import type { PlatformApiClient } from "../api/client";
import type { ServerFileDownloadResponse } from "../api/types";

export async function downloadServerFileResult(client: PlatformApiClient, result: ServerFileDownloadResponse): Promise<string> {
  if (result.status !== "ready") {
    return result.reason ?? "文件读取任务已派发，完成后可再次下载。";
  }
  if (result.content !== undefined) {
    saveBlob(new Blob([result.content], { type: result.contentType ?? "text/plain;charset=utf-8" }), result.filename || "server-file.txt");
    return `下载已开始：${result.filename || result.key}`;
  }
  if (!result.artifact) {
    return "文件内容尚未可用。";
  }
  const writer = await createFileWriter(result.filename || result.artifact.filename);
  let offset = 0;
  const chunkSize = Math.max(1, result.artifact.chunkSizeBytes || 1024 * 1024);
  try {
    while (offset < result.artifact.sizeBytes) {
      const chunk = await client.readArtifactContent(result.artifact.artifactId, offset, Math.min(chunkSize, result.artifact.sizeBytes - offset));
      if (chunk.contentLength <= 0) throw new Error("文件下载返回空数据");
      await writer.write(chunk.payload);
      offset += chunk.contentLength;
    }
    await writer.close();
  } catch (error) {
    await writer.abort();
    throw error;
  }
  return `下载已开始：${result.filename || result.artifact.filename}`;
}

interface FileWriter {
  write(data: ArrayBuffer): Promise<void>;
  close(): Promise<void>;
  abort(): Promise<void>;
}

async function createFileWriter(filename: string): Promise<FileWriter> {
  const picker = (window as Window & { showSaveFilePicker?: (options?: { suggestedName?: string }) => Promise<{ createWritable(): Promise<FileSystemWritableFileStream> }> }).showSaveFilePicker;
  if (picker) {
    const handle = await picker({ suggestedName: safeFilename(filename) });
    const writable = await handle.createWritable();
    return {
      write: async (data) => { await writable.write(data); },
      close: async () => { await writable.close(); },
      abort: async () => { await writable.abort(); }
    };
  }
  const chunks: ArrayBuffer[] = [];
  return {
    write: async (data) => { chunks.push(data); },
    close: async () => { saveBlob(new Blob(chunks, { type: "application/octet-stream" }), safeFilename(filename)); },
    abort: async () => { chunks.length = 0; }
  };
}

function saveBlob(blob: Blob, filename: string) {
  const url = URL.createObjectURL(blob);
  const anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = safeFilename(filename);
  document.body.appendChild(anchor);
  anchor.click();
  anchor.remove();
  window.setTimeout(() => URL.revokeObjectURL(url), 1000);
}

function safeFilename(filename: string): string {
  const cleaned = filename.replace(/[\\/:*?"<>|]+/g, "-").trim();
  return cleaned || "server-file.txt";
}