feat(challenge): complete Snappet challenge (#Challenge-ticket)

BackEnd/Domain/Domain.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

BackEnd/Domain/Models/DashboardSummary.cs

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+namespace Domain.Models;
+
+public class DashboardSummary
+{
+    public List<SubjectAverage> SubjectAverages { get; set; } = new();
+} 

BackEnd/Domain/Models/Student.cs

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+namespace Domain.Models;
+
+public class Student
+{
+    public int UserId { get; set; }
+    public string Name => $"Student {UserId}";
+} 

BackEnd/Domain/Models/StudentData.cs

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+using System;
+using System.Collections.Generic;
+
+namespace Domain.Models;
+
+public class StudentData
+{
+    public int UserId { get; set; }
+    public required string Name { get; set; }
+    public List<StudentSubjectAverage> SubjectAverages { get; set; } = new();
+    public IList<StudentExerciseResult> Exercises { get; set; } = new List<StudentExerciseResult>();
+}
+
+public class StudentExerciseResult
+{
+    public Subject Subject { get; set; }
+    public required string SubjectName { get; set; }
+    public long ExerciseId { get; set; }
+    public required string ExerciseName { get; set; }
+    public bool Correct { get; set; }
+    public decimal Difficulty { get; set; }
+    public decimal Progress { get; set; }
+    public DateTime SubmitDateTime { get; set; }
+} 

BackEnd/Domain/Models/StudentListItem.cs

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+namespace Domain.Models;
+
+public class StudentSubjectAverage
+{
+    public Subject Subject { get; set; }
+    public decimal Average { get; set; }
+}
+
+public class StudentListItem
+{
+    public int UserId { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public List<StudentSubjectAverage> SubjectAverages { get; set; } = new();
+} 

BackEnd/Domain/Models/Subject.cs

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+namespace Domain.Models;
+
+public enum Subject
+{
+    BegrijpendLezen,
+    Rekenen,
+    Spelling
+}
+
+public static class SubjectExtensions
+{
+    public static string ToDisplayName(this Subject subject)
+    {
+        return subject switch
+        {
+            Subject.BegrijpendLezen => "Begrijpend Lezen",
+            Subject.Rekenen => "Rekenen",
+            Subject.Spelling => "Spelling",
+            _ => throw new ArgumentException($"Unknown subject: {subject}")
+        };
+    }
+
+    public static Subject FromString(string subjectName)
+    {
+        return subjectName switch
+        {
+            "Begrijpend Lezen" => Subject.BegrijpendLezen,
+            "Rekenen" => Subject.Rekenen,
+            "Spelling" => Subject.Spelling,
+            _ => throw new ArgumentException($"Unknown subject name: {subjectName}")
+        };
+    }
+} 

BackEnd/Domain/Models/SubjectAverage.cs

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+namespace Domain.Models;
+
+public class SubjectAverage
+{
+    public Subject Subject { get; set; }
+    public required string SubjectName { get; set; }
+    public decimal Average { get; set; }
+    public int TotalExercises { get; set; }
+    public int StudentCount { get; set; }
+} 

BackEnd/Domain/Models/WorkResult.cs

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+namespace Domain.Models;
+
+public class WorkResult
+{
+    public long SubmittedAnswerId { get; set; }
+    public DateTime SubmitDateTime { get; set; }
+    public bool Correct { get; set; }
+    public decimal Progress { get; set; }
+    public int UserId { get; set; }
+    public long ExerciseId { get; set; }
+    public decimal Difficulty { get; set; }
+    public Subject Subject { get; set; }
+    public string Domain { get; set; } = string.Empty;
+    public string LearningObjective { get; set; } = string.Empty;
+} 

BackEnd/Domain/Queries/GetAllStudentsQuery.cs

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+using Domain.Models;
+using Domain.Repositories;
+using Domain.Services;
+
+namespace Domain.Queries;
+
+public class GetAllStudentsQuery
+{
+    private readonly IWorkDataRepository _workDataRepository;
+    private readonly AverageCalculationService _averageCalculationService;
+
+    public GetAllStudentsQuery(
+        IWorkDataRepository workDataRepository,
+        AverageCalculationService averageCalculationService)
+    {
+        _workDataRepository = workDataRepository;
+        _averageCalculationService = averageCalculationService;
+    }
+
+    public async Task<IList<StudentListItem>> ExecuteAsync(DateTime cutoffDate)
+    {
+        var workResults = await _workDataRepository.GetWorkResultsBeforeDateAsync(cutoffDate);
+        var students = await _workDataRepository.GetAllStudentsAsync(cutoffDate);
+
+        var studentsWithAverages = students.Select(student =>
+        {
+            var studentWorkResults = workResults.Where(wr => wr.UserId == student.UserId).ToList();
+            var subjectAverages = _averageCalculationService.CalculateStudentSubjectAverages(studentWorkResults);
+
+            return new StudentListItem
+            {
+                UserId = student.UserId,
+                Name = student.Name,
+                SubjectAverages = subjectAverages
+            };
+        }).ToList();
+
+        return studentsWithAverages;
+    }
+} 

