import sharp from 'sharp';
import type { GeneratedDerivatives, ImageDerivative } from './types';

export const THUMBNAIL_SIZE = 320;

const IMAGE_MIME_PREFIX = 'image/';

/**
 * 判断 MIME 类型是否为图片
 */
export function isImage(mimeType: string): boolean {
  return mimeType.startsWith(IMAGE_MIME_PREFIX);
}

/**
 * 获取图片宽高元数据
 * 非图片或解析失败时返回 null
 */
export async function getImageMetadata(
  buffer: Buffer
): Promise<{ width: number; height: number } | null> {
  try {
    const metadata = await sharp(buffer).metadata();
    if (!metadata.width || !metadata.height) return null;
    return { width: metadata.width, height: metadata.height };
  } catch {
    return null;
  }
}

function buildDerivativeFileName(originalName: string, suffix: string, ext: string): string {
  const baseName = originalName.replace(/\.[^.]+$/, '');
  return `${baseName}-${suffix}.${ext}`;
}

function buildDerivative(
  originalName: string,
  suffix: string,
  ext: string,
  width: number,
  height: number,
  buffer: Buffer
): ImageDerivative {
  const fileName = buildDerivativeFileName(originalName, suffix, ext);
  return {
    path: `public/uploads/${fileName}`,
    url: `/uploads/${fileName}`,
    width,
    height,
    buffer,
  };
}

/**
 * 为图片生成缩略图、WebP、AVIF 派生格式
 * 非图片返回空对象
 *
 * 实现说明：
 * - 缩略图限制长边为 THUMBNAIL_SIZE，保持比例
 * - WebP/AVIF 保持原图尺寸，用于现代浏览器优化
 */
export async function generateDerivatives(
  buffer: Buffer,
  mimeType: string
): Promise<GeneratedDerivatives> {
  if (!isImage(mimeType)) {
    return {};
  }

  const metadata = await getImageMetadata(buffer);
  if (!metadata) {
    return {};
  }

  const originalName = `image-${Date.now()}`;
  const derivatives: GeneratedDerivatives = {};

  // 缩略图
  const thumbnailBuffer = await sharp(buffer)
    .resize(THUMBNAIL_SIZE, THUMBNAIL_SIZE, { fit: 'inside', withoutEnlargement: true })
    .toBuffer();
  const thumbnailMeta = await sharp(thumbnailBuffer).metadata();
  derivatives.thumbnail = buildDerivative(
    originalName,
    'thumbnail',
    'webp',
    thumbnailMeta.width || THUMBNAIL_SIZE,
    thumbnailMeta.height || THUMBNAIL_SIZE,
    thumbnailBuffer
  );

  // WebP
  const webpBuffer = await sharp(buffer).webp({ quality: 85 }).toBuffer();
  const webpMeta = await sharp(webpBuffer).metadata();
  derivatives.webp = buildDerivative(
    originalName,
    'webp',
    'webp',
    webpMeta.width || metadata.width,
    webpMeta.height || metadata.height,
    webpBuffer
  );

  // AVIF
  const avifBuffer = await sharp(buffer).avif({ quality: 80 }).toBuffer();
  const avifMeta = await sharp(avifBuffer).metadata();
  derivatives.avif = buildDerivative(
    originalName,
    'avif',
    'avif',
    avifMeta.width || metadata.width,
    avifMeta.height || metadata.height,
    avifBuffer
  );

  return derivatives;
}