// Compile using: emcc example.cpp IndirectBuffer.cpp -std=c++11 -O3 -s NO_EXIT_RUNTIME=1 -s EXPORTED_FUNCTIONS="['_main','_DecodeImage_resize','_DecodeImage_finish']"

#include <emscripten.h>
#include <functional>
#include <stdio.h>
#include <string>
#include "IndirectBuffer.h"

struct DecodeImage {
  using Callback = std::function<void (int, int, IndirectBuffer)>;

  DecodeImage(const std::string &url, const Callback &callback) : _callback(callback) {
    EM_ASM_ARGS({
      var image = new Image;
      image.onload = function() {
        var width = image.width;
        var height = image.height;
        var canvas = document.createElement('canvas');
        canvas.width = width;
        canvas.height = height;
        var context = canvas.getContext('2d');
        context.drawImage(image, 0, 0);
        var pixels = context.getImageData(0, 0, width, height);
        var handle = Module._DecodeImage_resize($0, pixels.data.length);
        Module._IB_[handle].set(new Uint8Array(pixels.data.buffer));
        Module._DecodeImage_finish($0, width, height);
      };
      image.src = Module.Pointer_stringify($1);
    }, this, url.c_str());
  }

  int resize(size_t size) {
    _buffer.resize(size);
    return _buffer.handleForEmscripten();
  }

  void finish(int width, int height) {
    _callback(width, height, std::move(_buffer));
  }

private:
  Callback _callback;
  IndirectBuffer _buffer;
};

extern "C" int DecodeImage_resize(DecodeImage *self, size_t size) {
  return self->resize(size);
}

extern "C" void DecodeImage_finish(DecodeImage *self, int width, int height) {
  self->finish(width, height);
}

static bool isImageOpaque(const IndirectBuffer &buffer) {
  return EM_ASM_INT({
    var array = Module._IB_[$0];
    for (var i = 3, n = array.length; i < n; i += 4) {
      if (array[i] < 255) {
        return false;
      }
    }
    return true;
  }, buffer.handleForEmscripten());
}

int main() {
  static DecodeImage async("image.png", [](int width, int height, IndirectBuffer buffer) {
    printf("loaded %dx%d image outside main heap\n", width, height);
    printf("image is opaque: %d\n", isImageOpaque(buffer));
  });
  return 0;
}