import { newId } from "./id";

/** 編輯器內附圖（本地選檔或 mock 產圖） */
export type AttachedImage = {
  id: string;
  url: string;
  name?: string;
  /** 產圖 prompt；選檔可無 */
  prompt?: string;
};

export const MAX_ATTACHED_IMAGES = 10;

/** 單檔上限（讀成 data URL 前） */
const MAX_FILE_BYTES = 8 * 1024 * 1024;

export function withAttachedImageNote(text: string, count: number): string {
  const body = text.trim();
  if (!count || count <= 0) return body;
  if (/（附圖\s*\d+\s*張）/.test(body)) return body;
  return `${body}\n\n（附圖 ${count} 張）`;
}

function readFileAsDataUrl(file: File): Promise<string> {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => resolve(String(reader.result || ""));
    reader.onerror = () => reject(new Error(`讀取失敗：${file.name}`));
    reader.readAsDataURL(file);
  });
}

/**
 * 把本機圖檔讀成可預覽的 data URL。
 * mock 階段不真上傳；送出時 repo 只記張數／可選縮圖。
 */
export async function filesToAttachedImages(
  files: FileList | File[],
  opts?: { max?: number; existingCount?: number },
): Promise<AttachedImage[]> {
  const max = opts?.max ?? MAX_ATTACHED_IMAGES;
  const existing = opts?.existingCount ?? 0;
  const room = Math.max(0, max - existing);
  const list = Array.from(files).filter((f) => f.type.startsWith("image/"));
  if (list.length === 0) throw new Error("請選擇圖片檔");
  const take = list.slice(0, room);
  if (take.length === 0) throw new Error(`最多附 ${max} 張圖`);

  const out: AttachedImage[] = [];
  for (const file of take) {
    if (file.size > MAX_FILE_BYTES) {
      throw new Error(`${file.name} 超過 8MB`);
    }
    const url = await readFileAsDataUrl(file);
    if (!url.startsWith("data:image")) throw new Error(`無法讀取：${file.name}`);
    out.push({
      id: newId("img"),
      url,
      name: file.name,
    });
  }
  return out;
}

/** 大 data URL 不寫進 localStorage；改成可顯示的 mock 縮圖 seed */
export function toPersistableImageUrl(img: AttachedImage): string {
  if (img.url.startsWith("data:") && img.url.length > 1800) {
    const seed = encodeURIComponent((img.name || img.id || "attach").slice(0, 40));
    return `https://api.dicebear.com/9.x/shapes/svg?seed=${seed}&backgroundColor=c0aede,ffd5dc,b6e3f4`;
  }
  return img.url;
}