BackEnd/Domain/Queries/GetDashboardAveragesQuery.cs

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+using Domain.Models;
+using Domain.Repositories;
+using Domain.Services;
+
+namespace Domain.Queries;
+
+public class GetDashboardAveragesQuery
+{
+    private readonly IWorkDataRepository _workDataRepository;
+    private readonly AverageCalculationService _averageCalculationService;
+
+    public GetDashboardAveragesQuery(
+        IWorkDataRepository workDataRepository,
+        AverageCalculationService averageCalculationService)
+    {
+        _workDataRepository = workDataRepository;
+        _averageCalculationService = averageCalculationService;
+    }
+
+    public async Task<DashboardSummary> ExecuteAsync(DateTime cutoffDate)
+    {
+        var workResults = await _workDataRepository.GetWorkResultsBeforeDateAsync(cutoffDate);
+
+        var subjectAverages = _averageCalculationService.CalculateSubjectAverages(workResults);
+
+        return new DashboardSummary
+        {
+            SubjectAverages = subjectAverages
+        };
+    }
+} 

BackEnd/Domain/Queries/GetStudentDataQuery.cs

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+using Domain.Models;
+using Domain.Repositories;
+using Domain.Services;
+
+namespace Domain.Queries;
+
+public class GetStudentDataQuery
+{
+    private readonly IWorkDataRepository _workDataRepository;
+    private readonly AverageCalculationService _averageCalculationService;
+
+    public GetStudentDataQuery(
+        IWorkDataRepository workDataRepository,
+        AverageCalculationService averageCalculationService)
+    {
+        _workDataRepository = workDataRepository;
+        _averageCalculationService = averageCalculationService;
+    }
+
+    public async Task<StudentData?> ExecuteAsync(int studentId, DateTime cutoffDate)
+    {
+        var allWorkResults = await _workDataRepository.GetWorkResultsBeforeDateAsync(cutoffDate);
+        var studentWorkResults = allWorkResults.Where(wr => wr.UserId == studentId).ToList();
+
+        if (!studentWorkResults.Any())
+        {
+            return null;
+        }
+
+        var subjectAverages = _averageCalculationService.CalculateStudentSubjectAverages(studentWorkResults);
+
+        var exercises = studentWorkResults
+            .OrderByDescending(wr => wr.SubmitDateTime)
+            .Select(wr => new StudentExerciseResult
+            {
+                Subject = wr.Subject,
+                SubjectName = wr.Subject.ToDisplayName(),
+                ExerciseId = wr.ExerciseId,
+                ExerciseName = $"Exercise {wr.ExerciseId}",
+                Correct = wr.Correct,
+                Difficulty = wr.Difficulty,
+                Progress = wr.Progress,
+                SubmitDateTime = wr.SubmitDateTime
+            })
+            .ToList();
+
+        return new StudentData
+        {
+            UserId = studentId,
+            Name = $"Student {studentId}",
+            SubjectAverages = subjectAverages,
+            Exercises = exercises
+        };
+    }
+} 

BackEnd/Domain/Repositories/IWorkDataRepository.cs

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+using Domain.Models;
+
+namespace Domain.Repositories;
+
+public interface IWorkDataRepository
+{
+    Task<IList<WorkResult>> GetWorkResultsBeforeDateAsync(DateTime cutoffDate);
+    Task<HashSet<int>> GetUniqueStudentIdsAsync(DateTime cutoffDate);
+    Task<IList<StudentListItem>> GetAllStudentsAsync(DateTime cutoffDate);
+} 

BackEnd/Domain/Services/AverageCalculationService.cs

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+using Domain.Models;
+
+namespace Domain.Services;
+
+public class AverageCalculationService
+{
+    public List<SubjectAverage> CalculateSubjectAverages(IList<WorkResult> workResults)
+    {
+        var subjectGroups = workResults.GroupBy(wr => wr.Subject);
+        var subjectAverages = new List<SubjectAverage>();
+
+        foreach (var subjectGroup in subjectGroups)
+        {
+            var subjectResults = subjectGroup.ToList();
+            var correctAnswers = subjectResults.Count(wr => wr.Correct);
+            var totalAnswers = subjectResults.Count;
+            var averagePercentage = totalAnswers > 0 ? (decimal)correctAnswers / totalAnswers : 0;
+            var averageOnTenScale = averagePercentage * 10;
+
+            var uniqueStudents = subjectResults.Select(wr => wr.UserId).ToHashSet().Count;
+
+            subjectAverages.Add(new SubjectAverage
+            {
+                Subject = subjectGroup.Key,
+                SubjectName = subjectGroup.Key.ToDisplayName(),
+                Average = Math.Round(averageOnTenScale, 1),
+                TotalExercises = totalAnswers,
+                StudentCount = uniqueStudents
+            });
+        }
+
+        return subjectAverages.OrderBy(sa => sa.Subject).ToList();
+    }
+
+    public List<StudentSubjectAverage> CalculateStudentSubjectAverages(IList<WorkResult> studentWorkResults)
+    {
+        if (studentWorkResults == null || !studentWorkResults.Any())
+        {
+            return new List<StudentSubjectAverage>();
+        }
+
+        var subjectAverages = new List<StudentSubjectAverage>();
+        var subjectGroups = studentWorkResults.GroupBy(wr => wr.Subject);
+
+        foreach (var subjectGroup in subjectGroups)
+        {
+            var subjectResults = subjectGroup.ToList();
+            var correctAnswers = subjectResults.Count(wr => wr.Correct);
+            var totalAnswers = subjectResults.Count;
+
+            if (totalAnswers > 0)
+            {
+                var averagePercentage = (decimal)correctAnswers / totalAnswers;
+                var averageOnTenScale = averagePercentage * 10;
+
+                subjectAverages.Add(new StudentSubjectAverage
+                {
+                    Subject = subjectGroup.Key,
+                    Average = Math.Round(averageOnTenScale, 1)
+                });
+            }
+        }
+
+        return subjectAverages.OrderBy(sa => sa.Subject).ToList();
+    }
+}