/**
 * Cross-runtime compression abstraction
 *
 * Uses:
 * - Node.js: zlib module (native, full brotli support)
 * - Deno/Bun: CompressionStream API (Web Standard)
 */

import * as plugins from '../plugins.js';
import type { TCompressionAlgorithm } from '../utils/index.js';
import type { Transform } from 'stream';

// =============================================================================
// Compression Provider Interface
// =============================================================================

export interface ICompressionProvider {
  /**
   * Compress data to Uint8Array
   */
  compress(
    data: Uint8Array,
    algorithm: TCompressionAlgorithm,
    level?: number
  ): Promise<Uint8Array>;

  /**
   * Compress a ReadableStream
   */
  compressStream(
    stream: ReadableStream<Uint8Array>,
    algorithm: TCompressionAlgorithm,
    level?: number
  ): ReadableStream<Uint8Array>;

  /**
   * Get supported algorithms for this runtime
   */
  getSupportedAlgorithms(): TCompressionAlgorithm[];
}

// =============================================================================
// Node.js Compression Provider (using zlib)
// =============================================================================

class NodeCompressionProvider implements ICompressionProvider {
  getSupportedAlgorithms(): TCompressionAlgorithm[] {
    return ['br', 'gzip', 'deflate'];
  }

  async compress(
    data: Uint8Array,
    algorithm: TCompressionAlgorithm,
    level?: number
  ): Promise<Uint8Array> {
    if (algorithm === 'identity') {
      return data;
    }

    return new Promise((resolve, reject) => {
      const buffer = Buffer.from(data);

      const callback = (err: Error | null, result: Buffer) => {
        if (err) reject(err);
        else resolve(new Uint8Array(result));
      };

      switch (algorithm) {
        case 'br':
          plugins.zlib.brotliCompress(
            buffer,
            {
              params: {
                [plugins.zlib.constants.BROTLI_PARAM_QUALITY]: level ?? 4,
              },
            },
            callback
          );
          break;
        case 'gzip':
          plugins.zlib.gzip(buffer, { level: level ?? 6 }, callback);
          break;
        case 'deflate':
          plugins.zlib.deflate(buffer, { level: level ?? 6 }, callback);
          break;
        default:
          resolve(data);
      }
    });
  }

  compressStream(
    stream: ReadableStream<Uint8Array>,
    algorithm: TCompressionAlgorithm,
    level?: number
  ): ReadableStream<Uint8Array> {
    if (algorithm === 'identity') {
      return stream;
    }

    // Create zlib transform stream
    let zlibStream: Transform;
    switch (algorithm) {
      case 'br':
        zlibStream = plugins.zlib.createBrotliCompress({
          params: {
            [plugins.zlib.constants.BROTLI_PARAM_QUALITY]: level ?? 4,
          },
        });
        break;
      case 'gzip':
        zlibStream = plugins.zlib.createGzip({ level: level ?? 6 });
        break;
      case 'deflate':
        zlibStream = plugins.zlib.createDeflate({ level: level ?? 6 });
        break;
      default:
        return stream;
    }

    // Convert Web ReadableStream to Node stream, compress, and back
    const reader = stream.getReader();

    return new ReadableStream<Uint8Array>({
      async start(controller) {
        // Pipe data through zlib
        zlibStream.on('data', (chunk: Buffer) => {
          controller.enqueue(new Uint8Array(chunk));
        });

        zlibStream.on('end', () => {
          controller.close();
        });

        zlibStream.on('error', (err) => {
          controller.error(err);
        });

        // Read from source and write to zlib
        try {
          while (true) {
            const { done, value } = await reader.read();
            if (done) {
              zlibStream.end();
              break;
            }
            zlibStream.write(Buffer.from(value));
          }
        } catch (err) {
          controller.error(err);
        }
      },

      cancel() {
        reader.cancel();
        zlibStream.destroy();
      },
    });
  }
}

// =============================================================================
// Web Standard Compression Provider (Deno/Bun/Browser)
// =============================================================================

class WebStandardCompressionProvider implements ICompressionProvider {
  private _brotliSupported: boolean | null = null;
  private _isDeno: boolean;

  constructor() {
    this._isDeno = typeof (globalThis as any).Deno !== 'undefined';
  }

