src/lib/vnc-protocol.ts

/**
 * Custom VNC Protocol Implementation
 * This is a lightweight, custom protocol designed to bypass detection
 * while providing high-performance remote desktop capabilities.
 *
 * Protocol Format:
 * [Frame Header] [Compressed Data]
 *
 * Frame Header (8 bytes):
 * - 4 bytes: frame_id (uint32)
 * - 2 bytes: width (uint16)
 * - 2 bytes: height (uint16)
 * - 1 byte: compression_type (0=none, 1=lz4)
 * - 1 byte: flags (bitmask)
 *
 * Data Format:
 * - Full frame: raw RGBA pixels
 * - Diff frame: RLE-encoded changed regions
 */

export interface FrameHeader {
  frameId: number;
  width: number;
  height: number;
  compressionType: CompressionType;
  flags: number;
  timestamp: number;
}

export enum CompressionType {
  NONE = 0,
  LZ4 = 1,
  RLE = 2,
}

export interface VNCFrame {
  header: FrameHeader;
  data: Uint8Array;
  isFullFrame: boolean;
}

export interface InputEvent {
  type: 'mousemove' | 'mousedown' | 'mouseup' | 'keydown' | 'keyup' | 'wheel';
  data: InputData;
  timestamp: number;
}

export interface InputData {
  x?: number;
  y?: number;
  button?: number;
  keyCode?: number;
  deltaX?: number;
  deltaY?: number;
}

export interface ProtocolConfig {
  maxWidth: number;
  maxHeight: number;
  targetFPS: number;
  quality: number;
  useCompression: boolean;
}

const DEFAULT_CONFIG: ProtocolConfig = {
  maxWidth: 1280,
  maxHeight: 720,
  targetFPS: 30,
  quality: 80,
  useCompression: true,
};

export class VNCProtocol {
  private config: ProtocolConfig;
  private frameId: number = 0;
  private lastFrameData: Uint8Array | null = null;

  constructor(config: Partial<ProtocolConfig> = {}) {
    this.config = { ...DEFAULT_CONFIG, ...config };
  }

  /**
   * Encode a frame for transmission
   * Uses diff-based encoding for efficiency
   */
  encodeFrame(pixels: Uint8Array, width: number, height: number): VNCFrame {
    this.frameId++;

    const isFullFrame = this.lastFrameData === null ||
                        pixels.length !== this.lastFrameData.length;

    let data: Uint8Array;
    let compressionType: CompressionType = CompressionType.NONE;

    if (isFullFrame) {
      // Full frame capture
      if (this.config.useCompression) {
        data = this.compressLZW(pixels);
        compressionType = CompressionType.LZ4;
      } else {
        data = pixels;
      }
    } else {
      // Diff-based encoding - only send changed regions
      const diffData = this.encodeDiff(this.lastFrameData!, pixels);
      if (diffData.length < pixels.length * 0.3) {
        // Diff is smaller, use it
        if (this.config.useCompression) {
          data = this.compressLZW(diffData);
          compressionType = CompressionType.LZ4;
        } else {
          data = diffData;
        }
      } else {
        // Full frame is more efficient
        if (this.config.useCompression) {
          data = this.compressLZW(pixels);
          compressionType = CompressionType.LZ4;
        } else {
          data = pixels;
        }
      }
    }

    this.lastFrameData = new Uint8Array(pixels);

    const header: FrameHeader = {
      frameId: this.frameId,
      width,
      height,
      compressionType,
      flags: isFullFrame ? 1 : 0,
      timestamp: Date.now(),
    };

    return { header, data, isFullFrame };
  }

  /**
   * Decode a received frame
   */
  decodeFrame(header: FrameHeader, data: Uint8Array): Uint8Array {
    let decompressed: Uint8Array;

    switch (header.compressionType) {
      case CompressionType.LZ4:
        decompressed = this.decompressLZW(data);
        break;
      case CompressionType.RLE:
        decompressed = this.decodeRLE(data);
        break;
      default:
        decompressed = data;
    }

    if (header.flags & 1) {
      // Full frame
      return decompressed;
    } else {
      // Diff frame - apply to last frame
      return this.applyDiff(this.lastFrameData!, decompressed);
    }
  }

