// /components/courses/courseService.js

const Course = require('./courseModel');
const Professor = require('../professors/professorModel');
const AppError = require('../../utils/AppError');
const eventEmitter = require('../../events/eventEmitter');
const EVENT_NAMES = require('../../constants/eventNames');
const { parsePaginationAndSort, buildFilterQuery, calculateMeta } = require('../../utils/pagination');

const normalizeHighlights = (value) => {
  if (!Array.isArray(value)) return undefined;
  return value.map((item) => String(item).trim()).filter(Boolean);
};

const createCourse = async (data, actorId = null) => {
  if (data.professor) {
    const professor = await Professor.findById(data.professor);
    if (!professor) {
      throw new AppError('PROFESSOR_NOT_FOUND');
    }
  }

  const payload = {
    ...data,
    highlights: normalizeHighlights(data.highlights) ?? data.highlights
  };

  const course = await Course.create(payload);

  if (data.professor) {
    await Professor.findByIdAndUpdate(data.professor, { $addToSet: { courses: course._id } });
  }

  eventEmitter.emit(EVENT_NAMES.COURSE_CREATED, { courseId: course._id, title: course.title, actorId });
  return course;
};

const getCourseById = async (id, { publicOnly = false } = {}) => {
  const filter = { _id: id };
  if (publicOnly) filter.showOnFrontend = { $ne: false };

  const course = await Course.findOne(filter).populate('professor', 'name surname title expertise email phoneNumber');
  if (!course) {
    throw new AppError('COURSE_NOT_FOUND');
  }
  return course;
};

const getAllCourses = async (queryParams, { publicOnly = false } = {}) => {
  const { page, limit, skip, sort } = parsePaginationAndSort(queryParams);
  const filter = buildFilterQuery(queryParams, ['title', 'description'], [
    'page', 'limit', 'sortBy', 'sortOrder', 'q', 'lang', 'sort'
  ]);

  if (publicOnly) {
    // Include legacy docs that predate the field (treat missing as visible)
    filter.showOnFrontend = { $ne: false };
  }

  // Support legacy ?sort=-createdAt style from frontend
  let finalSort = sort;
  if (queryParams.sort && typeof queryParams.sort === 'string') {
    const raw = queryParams.sort.trim();
    if (raw.startsWith('-')) {
      finalSort = { [raw.slice(1)]: -1 };
    } else {
      finalSort = { [raw]: 1 };
    }
  }

  const [courses, totalCount] = await Promise.all([
    Course.find(filter).populate('professor', 'name surname').sort(finalSort).skip(skip).limit(limit),
    Course.countDocuments(filter)
  ]);

  const meta = calculateMeta(totalCount, page, limit);
  return { data: courses, meta };
};

const updateCourse = async (id, updateData, actorId = null) => {
  const course = await Course.findById(id);
  if (!course) {
    throw new AppError('COURSE_NOT_FOUND');
  }

  if (updateData.professor && updateData.professor !== String(course.professor)) {
    const professor = await Professor.findById(updateData.professor);
    if (!professor) throw new AppError('PROFESSOR_NOT_FOUND');

    if (course.professor) {
      await Professor.findByIdAndUpdate(course.professor, { $pull: { courses: course._id } });
    }
    await Professor.findByIdAndUpdate(updateData.professor, { $addToSet: { courses: course._id } });
  }

  if (updateData.price !== undefined && updateData.price !== course.price) {
    eventEmitter.emit(EVENT_NAMES.COURSE_PRICE_CHANGED, {
      courseId: course._id,
      oldPrice: course.price,
      newPrice: updateData.price,
      actorId
    });
  }

  if (updateData.highlights !== undefined) {
    updateData.highlights = normalizeHighlights(updateData.highlights) || [];
  }

  Object.assign(course, updateData);
  await course.save();
  return course;
};

const deleteCourse = async (id) => {
  const course = await Course.findById(id);
  if (!course) {
    throw new AppError('COURSE_NOT_FOUND');
  }

  if (course.professor) {
    await Professor.findByIdAndUpdate(course.professor, { $pull: { courses: course._id } });
  }

  await Course.findByIdAndDelete(id);
  return null;
};

const searchCourses = async (queryParams) => {
  return getAllCourses(queryParams);
};

module.exports = {
  createCourse,
  getCourseById,
  getAllCourses,
  updateCourse,
  deleteCourse,
  searchCourses
};