feat: add pagination and random sorting to course listing endpoint with configurable page size and Fisher-Yates shuffle algorithm

Backend/src/services/courses.service.ts

@@ -2,13 +2,15 @@ import { prisma } from '../config/database';
 import { Prisma } from '@prisma/client';
 import { config } from '../config';
 import { logger } from '../config/logger';
-import { listCourseResponse, getCourseResponse } from '../types/courses.types';
+import { listCourseResponse, getCourseResponse, ListCoursesInput } from '../types/courses.types';
 import { UnauthorizedError, ValidationError, ForbiddenError } from '../middleware/errorHandler';
 import { getPresignedUrl } from '../config/minio';
 
 export class CoursesService {
-    async ListCourses(category_id?: number): Promise<listCourseResponse> {
+    async ListCourses(input: ListCoursesInput): Promise<listCourseResponse> {
         try {
+            const { category_id, page = 1, limit = 10, random = false } = input;
+
             const where: Prisma.CourseWhereInput = {
                 status: 'APPROVED', 
             };
@@ -17,7 +19,35 @@ export class CoursesService {
                 where.category_id = category_id;
             }
 
-            const courses = await prisma.course.findMany({ where });
+            // Get total count for pagination
+            const total = await prisma.course.count({ where });
+            const totalPages = Math.ceil(total / limit);
+
+            let courses;
+
+            if (random) {
+                // Random mode: ดึงทั้งหมดแล้วสุ่ม
+                const allCourses = await prisma.course.findMany({ where });
+                
+                // Fisher-Yates shuffle
+                for (let i = allCourses.length - 1; i > 0; i--) {
+                    const j = Math.floor(Math.random() * (i + 1));
+                    [allCourses[i], allCourses[j]] = [allCourses[j], allCourses[i]];
+                }
+                
+                // Apply pagination after shuffle
+                const skip = (page - 1) * limit;
+                courses = allCourses.slice(skip, skip + limit);
+            } else {
+                // Normal mode: pagination with skip/take
+                const skip = (page - 1) * limit;
+                courses = await prisma.course.findMany({
+                    where,
+                    skip,
+                    take: limit,
+                    orderBy: { created_at: 'desc' }
+                });
+            }
 
             // Generate presigned URLs for thumbnails
             const coursesWithUrls = await Promise.all(
@@ -40,7 +70,10 @@ export class CoursesService {
             return {
                 code: 200,
                 message: 'Courses fetched successfully',
-                total: coursesWithUrls.length,
+                total,
+                page,
+                limit,
+                totalPages,
                 data: coursesWithUrls,
             };
         } catch (error) {