// /components/certificates/certificateService.js

const path = require('path');
const Certificate = require('./certificateModel');
const User = require('../users/userModel');
const AppError = require('../../utils/AppError');
const { commitTempFile, generatePresignedUrl, deleteFromBucket } = require('../../utils/s3Client');
const eventEmitter = require('../../events/eventEmitter');
const EVENT_NAMES = require('../../constants/eventNames');
const { parsePaginationAndSort, buildFilterQuery, calculateMeta } = require('../../utils/pagination');

const createCertificate = async (data) => {
  const user = await User.findById(data.user);
  if (!user) throw new AppError('USER_NOT_FOUND');

  // Move file from Temp bucket to Permanent Storage bucket
  const targetKey = `certificates/cert-${Date.now()}-${path.basename(data.tempFileName)}`;
  const { fileKey } = await commitTempFile(data.tempFileName, targetKey);

  const certificate = await Certificate.create({
    user: data.user,
    course: data.course || null,
    title: data.title,
    issuer: data.issuer || '',
    fileKey,
    originalName: data.originalName || path.basename(data.tempFileName),
    isOfficial: data.isOfficial || false
  });

  user.certificates.push(certificate._id);
  await user.save();

  eventEmitter.emit(EVENT_NAMES.CERTIFICATE_ISSUED, { certificateId: certificate._id, userId: user._id });

  const resultObj = certificate.toObject();
  resultObj.presignedUrl = await generatePresignedUrl(certificate.fileKey);
  return resultObj;
};

const getCertificateById = async (id) => {
  const certificate = await Certificate.findById(id)
    .populate('user', 'name surname username nationalIdCode')
    .populate('course', 'title type');
  if (!certificate) {
    throw new AppError('CERTIFICATE_NOT_FOUND');
  }

  const resultObj = certificate.toObject();
  resultObj.presignedUrl = await generatePresignedUrl(certificate.fileKey);
  return resultObj;
};

const getAllCertificates = async (queryParams) => {
  const { page, limit, skip, sort } = parsePaginationAndSort(queryParams);
  const filter = buildFilterQuery(queryParams, ['title', 'issuer']);

  const [certificates, totalCount] = await Promise.all([
    Certificate.find(filter)
      .populate('user', 'name surname username')
      .populate('course', 'title')
      .sort(sort)
      .skip(skip)
      .limit(limit),
    Certificate.countDocuments(filter)
  ]);

  const listWithUrls = await Promise.all(
    certificates.map(async (cert) => {
      const item = cert.toObject();
      item.presignedUrl = await generatePresignedUrl(cert.fileKey);
      return item;
    })
  );

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

const updateCertificate = async (id, updateData) => {
  const certificate = await Certificate.findById(id);
  if (!certificate) {
    throw new AppError('CERTIFICATE_NOT_FOUND');
  }

  if (updateData.tempFileName) {
    const targetKey = `certificates/cert-${Date.now()}-${path.basename(updateData.tempFileName)}`;
    const { fileKey } = await commitTempFile(updateData.tempFileName, targetKey);
    // Delete old file from storage bucket
    await deleteFromBucket(certificate.fileKey);
    certificate.fileKey = fileKey;
  }

  if (updateData.title) certificate.title = updateData.title;
  if (updateData.issuer !== undefined) certificate.issuer = updateData.issuer;
  if (updateData.isOfficial !== undefined) certificate.isOfficial = updateData.isOfficial;

  await certificate.save();

  const resultObj = certificate.toObject();
  resultObj.presignedUrl = await generatePresignedUrl(certificate.fileKey);
  return resultObj;
};

const deleteCertificate = async (id) => {
  const certificate = await Certificate.findById(id);
  if (!certificate) {
    throw new AppError('CERTIFICATE_NOT_FOUND');
  }

  await deleteFromBucket(certificate.fileKey);
  await User.findByIdAndUpdate(certificate.user, { $pull: { certificates: certificate._id } });
  await Certificate.findByIdAndDelete(id);
  return null;
};

const searchCertificates = async (queryParams) => {
  return getAllCertificates(queryParams);
};

const uploadUserCertificate = async (userId, data) => {
  const user = await User.findById(userId);
  if (!user) throw new AppError('USER_NOT_FOUND');

  const targetKey = `certificates/cert-${Date.now()}-${path.basename(data.tempFileName)}`;
  const { fileKey } = await commitTempFile(data.tempFileName, targetKey);

  const certificate = await Certificate.create({
    user: userId,
    course: data.course || null,
    title: data.title,
    issuer: data.issuer || 'Self-Uploaded',
    fileKey,
    originalName: data.originalName || path.basename(data.tempFileName),
    isOfficial: false
  });

  user.certificates.push(certificate._id);
  await user.save();

  eventEmitter.emit(EVENT_NAMES.CERTIFICATE_UPLOADED, { certificateId: certificate._id, userId });

  const resultObj = certificate.toObject();
  resultObj.presignedUrl = await generatePresignedUrl(certificate.fileKey);
  return resultObj;
};

const getMyCertificates = async (userId, queryParams) => {
  const filter = { user: userId, ...buildFilterQuery(queryParams) };
  const { page, limit, skip, sort } = parsePaginationAndSort(queryParams);

  const [certificates, totalCount] = await Promise.all([
    Certificate.find(filter)
      .populate('course', 'title type')
      .sort(sort)
      .skip(skip)
      .limit(limit),
    Certificate.countDocuments(filter)
  ]);

  const listWithUrls = await Promise.all(
    certificates.map(async (cert) => {
      const item = cert.toObject();
      item.presignedUrl = await generatePresignedUrl(cert.fileKey);
      return item;
    })
  );

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

module.exports = {
  createCertificate,
  getCertificateById,
  getAllCertificates,
  updateCertificate,
  deleteCertificate,
  searchCertificates,
  uploadUserCertificate,
  getMyCertificates
};