export function readFileAsDataURL(file) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => resolve(reader.result);
    reader.onerror = reject;
    reader.readAsDataURL(file);
  });
}

function getBase64Size(base64) {
  const str = base64.split(',')[1] || base64;
  return Math.ceil((str.length * 3) / 4);
}

function createResizedImage(dataUrl, options) {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.onload = () => {
      const scale = Math.min(
        options.width / img.width,
        options.height / img.height,
        1
      );
      const w = Math.round(img.width * scale);
      const h = Math.round(img.height * scale);

      const canvas = document.createElement('canvas');
      canvas.width = w;
      canvas.height = h;
      const ctx = canvas.getContext('2d');

      ctx.fillStyle = '#fff';
      ctx.fillRect(0, 0, w, h);
      ctx.imageSmoothingEnabled = true;
      ctx.imageSmoothingQuality = 'high';
      ctx.drawImage(img, 0, 0, w, h);

      resolve({
        dataUrl: canvas.toDataURL('image/jpeg', options.quality),
        width: w,
        height: h
      });
    };
    img.onerror = reject;
    img.src = dataUrl;
  });
}

export async function resizeImage(dataUrl, opts) {
  let bestResult = null;
  let minQuality = 0;
  let maxQuality = 100;

  while (maxQuality - minQuality > 1) {
    const quality = Math.round((minQuality + maxQuality) / 2);
    const result = await createResizedImage(dataUrl, {
      width: opts.width,
      height: opts.height,
      quality: quality / 100
    });

    const size = getBase64Size(result.dataUrl);
    if (size <= opts.maxSize) {
      bestResult = result;
      minQuality = quality;
    } else {
      maxQuality = quality;
    }
  }

  if (!bestResult) {
    throw new Error('Failed to compress image within size limit');
  }

  return bestResult;
}

export async function processPhotos(files) {
  const processed = [];
  for (const file of files) {
    const dataUrl = await readFileAsDataURL(file);
    const resized = await resizeImage(dataUrl, {
      width: 2000,
      height: 2000,
      maxSize: 900000
    });
    processed.push({
      dataUrl: resized.dataUrl,
      width: resized.width,
      height: resized.height
    });
  }
  return processed;
}