import 'dart:typed_data';

import 'package:wolf_dart/classes/matrix.dart';
import 'package:wolf_dart/classes/sprite.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<Sprite> 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)
      Sprite 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;
  }

  /// Extracts the compiled scaled sprites from VSWAP.WL1
  static List<Matrix<int>> parseSprites(ByteData vswap) {
    int chunks = vswap.getUint16(0, Endian.little);
    int spriteStart = vswap.getUint16(2, Endian.little);
    int soundStart = vswap.getUint16(4, Endian.little);

    List<int> offsets = [];
    for (int i = 0; i < chunks; i++) {
      offsets.add(vswap.getUint32(6 + (i * 4), Endian.little));
    }

    List<Matrix<int>> sprites = [];

    // Sprites are located between the walls and the sounds
    for (int i = spriteStart; i < soundStart; i++) {
      int offset = offsets[i];
      if (offset == 0) continue; // Some chunks are empty placeholders

      // Initialize the 64x64 grid with 255 (The Magenta Transparency Color!)
      Matrix<int> sprite = List.generate(64, (_) => List.filled(64, 255));

      int leftPix = vswap.getUint16(offset, Endian.little);
      int rightPix = vswap.getUint16(offset + 2, Endian.little);

      // Read the offsets for each vertical column of the sprite
      List<int> colOffsets = [];
      for (int x = leftPix; x <= rightPix; x++) {
        colOffsets.add(
          vswap.getUint16(offset + 4 + ((x - leftPix) * 2), Endian.little),
        );
      }

      for (int x = leftPix; x <= rightPix; x++) {
        int colOffset = colOffsets[x - leftPix];
        if (colOffset == 0) continue;

        int cmdOffset = offset + colOffset;

        // Execute the column drawing commands
        while (true) {
          int endY = vswap.getUint16(cmdOffset, Endian.little);
          if (endY == 0) break; // 0 marks the end of the column
          endY ~/= 2; // Wolf3D stores Y coordinates multiplied by 2

          int pixelOfs = vswap.getUint16(cmdOffset + 2, Endian.little);

          int startY = vswap.getUint16(cmdOffset + 4, Endian.little);
          startY ~/= 2;

          for (int y = startY; y < endY; y++) {
            // The Carmack 286 Hack: pixelOfs + y gives the exact byte address!
            sprite[x][y] = vswap.getUint8(offset + pixelOfs + y);
          }
          cmdOffset += 6; // Move to the next 6-byte instruction
        }
      }
      sprites.add(sprite);
    }
    return sprites;
  }
}