feat(submission): allow resubmission and add file size limit

src/app/api/assignments/[assignmentId]/submissions/route.ts

@@ -1,11 +1,12 @@
 import { NextResponse } from "next/server";
 import { prisma } from "@/lib/prisma";
-import { uploadAssignmentFile } from "@/lib/s3";
+import { deleteAssignmentFile, uploadAssignmentFile } from "@/lib/s3";
 import { evaluateAssignment } from "@/lib/grading";
 import { getNumericParam } from "@/lib/route-params";
 import { submissionSchema } from "@/lib/validators";
 
 const ACCEPT_EXTENSIONS = new Set([".pdf"]);
+const MAX_FILE_SIZE_BYTES = 20 * 1024 * 1024; // 20MB
 
 type AssignmentRouteParams = { assignmentId: string | string[] | undefined };
 
@@ -45,17 +46,22 @@ export async function POST(
     return NextResponse.json({ error: "请上传作业文件" }, { status: 400 });
   }
 
-  let metadata: unknown = {};
-  if (metadataRaw) {
-    try {
-      metadata = JSON.parse(String(metadataRaw));
-    } catch (error) {
-      console.error("Failed to parse submission metadata", error);
-      return NextResponse.json({ error: "表单信息格式错误" }, { status: 400 });
+  let metadata: Record<string, unknown> & { formPayload?: unknown } = {};
+  try {
+    if (metadataRaw) {
+      const parsedMetadata = JSON.parse(String(metadataRaw));
+      if (parsedMetadata && typeof parsedMetadata === "object" && !Array.isArray(parsedMetadata)) {
+        metadata = parsedMetadata as Record<string, unknown>;
+      }
     }
+  } catch (error) {
+    console.error("Failed to parse submission metadata", error);
+    return NextResponse.json({ error: "表单信息格式错误" }, { status: 400 });
   }
 
-  const parsed = submissionSchema.safeParse(metadata ?? {});
+  const parsed = submissionSchema.safeParse({
+    ...metadata,
+  });
   if (!parsed.success) {
     return NextResponse.json(
       { error: parsed.error.flatten() },
@@ -73,6 +79,10 @@ export async function POST(
     return NextResponse.json({ error: "作业不存在" }, { status: 404 });
   }
 
+  if (file.size > MAX_FILE_SIZE_BYTES) {
+    return NextResponse.json({ error: "PDF 文件大小不能超过 20MB" }, { status: 400 });
+  }
+
   const studentIdRaw = parsed.data.studentId.trim();
   const studentNameRaw = parsed.data.studentName.trim();
 
@@ -93,13 +103,6 @@ export async function POST(
     },
   });
 
-  if (existingSubmission) {
-    return NextResponse.json(
-      { error: "该学号已提交，请勿重复提交" },
-      { status: 409 },
-    );
-  }
-
   const arrayBuffer = await file.arrayBuffer();
   const buffer = Buffer.from(arrayBuffer);
   const studentId = studentIdRaw;
@@ -121,18 +124,35 @@ export async function POST(
   let autoEvaluated = false;
   try {
     const uploadResult = await uploadAssignmentFile(buffer, file.name, assignmentId);
+    const previousFileKey = existingSubmission?.fileKey ?? null;
 
-    const submission = await prisma.submission.create({
-      data: {
-        assignmentId,
-        studentId,
-        studentName,
-        originalFilename: file.name,
-        fileUrl: uploadResult.url,
-        fileKey: uploadResult.key,
-        formPayload: parsed.data.formPayload ?? undefined,
-      },
-    });
+    const submission = existingSubmission
+      ? await prisma.submission.update({
+          where: { id: existingSubmission.id },
+          data: {
+            studentId,
+            studentName,
+            originalFilename: file.name,
+            fileUrl: uploadResult.url,
+            fileKey: uploadResult.key,
+            formPayload: parsed.data.formPayload ?? undefined,
+            submittedAt: new Date(),
+            evaluationScore: null,
+            evaluationComment: null,
+            evaluatedAt: null,
+          },
+        })
+      : await prisma.submission.create({
+          data: {
+            assignmentId,
+            studentId,
+            studentName,
+            originalFilename: file.name,
+            fileUrl: uploadResult.url,
+            fileKey: uploadResult.key,
+            formPayload: parsed.data.formPayload ?? undefined,
+          },
+        });
 
     const shouldAutoEvaluate = Boolean(
       assignment.autoEvaluate && assignment.gradingCriteria?.trim(),
@@ -160,6 +180,13 @@ export async function POST(
         console.error("Auto evaluation failed", error);
       }
     }
+    if (previousFileKey) {
+      try {
+        await deleteAssignmentFile(previousFileKey);
+      } catch (error) {
+        console.error("Failed to delete previous submission file", error);
+      }
+    }
   } catch (error) {
     console.error("Failed to submit assignment", error);
     return NextResponse.json({ error: "上传失败" }, { status: 500 });