YouGrade - Asp.NET MVC Multimedia Exam Suite

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using YouGrade.Model;
using YouGrade.Dtos;
using AutoMapper;

namespace YouGrade
{
    public class ExamManager
    {
        static ExamManager instance = null;
        ExamDef examDef;
        ExamTakeDto examTakeDto;
        int questionId = 1;
        private ExamManager()
        {
            var service = new YouGradeService();
            examDef = service.GetExamDef();

            var examDefDto = new ExamDefDto();
            Mapper.Map(examDef, examDefDto);

            examTakeDto = new ExamTakeDto();
            examTakeDto.ExamId = 1;
            examTakeDto.UserId = 1;
            examTakeDto.Answers = new List<AnswerDto>();
            examTakeDto.StartDateTime = DateTime.Now;
            examTakeDto.Status = ExamTakeStatus.Open.ToString();
            foreach (var q in examDefDto.Questions)
            {
                foreach (var a in q.Alternatives)
                {
                    examTakeDto.Answers.Add(new AnswerDto()
                    {
                        QuestionId = q.Id,
                        AlternativeId = a.Id,
                        ExamTakeId = 0,
                        IsChecked = false
                    });
                }
            }
        }

        public static ExamManager Instance
        {
            get
            {
                if (instance == null)
                    instance = new ExamManager();
                return instance;
            }
        }

        public ExamDefDto GetExam()
        {
            var examDefDto = new ExamDefDto();
            Mapper.Map(examDef, examDefDto);

            return examDefDto;
        }

        public QuestionDefDto GetQuestion()
        {
            var questionDef = examDef.QuestionDef.Where(e => e.Id == questionId).First();
            var questionDefDto = new QuestionDefDto();
            Mapper.Map(questionDef, questionDefDto);
            var query = from alt in questionDefDto.Alternatives
                        join ans in examTakeDto.Answers
                            on new { qId = alt.QuestionId, aId = alt.Id }
                            equals new { qId = ans.QuestionId, aId = ans.AlternativeId }
                        select new { ans = ans, alt = alt };

            foreach (var a in query)
            {
                a.alt.IsChecked = a.ans.IsChecked;
            }
                        
            return questionDefDto;
        }

        public void SaveAnswer(int questionId, string answers)
        {
            var question = examDef.QuestionDef.Where(e => e.Id == questionId).First();

            var query = from ans in examTakeDto.Answers
                        where ans.QuestionId == questionId
                        select ans;

            foreach (var a in query)
            {
                a.IsChecked = (answers.ToCharArray().Contains(a.AlternativeId[0]));
            }
        }

        public bool MoveToPreviousQuestion()
        {
            bool canMove = false;

            if (questionId > 1)
            {
                questionId--;
                canMove = true;
            }

            return canMove;
        }

        public bool MoveToNextQuestion()
        {
            bool canMove = false;

            if (examDef.QuestionDef.Count > questionId)
            {
                questionId++;
                canMove = true;
            }

            return canMove;
        }

        public int EndExam()
        {
            var result = 0d;
            var service = new YouGradeService();
            var examDefDto = new ExamDefDto();
            Mapper.Map(examDef, examDefDto);

            result = service.SaveExamTake(examTakeDto);

            return (int)((100 * result) / examDefDto.Questions.Count());
        }
    }
}