feat(levels): flexible cefr_level codes up to 64 chars

- Migration 000038 drops fixed A1-C3 check and widens cefr_level column
- CreateLevel validates length and NUL only; preserve client casing
- Regenerate Swagger docs

Made-with: Cursor

db/migrations/000038_levels_flexible_cefr_level.down.sql

@@ -0,0 +1,7 @@
+-- Restores fixed CEFR list; fails if any row has cefr_level outside the old set or longer than 2 characters.
+ALTER TABLE levels
+    ALTER COLUMN cefr_level TYPE VARCHAR(2);
+
+ALTER TABLE levels
+    ADD CONSTRAINT levels_cefr_level_check
+        CHECK (cefr_level IN ('A1', 'A2', 'A3', 'B1', 'B2', 'B3', 'C1', 'C2', 'C3'));

db/migrations/000038_levels_flexible_cefr_level.up.sql

@@ -0,0 +1,20 @@
+-- Allow arbitrary level codes/labels per course (not only fixed CEFR bands).
+DO $$
+DECLARE
+    con_name text;
+BEGIN
+    SELECT c.conname INTO con_name
+    FROM pg_constraint c
+    JOIN pg_class t ON c.conrelid = t.oid
+    JOIN pg_namespace n ON t.relnamespace = n.oid
+    WHERE n.nspname = current_schema()
+      AND t.relname = 'levels'
+      AND c.contype = 'c'
+      AND pg_get_constraintdef(c.oid) LIKE '%cefr_level%IN (%A1%';
+    IF con_name IS NOT NULL THEN
+        EXECUTE format('ALTER TABLE levels DROP CONSTRAINT %I', con_name);
+    END IF;
+END $$;
+
+ALTER TABLE levels
+    ALTER COLUMN cefr_level TYPE VARCHAR(64);

docs/docs.go

@@ -1522,7 +1522,7 @@ const docTemplate = `{
                 }
             },
             "post": {
-                "description": "Creates a CEFR level under a course with optional title (defaults to cefr_level), description, and thumbnail",
+                "description": "Creates a level under a course. cefr_level is a short level code or label (1–64 characters), unique per course; optional title defaults to that value; optional description and thumbnail",
                 "consumes": [
                     "application/json"
                 ],

docs/swagger.json

@@ -1514,7 +1514,7 @@
                 }
             },
             "post": {
-                "description": "Creates a CEFR level under a course with optional title (defaults to cefr_level), description, and thumbnail",
+                "description": "Creates a level under a course. cefr_level is a short level code or label (1–64 characters), unique per course; optional title defaults to that value; optional description and thumbnail",
                 "consumes": [
                     "application/json"
                 ],

docs/swagger.yaml

@@ -3095,8 +3095,9 @@ paths:
     post:
       consumes:
       - application/json
-      description: Creates a CEFR level under a course with optional title (defaults
-        to cefr_level), description, and thumbnail
+      description: Creates a level under a course. cefr_level is a short level code
+        or label (1–64 characters), unique per course; optional title defaults to
+        that value; optional description and thumbnail
       parameters:
       - description: Create level payload
         in: body

internal/web_server/handlers/hierarchy_handler.go

@@ -5,6 +5,7 @@ import (
 	"Yimaru-Backend/internal/domain"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/gofiber/fiber/v2"
 	"github.com/jackc/pgx/v5/pgtype"
@@ -1494,7 +1495,7 @@ func (h *Handler) DeleteCourseSubCategory(c *fiber.Ctx) error {
 
 // CreateLevel godoc
 // @Summary Create level
-// @Description Creates a CEFR level under a course with optional title (defaults to cefr_level), description, and thumbnail
+// @Description Creates a level under a course. cefr_level is a short level code or label (1–64 characters), unique per course; optional title defaults to that value; optional description and thumbnail
 // @Tags course-management
 // @Accept json
 // @Produce json
@@ -1508,12 +1509,18 @@ func (h *Handler) CreateLevel(c *fiber.Ctx) error {
 	if err := c.BodyParser(&req); err != nil {
 		return c.Status(fiber.StatusBadRequest).JSON(domain.ErrorResponse{Message: "Invalid request body", Error: err.Error()})
 	}
-	req.CEFRLevel = strings.ToUpper(strings.TrimSpace(req.CEFRLevel))
-	validCEFR := map[string]bool{"A1": true, "A2": true, "A3": true, "B1": true, "B2": true, "B3": true, "C1": true, "C2": true, "C3": true}
-	if req.CourseID <= 0 || !validCEFR[req.CEFRLevel] {
-		return c.Status(fiber.StatusBadRequest).JSON(domain.ErrorResponse{Message: "course_id and valid cefr_level are required"})
+	cefr := strings.TrimSpace(req.CEFRLevel)
+	if req.CourseID <= 0 || cefr == "" {
+		return c.Status(fiber.StatusBadRequest).JSON(domain.ErrorResponse{Message: "course_id and cefr_level are required"})
 	}
-	title := req.CEFRLevel
+	if strings.Contains(cefr, "\x00") {
+		return c.Status(fiber.StatusBadRequest).JSON(domain.ErrorResponse{Message: "cefr_level must not contain NUL characters"})
+	}
+	const maxCefrLevelRunes = 64
+	if utf8.RuneCountInString(cefr) > maxCefrLevelRunes {
+		return c.Status(fiber.StatusBadRequest).JSON(domain.ErrorResponse{Message: "cefr_level must be at most 64 characters"})
+	}
+	title := cefr
 	if req.Title != nil {
 		if t := strings.TrimSpace(*req.Title); t != "" {
 			title = t
@@ -1521,7 +1528,7 @@ func (h *Handler) CreateLevel(c *fiber.Ctx) error {
 	}
 	created, err := h.analyticsDB.CreateLevel(c.Context(), dbgen.CreateLevelParams{
 		CourseID:    req.CourseID,
-		CefrLevel:   req.CEFRLevel,
+		CefrLevel:   cefr,
 		Title:       title,
 		Description: toText(req.Description),
 		Thumbnail:   toText(req.Thumbnail),