  /**
   * Check if brotli is supported via Deno.compress API
   */
  private hasDenoBrotli(): boolean {
    if (this._brotliSupported === null) {
      if (this._isDeno) {
        // Deno 1.37+ has Deno.compress/decompress with brotli support
        const Deno = (globalThis as any).Deno;
        this._brotliSupported = typeof Deno?.compress === 'function';
      } else {
        this._brotliSupported = false;
      }
    }
    return this._brotliSupported;
  }

  getSupportedAlgorithms(): TCompressionAlgorithm[] {
    // CompressionStream supports gzip and deflate
    const algorithms: TCompressionAlgorithm[] = ['gzip', 'deflate'];

    // Deno has native brotli via Deno.compress
    if (this.hasDenoBrotli()) {
      algorithms.unshift('br');
    }

    return algorithms;
  }

  async compress(
    data: Uint8Array,
    algorithm: TCompressionAlgorithm,
    _level?: number
  ): Promise<Uint8Array> {
    if (algorithm === 'identity') {
      return data;
    }

    // Use Deno's native brotli if available
    if (algorithm === 'br' && this.hasDenoBrotli()) {
      try {
        const Deno = (globalThis as any).Deno;
        return await Deno.compress(data, 'br');
      } catch {
        // Fall through to return original
        return data;
      }
    }

    // Use CompressionStream for gzip/deflate
    if (algorithm === 'gzip' || algorithm === 'deflate') {
      try {
        const stream = new CompressionStream(algorithm);
        const writer = stream.writable.getWriter();
        const reader = stream.readable.getReader();

        // Write data and close
        await writer.write(data as unknown as BufferSource);
        await writer.close();

        // Collect compressed chunks
        const chunks: Uint8Array[] = [];
        while (true) {
          const { done, value } = await reader.read();
          if (done) break;
          chunks.push(value);
        }

        // Concatenate chunks
        const totalLength = chunks.reduce((sum, chunk) => sum + chunk.length, 0);
        const result = new Uint8Array(totalLength);
        let offset = 0;
        for (const chunk of chunks) {
          result.set(chunk, offset);
          offset += chunk.length;
        }

        return result;
      } catch {
        // Compression failed, return original
        return data;
      }
    }

    // Unsupported algorithm
    return data;
  }

  compressStream(
    stream: ReadableStream<Uint8Array>,
    algorithm: TCompressionAlgorithm,
    _level?: number
  ): ReadableStream<Uint8Array> {
    if (algorithm === 'identity') {
      return stream;
    }

    // Brotli streaming not supported in Web Standard (Deno.compress is not streaming)
    // Only gzip/deflate work with CompressionStream
    if (algorithm !== 'gzip' && algorithm !== 'deflate') {
      return stream;
    }

    try {
      const compressionStream = new CompressionStream(algorithm);
      return stream.pipeThrough(compressionStream as unknown as TransformStream<Uint8Array, Uint8Array>);
    } catch {
      // Compression not supported, return original stream
      return stream;
    }
  }
}

// =============================================================================
// Factory & Singleton
// =============================================================================

let compressionProvider: ICompressionProvider | null = null;

/**
 * Create appropriate compression provider for the current runtime
 */
export function createCompressionProvider(): ICompressionProvider {
  // Check for Node.js (has zlib module)
  if (typeof process !== 'undefined' && process.versions?.node) {
    return new NodeCompressionProvider();
  }

  // Check for Deno
  if (typeof (globalThis as any).Deno !== 'undefined') {
    return new WebStandardCompressionProvider();
  }

  // Check for Bun
  if (typeof (globalThis as any).Bun !== 'undefined') {
    return new WebStandardCompressionProvider();
  }

  // Fallback to Web Standard
  return new WebStandardCompressionProvider();
}

/**
 * Get the singleton compression provider
 */
export function getCompressionProvider(): ICompressionProvider {
  if (!compressionProvider) {
    compressionProvider = createCompressionProvider();
  }
  return compressionProvider;
}