ai-chatbot/app/api/canvas/download-image/route.ts

import { resolveCanvasCdnDownload } from "@/lib/storage/canvas-cdn-download";
import { prepareImageArchiveDownload } from "@/lib/storage/image-download-preparation";
import { after, NextRequest, NextResponse } from "next/server";
import { auth } from "@/app/(auth)/auth";
import { getDownloadPreparationQueue, type DownloadPreparationInput } from "@/lib/canvas/download-preparation";
import { extractImageProxySourceUrl, inferOriginalImageUrl } from "@/lib/image-url";
import {
  buildAttachmentContentDisposition,
  fetchCanvasDownloadAsset,
  sanitizeCanvasDownloadFileName,
} from "@/lib/canvas/photoshop-safe-download";

export const runtime = "nodejs";
export const maxDuration = 120;

async function prepareDownload(input: DownloadPreparationInput, signal: AbortSignal) {
  // A proxy candidate for the same original must not repeat the same slow
  // upstream request through our own server (and create another HTTP timeout).
  const sources = [...new Set(input.urls.map(url => {
    const source = extractImageProxySourceUrl(url) || url;
    return inferOriginalImageUrl(source) || source;
  }))];
  for (let attempt = 0; attempt < 3; attempt++) {
    signal.throwIfAborted();
    for (const url of sources) {
      signal.throwIfAborted();
      const result = await fetchCanvasDownloadAsset({
        file: { url, name: "original" }, index: 0,
        requestOrigin: input.requestOrigin, cookie: input.cookie,
        includeSequencePrefix: false, timeoutMs: 12_000, retryCount: 1, signal,
      });
      if (result.ok) return { buffer: result.bytes, contentType: result.contentType };
    }
    // Each pass resolves the latest archive URL inside fetchCanvasDownloadAsset.
    // No AI/model request is involved and a completed source fetch is shared.
    if (attempt < 2) await new Promise(resolve => setTimeout(resolve, 1_000));
  }
  throw new Error("Original image sources unavailable");
}

function getRequestOrigin(request: NextRequest): string {
  const forwardedHost = (request.headers.get("x-forwarded-host") || "").split(",")[0]?.trim();
  const forwardedProto = (request.headers.get("x-forwarded-proto") || "").split(",")[0]?.trim();
  if (forwardedHost && forwardedProto) {
    return `${forwardedProto}://${forwardedHost}`;
  }
  return new URL(request.url).origin;
}

function resolveDownloadUrl(rawUrl: unknown, origin: string): string {
  const value = String(rawUrl || "").trim();
  if (!value) return "";
  try {
    const parsed = new URL(value, origin);
    if (!/^https?:$/i.test(parsed.protocol)) return "";
    return parsed.toString();
  } catch (_error) {
    return "";
  }
}

function resolveDownloadUrls(body: Record<string, unknown>, origin: string): string[] {
  const rawCandidates = Array.isArray(body.urls) ? body.urls : [body.url];
  const urls: string[] = [];
  const seen = new Set<string>();

  for (const rawUrl of rawCandidates) {
    const url = resolveDownloadUrl(rawUrl, origin);
    if (!url || seen.has(url)) continue;
    seen.add(url);
    urls.push(url);
  }

  return urls.slice(0, 6);
}

export async function POST(request: NextRequest) {
  try {
    const session = await auth();
    if (!session?.user?.id) {
      return NextResponse.json({ success: false, error: "未登录" }, { status: 401 });
    }

    const body = (await request.json().catch(() => ({}))) as Record<string, unknown>;
    const requestOrigin = getRequestOrigin(request);
    const urls = resolveDownloadUrls(body, requestOrigin);
    const requestedUrls = [...urls];
    if (urls.length === 0) {
      return NextResponse.json({ success: false, error: "图片地址无效" }, { status: 400 });
    }

    const name = sanitizeCanvasDownloadFileName(String(body.name || ""), "canvas-image");
    if (body.preferDirect === true) {
      const { task, direct } = await resolveCanvasCdnDownload(urls, `${name}.png`).catch(() => ({ task: null, direct: null }));
      if (direct) return NextResponse.json(direct, { headers: { "Cache-Control": "no-store" } });
      if (task?.targetUrl) {
        if (!urls.includes(task.targetUrl)) urls.unshift(task.targetUrl);
        after(() => prepareImageArchiveDownload(task.id));
      }
    }
    const cookie = request.headers.get("cookie") || "";
    if (body.preparation === "async") {
      const result = await getDownloadPreparationQueue(prepareDownload, after).request({
        userId: session.user.id, urls: requestedUrls, requestOrigin, cookie,
      });
      if (result.status === "preparing") {
        return NextResponse.json({ delivery: "preparing", retryAfter: 3,
          message: "正在准备原图，完成后将自动下载" }, {
          status: 202, headers: { "Retry-After": "3", "Cache-Control": "no-store" },
        });
      }
      if (result.status === "failed") {
        return NextResponse.json({ success: false, error: result.error }, { status: 502 });
      }
      return new NextResponse(new Uint8Array(result.asset.buffer), { headers: {
        "Content-Type": result.asset.contentType,
        "Content-Length": String(result.asset.buffer.length),
        "Content-Disposition": buildAttachmentContentDisposition(`${name}.png`),
        "Cache-Control": "no-store",
      } });
    }
    let result: Awaited<ReturnType<typeof fetchCanvasDownloadAsset>> | null = null;
    const failures: string[] = [];

    for (const url of urls) {
      result = await fetchCanvasDownloadAsset({
        file: { url, name },
        index: 0,
        requestOrigin,
        cookie,
        includeSequencePrefix: false,
      });
      if (result.ok) break;
      failures.push(`${url}: ${result.error}`);
    }

    if (!result?.ok) {
      if (failures.length > 0) {
        console.warn("[CanvasDownloadImage] All candidates failed:", failures);
      }
      return NextResponse.json(
        { success: false, error: result?.error || "图片源文件暂时不可访问" },
        { status: 502 }
      );
    }

    return new NextResponse(result.bytes, {
      status: 200,
      headers: {
        "Content-Type": result.contentType,
        "Content-Length": String(result.bytes.length),
        "Content-Disposition": buildAttachmentContentDisposition(result.filename),
        "Cache-Control": "no-store",
      },
    });
  } catch (error) {
    console.error("[CanvasDownloadImage] Failed:", error);
    return NextResponse.json({ success: false, error: "图片下载失败" }, { status: 500 });
  }
}