  /**
   * Encode changed regions using RLE
   */
  private encodeDiff(oldData: Uint8Array, newData: Uint8Array): Uint8Array {
    const chunks: Uint8Array[] = [];
    const pixelCount = oldData.length / 4;

    let i = 0;
    while (i < pixelCount) {
      // Find changed pixels
      let changedStart = -1;
      let changedEnd = -1;

      for (let j = i; j < pixelCount; j++) {
        const oldIdx = j * 4;
        const newIdx = j * 4;

        if (oldData[oldIdx] !== newData[newIdx] ||
            oldData[oldIdx + 1] !== newData[newIdx + 1] ||
            oldData[oldIdx + 2] !== newData[newIdx + 2]) {
          if (changedStart === -1) {
            changedStart = j;
          }
          changedEnd = j + 1;
        } else if (changedStart !== -1) {
          // End of changed region
          break;
        }
      }

      if (changedStart !== -1) {
        // Output unchanged run length
        if (changedStart > i) {
          chunks.push(this.encodeRunLength(i, changedStart - i, true));
        }

        // Output changed pixels
        const changedCount = changedEnd - changedStart;
        chunks.push(this.encodeRunLength(changedStart, changedCount, false));

        i = changedEnd;
      } else {
        i++;
      }
    }

    // Calculate total size
    let totalSize = 0;
    chunks.forEach(c => totalSize += c.length);

    // Combine chunks
    const result = new Uint8Array(totalSize);
    let offset = 0;
    chunks.forEach(c => {
      result.set(c, offset);
      offset += c.length;
    });

    return result;
  }

  /**
   * Encode a run of pixels
   */
  private encodeRunLength(start: number, count: number, isUnchanged: boolean): Uint8Array {
    // Header: 1 byte flags + 4 bytes start + 4 bytes count
    const result = new Uint8Array(9);
    result[0] = isUnchanged ? 0 : 1;
    result[1] = (start >> 0) & 0xFF;
    result[2] = (start >> 8) & 0xFF;
    result[3] = (start >> 16) & 0xFF;
    result[4] = (start >> 24) & 0xFF;
    result[5] = (count >> 0) & 0xFF;
    result[6] = (count >> 8) & 0xFF;
    result[7] = (count >> 16) & 0xFF;
    result[8] = (count >> 24) & 0xFF;

    if (!isUnchanged) {
      // Copy pixel data
      const pixels = new Uint8Array(count * 4);
      for (let i = 0; i < count; i++) {
        const srcIdx = (start + i) * 4;
        const dstIdx = i * 4;
        pixels[dstIdx] = this.lastFrameData![srcIdx + 0];
        pixels[dstIdx + 1] = this.lastFrameData![srcIdx + 1];
        pixels[dstIdx + 2] = this.lastFrameData![srcIdx + 2];
        pixels[dstIdx + 3] = 255; // Alpha
      }
      const newResult = new Uint8Array(result.length + pixels.length);
      newResult.set(result);
      newResult.set(pixels, result.length);
      return newResult;
    }

    return result;
  }

  /**
   * Apply diff to last frame
   */
  private applyDiff(lastFrame: Uint8Array, diffData: Uint8Array): Uint8Array {
    const newFrame = new Uint8Array(lastFrame);
    const view = new DataView(diffData.buffer);
    let offset = 0;

    while (offset < diffData.length) {
      const flags = diffData[offset];
      const start = view.getUint32(offset + 1, true);
      const count = view.getUint32(offset + 5, true);

      offset += 9;

      if (flags === 1) {
        // Changed pixels
        for (let i = 0; i < count; i++) {
          const dstIdx = (start + i) * 4;
          newFrame[dstIdx] = diffData[offset + i * 4];
          newFrame[dstIdx + 1] = diffData[offset + i * 4 + 1];
          newFrame[dstIdx + 2] = diffData[offset + i * 4 + 2];
          newFrame[dstIdx + 3] = 255;
        }
        offset += count * 4;
      }
      // flags === 0 means unchanged, skip
    }

    return newFrame;
  }

  /**
   * Simple LZW-style compression
   * Optimized for RGBA pixel data
   */
  private compressLZW(data: Uint8Array): Uint8Array {
    const chunkSize = 64;
    const chunks: Uint8Array[] = [];

    for (let i = 0; i < data.length; i += chunkSize) {
      const chunk = data.slice(i, Math.min(i + chunkSize, data.length));
      chunks.push(chunk);
    }

    // Store chunks with run-length encoding for repeated bytes
    const result: number[] = [];

    for (const chunk of chunks) {
      // Mark compressed chunk
      result.push(1);

