using System.Diagnostics;
using HSchool.Content;
using HSchool.People;
using HSchool.Schedule;
using HSchool.Simulation;

namespace HSchool.Server.Game;

internal sealed partial class SchoolWorker
{
    /// <summary>
    /// Writes pause/speed changes, at most once per <see cref="SimulationOptions.MinSaveInterval"/>.
    /// A single click still lands within that window; a burst collapses into one write.
    /// </summary>
    private void FlushSettings()
    {
        if (!_settingsDirty || Stopwatch.GetElapsedTime(_lastSettingsSave) < _options.MinSaveInterval)
        {
            return;
        }

        Persist();
        _settingsDirty = false;
        _lastSettingsSave = Stopwatch.GetTimestamp();
    }

    private void PublishSnapshot()
    {
        var school = _school;
        if (school is null)
        {
            return;
        }

        Volatile.Write(
            ref _snapshot,
            new SchoolState(
                school.Id,
                school.Name,
                school.Clock.Time,
                school.Clock.IsRunning,
                (byte)school.Clock.SpeedIndex,
                school.Catalog?.PackIds ?? _modIds ?? [],
                school.PeopleSeed,
                _owner));
        Volatile.Write(ref _rosterSnapshot, school.Roster);
        Volatile.Write(ref _applicantSnapshot, school.Applicants);
        Volatile.Write(ref _timetableSnapshot, school.Timetable);
        Volatile.Write(ref _mapSnapshot, school.Map);
    }

    /// <summary>
    /// Writes the composition file. Not called from the 30-second clock save — the roster and
    /// applicant pool change on create, hire, weekly refresh and yearly intake, not every tick.
    /// </summary>
    private void PersistPeople()
    {
        var school = _school;
        if (school?.Roster is null)
        {
            return;
        }

        try
        {
            _store.SavePeople(school.Id, RosterDocument.From(school.PeopleSeed, school.Roster, school.Applicants));
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Could not save people for school {SchoolId}; composition stays in memory.", _id);
        }
    }

    private void InstallTimetable(School school)
    {
        if (!_isNew)
        {
            var saved = _store.TryReadTimetable(_id);
            if (saved is not null)
            {
                var restored = RestoreTimetable(school, saved);
                school.SetTimetable(restored);
                if (!saved.Lessons.SequenceEqual(restored.Lessons)
                    || !saved.Uncovered.SequenceEqual(restored.Uncovered))
                {
                    PersistTimetable(school);
                }

                return;
            }
        }

        RebuildTimetable(school, broadcast: false);
    }

    private Timetable RestoreTimetable(School school, Timetable saved)
    {
        if (school.Catalog is null || school.Map is null || school.Roster is null)
        {
            return saved;
        }

        var classIds = school.Roster.Classes.Select(item => item.Id).ToHashSet(StringComparer.Ordinal);
        var peopleIds = school.Roster.People.Select(person => person.Id).ToHashSet(StringComparer.Ordinal);
        var valid = saved.Lessons
            .Where(lesson => classIds.Contains(lesson.ClassId) && peopleIds.Contains(lesson.TeacherId))
            .ToArray();
        if (valid.Length == saved.Lessons.Count)
        {
            return saved;
        }

        var locks = valid.Where(lesson => lesson.Locked).ToArray();
        return SchoolTimetables.Build(
            school.Catalog,
            school.Map,
            school.Roster,
            locks,
            _options.SchoolWeekDays);
    }

    private void RebuildTimetable(School school, bool broadcast = true)
    {
        if (school.Catalog is null || school.Map is null || school.Roster is null)
        {
            return;
        }

        var locks = school.Timetable?.Lessons.Where(lesson => lesson.Locked).ToArray() ?? [];
        ApplyTable(
            school,
            SchoolTimetables.Build(school.Catalog, school.Map, school.Roster, locks, _options.SchoolWeekDays),
            broadcast);
    }

    private static string? TeacherFor(School school, string classId, string subject)
    {
        var existing = school.Timetable?.Lessons.FirstOrDefault(lesson =>
            lesson.ClassId == classId && lesson.Subject == subject);
        if (existing is not null)
        {
            return existing.TeacherId;
        }

        return school.Roster?.People
            .Where(person => person.IsStaff && person.Subjects.Contains(subject, StringComparer.Ordinal))
            .OrderBy(person => person.Id, StringComparer.Ordinal)
            .Select(person => person.Id)
            .FirstOrDefault();
    }

    private void ApplyTable(School school, Timetable table, bool broadcast)
    {
        school.SetTimetable(table);
        PersistTimetable(school);
        PublishSnapshot();
        if (broadcast)
        {
            BroadcastPresence();
        }
    }

    /// <summary>
    /// Writes the lesson table. Not called from the 30-second clock save — the table changes on
    /// hire, unassign, pin and yearly intake, not every tick.
    /// </summary>
    private void PersistTimetable(School school)
    {
        if (school.Timetable is null)
        {
            return;
        }

        try
        {
            _store.SaveTimetable(school.Id, school.Timetable);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Could not save the timetable for school {SchoolId}; it stays in memory.", _id);
        }
    }

    private void Persist()
    {
        var school = _school;
        if (school is null)
        {
            return;
        }

        // A full disk or a locked file must not end the school; the next save will try again.
        try
        {
            _store.Save(new SchoolSave
            {
                Format = SchoolStore.CurrentFormat,
                Id = school.Id,
                Name = school.Name,
                GameTime = school.Clock.Time,
                Running = school.Clock.IsRunning,
                SpeedIndex = school.Clock.SpeedIndex,
                ModIds = school.Catalog?.PackIds,
                Map = school.Map,
                CountryId = school.CountryId,
                ClimatePresetId = school.ClimatePresetId,
                NativeLanguage = _nativeLanguage,
                Presence = school.CapturePresence(),
                DressRules = school.DressRules,
                SpeechRules = school.SpeechRules,
                Owner = _owner,
                PortraitSettings = _portraitSettings,
                Notices = _notices.ToSave(),
            });
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Could not save school {SchoolId}; it keeps running unsaved.", _id);
        }
    }
}