Add assignment regrade update flow

backend/main.go

@@ -123,6 +123,7 @@ func main() {
 		r.Get("/assignments/{id}", handleGetAssignment(db))
 		r.Get("/assignments/{id}/image", handleGetAssignmentImage(db, cfg.UploadDir))
 		r.Post("/assignments", handleCreateAssignment(db, llmClient, cfg.UploadDir))
+		r.Put("/assignments/{id}", handleUpdateAssignment(db, llmClient, cfg.UploadDir))
 		r.Delete("/assignments/{id}", handleDeleteAssignment(db))
 	})
 
@@ -396,6 +397,153 @@ func handleCreateAssignment(db *sql.DB, llm *LLMClient, uploadDir string) http.H
 	}
 }
 
+func handleUpdateAssignment(db *sql.DB, llm *LLMClient, uploadDir string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		contentType := r.Header.Get("Content-Type")
+		if !strings.HasPrefix(contentType, "multipart/form-data") {
+			writeError(w, http.StatusBadRequest, "multipart form required")
+			return
+		}
+
+		r.Body = http.MaxBytesReader(w, r.Body, 50<<20)
+		if err := r.ParseMultipartForm(60 << 20); err != nil {
+			writeError(w, http.StatusBadRequest, "invalid multipart form")
+			return
+		}
+
+		username := strings.TrimSpace(r.FormValue("username"))
+		if username == "" {
+			username = strings.TrimSpace(r.URL.Query().Get("username"))
+		}
+		if username == "" {
+			writeError(w, http.StatusBadRequest, "username is required")
+			return
+		}
+
+		id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
+		if err != nil {
+			writeError(w, http.StatusBadRequest, "invalid assignment id")
+			return
+		}
+
+		var existingTitle string
+		var createdAt time.Time
+		var existingImagePath sql.NullString
+		row := db.QueryRow(`
+      SELECT title, created_at, image_path
+      FROM assignments
+      WHERE id = ? AND username = ?
+      LIMIT 1
+    `, id, username)
+		if err := row.Scan(&existingTitle, &createdAt, &existingImagePath); err != nil {
+			if errors.Is(err, sql.ErrNoRows) {
+				writeError(w, http.StatusNotFound, "assignment not found")
+				return
+			}
+			writeError(w, http.StatusInternalServerError, "failed to query assignment")
+			return
+		}
+
+		title := strings.TrimSpace(r.FormValue("title"))
+		if title == "" {
+			title = existingTitle
+		}
+		if title == "" {
+			title = fmt.Sprintf("%s %s", defaultTitlePrefix, time.Now().Format("2006-01-02 15:04"))
+		}
+
+		files := r.MultipartForm.File["images"]
+		if len(files) == 0 {
+			files = r.MultipartForm.File["image"]
+		}
+		if len(files) == 0 {
+			writeError(w, http.StatusBadRequest, "image is required")
+			return
+		}
+
+		if err := os.MkdirAll(uploadDir, 0o755); err != nil {
+			writeError(w, http.StatusInternalServerError, "failed to prepare upload dir")
+			return
+		}
+
+		imagePaths := make([]string, 0, len(files))
+		images := make([]LLMImage, 0, len(files))
+		for _, header := range files {
+			file, err := header.Open()
+			if err != nil {
+				writeError(w, http.StatusBadRequest, "failed to read image")
+				return
+			}
+
+			data, err := io.ReadAll(file)
+			file.Close()
+			if err != nil || len(data) == 0 {
+				writeError(w, http.StatusBadRequest, "failed to read image")
+				return
+			}
+
+			mimeType := header.Header.Get("Content-Type")
+			if mimeType == "" {
+				mimeType = http.DetectContentType(data)
+			}
+			if !strings.HasPrefix(mimeType, "image/") {
+				writeError(w, http.StatusBadRequest, "invalid image type")
+				return
+			}
+
+			filename := fmt.Sprintf("%s_%s%s", time.Now().Format("20060102_150405"), randomToken(6), extFromMime(mimeType))
+			imagePath := filepath.Join(uploadDir, filename)
+			if err := os.WriteFile(imagePath, data, 0o644); err != nil {
+				writeError(w, http.StatusInternalServerError, "failed to save image")
+				return
+			}
+
+			imagePaths = append(imagePaths, imagePath)
+			images = append(images, LLMImage{
+				MimeType: mimeType,
+				Base64:   base64.StdEncoding.EncodeToString(data),
+			})
+		}
+
+		markdown, feedback, score, err := llm.FormatAndGradeFromImages(r.Context(), title, images)
+		if err != nil {
+			writeError(w, http.StatusBadGateway, fmt.Sprintf("llm failed: %v", err))
+			return
+		}
+
+		imagePathsJSON, _ := json.Marshal(imagePaths)
+
+		_, err = db.Exec(`
+      UPDATE assignments
+      SET title = ?, ocr_text = ?, markdown = ?, feedback = ?, score = ?, image_path = ?
+      WHERE id = ? AND username = ?
+    `, title, "", markdown, feedback, score, string(imagePathsJSON), id, username)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "failed to update assignment")
+			return
+		}
+
+		if existingImagePath.Valid {
+			cleanupImages(uploadDir, existingImagePath.String)
+		}
+
+		assignment := Assignment{
+			ID:         id,
+			Username:   username,
+			Title:      title,
+			OCRText:    "",
+			Markdown:   markdown,
+			Feedback:   feedback,
+			Score:      score,
+			ImagePath:  firstPath(imagePaths),
+			ImagePaths: imagePaths,
+			CreatedAt:  createdAt,
+		}
+
+		writeJSON(w, http.StatusOK, assignment)
+	}
+}
+
 func handleCreateAssignmentWithImage(db *sql.DB, llm *LLMClient, uploadDir string, w http.ResponseWriter, r *http.Request) {
 	r.Body = http.MaxBytesReader(w, r.Body, 50<<20)
 	if err := r.ParseMultipartForm(60 << 20); err != nil {
@@ -566,7 +714,7 @@ func (c *LLMClient) FormatAndGrade(ctx context.Context, title, ocrText string) (
 		return "", "", 0, errors.New("LLM_BASE_URL or LLM_API_KEY missing")
 	}
 
