// Client-side image normalisation. Resizes to MAX_EDGE px on the long axis
// and re-encodes to WebP (smaller than JPEG at equivalent quality). Output
// is typically <200KB even from a 12MP iPhone photo.
//
// CLAUDE.md: "resize about max 1200px and compress below 1MB before upload,
// use canvas API at client".

export const MAX_EDGE = 1200;
export const OUTPUT_MIME = "image/webp";
export const OUTPUT_QUALITY = 0.85;
export const HARD_LIMIT_BYTES = 1024 * 1024; // 1MB after re-encode

export const ACCEPTED_TYPES = ["image/jpeg", "image/png", "image/webp"];

export type ResizeResult = {
  blob: Blob;
  width: number;
  height: number;
  bytes: number;
  mimeType: string;
};

export async function resizeImage(file: File): Promise<ResizeResult> {
  if (!ACCEPTED_TYPES.includes(file.type)) {
    throw new Error(
      "Định dạng không hỗ trợ. Hãy chọn JPG, PNG hoặc WebP (HEIC không xử lý được trực tiếp).",
    );
  }

  const img = await loadImage(file);
  const scale = Math.min(1, MAX_EDGE / Math.max(img.width, img.height));
  const w = Math.max(1, Math.round(img.width * scale));
  const h = Math.max(1, Math.round(img.height * scale));

  const canvas = document.createElement("canvas");
  canvas.width = w;
  canvas.height = h;
  const ctx = canvas.getContext("2d");
  if (!ctx) throw new Error("Trình duyệt không hỗ trợ canvas.");
  ctx.imageSmoothingQuality = "high";
  ctx.drawImage(img, 0, 0, w, h);
  URL.revokeObjectURL(img.src);

  const blob = await new Promise<Blob | null>((resolve) =>
    canvas.toBlob(resolve, OUTPUT_MIME, OUTPUT_QUALITY),
  );
  if (!blob) throw new Error("Không re-encode được ảnh.");
  if (blob.size > HARD_LIMIT_BYTES) {
    throw new Error("Ảnh vẫn quá lớn sau khi nén (> 1MB). Hãy chọn ảnh khác.");
  }

  return {
    blob,
    width: w,
    height: h,
    bytes: blob.size,
    mimeType: OUTPUT_MIME,
  };
}

function loadImage(file: File): Promise<HTMLImageElement> {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.onload = () => resolve(img);
    img.onerror = () => reject(new Error("Không đọc được ảnh."));
    img.src = URL.createObjectURL(file);
  });
}