/**
 * src/services/zipService.ts
 *
 * All ZIP I/O is handled through Node.js streams to keep RAM usage flat
 * regardless of archive size — critical on Hugging Face Spaces where
 * memory is limited (typically 16 GB shared across all processes).
 *
 * Key design decisions:
 *   - Extract via `unzipper.Parse({ forceStream: true })` — never buffers
 *     the whole archive.
 *   - Each extracted file is written to disk first, then read; files
 *     exceeding MAX_FILE_SIZE_BYTES are skipped entirely.
 *   - Archives are created via `archiver` which also streams.
 *   - `createTempDir` uses `fs.mkdtemp` for atomic, collision-free paths.
 *   - `cleanup()` must always be called in a `finally` block — see examples
 *     in llmOrchestrator.ts.
 */

import fs from 'fs';
import path from 'path';
import archiver from 'archiver';
import unzipper from 'unzipper';
import { logger } from '../utils/logger';
import { ENV } from '../config/env';

// ─── Types ────────────────────────────────────────────────────────────────────

export interface ExtractedFile {
  /** Path relative to the ZIP root, e.g. "src/components/Header.jsx" */
  relativePath: string;
  /** Absolute path on disk inside the temp extraction directory */
  absolutePath: string;
  /** UTF-8 file contents */
  content: string;
  /** Lowercase file extension including dot, e.g. ".jsx" */
  extension: string;
}

// ─── Constants ────────────────────────────────────────────────────────────────

/** Extensions we care about for transpilation. Everything else is drained. */
const RELEVANT_EXTENSIONS = new Set([
  '.js', '.jsx', '.ts', '.tsx',
  '.css', '.scss', '.sass',
  '.json', '.html', '.svg', '.env',
]);

/** Path segments that indicate the file should be skipped entirely. */
const SKIP_SEGMENTS = [
  'node_modules/',
  '/.git/',
  '/dist/',
  '/build/',
  '/.next/',
  '/coverage/',
  '/out/',
];

// ─── Temp Directory Management ────────────────────────────────────────────────

/**
 * Creates a unique temporary directory.
 * Uses `fs.mkdtemp` which is atomic and guaranteed collision-free.
 *
 * @param prefix - Short label for easier log tracing
 */
export async function createTempDir(prefix = 'titan-'): Promise<string> {
  const base = path.join(ENV.TEMP_DIR, prefix);
  const dir = await fs.promises.mkdtemp(base);
  logger.debug(`ZipService: created temp dir ${dir}`);
  return dir;
}

/**
 * Recursively removes a directory. Safe to call even if the path doesn't exist.
 *
 * ALWAYS call this inside `finally {}` — never rely on GC for disk cleanup.
 */
export async function cleanup(dirPath: string): Promise<void> {
  try {
    await fs.promises.rm(dirPath, { recursive: true, force: true });
    logger.info(`ZipService: cleaned up ${dirPath}`);
  } catch (err) {
    // Non-fatal: log and continue — a dirty /tmp is better than a crash
    logger.warn(`ZipService: cleanup failed for "${dirPath}"`, { err: String(err) });
  }
}

// ─── ZIP Extraction ───────────────────────────────────────────────────────────

/**
 * Extracts a ZIP archive into `destDir` using a streaming parser.
 *
 * Memory model:
 *   - Each entry is piped to a WriteStream on disk, never fully buffered.
 *   - After writing, files are stat-checked against MAX_FILE_SIZE_BYTES.
 *   - Only RELEVANT_EXTENSIONS are kept; others are autodrained.
 *
 * @param zipPath  - Absolute path to the .zip file
 * @param destDir  - Absolute path to the destination directory (must exist or be created)
 * @returns        - Array of text files with their content
 */
export async function extractZip(zipPath: string, destDir: string): Promise<ExtractedFile[]> {
  logger.info(`ZipService: extracting "${path.basename(zipPath)}" → "${destDir}"`);
  await fs.promises.mkdir(destDir, { recursive: true });

  const extracted: ExtractedFile[] = [];

  await new Promise<void>((resolve, reject) => {
    const readStream = fs.createReadStream(zipPath);

    readStream
      .pipe(unzipper.Parse({ forceStream: true }))
      .on('entry', (entry: unzipper.Entry) => {
        const entryPath: string = entry.path;
        const entryType: string = entry.type; // 'Directory' | 'File'

        // ── Skip directories ─────────────────────────────────────────────
        if (entryType === 'Directory') { entry.autodrain(); return; }

        // ── Skip hidden files and ignored directories ─────────────────────
        const basename = path.basename(entryPath);
        const normalised = entryPath.replace(/\\/g, '/');
        if (
          basename.startsWith('.') ||
          SKIP_SEGMENTS.some(seg => normalised.includes(seg))
        ) {
          entry.autodrain();
          return;
        }

