// /components/certificates/certificateService.js

const path = require('path');
const Certificate = require('./certificateModel');
const User = require('../users/userModel');
const AppError = require('../../utils/AppError');
const config = require('../../config/config');
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 BUCKET = 'certificates';

const withAccessUrl = async (cert) => {
  const item = typeof cert.toObject === 'function' ? cert.toObject() : { ...cert };
  item.fileUrl = item.fileUrl || null;
  try {
    item.signedUrl = await generatePresignedUrl(item.fileKey, item.bucket || config.S3_CERTIFICATES_BUCKET);
  } catch {
    item.signedUrl = null;
  }
  item.presignedUrl = item.signedUrl;
  item.url = item.fileUrl || item.signedUrl;
  return item;
};

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

  const safeName = path.basename(data.tempFileName);
  const targetKey = `cert-${Date.now()}-${safeName}`;
  const { fileKey, bucket, fileUrl } = await commitTempFile(data.tempFileName, targetKey, BUCKET);
  const fileName = data.originalName || data.fileName || safeName;

  const certificate = await Certificate.create({
    user: data.user,
    course: data.course || null,
    title: data.title || fileName,
    issuer: data.issuer || '',
    fileKey,
    fileName,
    originalName: fileName,
    fileUrl: fileUrl || null,
    bucket,
    mimeType: data.mimeType || '',
    isOfficial: data.isOfficial || false
  });

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

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

  return withAccessUrl(certificate);
};

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

const getCertificatesByUser = async (userId) => {
  const certificates = await Certificate.find({ user: userId })
    .populate('course', 'title type')
    .sort({ createdAt: -1 });
  return Promise.all(certificates.map(withAccessUrl));
};

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

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

  const data = await Promise.all(certificates.map(withAccessUrl));
  return { data, meta: calculateMeta(totalCount, page, limit) };
};

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

  if (updateData.tempFileName) {
    const safeName = path.basename(updateData.tempFileName);
    const targetKey = `cert-${Date.now()}-${safeName}`;
    const { fileKey, bucket, fileUrl } = await commitTempFile(updateData.tempFileName, targetKey, BUCKET);
    await deleteFromBucket(certificate.fileKey, certificate.bucket || config.S3_CERTIFICATES_BUCKET);
    certificate.fileKey = fileKey;
    certificate.bucket = bucket;
    certificate.fileUrl = fileUrl || null;
    const fileName = updateData.originalName || updateData.fileName;
    if (fileName) {
      certificate.fileName = fileName;
      certificate.originalName = fileName;
    }
    if (updateData.mimeType) certificate.mimeType = updateData.mimeType;
  }

  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();
  return withAccessUrl(certificate);
};

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

  await deleteFromBucket(certificate.fileKey, certificate.bucket || config.S3_CERTIFICATES_BUCKET);
  await User.findByIdAndUpdate(certificate.user, { $pull: { certificates: certificate._id } });
  await Certificate.findByIdAndDelete(id);
  return null;
};

const searchCertificates = async (queryParams) => getAllCertificates(queryParams);

const uploadUserCertificate = async (userId, data) => {
  return createCertificate({
    ...data,
    user: userId,
    issuer: data.issuer || 'Self-Uploaded',
    isOfficial: false
  });
};

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 data = await Promise.all(certificates.map(withAccessUrl));
  return { data, meta: calculateMeta(totalCount, page, limit) };
};

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