using System;
using System.Collections.Generic;
using System.Linq;

namespace spplus;

public class CourseCrafter
{
    public class CourseInstance
    {
        public Sport Sport = null!;
        public int Remaining;
        public List<Student> Students = new();
    }
    public static List<(int Semester, CourseInstance Instance)> GeneratedCourses 
        = new();
    public static void Craft()
    {
        GeneratedCourses = new();
        var settings = Settings.Instance;
        var students = settings.Students;
        var sports = settings.Sports;

        if (students.Count == 0 || sports.Count == 0)
            return;

        int semesterCount = sports.Max(s => s.Semester.Length);

        // Result initialisieren
        foreach (var st in students)
            st.Result = Enumerable.Repeat("Fehler", semesterCount).ToList();

        // Mapping Name + Alternativen → Sport
        var nameMap = new Dictionary<string, Sport>(StringComparer.OrdinalIgnoreCase);
        foreach (var sp in sports)
        {
            nameMap[sp.Name] = sp;
            foreach (var alt in sp.AlternativeNames)
                nameMap[alt] = sp;
        }

        // ===== Semesterweise Planung =====
        for (int sem = 0; sem < semesterCount; sem++)
        {
            int remainingCourseSlots = settings.NumCoursesPerSemester;

            // Interessenten dieses Semesters
            var interested = new Dictionary<Sport, List<Student>>();
            foreach (var sp in sports)
                interested[sp] = new List<Student>();

            foreach (var st in students)
            {
                if (st.SelectedCourseNames.Count <= sem)
                    continue;

                var sel = st.SelectedCourseNames[sem];
                if (nameMap.TryGetValue(sel, out var sp))
                    interested[sp].Add(st);
            }

            var instances = new List<CourseInstance>();

            // ===== Kurse erzeugen =====
            foreach (var sp in sports)
            {
                if (sem >= sp.Semester.Length)
                    continue;

                int demand = interested[sp].Count;
                if (demand < sp.MinStudents)
                    continue;

                int needed = (int)Math.Ceiling(demand / (double)sp.MaxStudents);
                int allowed = Math.Min(needed, sp.Semester[sem]);
                allowed = Math.Min(allowed, remainingCourseSlots);

                if (allowed <= 0)
                    continue;

                remainingCourseSlots -= allowed;

                for (int i = 0; i < allowed; i++)
                {
                    var instance = new CourseInstance
                    {
                        Sport = sp,
                        Remaining = sp.MaxStudents
                    };
                    instances.Add(instance);
                    GeneratedCourses.Add((sem, instance));
                }
            }

            // ===== Schüler verteilen =====
            foreach (var sp in sports)
            {
                var pool = interested[sp];
                if (pool.Count == 0)
                    continue;

                var targets = instances.Where(i => i.Sport == sp).ToList();
                if (targets.Count == 0)
                    continue;

                int idx = 0;
                foreach (var st in pool)
                {
                    if (st.SelectedCourseNames.Count <= sem)
                        continue;

                    if (st.Result![sem] != "Fehler")
                        continue;

                    bool assigned = false;

                    for (int t = 0; t < targets.Count; t++)
                    {
                        var inst = targets[(idx + t) % targets.Count];
                        if (inst.Remaining > 0)
                        {
                            inst.Remaining--;
                            inst.Students.Add(st);
                            st.Result[sem] = sp.Name;
                            idx++;
                            assigned = true;
                            break;
                        }
                    }

                    if (!assigned)
                        continue;
                }
            }

            // ===== Alternativen =====
            foreach (var st in students)
            {
                if (st.SelectedCourseNames.Count <= sem)
                    continue;

                if (st.Result![sem] != "Fehler")
                    continue;

                var sel = st.SelectedCourseNames[sem];
                if (!nameMap.TryGetValue(sel, out var wanted))
                    continue;

                foreach (var altId in wanted.AlternativeCourses)
                {
                    var altSport = sports.FirstOrDefault(s => s.ID == altId);
                    if (altSport == null)
                        continue;

                    var inst = instances.FirstOrDefault(i => i.Sport == altSport && i.Remaining > 0);
                    if (inst == null)
                        continue;

                    inst.Remaining--;
                    inst.Students.Add(st);
                    st.Result[sem] = altSport.Name;
                    break;
                }
            }
        }
    }
    
    public static string GenerateStatistics()
    {
        var settings = Settings.Instance;
        var students = settings.Students;

        if (GeneratedCourses == null || GeneratedCourses.Count == 0)
            return "Keine Kurse generiert.";

        int semesterCount = students
            .Where(s => s.Result != null)
            .Select(s => s.Result!.Count)
            .DefaultIfEmpty(0)
            .Max();

        var sb = new System.Text.StringBuilder();

        sb.AppendLine($"Anzahl generierter Kurse: {GeneratedCourses.Count}");
        sb.AppendLine("Übersicht:");

        // ===== Kursübersicht =====
        var grouped = GeneratedCourses
            .GroupBy(g => new { g.Semester, g.Instance.Sport.Name })
            .OrderBy(g => g.Key.Semester)
            .ThenBy(g => g.Key.Name);

        foreach (var group in grouped)
        {
            int counter = 1;

            foreach (var entry in group)
            {
                int semester = group.Key.Semester + 1;
                string sportName = group.Key.Name;
                string number = counter.ToString("D2");
                int count = entry.Instance.Students.Count;

                sb.AppendLine(
                    $"Semester {semester}: {sportName} {number}: {count} Schüler*innen"
                );

                counter++;
            }
        }

        sb.AppendLine();
        sb.AppendLine("Fehlerübersicht:");

        // ===== Fehler pro Semester =====
        for (int sem = 0; sem < semesterCount; sem++)
        {
            int errors = students.Count(st =>
                st.Result != null &&
                st.Result.Count > sem &&
                st.Result[sem] == "Fehler");

            sb.AppendLine($"Semester {sem + 1}: {errors} Fehler");
        }

        return sb.ToString();
    }
}