/**
 * 测试共享 — 真实语义 OPFS mock
 *
 * 模拟 OPFS 的完整语义：
 * - createWritable({ keepExistingData }) + position 追加写
 * - 文件内容以 ArrayBuffer 存储（跨 backend 实例共享于同一 Map）
 * - entries() 迭代、removeEntry 删除
 *
 * 用法：
 *   const files = installOPFSMock(new Map());
 *   const backend = new OPFSBackend();
 *   await backend.open('any');
 */

export interface MockOpfsFile {
  content: ArrayBuffer;
}

export function installOPFSMock(files: Map<string, MockOpfsFile>): {
  files: Map<string, MockOpfsFile>;
  dir: {
    getFileHandle: (name: string, opts?: { create?: boolean }) => Promise<{
      getFile: () => Promise<{ size: number; arrayBuffer: () => Promise<ArrayBuffer> }>;
      createWritable: (wOpts?: { keepExistingData?: boolean }) => Promise<{
        write: (arg: ArrayBuffer | { type: string; position: number; data: ArrayBuffer }) => Promise<void>;
        close: () => Promise<void>;
      }>;
    }>;
    entries: () => AsyncGenerator<[string]>;
    removeEntry: (name: string) => Promise<void>;
  };
} {
  const getFileHandle = async (name: string, opts?: { create?: boolean }) => {
    if (!files.has(name)) {
      if (!opts?.create) throw new Error(`NotFoundError: ${name}`);
      files.set(name, { content: new ArrayBuffer(0) });
    }
    const entry = files.get(name)!;
    return {
      getFile: async () => ({ size: entry.content.byteLength, arrayBuffer: async () => entry.content }),
      createWritable: async (wOpts?: { keepExistingData?: boolean }) => {
        const w: {
          write: (arg: ArrayBuffer | { type: string; position: number; data: ArrayBuffer }) => Promise<void>;
          close: () => Promise<void>;
        } = {
          write: async (arg) => {
            const keepExisting = wOpts?.keepExistingData ?? false;
            const chunk = (arg as { type?: string }).type === 'write'
              ? { data: (arg as { data: ArrayBuffer }).data, position: (arg as { position: number }).position }
              : { data: arg as ArrayBuffer, position: keepExisting ? entry.content.byteLength : 0 };
            const merged = new Uint8Array(chunk.position + chunk.data.byteLength);
            if (keepExisting || chunk.position > 0) {
              merged.set(new Uint8Array(entry.content), 0);
            }
            merged.set(new Uint8Array(chunk.data), chunk.position);
            entry.content = merged.buffer;
          },
          close: async () => { /* no-op */ },
        };
        return w;
      },
    };
  };

  const dir = {
    getFileHandle,
    entries: async function* () {
      for (const [name] of files) yield [name];
    },
    removeEntry: async (name: string) => {
      files.delete(name);
    },
  };

  Object.defineProperty(globalThis, 'navigator', {
    value: {
      storage: {
        getDirectory: async () => ({
          getDirectoryHandle: async (_name: string, _opts?: unknown) => dir,
        }),
      },
    },
    configurable: true,
    writable: true,
  });

  return { files, dir };
}