using System.Globalization;

static double? CalculateAverageSession(List<CodeSession?>? allSessions)
{
    List<double?>? values = GetTotalSessionTime(allSessions);

    double? totalSeconds = 0;

    foreach (double? value in values)
    {
        totalSeconds += value;
    }

    double? averateTime = totalSeconds / values.Count;

    return averateTime;
}

static List<double?>? GetTotalSessionTime(List<CodeSession?>? allSessions)
{
    List<double?>? values = new();

    string format = @"hh\:mm";
    CultureInfo? provider = CultureInfo.InvariantCulture;

    foreach (CodeSession? session in allSessions)
    {
        TimeSpan startTime;
        TimeSpan endTime;

        TimeSpan start = TimeSpan.ParseExact(session.StartTime, format, provider);
        TimeSpan end = TimeSpan.ParseExact(session.EndTime, format, provider);
        TimeSpan difference = end.Subtract(start);

        double? timeInSeconds = difference.TotalSeconds;

        values.Add(timeInSeconds);
    }

    return values;
}

List<CodeSession?>? allSessions = new() {};


CodeSession? session = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "8:00", EndTime = "12:00", Duration = "04:00:00" };
CodeSession? session1 = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "9:00", EndTime = "13:00", Duration = "04:00:00" };
CodeSession? session2 = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "10:00", EndTime = "14:00", Duration = "04:00:00" };
CodeSession? session3 = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "11:00", EndTime = "15:00", Duration = "04:00:00" };
CodeSession? session4 = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "12:00", EndTime = "16:00", Duration = "04:00:00" };
CodeSession? session5 = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "13:00", EndTime = "17:00", Duration = "04:00:00" };
CodeSession? session6 = new() { Id = 1, TodaysDate = "10/05/2023", StartTime = "14:00", EndTime = "18:00", Duration = "04:00:00" };

allSessions.Add(session);
allSessions.Add(session1);
allSessions.Add(session2);
allSessions.Add(session3);
allSessions.Add(session4);
allSessions.Add(session5);
allSessions.Add(session6);

var totalTime = GetTotalSessionTime(allSessions);
var averateTime = CalculateAverageSession(allSessions);

Console.WriteLine("Total Time: {0}", totalTime);
Console.WriteLine("Average Time: {0}", averateTime);

class CodeSession
{
    public int? Id { get; set; }
    public string? TodaysDate { get; set; }
    public string? StartTime { get; set; }
    public string? EndTime { get; set; }
    public string? Duration { get; set; }
}