Implemented the importing

MeetTheTeacher/Import/TeacherDataCsvImporter.cs

@@ -26,29 +26,114 @@ public sealed class TeacherDataCsvImporter : ITeacherDataImporter
 
     public IEnumerable<Teacher> LoadTeacherData()
     {
-        // TODO
-        return null!;
+        var basicData = ReadTeacherData() ?? new Dictionary<string, Teacher>();
+        var advancedData = ReadTeacherBusinessCardData() ?? new List<(string, int)>();
+        var completeData = CombineData(basicData, advancedData);
+
+        var teacherList = new List<Teacher>();
+        foreach (var teacher in completeData)
+        {
+            teacherList.Add(teacher.Value);
+        }
+        return teacherList;
     }
 
     private static Dictionary<string, Teacher> CombineData(Dictionary<string, Teacher> generalData,
                                                            IEnumerable<(string name, int id)> businessCardData)
     {
-        // Note: this method is designed specifically to force you to deal with the dictionary and 
-        // different teacher classes as value. It could be done in different ways as well, of course.
 
-        // TODO
-        return null!;
+        Dictionary<string, Teacher> result = new Dictionary<string, Teacher>();
+        
+        Dictionary<string, int> businessCardDict = new Dictionary<string, int>();
+        foreach (var item in businessCardData)
+        {
+            businessCardDict[item.name] = item.id;
+        }
+
+        foreach (var (name, teacher) in generalData)
+        {
+            if (businessCardDict.TryGetValue(name, out int id))
+            {
+                var teacherWithCard = new TeacherWithBusinessCard(name, id)
+                {
+                    ConsultingHourWeekDay = teacher.ConsultingHourWeekDay,
+                    ConsultingHourUnit = teacher.ConsultingHourUnit,
+                    ConsultingHour = teacher.ConsultingHour,
+                    Room = teacher.Room
+                };
+
+                result.Add(name, teacherWithCard);
+            }
+            else
+            {
+                result.Add(name, teacher);
+            }
+        }
+
+        return result;
     }
 
     private IEnumerable<(string name, int id)>? ReadTeacherBusinessCardData()
     {
-        // TODO - CSV import (mind the return type: ValueTuple!)
-        return null!;
+        if (!File.Exists(_businessCardDataFilePath))
+        {
+            return null;
+        }
+        
+        string[] lines = File.ReadAllLines(_businessCardDataFilePath);
+
+        List<(string name, int id)> businessData = new List<(string name, int id)>();
+        foreach (string line in lines)
+        {
+            IReadOnlyList<string> dataLine = line.Split(CsvData.Separator);
+            if (dataLine.Count != 2)
+            {
+                continue;
+            }
+            
+            bool success = int.TryParse(dataLine[0], out int id);
+            if (!success)
+            {
+                continue;
+            }
+            string name = dataLine[1];
+            
+            businessData.Add((name, id));
+        }
+        
+        return businessData;
     }
 
     private Dictionary<string, Teacher>? ReadTeacherData()
     {
-        // TODO - CSV import
-        return null!;
+        if (!File.Exists(_generalDataFilePath))
+        {
+            return null;
+        }
+        
+        string[] lines = File.ReadAllLines(_generalDataFilePath);
+        
+        Dictionary<string, Teacher> generalData = new Dictionary<string, Teacher>();
+        foreach (string line in lines)
+        {
+            IReadOnlyList<string> dataLine = line.Split(CsvData.Separator);
+            string name = dataLine[0];
+            DayOfWeek? consultingDay = Enum.TryParse<DayOfWeek>(dataLine[1], true, out var day) ? day : null;
+            SchoolUnit? consultingHourUnit = int.TryParse(dataLine[2], out var consultingHourUnitOut) ? (SchoolUnit?)consultingHourUnitOut : null;
+            TimeFrame? consultingHour = TimeFrame.TryParse(dataLine[3], out TimeFrame? frame) ? frame : null;
+            string? room = string.IsNullOrWhiteSpace(dataLine[4]) ? null : dataLine[4];
+            
+            var teacher = new Teacher(name)
+            {
+                ConsultingHourWeekDay = consultingDay,
+                ConsultingHourUnit = consultingHourUnit,
+                ConsultingHour = consultingHour,
+                Room = room,
+            };
+            
+            generalData.Add(name, teacher);
+        }
+        
+        return generalData;
     }
 }