using LehrerApp.Core.Models;

namespace LehrerApp.Core.Services;

public record AttendanceBalance(
    int TotalChecked, int Present, int Excused, int Unexcused,
    int SchoolEvent, int ExcusePending, double AbsenceRatePercent)
{
    public bool ExceedsThreshold => AbsenceRatePercent > AttendanceBalanceService.WarningThresholdPercent;
}

/// <summary>
/// Fehlzeitenbilanz (5.2.2/5.2.3) — reine Auswertung der bereits im Mitarbeit-Feature
/// erfassten <see cref="AttendanceStatus"/>-Werte, keine zweite Erfassung.
/// </summary>
public class AttendanceBalanceService
{
    public const double WarningThresholdPercent = 20.0;

    public AttendanceBalance Calculate(IEnumerable<(DateOnly Date, AttendanceStatus? Status)> entries,
        DateOnly from, DateOnly to)
    {
        var relevant = entries
            .Where(e => e.Status.HasValue && e.Date >= from && e.Date <= to)
            .Select(e => e.Status!.Value)
            .ToList();

        var present      = relevant.Count(s => s == AttendanceStatus.Present);
        var excused      = relevant.Count(s => s == AttendanceStatus.Excused);
        var unexcused    = relevant.Count(s => s is AttendanceStatus.Unexcused or AttendanceStatus.Truant);
        var schoolEvent  = relevant.Count(s => s == AttendanceStatus.OtherSchoolEvent);
        var pending      = relevant.Count(s => s == AttendanceStatus.ExcusePending);
        var total        = relevant.Count;

        // Schulisch veranlasste Abwesenheit (Exkursion o.ä.) zählt nicht als Fehlzeit des Schülers.
        var absenceCount = excused + unexcused + pending;
        var rate = total == 0 ? 0.0 : Math.Round(100.0 * absenceCount / total, 1);

        return new AttendanceBalance(total, present, excused, unexcused, schoolEvent, pending, rate);
    }
}