import { mkdir, readdir, rename, rm, stat } from 'node:fs/promises';
import { join } from 'node:path';

import { archiveFileName, dumpFileName, expiredSets, listSets, newBackupId } from './backup-set.js';
import type { BackupMirrorStatus, BackupRemoteStatus } from '@dorfteich/shared';

import {
  readStatus,
  writeStatus,
  type BackupRun,
  type BackupSizes,
  type BackupStatus,
} from './status.js';

/**
 * One nightly run (ADR 0015): dump first, then the volume archive (files may
 * be minutes newer than the dump — documented consistency model), then prune,
 * then `status.json`. Artifacts are written under a `.partial` suffix and
 * renamed on completion, so a crash never leaves a file that looks like a
 * restorable artifact, and prune (which ignores `.partial`) never counts a
 * torn set as the "newest complete" one.
 */

export interface RunnerDeps {
  backupsDir: string;
  retentionDays: number;
  now(): Date;
  /** Real implementation: pg_dump -Fc (pg.ts). */
  dump(outFile: string): Promise<void>;
  /** Real implementation: tar of the uploads/plugins mounts (archive.ts). */
  archive(outFile: string): Promise<void>;
  /** Failure alert (mail.ts); errors here are logged, never rethrown. */
  onFailure(run: { backupId: string; error: string; lastSuccessAt: string | null }): Promise<void>;
  /**
   * Off-host upload of the completed set (issue #103, remote.ts). Called
   * only after a successful local run; returns the new remote status, or
   * undefined when no upload happened (not configured / not due) — the
   * previous remote status is then carried unchanged. Upload failures are
   * reported inside the returned status, never thrown: the local set exists
   * and the run must count as succeeded.
   */
  upload?(input: {
    backupId: string;
    previous: BackupRemoteStatus | undefined;
  }): Promise<BackupRemoteStatus | undefined>;
  /**
   * rsync mirror to a private host (issue #84, mirror.ts). Runs after the
   * prune so the remote retention aligns with the local one. Failures are
   * reported inside the returned status, never thrown.
   */
  mirror?(input: {
    previous: BackupMirrorStatus | undefined;
  }): Promise<BackupMirrorStatus | undefined>;
  log: {
    info(details: object, message: string): void;
    error(details: object, message: string): void;
  };
}

export async function runBackup(deps: RunnerDeps): Promise<BackupStatus> {
  const startedAt = deps.now();
  const backupId = newBackupId(startedAt);
  const previous = readStatus(deps.backupsDir);
  const lastSuccess = previous?.lastSuccess ?? null;
  let remote = previous?.remote;
  let mirror = previous?.mirror;
  await mkdir(deps.backupsDir, { recursive: true });

  const dumpFile = join(deps.backupsDir, dumpFileName(backupId));
  const archiveFile = join(deps.backupsDir, archiveFileName(backupId));

  let run: BackupRun;
  let success: BackupStatus['lastSuccess'] = lastSuccess;
  try {
    const sizes = await produceArtifacts(deps, dumpFile, archiveFile);
    const finishedAt = deps.now();
    run = {
      backupId,
      startedAt: startedAt.toISOString(),
      finishedAt: finishedAt.toISOString(),
      durationMs: finishedAt.getTime() - startedAt.getTime(),
      outcome: 'succeeded',
      sizes,
    };
    success = { backupId, finishedAt: run.finishedAt, sizes };
    deps.log.info({ backupId, sizes }, 'backup run succeeded');
    if (deps.upload) {
      try {
        remote = (await deps.upload({ backupId, previous: remote })) ?? remote;
      } catch (uploadError) {
        // Defensive: remote.ts reports failures in its return value; a throw
        // here is a bug, but it must never turn a good local run into a
        // failed one.
        deps.log.error({ backupId, error: String(uploadError) }, 'upload hook threw unexpectedly');
      }
    }
  } catch (error) {
    await removePartials(deps.backupsDir);
    const message = error instanceof Error ? error.message : String(error);
    const finishedAt = deps.now();
    run = {
      backupId,
      startedAt: startedAt.toISOString(),
      finishedAt: finishedAt.toISOString(),
      durationMs: finishedAt.getTime() - startedAt.getTime(),
      outcome: 'failed',
      error: message,
    };
    deps.log.error({ backupId, error: message }, 'backup run failed');
    try {
      await deps.onFailure({
        backupId,
        error: message,
        lastSuccessAt: lastSuccess?.finishedAt ?? null,
      });
    } catch (mailError) {
      deps.log.error({ backupId, error: String(mailError) }, 'failure alert could not be sent');
    }
  }

  await prune(deps);

  // After the prune, so `--delete` aligns the remote retention with the
  // local one — including the newest-complete-set guarantee.
  if (run.outcome === 'succeeded' && deps.mirror) {
    try {
      mirror = (await deps.mirror({ previous: mirror })) ?? mirror;
    } catch (mirrorError) {
      // Defensive like the upload hook: mirror.ts reports failures in its
      // return value; a throw here must never fail the local run.
      deps.log.error({ error: String(mirrorError) }, 'mirror hook threw unexpectedly');
    }
  }

  const status: BackupStatus = {
    schemaVersion: 1,
    updatedAt: deps.now().toISOString(),
    retentionDays: deps.retentionDays,
    lastRun: run,
    lastSuccess: success,
    ...(remote ? { remote } : {}),
    ...(mirror ? { mirror } : {}),
  };
  await writeStatus(deps.backupsDir, status);
  return status;
}

/** Dump, then archive — each staged as `.partial` and renamed only when done. */
async function produceArtifacts(
  deps: RunnerDeps,
  dumpFile: string,
  archiveFile: string,
): Promise<BackupSizes> {
  await deps.dump(`${dumpFile}.partial`);
  await rename(`${dumpFile}.partial`, dumpFile);
  await deps.archive(`${archiveFile}.partial`);
  await rename(`${archiveFile}.partial`, archiveFile);
  return {
    dumpBytes: (await stat(dumpFile)).size,
    archiveBytes: (await stat(archiveFile)).size,
  };
}

/** Leftover staging files: from this failed run or an earlier crash — no
 * resumption path exists, so they are dead weight either way. */
async function removePartials(backupsDir: string): Promise<void> {
  for (const name of await readdir(backupsDir)) {
    if (name.endsWith('.partial')) await rm(join(backupsDir, name), { force: true });
  }
}

async function prune(deps: RunnerDeps): Promise<void> {
  const names = await readdir(deps.backupsDir);
  for (const set of expiredSets(listSets(names), deps.now(), deps.retentionDays)) {
    for (const file of set.files) {
      await rm(join(deps.backupsDir, file), { force: true });
    }
    deps.log.info({ backupId: set.id }, 'pruned expired backup set');
  }
}