text: const { body, validationResult } = require('express-validator/check');
  const { sanitizeBody } = require('express-validator/filter');
  
  var Author = require('../models/author');
  var Book = require('../models/book');
  
  var async = require('async');
  
  //Display list of all authors
  exports.author_list = function (req, res) {
      
      Author.find()
          .sort([['family_name', 'ascending']])
          .exec(function (err, list_authors  ) {
              if(err) {return next(err); }
              //Successful, so render
              res.render('author_list', { title: 'Author List', author_list: list_authors});
          });
          
  };
  
  // Display detail page for a specific Author.
  exports.author_detail = function(req, res, next) {
  
      async.parallel({
          author: function(callback) {
              Author.findById(req.params.id)
                .exec(callback)
          },
          authors_books: function(callback) {
            Book.find({ 'author': req.params.id },'title summary')
            .exec(callback)
          },
      }, function(err, results) {
          if (err) { return next(err); } // Error in API usage.
          if (results.author==null) { // No results.
              var err = new Error('Author not found');
              err.status = 404;
              return next(err);
          }
          // Successful, so render.
          res.render('author_detail', { title: 'Author Detail', author: results.author, author_books: results.authors_books } );
      });
  
  };
  
  //Display Author create form on GET
  exports.author_create_get = function (req, res, next) {
      res.render('author_form', { title: 'Create Author' });
  };
  
  //Handle Author create on POST
  exports.author_create_post = [
  
      //Validate fields
      body('first_name').isLength({min:1}).trim().withMessage('First name must be specified').isAlphanumeric().withMessage('First name has non-alphanumeric characters.'),
      body('family_name').isLength({min:1}).trim().withMessage('Family name must be specified.').isAlphanumeric().withMessage('Family name has non-alphanumeric characters.'),
      body('date_of_birth', 'Invalid date of birth').optional({ checkFalsy: true }).isISO8601(),
      body('date_of_death', 'Invalid date of death').optional({ checkFalsy: true }).isISO8601(),
  
      //Sanitize fields
      sanitizeBody('first_name').trim().escape(),
      sanitizeBody('family_name').trim().escape(),
      sanitizeBody('date_of_birth').toDate(),
      sanitizeBody('date_of_death').toDate(),
  
      //Process request after validation and sanitization
      (req, res, next) => {
  
          //Extract the validation errors from a request
          const errors = validationResults(req);
  
          if (!errors.isEmpty()) {
              //There are errors. Render the form again with sanitized values/errors messages
              res.render('author_form', { title: 'Create Author', author: req.body, errors: errors.array() });
              return;
          }
          else {
              //Data on the form is valid
  
              //Create an Author object with escaped and trimmed data
              var author = new Author(
                  {
                      first_name: req.body.first_name,
                      family_name: req.body.family_name,
                      date_of_birth: req.body.date_of_birth,
                      date_of_death: req.body.date_of_death
                  });
              author.save(function(err) {
                  if(err) { return next(err); }
                  //Successful, redirect to new author record
                  res.redirect(author.url);
              });
          }
      }
  ];
  
  
  // Display Author delete form on GET.
  exports.author_delete_get = function(req, res, next) {
  
      async.parallel({
          author: function(callback) {
              Author.findById(req.params.id).exec(callback)
          },
          authors_books: function(callback) {
            Book.find({ 'author': req.params.id }).exec(callback)
          },
      }, function(err, results) {
          if (err) { return next(err); }
          if (results.author==null) { // No results.
              res.redirect('/catalog/authors');
          }
          // Successful, so render.
          res.render('author_delete', { title: 'Delete Author', author: results.author, author_books: results.authors_books } );
      });
  
  };
  
  // Handle Author delete on POST.
  exports.author_delete_post = function(req, res, next) {
  
      async.parallel({
          author: function(callback) {
            Author.findById(req.body.authorid).exec(callback)
          },
          authors_books: function(callback) {
            Book.find({ 'author': req.body.authorid }).exec(callback)
          },
      }, function(err, results) {
          if (err) { return next(err); }
          // Success
          if (results.authors_books.length > 0) {
              // Author has books. Render in same way as for GET route.
              res.render('author_delete', { title: 'Delete Author', author: results.author, author_books: results.authors_books } );
              return;
          }
          else {
              // Author has no books. Delete object and redirect to the list of authors.
              Author.findByIdAndRemove(req.body.authorid, function deleteAuthor(err) {
                  if (err) { return next(err); }
                  // Success - go to author list
                  res.redirect('/catalog/authors')
              })
          }
      });
  };
  
  //Display Author update form on GET
  exports.author_update_get = function (req, res, next) {
  
      Author.findById(req.params.id, function(err, author) {
          if(err) { return next(err); }
          if(author==null) { //no results 
              var err = new Error('Author not found');
              err.status=404;
              return next(err);
          }
          //Success
          res.render('author_form', { title: 'Author Update', author: author});
      });
      
  };
  
  //Handle Author update on POST
  exports.author_update_post = [
  
      // Validate fields.
      body('first_name').isLength({ min: 1 }).trim().withMessage('First name must be specified.')
          .isAlphanumeric().withMessage('First name has non-alphanumeric characters.'),
      body('family_name').isLength({ min: 1 }).trim().withMessage('Family name must be specified.')
          .isAlphanumeric().withMessage('Family name has non-alphanumeric characters.'),
      body('date_of_birth', 'Invalid date of birth').optional({ checkFalsy: true }).isISO8601(),
      body('date_of_death', 'Invalid date of death').optional({ checkFalsy: true }).isISO8601(),
  
      // Sanitize fields.
      sanitizeBody('first_name').trim().escape(),
      sanitizeBody('family_name').trim().escape(),
      sanitizeBody('date_of_birth').toDate(),
      sanitizeBody('date_of_death').toDate(),
  
      // Process request after validation and sanitization.
      (req, res, next) => {
  
          // Extract the validation errors from a request.
          const errors = validationResult(req);
  
          // Create Author object with escaped and trimmed data (and the old id!)
          var author = new Author(
              {
                  first_name: req.body.first_name,
                  family_name: req.body.family_name,
                  date_of_birth: req.body.date_of_birth,
                  date_of_death: req.body.date_of_death,
                  _id: req.params.id
              }
          );
  
          if (!errors.isEmpty()) {
              // There are errors. Render the form again with sanitized values and error messages.
              res.render('author_form', { title: 'Update Author', author: author, errors: errors.array() });
              return;
          }
          else {
              // Data from form is valid. Update the record.
              Author.findByIdAndUpdate(req.params.id, author, {}, function (err, theauthor) {
                  if (err) { return next(err); }
                  // Successful - redirect to genre detail page.
                  res.redirect(theauthor.url);
              });
          }
      }
  ];