        // ── Skip irrelevant extensions ────────────────────────────────────
        const ext = path.extname(basename).toLowerCase();
        if (!RELEVANT_EXTENSIONS.has(ext)) {
          entry.autodrain();
          return;
        }

        // ── Stream → disk ─────────────────────────────────────────────────
        const absolutePath = path.join(destDir, entryPath);
        const dir = path.dirname(absolutePath);

        // Create parent dirs synchronously is not possible inside a stream
        // callback — we queue the work instead.
        (async () => {
          try {
            await fs.promises.mkdir(dir, { recursive: true });
            const writeStream = fs.createWriteStream(absolutePath);

            await new Promise<void>((res, rej) => {
              entry.pipe(writeStream);
              writeStream.on('finish', res);
              writeStream.on('error', rej);
              entry.on('error', rej);
            });

            // ── Size guard ───────────────────────────────────────────────
            const { size } = await fs.promises.stat(absolutePath);
            if (size > ENV.MAX_FILE_SIZE_BYTES) {
              logger.warn(
                `ZipService: skipping "${entryPath}" — ${size} bytes exceeds limit`
              );
              await fs.promises.unlink(absolutePath).catch(() => undefined);
              return;
            }

            const content = await fs.promises.readFile(absolutePath, 'utf-8');
            extracted.push({ relativePath: entryPath, absolutePath, content, extension: ext });

          } catch (fileErr) {
            logger.warn(`ZipService: failed to extract "${entryPath}"`, { err: String(fileErr) });
            entry.autodrain();
          }
        })();
      })
      .on('finish', resolve)
      .on('error', reject);

    readStream.on('error', reject);
  });

  logger.info(`ZipService: extraction complete — ${extracted.length} usable file(s)`);
  return extracted;
}

// ─── ZIP Creation ─────────────────────────────────────────────────────────────

/**
 * Creates a ZIP archive of an entire directory using streaming.
 * Compression level 9 (maximum). Does NOT load the full archive into RAM.
 *
 * @param sourceDir  - Root directory whose contents will be zipped
 * @param outputPath - Destination .zip path
 */
export async function createZip(sourceDir: string, outputPath: string): Promise<void> {
  return new Promise((resolve, reject) => {
    const output = fs.createWriteStream(outputPath);
    const arc = archiver('zip', { zlib: { level: 9 } });

    output.on('close', () => {
      logger.info(
        `ZipService: archive created — ${outputPath} (${arc.pointer()} bytes)`
      );
      resolve();
    });

    arc.on('warning', (warn) => {
      logger.warn('ZipService: archiver warning', { warn: String(warn) });
    });
    arc.on('error', reject);

    arc.pipe(output);
    // `false` as second arg means files go at the root of the ZIP, not inside a sub-folder
    arc.directory(sourceDir, false);
    arc.finalize();
  });
}

// ─── Flutter Project Packager ─────────────────────────────────────────────────

export interface DartFileEntry {
  /** Path relative to the Flutter `lib/` directory, e.g. "screens/home_screen.dart" */
  relativePath: string;
  content: string;
}

/**
 * Writes generated Dart files + pubspec.yaml into a temp directory,
 * zips the whole thing, and returns both paths for upload and cleanup.
 *
 * Layout inside the ZIP:
 *   pubspec.yaml
 *   lib/
 *     screens/home_screen.dart
 *     models/user_model.dart
 *     ...
 *
 * Caller is responsible for calling `cleanup(tempDir)` in a finally block.
 */
export async function packageFlutterCode(
  dartFiles: DartFileEntry[],
  pubspecContent: string
): Promise<{ zipPath: string; tempDir: string }> {
  const tempDir = await createTempDir('flutter-out-');
  const libDir = path.join(tempDir, 'lib');
  await fs.promises.mkdir(libDir, { recursive: true });

  // Write pubspec.yaml at the project root
  await fs.promises.writeFile(
    path.join(tempDir, 'pubspec.yaml'),
    pubspecContent,
    'utf-8'
  );

  // Write each Dart file under lib/
  for (const file of dartFiles) {
    const filePath = path.join(libDir, file.relativePath);
    await fs.promises.mkdir(path.dirname(filePath), { recursive: true });
    await fs.promises.writeFile(filePath, file.content, 'utf-8');
  }

  // Create the ZIP
  const zipPath = path.join(ENV.TEMP_DIR, `flutter-${Date.now()}.zip`);
  await createZip(tempDir, zipPath);

  logger.info(
    `ZipService: packaged ${dartFiles.length} Dart file(s) → ${path.basename(zipPath)}`
  );
  return { zipPath, tempDir };
}