import * as plugins from '../plugins.js';
import { BaseUpstream } from '../upstream/classes.baseupstream.js';
import type {
  IProtocolUpstreamConfig,
  IUpstreamFetchContext,
  IUpstreamRegistryConfig,
} from '../upstream/interfaces.upstream.js';

/**
 * Cargo-specific upstream implementation.
 *
 * Handles:
 * - Crate metadata (index) fetching
 * - Crate file (.crate) downloading
 * - Sparse index protocol support
 * - Content-addressable caching for .crate files
 */
export class CargoUpstream extends BaseUpstream {
  protected readonly protocolName = 'cargo';

  /** Base URL for crate downloads (may differ from index URL) */
  private readonly downloadUrl: string;

  constructor(
    config: IProtocolUpstreamConfig,
    downloadUrl?: string,
    logger?: plugins.smartlog.Smartlog,
  ) {
    super(config, logger);
    // Default to crates.io download URL if not specified
    this.downloadUrl = downloadUrl || 'https://static.crates.io/crates';
  }

  /**
   * Fetch crate metadata from the sparse index.
   */
  public async fetchCrateIndex(crateName: string): Promise<string | null> {
    const path = this.buildIndexPath(crateName);

    const context: IUpstreamFetchContext = {
      protocol: 'cargo',
      resource: crateName,
      resourceType: 'index',
      path,
      method: 'GET',
      headers: {
        'accept': 'text/plain',
      },
      query: {},
    };

    const result = await this.fetch(context);

    if (!result || !result.success) {
      return null;
    }

    if (Buffer.isBuffer(result.body)) {
      return result.body.toString('utf8');
    }

    return typeof result.body === 'string' ? result.body : null;
  }

  /**
   * Fetch a crate file from upstream.
   */
  public async fetchCrate(crateName: string, version: string): Promise<Buffer | null> {
    // Crate downloads typically go to a different URL than the index
    const path = `/${crateName}/${crateName}-${version}.crate`;

    const context: IUpstreamFetchContext = {
      protocol: 'cargo',
      resource: crateName,
      resourceType: 'crate',
      path,
      method: 'GET',
      headers: {
        'accept': 'application/octet-stream',
      },
      query: {},
    };

    // Use special handling for crate downloads
    const result = await this.fetchCrateFile(crateName, version);
    return result;
  }

  /**
   * Fetch crate file directly from the download URL.
   */
  private async fetchCrateFile(crateName: string, version: string): Promise<Buffer | null> {
    const context: IUpstreamFetchContext = {
      protocol: 'cargo',
      resource: crateName,
      resourceType: 'crate',
      path: `/${crateName}/${crateName}-${version}.crate`,
      method: 'GET',
      headers: {
        'accept': 'application/octet-stream',
      },
      query: {},
    };

    const result = await this.fetch(context);

    if (!result || !result.success) {
      return null;
    }

    return Buffer.isBuffer(result.body) ? result.body : Buffer.from(result.body);
  }

  /**
   * Build the sparse index path for a crate.
   *
   * Path structure:
   * - 1 char: /1/{name}
   * - 2 chars: /2/{name}
   * - 3 chars: /3/{first char}/{name}
   * - 4+ chars: /{first 2}/{next 2}/{name}
   */
  private buildIndexPath(crateName: string): string {
    const lowerName = crateName.toLowerCase();
    const len = lowerName.length;

    if (len === 1) {
      return `/1/${lowerName}`;
    } else if (len === 2) {
      return `/2/${lowerName}`;
    } else if (len === 3) {
      return `/3/${lowerName[0]}/${lowerName}`;
    } else {
      return `/${lowerName.slice(0, 2)}/${lowerName.slice(2, 4)}/${lowerName}`;
    }
  }

  /**
   * Override URL building for Cargo-specific handling.
   */
  protected buildUpstreamUrl(
    upstream: IUpstreamRegistryConfig,
    context: IUpstreamFetchContext,
  ): string {
    let baseUrl = upstream.url;

    // For crate downloads, use the download URL
    if (context.resourceType === 'crate') {
      baseUrl = this.downloadUrl;
    }

    // Remove trailing slash
    if (baseUrl.endsWith('/')) {
      baseUrl = baseUrl.slice(0, -1);
    }

    return `${baseUrl}${context.path}`;
  }
}