elearning/Backend/src/services/courses.service.ts

import { prisma } from '../config/database';
import { Prisma } from '@prisma/client';
import { config } from '../config';
import { logger } from '../config/logger';
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(input: ListCoursesInput): Promise<listCourseResponse> {
        try {
            const { category_id, is_recommended, page = 1, limit = 10, random = false } = input;

            const where: Prisma.CourseWhereInput = {
                status: 'APPROVED',
            };

            if (category_id) {
                where.category_id = category_id;
            }

            if (is_recommended !== undefined) {
                where.is_recommended = is_recommended;
            }

            // 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(
                courses.map(async (course) => {
                    let thumbnail_presigned_url: string | null = null;
                    if (course.thumbnail_url) {
                        try {
                            thumbnail_presigned_url = await getPresignedUrl(course.thumbnail_url, 3600);
                        } catch (err) {
                            logger.warn(`Failed to generate presigned URL for thumbnail: ${err}`);
                        }
                    }
                    return {
                        ...course,
                        thumbnail_url: thumbnail_presigned_url,
                    };
                })
            );

            return {
                code: 200,
                message: 'Courses fetched successfully',
                total,
                page,
                limit,
                totalPages,
                data: coursesWithUrls,
            };
        } catch (error) {
            logger.error('Failed to fetch courses', { error });
            throw error;
        }
    }

    async GetCourseById(id: number): Promise<getCourseResponse> {
        try {
            const course = await prisma.course.findFirst({
                where: {
                    id,
                    status: 'APPROVED' // Only show approved courses to students
                }
            });

            if (!course) {
                return {
                    code: 200,
                    message: 'no Course fetched successfully',
                    data: null,
                };
            }

            // Generate presigned URL for thumbnail
            let thumbnail_presigned_url: string | null = null;
            if (course.thumbnail_url) {
                try {
                    thumbnail_presigned_url = await getPresignedUrl(course.thumbnail_url, 3600);
                } catch (err) {
                    logger.warn(`Failed to generate presigned URL for thumbnail: ${err}`);
                }
            }
            return {
                code: 200,
                message: 'Course fetched successfully',
                data: {
                    ...course,
                    thumbnail_url: thumbnail_presigned_url,
                },
            };
        } catch (error) {
            logger.error('Failed to fetch course', { error });
            throw error;
        }
    }
}