"use client";

import { t } from "./i18n";

/** Client-side image helpers: validation, resizing and compression. */

export const MAX_IMAGE_DIMENSION = 1600;
export const JPEG_QUALITY = 0.82;
export const MAX_FILE_BYTES = 20 * 1024 * 1024; // 20 MB per source file
export const MAX_IMAGES = 8;
export const ACCEPTED_TYPES = ["image/jpeg", "image/png", "image/webp", "image/gif", "image/heic", "image/heif"];

export type PreparedImage = {
  id: string;
  dataUrl: string;
  name: string;
  width: number;
  height: number;
  bytes: number;
};

export function isImageFile(file: File): boolean {
  if (file.type.startsWith("image/")) return true;
  return /\.(jpe?g|png|webp|gif|heic|heif|bmp)$/i.test(file.name);
}

export function describeFileError(file: File): string | null {
  if (!isImageFile(file)) return t("file.notImage", { name: file.name });
  if (file.size > MAX_FILE_BYTES) return t("file.imageTooLarge", { name: file.name });
  return null;
}

/** Rough byte length of a base64 data URL. */
export function dataUrlBytes(dataUrl: string): number {
  const index = dataUrl.indexOf(",");
  if (index === -1) return dataUrl.length;
  return Math.floor(((dataUrl.length - index - 1) * 3) / 4);
}

async function loadBitmap(blob: Blob, fallbackName: string): Promise<{ width: number; height: number; draw: (ctx: CanvasRenderingContext2D, w: number, h: number) => void }> {
  // Prefer createImageBitmap: it respects EXIF orientation and is fast.
  if (typeof createImageBitmap === "function") {
    try {
      const bitmap = await createImageBitmap(blob, { imageOrientation: "from-image" });
      return {
        width: bitmap.width,
        height: bitmap.height,
        draw: (ctx, w, h) => ctx.drawImage(bitmap, 0, 0, w, h),
      };
    } catch {
      /* fall through to the <img> path (Safari/HEIC edge cases) */
    }
  }

  const url = URL.createObjectURL(blob);
  try {
    const image = await new Promise<HTMLImageElement>((resolve, reject) => {
      const element = new Image();
      element.onload = () => resolve(element);
      element.onerror = () => reject(new Error(`Could not read "${fallbackName}".`));
      element.src = url;
    });
    return {
      width: image.naturalWidth || image.width,
      height: image.naturalHeight || image.height,
      draw: (ctx, w, h) => ctx.drawImage(image, 0, 0, w, h),
    };
  } finally {
    URL.revokeObjectURL(url);
  }
}

/**
 * Resize to max 1600px and re-encode as JPEG to keep uploads small.
 * Accepts any image blob (photos, canvas output from PDF pages, images
 * embedded in documents).
 */
export async function prepareImageFromBlob(blob: Blob, name = "image.jpg"): Promise<PreparedImage> {
  const bitmap = await loadBitmap(blob, name);
  const scale = Math.min(1, MAX_IMAGE_DIMENSION / Math.max(bitmap.width, bitmap.height));
  const width = Math.max(1, Math.round(bitmap.width * scale));
  const height = Math.max(1, Math.round(bitmap.height * scale));

  const canvas = document.createElement("canvas");
  canvas.width = width;
  canvas.height = height;
  const ctx = canvas.getContext("2d");
  if (!ctx) throw new Error("Your browser could not process this image.");
  ctx.fillStyle = "#ffffff"; // flatten transparency before JPEG encoding
  ctx.fillRect(0, 0, width, height);
  bitmap.draw(ctx, width, height);

  const dataUrl = canvas.toDataURL("image/jpeg", JPEG_QUALITY);

  return {
    id: `${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 8)}`,
    dataUrl,
    name,
    width,
    height,
    bytes: dataUrlBytes(dataUrl),
  };
}

/** Resize to max 1600px and re-encode as JPEG to keep uploads small. */
export async function prepareImage(file: File): Promise<PreparedImage> {
  return prepareImageFromBlob(file, file.name || "photo.jpg");
}

/** Extract image files from a paste or drop event. */
export function imageFilesFromDataTransfer(data: DataTransfer | null): File[] {
  if (!data) return [];
  const files: File[] = [];
  if (data.files?.length) {
    for (const file of Array.from(data.files)) if (isImageFile(file)) files.push(file);
  }
  if (data.items?.length) {
    for (const item of Array.from(data.items)) {
      if (item.kind !== "file") continue;
      const file = item.getAsFile();
      if (file && isImageFile(file) && !files.some((f) => f.name === file.name && f.size === file.size)) {
        files.push(file);
      }
    }
  }
  return files;
}

export function formatBytes(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1024 * 1024) return `${Math.round(bytes / 1024)} KB`;
  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
}