import 'dart:typed_data';

import 'package:wolf_dart/classes/matrix.dart';

class VswapParser {
  /// Extracts the 64x64 wall textures from VSWAP.WL1
  static List<Matrix<int>> parseWalls(ByteData vswap) {
    // 1. Read Header
    int chunks = vswap.getUint16(0, Endian.little);
    int spriteStart = vswap.getUint16(2, Endian.little);
    // int soundStart = vswap.getUint16(4, Endian.little); // We don't need this yet

    // 2. Read Offsets (Where does each chunk start in the file?)
    List<int> offsets = [];
    for (int i = 0; i < spriteStart; i++) {
      offsets.add(vswap.getUint32(6 + (i * 4), Endian.little));
    }

    // 3. Extract the Wall Textures
    List<List<List<int>>> textures = [];

    // Walls are chunks 0 through (spriteStart - 1)
    for (int i = 0; i < spriteStart; i++) {
      int offset = offsets[i];
      if (offset == 0) continue; // Empty chunk

      // Walls are always exactly 64x64 pixels (4096 bytes)
      // Note: Wolf3D stores pixels in COLUMN-MAJOR order (Top to bottom, then left to right)
      List<List<int>> texture = List.generate(64, (_) => List.filled(64, 0));

      for (int x = 0; x < 64; x++) {
        for (int y = 0; y < 64; y++) {
          int byteIndex = offset + (x * 64) + y;
          texture[x][y] = vswap.getUint8(byteIndex);
        }
      }
      textures.add(texture);
    }

    return textures;
  }
}