/**
 * ISO Downloader
 * Downloads Ubuntu Server ISOs from official mirrors
 */

import { log } from '../logging.ts';
import { path } from '../plugins.ts';

export interface IDownloadOptions {
  ubuntuVersion: string;  // e.g., "24.04", "22.04"
  architecture: 'amd64' | 'arm64';
  outputPath: string;
  onProgress?: (downloaded: number, total: number) => void;
}

export class IsoDownloader {
  /**
   * Ubuntu release URLs
   */
  private static readonly UBUNTU_MIRROR = 'https://releases.ubuntu.com';

  /**
   * Get the ISO filename for a given version and architecture
   */
  static getIsoFilename(version: string, arch: 'amd64' | 'arm64'): string {
    // Ubuntu Server ISO naming pattern
    if (arch === 'amd64') {
      return `ubuntu-${version}-live-server-${arch}.iso`;
    } else {
      // ARM64 uses preinstalled server images
      return `ubuntu-${version}-preinstalled-server-${arch}.img.xz`;
    }
  }

  /**
   * Get the download URL for a given Ubuntu version and architecture
   */
  static getDownloadUrl(version: string, arch: 'amd64' | 'arm64'): string {
    const filename = this.getIsoFilename(version, arch);
    return `${this.UBUNTU_MIRROR}/${version}/${filename}`;
  }

  /**
   * Get the checksum URL for verification
   */
  static getChecksumUrl(version: string): string {
    return `${this.UBUNTU_MIRROR}/${version}/SHA256SUMS`;
  }

  /**
   * Download an Ubuntu ISO
   */
  async download(options: IDownloadOptions): Promise<void> {
    const { ubuntuVersion, architecture, outputPath, onProgress } = options;
    const url = IsoDownloader.getDownloadUrl(ubuntuVersion, architecture);

    log.info(`Downloading Ubuntu ${ubuntuVersion} ${architecture} from ${url}`);

    // Download the ISO
    const response = await fetch(url);

    if (!response.ok) {
      throw new Error(`Failed to download ISO: HTTP ${response.status}`);
    }

    const totalSize = parseInt(response.headers.get('content-length') || '0', 10);
    let downloadedSize = 0;

    // Open file for writing
    const file = await Deno.open(outputPath, { write: true, create: true, truncate: true });

    try {
      const reader = response.body?.getReader();
      if (!reader) {
        throw new Error('Failed to get response body reader');
      }

      while (true) {
        const { done, value } = await reader.read();

        if (done) break;

        await file.write(value);
        downloadedSize += value.length;

        if (onProgress && totalSize > 0) {
          onProgress(downloadedSize, totalSize);
        }
      }

      log.success(`ISO downloaded successfully to ${outputPath}`);
    } finally {
      file.close();
    }
  }

  /**
   * Download and verify checksum
   */
  async downloadWithVerification(options: IDownloadOptions): Promise<void> {
    const { ubuntuVersion, architecture, outputPath } = options;

    // Download the ISO
    await this.download(options);

    // Download checksums
    log.info('Downloading checksums for verification...');
    const checksumUrl = IsoDownloader.getChecksumUrl(ubuntuVersion);
    const checksumResponse = await fetch(checksumUrl);

    if (!checksumResponse.ok) {
      log.warn('Could not download checksums for verification');
      return;
    }

    const checksumText = await checksumResponse.text();
    const filename = path.basename(outputPath);

    // Find the checksum for our file
    const lines = checksumText.split('\n');
    let expectedChecksum: string | null = null;

    for (const line of lines) {
      if (line.includes(filename)) {
        expectedChecksum = line.split(/\s+/)[0];
        break;
      }
    }

    if (!expectedChecksum) {
      log.warn(`No checksum found for ${filename}`);
      return;
    }

    // Verify the checksum
    log.info('Verifying checksum...');
    const actualChecksum = await this.calculateSha256(outputPath);

    if (actualChecksum === expectedChecksum) {
      log.success('Checksum verified successfully ✓');
    } else {
      throw new Error(`Checksum mismatch!\nExpected: ${expectedChecksum}\nActual: ${actualChecksum}`);
    }
  }

  /**
   * Calculate SHA256 checksum of a file
   */
  private async calculateSha256(filePath: string): Promise<string> {
    const file = await Deno.open(filePath, { read: true });
    const buffer = new Uint8Array(8192);
    const hasher = await crypto.subtle.digest('SHA-256', new Uint8Array(0)); // Initialize

    try {
      while (true) {
        const bytesRead = await file.read(buffer);
        if (bytesRead === null) break;

        // Hash the chunk
        const chunk = buffer.slice(0, bytesRead);
        await crypto.subtle.digest('SHA-256', chunk);
      }
    } finally {
      file.close();
    }

    // Convert to hex string
    const hashArray = Array.from(new Uint8Array(hasher));
    const hashHex = hashArray.map((b) => b.toString(16).padStart(2, '0')).join('');
    return hashHex;
  }
}