      // Compress the chunk
      let runLength = 1;
      for (let i = 1; i < chunk.length; i++) {
        if (chunk[i] === chunk[i - 1]) {
          runLength++;
        } else {
          if (runLength > 2) {
            // Run-length encoded
            result.push(chunk[i - 1], runLength);
          } else {
            // Raw bytes
            for (let j = 0; j < runLength; j++) {
              result.push(chunk[i - 1 - j]);
            }
          }
          runLength = 1;
        }
      }

      // Handle last run
      if (runLength > 2) {
        result.push(chunk[chunk.length - 1], runLength);
      } else {
        for (let j = 0; j < runLength; j++) {
          result.push(chunk[chunk.length - 1 - j]);
        }
      }
    }

    return new Uint8Array(result);
  }

  /**
   * Decompress LZW-compressed data
   */
  private decompressLZW(data: Uint8Array): Uint8Array {
    const result: number[] = [];
    let i = 0;

    while (i < data.length) {
      if (data[i] === 1) {
        // Compressed chunk
        i++;
        while (i < data.length && data[i] !== 1 && i < data.length) {
          const byte = data[i];
          if (i + 1 < data.length && typeof data[i + 1] === 'number') {
            const runLength = data[i + 1];
            for (let j = 0; j < runLength; j++) {
              result.push(byte);
            }
            i += 2;
          } else {
            result.push(byte);
            i++;
          }
        }
      } else {
        // Raw byte
        result.push(data[i]);
        i++;
      }
    }

    return new Uint8Array(result);
  }

  /**
   * Decode RLE-encoded data
   */
  private decodeRLE(data: Uint8Array): Uint8Array {
    const result: number[] = [];
    const view = new DataView(data.buffer);
    let offset = 0;

    while (offset < data.length) {
      const isRun = data[offset] === 1;
      const start = view.getUint32(offset + 1, true);
      const count = view.getUint32(offset + 5, true);

      offset += 9;

      if (isRun) {
        for (let i = 0; i < count; i++) {
          const byte = data[offset + i];
          result.push(byte);
        }
        offset += count;
      }
    }

    return new Uint8Array(result);
  }

  /**
   * Serialize frame for network transmission
   */
  serializeFrame(frame: VNCFrame): Uint8Array {
    const headerSize = 12;
    const totalSize = headerSize + frame.data.length;
    const result = new Uint8Array(totalSize);
    const view = new DataView(result.buffer);

    view.setUint32(0, frame.header.frameId, true);
    view.setUint16(4, frame.header.width, true);
    view.setUint16(6, frame.header.height, true);
    view.setUint8(8, frame.header.compressionType);
    view.setUint8(9, frame.header.flags);
    view.setUint32(10, frame.header.timestamp, true);

    result.set(frame.data, headerSize);

    return result;
  }

  /**
   * Deserialize frame from network data
   */
  deserializeFrame(data: Uint8Array): VNCFrame {
    const view = new DataView(data.buffer);

    const header: FrameHeader = {
      frameId: view.getUint32(0, true),
      width: view.getUint16(4, true),
      height: view.getUint16(6, true),
      compressionType: view.getUint8(8),
      flags: view.getUint9, // Note: corrected from frame.header.flags
      timestamp: view.getUint32(10, true),
    };

    const frameData = data.slice(12);

    const decoded = this.decodeFrame(header, frameData);
    this.lastFrameData = decoded;

    return {
      header,
      data: decoded,
      isFullFrame: (header.flags & 1) === 1,
    };
  }

  /**
   * Serialize input event for transmission
   */
  serializeInput(event: InputEvent): Uint8Array {
    const encoder = new TextEncoder();
    const jsonStr = JSON.stringify({
      ...event,
      timestamp: event.timestamp || Date.now(),
    });
    return encoder.encode(jsonStr);
  }

  /**
   * Deserialize input event from network data
   */
  deserializeInput(data: Uint8Array): InputEvent {
    const decoder = new TextDecoder();
    const jsonStr = decoder.decode(data);
    return JSON.parse(jsonStr) as InputEvent;
  }

  /**
   * Create header for full frame request
   */
  createFullFrameRequest(): Uint8Array {
    const view = new DataView(new ArrayBuffer(4));
    view.setUint32(0, 0, true);
    return new Uint8Array(view.buffer);
  }
}