-	systemPrompt := "你是一位细致的老师。请把 OCR 文字整理成清晰的 Markdown，保持原有题号、分点、段落与格式。然后给出作业批改意见。只输出 JSON，包含 markdown、feedback、score(0-100整数)。不要加代码块或多余文字。"
+	systemPrompt := "你是一位严谨的阅卷老师。请把 OCR 文字整理成清晰的 Markdown，保持原有题号、分点、段落与格式。然后进行详细批改：对每一道题给出参考答案、解题过程拆解、学生答案摘录、正确性判定（正确/部分正确/错误）、正确答案对比说明、考察知识点说明。最后给出整体评价与改进建议。仅输出 JSON，字段为 markdown、feedback、score(0-100整数)。不要加代码块或多余文字。"
 	userPrompt := fmt.Sprintf("标题: %s\n\nOCR文本:\n%s", title, ocrText)
 
 	payload := map[string]any{
@@ -614,7 +762,7 @@ func (c *LLMClient) FormatAndGradeFromImages(ctx context.Context, title string,
 		return "", "", 0, errors.New("no images provided")
 	}
 
-	systemPrompt := "你是一位细致的老师。请根据作业图片识别内容，整理为清晰的 Markdown，保持题号、分点、段落与格式。然后给出作业批改意见。只输出 JSON，包含 markdown、feedback、score(0-100整数)。不要加代码块或多余文字。"
+	systemPrompt := "你是一位严谨的阅卷老师。请根据作业图片识别内容，整理为清晰的 Markdown，保持题号、分点、段落与格式。然后进行详细批改：对每一道题给出参考答案、解题过程拆解、学生答案摘录、正确性判定（正确/部分正确/错误）、正确答案对比说明、考察知识点说明。最后给出整体评价与改进建议。若题目或答案无法识别，请明确标注“无法辨识”。仅输出 JSON，字段为 markdown、feedback、score(0-100整数)。不要加代码块或多余文字。"
 	userText := fmt.Sprintf("标题: %s\n以下图片按上传顺序依次为第1页、第2页……请综合批改。", title)
 
 	contentParts := make([]map[string]any, 0, len(images)+1)
@@ -801,6 +949,29 @@ func firstPath(paths []string) string {
 	return paths[0]
 }
 
+func cleanupImages(uploadDir, raw string) {
+	paths := parseImagePaths(raw)
+	if len(paths) == 0 {
+		return
+	}
+
+	absUpload, err := filepath.Abs(uploadDir)
+	if err != nil {
+		return
+	}
+
+	for _, path := range paths {
+		absImage, err := filepath.Abs(path)
+		if err != nil {
+			continue
+		}
+		if !strings.HasPrefix(absImage, absUpload+string(os.PathSeparator)) && absImage != absUpload {
+			continue
+		}
+		_ = os.Remove(absImage)
+	}
+}
+
 func randomToken(length int) string {
 	const charset = "abcdefghijklmnopqrstuvwxyz0123456789"
 	buf := make([]byte, length)
@@ -845,7 +1016,7 @@ func basicAuth(user, pass string) func(http.Handler) http.Handler {
 func corsMiddleware(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Access-Control-Allow-Origin", "*")
-		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, DELETE, OPTIONS")
+		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
 		w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
 		if r.Method == http.MethodOptions {
 			w.WriteHeader(http.StatusNoContent)