 * Kept as a callable function so existing call sites in `connect()` and
 * `PostgresEngine.connect()` don't need to be touched on the merge —
 * the work has already happened by the time this function would run.
 */
export async function setSessionDefaults(_sql: ReturnType<typeof postgres>): Promise<void> {
  // No-op: timeouts are now applied as startup parameters in resolveSessionTimeouts().
}

export function getConnection(): ReturnType<typeof postgres> {
  if (!sql) {
    throw new GBrainError(
      'No database connection',
      'connect() has not been called',
      'Run gbrain init --supabase or gbrain init --url <connection_string>',
    );
  }
  return sql;
}

export async function connect(config: EngineConfig): Promise<void> {
  if (sql) {
    // Warn if a different URL is passed — the old connection is still in use
    if (config.database_url && connectedUrl && config.database_url !== connectedUrl) {
      console.warn('[gbrain] connect() called with a different database_url but a connection already exists. Using existing connection.');
    }
    return;
  }

  const url = config.database_url;
  if (!url) {
    throw new GBrainError(
      'No database URL',
      'database_url is missing from config',
      'Run gbrain init --supabase or gbrain init --url <connection_string>',
    );
  }

  try {
    const prepare = resolvePrepare(url);
    const timeouts = resolveSessionTimeouts();
    const opts: Record<string, unknown> = {
      max: resolvePoolSize(),
      idle_timeout: 20,
      connect_timeout: 10,
      types: {
        // Register pgvector type
        bigint: postgres.BigInt,
      },
      // Silence postgres NOTICE-level messages by default ("relation already
      // exists, skipping" floods stdout under idempotent CREATE statements
      // during migrations + initSchema, and breaks stdout-parsing callers like
      // `gbrain jobs submit --json | ...`). Opt back in with GBRAIN_PG_NOTICES=1.
      onnotice: process.env.GBRAIN_PG_NOTICES === '1' ? undefined : () => {},
    };
    if (Object.keys(timeouts).length > 0) {
      opts.connection = timeouts;
    }
    if (typeof prepare === 'boolean') {
      opts.prepare = prepare;
      if (!prepare) {
        console.warn(
          '[gbrain] Prepared statements disabled (PgBouncer transaction-mode convention on port 6543). Override with GBRAIN_PREPARE=true if your pooler runs in session mode.',
        );
      }
    }
    sql = postgres(url, opts);

    // Test connection
    await sql`SELECT 1`;
    connectedUrl = url;

    await setSessionDefaults(sql);
  } catch (e: unknown) {
    sql = null;
    connectedUrl = null;
    const msg = e instanceof Error ? e.message : String(e);
    throw new GBrainError(
      'Cannot connect to database',
      msg,
      'Check your connection URL in ~/.gbrain/config.json',
    );
  }
}

export async function disconnect(): Promise<void> {
  // v0.41.25.0 (#1570) — instrument every disconnect call site so v0.41.26
  // can identify the caller that's nulling the module singleton mid-cycle.
  // Best-effort: audit failure must never block the actual disconnect.
  // The audit module is lazy-imported to keep db.ts cold-path-free for
  // tools that import db without ever calling disconnect.
  try {
    const { logDbDisconnect } = await import('./audit/db-disconnect-audit.ts');
    // db.ts is always the module-singleton path by construction; no
    // instance-pool callers go through here.
    logDbDisconnect('postgres', 'module');
  } catch { /* best-effort; never block disconnect on audit failure */ }
  if (sql) {
    await sql.end();
    sql = null;
    connectedUrl = null;
  }
}

export async function initSchema(): Promise<void> {
  const conn = getConnection();
  // Advisory lock prevents concurrent initSchema() calls from deadlocking
  await conn`SELECT pg_advisory_lock(42)`;
  try {
    await conn.unsafe(SCHEMA_SQL);
  } finally {
    await conn`SELECT pg_advisory_unlock(42)`;
  }
}

export { verifySchema } from './schema-verify.ts';

export async function withTransaction<T>(fn: (tx: ReturnType<typeof postgres>) => Promise<T>): Promise<T> {
  const conn = getConnection();
  return conn.begin(async (tx) => {
    return fn(tx as unknown as ReturnType<typeof postgres>);
  }) as Promise<T>;
}

const RETRYABLE_DB_CONNECT_PATTERNS = [
  /password authentication failed/i,
  /connection refused/i,
  /the database system is starting up/i,
  /Connection terminated unexpectedly/i,
  /ECONNRESET/i,
];

export function isRetryableDbConnectError(err: unknown): boolean {
  const msg = err instanceof Error ? err.message : String(err);
  if (!msg) return false;
  return RETRYABLE_DB_CONNECT_PATTERNS.some(p => p.test(msg));
}

export interface ConnectWithRetryOpts {
  attempts?: number;
  baseDelayMs?: number;
  noRetry?: boolean;
  log?: (line: string) => void;
}

export async function connectWithRetry(
  engine: BrainEngine,
  config: EngineConfig & { poolSize?: number },
  opts: ConnectWithRetryOpts = {},
): Promise<void> {
  const noRetry = opts.noRetry ?? (process.env.GBRAIN_NO_RETRY_CONNECT === '1');
  const attempts = noRetry ? 1 : (opts.attempts ?? 3);
  const baseDelayMs = opts.baseDelayMs ?? 1000;
  const log = opts.log ?? ((line) => console.warn(line));

  let lastErr: unknown;
  for (let i = 0; i < attempts; i++) {
    try {
      await engine.connect(config);
      return;
    } catch (e: unknown) {
      lastErr = e;
      const retryable = isRetryableDbConnectError(e);
      const isLast = i === attempts - 1;
      if (!retryable || isLast) {
        throw e;
      }
      const delay = baseDelayMs * Math.pow(2, i);
      const msg = e instanceof Error ? e.message : String(e);
      log(`[connect] attempt ${i + 1} failed (${msg.slice(0, 80)}), retrying in ${delay}ms`);
      await new Promise(resolve => setTimeout(resolve, delay));
    }
  }
  // Unreachable, but TS needs the throw.
  throw lastErr;
}