// backup.mjs — Backup + sentinel-guarded rollback for skills/-tree.
// Zero dependencies. Uses fs.cpSync (recursive + preserveTimestamps) without
// dereference (Node 22.17.x regression) and without filter (Windows symlink-
// type bug). Rollback writes a .rollback-in-progress sentinel at backupRoot
// BEFORE destructive operations and removes it on success — a crash mid-
// restore leaves the sentinel behind so detectStaleRollback() can flag it.

import {
  cpSync,
  rmSync,
  statSync,
  readdirSync,
  readFileSync,
  existsSync,
  unlinkSync,
  mkdirSync,
} from 'node:fs';
import { join } from 'node:path';
import { atomicWriteJson } from './atomic-write.mjs';

const META_FILENAME = '.backup-meta.json';
const SENTINEL_FILENAME = '.rollback-in-progress';
const DEFAULT_RETENTION_DAYS = 7;

/**
 * Produce a filesystem-safe ISO-ish timestamp: YYYY-MM-DDTHH-MM-SS.
 * No colons, no fractional seconds, no Z.
 * @returns {string}
 */
export function backupTimestamp(now = new Date()) {
  return now.toISOString().slice(0, 19).replace(/:/g, '-');
}

function readMetaCreatedAt(dir) {
  try {
    const text = readFileSync(join(dir, META_FILENAME), 'utf8');
    const obj = JSON.parse(text);
    if (obj && typeof obj.created_at === 'string') {
      const t = Date.parse(obj.created_at);
      return Number.isFinite(t) ? t : null;
    }
    return null;
  } catch {
    return null;
  }
}

/**
 * Back up srcDir into backupRoot/<timestamp>/. Writes a meta sentinel inside
 * the new backup dir as the first post-copy action.
 *
 * @param {string} srcDir — directory to back up (must exist)
 * @param {string} backupRoot — parent dir for backup-id subdirs
 * @param {object} [opts]
 * @param {number} [opts.retentionDays] — default 7
 * @param {Date} [opts.now] — override clock for testing
 * @returns {{backupPath: string, retentionDays: number, restore: () => void}}
 */
export function backupDir(srcDir, backupRoot, opts = {}) {
  if (!srcDir || typeof srcDir !== 'string') {
    throw new Error('backupDir: srcDir is required');
  }
  if (!backupRoot || typeof backupRoot !== 'string') {
    throw new Error('backupDir: backupRoot is required');
  }
  if (!existsSync(srcDir)) {
    throw new Error(`backupDir: srcDir does not exist: ${srcDir}`);
  }
  const retentionDays = opts.retentionDays ?? DEFAULT_RETENTION_DAYS;
  const now = opts.now ?? new Date();
  mkdirSync(backupRoot, { recursive: true });
  const backupPath = join(backupRoot, backupTimestamp(now));

  cpSync(srcDir, backupPath, {
    recursive: true,
    force: true,
    preserveTimestamps: true,
  });

  // First action inside backupPath after cpSync — write meta sentinel.
  atomicWriteJson(join(backupPath, META_FILENAME), {
    created_at: now.toISOString(),
    src_dir: srcDir,
    schema_version: 1,
  });

  const restore = () => {
    const sentinelPath = join(backupRoot, SENTINEL_FILENAME);
    atomicWriteJson(sentinelPath, {
      backup_path: backupPath,
      src_dir: srcDir,
      started_at: new Date().toISOString(),
      schema_version: 1,
    });
    try {
      rmSync(srcDir, {
        recursive: true,
        force: true,
        maxRetries: 3,
        retryDelay: 200,
      });
      cpSync(backupPath, srcDir, {
        recursive: true,
        force: true,
        preserveTimestamps: true,
      });
      // Remove the meta file we copied back into srcDir so srcDir is clean.
      const restoredMeta = join(srcDir, META_FILENAME);
      if (existsSync(restoredMeta)) {
        try {
          unlinkSync(restoredMeta);
        } catch {
          // best-effort
        }
      }
    } finally {
      // Sentinel removed only on success path — leave it on throw so the
      // post-mortem detector can see the orphan.
    }
    try {
      unlinkSync(sentinelPath);
    } catch {
      // best-effort
    }
  };

  return { backupPath, retentionDays, restore };
}

/**
 * True if a stale rollback sentinel exists at backupRoot.
 * @param {string} backupRoot
 * @returns {boolean}
 */
export function detectStaleRollback(backupRoot) {
  if (!backupRoot || typeof backupRoot !== 'string') return false;
  return existsSync(join(backupRoot, SENTINEL_FILENAME));
}

/**
 * Resolve the effective creation time of a backup dir.
 * Order: meta.created_at → dir mtime → null (skip with warning upstream).
 */
function resolveBackupAge(dir) {
  const fromMeta = readMetaCreatedAt(dir);
  if (fromMeta != null) return fromMeta;
  try {
    return statSync(dir).mtimeMs;
  } catch {
    return null;
  }
}

/**
 * Delete backup directories under backupRoot older than retentionDays.
 * Skips dirs with unresolvable age (logs a warning) rather than deleting them.
 *
 * @param {string} backupRoot
 * @param {number} [retentionDays] — default 7
 * @param {object} [opts]
 * @param {(msg: string) => void} [opts.warn] — default console.warn
 * @param {Date} [opts.now] — override clock for testing
 * @returns {{kept: string[], deleted: string[], skipped: string[]}}
 */
export function cleanupOldBackups(backupRoot, retentionDays = DEFAULT_RETENTION_DAYS, opts = {}) {
  const result = { kept: [], deleted: [], skipped: [] };
  if (!backupRoot || !existsSync(backupRoot)) return result;
  const warn = opts.warn ?? ((m) => console.warn(m));
  const now = opts.now ?? new Date();
  const cutoffMs = now.getTime() - retentionDays * 24 * 60 * 60 * 1000;

  let entries;
  try {
    entries = readdirSync(backupRoot, { withFileTypes: true });
  } catch (err) {
    warn(`cleanupOldBackups: cannot read ${backupRoot}: ${err.message}`);
    return result;
  }

  for (const entry of entries) {
    if (!entry.isDirectory()) continue;
    const full = join(backupRoot, entry.name);
    const ageMs = resolveBackupAge(full);
    if (ageMs == null) {
      warn(`cleanupOldBackups: skipping ${full} — cannot resolve age`);
      result.skipped.push(full);
      continue;
    }
    if (ageMs < cutoffMs) {
      try {
        rmSync(full, { recursive: true, force: true, maxRetries: 3, retryDelay: 200 });
        result.deleted.push(full);
      } catch (err) {
        warn(`cleanupOldBackups: failed to delete ${full}: ${err.message}`);
        result.skipped.push(full);
      }
    } else {
      result.kept.push(full);
    }
  }
  return result;
}