import { existsSync } from 'node:fs';
import { join } from 'node:path';
import { setTimeout as sleep } from 'node:timers/promises';

import type { BackupCommand, MaintenanceEvent, RestoreStatus } from '@dorfteich/shared';

import { archiveFileName, dumpFileName } from './backup-set.js';
import type { RemoteLogger } from './remote.js';
import { writeRestoreStatus } from './status.js';

/**
 * The in-app restore, orchestrated by the sidecar (issue #103):
 *
 * 1. `restore-status.json` → `running` — the api's maintenance gate flips
 *    to 503 for everything but health and the status endpoint.
 * 2. NOTIFY maintenance `enter` — the collab server persists + closes every
 *    live session and refuses new ones, so no in-memory document writes
 *    pre-restore content back afterwards.
 * 3. Grace period, then terminate all other database connections.
 * 4. Fetch the set (remote source: download + unpack the bundle), verify
 *    both artifacts exist, `pg_restore --clean` + volume archive extract —
 *    the exact path of the operator's `restore.sh`.
 * 5. `restore-status.json` → final state; NOTIFY `exit`. The api restarts
 *    itself on `succeeded` (fresh caches, migrate-on-start for older dumps).
 *
 * Every failure lands in `restore-status.json` — the admin watches that
 * file through the exempt status endpoint, so it must always resolve.
 */

export interface RestoreOrchestratorDeps {
  backupsDir: string;
  now(): Date;
  /** NOTIFY on a short-lived connection (maintenance enter/exit). */
  notifyMaintenance(event: MaintenanceEvent): Promise<void>;
  /** Kills every other DB connection right before pg_restore. */
  terminateOtherConnections(): Promise<void>;
  /** Downloads + unpacks the remote bundle into backupsDir (remote.ts). */
  fetchRemoteSet(backupId: string): Promise<void>;
  /** pg_restore + volume extract — shared with the restore.js CLI. */
  restoreSet(backupId: string): Promise<void>;
  /** Milliseconds between maintenance enter and connection termination. */
  graceMs?: number;
  log: RemoteLogger;
}

export async function orchestrateRestore(
  deps: RestoreOrchestratorDeps,
  command: Extract<BackupCommand, { kind: 'restore' }>,
): Promise<RestoreStatus> {
  const startedAt = deps.now().toISOString();
  const base: Omit<RestoreStatus, 'state' | 'finishedAt'> = {
    schemaVersion: 1,
    backupId: command.backupId,
    source: command.source,
    requestedBy: command.requestedBy,
    startedAt,
  };
  await writeRestoreStatus(deps.backupsDir, { ...base, state: 'running', finishedAt: null });
  deps.log.info(
    { backupId: command.backupId, source: command.source, requestedBy: command.requestedBy },
    'restore started — instance entering maintenance mode',
  );

  let entered = false;
  try {
    await deps.notifyMaintenance({ phase: 'enter' });
    entered = true;
    await sleep(deps.graceMs ?? 5000);

    if (command.source === 'remote') {
      await deps.fetchRemoteSet(command.backupId);
    }
    for (const file of [dumpFileName(command.backupId), archiveFileName(command.backupId)]) {
      if (!existsSync(join(deps.backupsDir, file))) {
        throw new Error(`restore set is incomplete — ${file} not found`);
      }
    }

    await deps.terminateOtherConnections();
    await deps.restoreSet(command.backupId);

    const status: RestoreStatus = {
      ...base,
      state: 'succeeded',
      finishedAt: deps.now().toISOString(),
    };
    await writeRestoreStatus(deps.backupsDir, status);
    deps.log.info({ backupId: command.backupId }, 'restore succeeded — api will restart');
    return status;
  } catch (error) {
    const message = error instanceof Error ? error.message : String(error);
    const status: RestoreStatus = {
      ...base,
      state: 'failed',
      finishedAt: deps.now().toISOString(),
      error: message,
    };
    // Best effort — if even this write fails the api's staleness bound
    // (RESTORE_STALE_MAX_AGE_MINUTES) unblocks the instance eventually.
    await writeRestoreStatus(deps.backupsDir, status).catch(() => undefined);
    deps.log.error({ backupId: command.backupId, error: message }, 'restore failed');
    return status;
  } finally {
    if (entered) {
      await deps.notifyMaintenance({ phase: 'exit' }).catch((error: unknown) => {
        deps.log.warn({ error: String(error) }, 'maintenance exit notify failed');
      });
    }
  }
}