import 'dart:math' as math;
import 'dart:typed_data';
import 'dart:ui' as ui;

import 'package:flutter/services.dart';

class Bitmap<T> {
  // This idiosyncratic usage of "bitmap" comes from some other technology.
  // What I'm saying is "don't blame me"
  final math.Rectangle<int> rect;
  final List<T> data;

  Bitmap(this.rect, this.data) {
    assert(this.data.length == this.rect.width * this.rect.height);
  }

  static Future<Bitmap<T>> load<T>(String name, T Function(int) cb) async {
    final assetImageByteData = await rootBundle.load(name);
    final codec =
        await ui.instantiateImageCodec(assetImageByteData.buffer.asUint8List());
    final image = (await codec.getNextFrame()).image;

    final bytedata =
        (await image.toByteData(format: ui.ImageByteFormat.rawStraightRgba))!;

    final sx = image.width;
    final sy = image.height;

    final List<T> data = [];
    for (var i = 0; i < sx * sy; i++) {
      var pixel = bytedata.getUint32(i * 4, Endian.big);
      data.add(cb(pixel));
    }

    return Bitmap(math.Rectangle(0, 0, sx, sy), data);
  }

  T? get(int x, int y) {
    var realX = x - rect.top;
    var realY = y - rect.left;
    if (realX < 0 || realY < 0 || realX > rect.width || realY > rect.height) {
      return null;
    }
    return data[realY * rect.width + realX];
  }
}