using HSchool.Content;

namespace HSchool.Schedule.Tests;

public class TimetablePlannerTests
{
    private readonly DefCatalog _catalog = Fixtures.Catalog();

    [Fact]
    public void OneGym_SpreadsPhysicalEducationAcrossSlots()
    {
        var classes = Enumerable.Range(1, 11).Select(year => Fixtures.Class(year - 1, year, pupils: 16)).ToArray();
        var map = Fixtures.ClassroomsAndGym(11);
        var teachers = new[] { Fixtures.Teacher("pe", "PhysicalEducation") };

        var table = TimetablePlanner.Build(_catalog, map, classes, teachers);

        var pe = table.Lessons.Where(lesson => lesson.Subject == "PhysicalEducation").ToArray();
        Assert.Equal(11 * 3, pe.Length);
        Assert.All(pe, lesson => Assert.Equal("gym-hall", lesson.RoomId));
        Assert.Equal(pe.Length, pe.Select(lesson => (lesson.Day, lesson.Period)).Distinct().Count());
        Assert.All(pe, lesson => Assert.Equal("pe", lesson.TeacherId));
    }

    [Fact]
    public void TeacherWithTwoSubjects_IsNeverInTwoRoomsAtOnce()
    {
        var classes = new[]
        {
            Fixtures.Class(0, year: 5, pupils: 16, letter: "A"),
            Fixtures.Class(1, year: 5, pupils: 16, letter: "B"),
        };
        var map = Fixtures.ClassroomsAndGym(2);
        var teachers = new[] { Fixtures.Teacher("t1", "Mathematics", "PhysicalEducation") };

        var table = TimetablePlanner.Build(_catalog, map, classes, teachers);

        Assert.Contains(table.Lessons, lesson => lesson.Subject == "Mathematics");
        Assert.Contains(table.Lessons, lesson => lesson.Subject == "PhysicalEducation");
        Assert.Equal(
            table.Lessons.Count,
            table.Lessons.Select(lesson => (lesson.TeacherId, lesson.Day, lesson.Period)).Distinct().Count());
        Assert.Equal(
            table.Lessons.Count,
            table.Lessons.Select(lesson => (lesson.ClassId, lesson.Day, lesson.Period)).Distinct().Count());
        Assert.Equal(
            table.Lessons.Count,
            table.Lessons.Select(lesson => (lesson.RoomId, lesson.Day, lesson.Period)).Distinct().Count());
    }

    [Fact]
    public void ClassOfSixteen_DoesNotEnterALabOfTwelve()
    {
        var classes = new[] { Fixtures.Class(0, year: 5, pupils: 16) };
        var map = Fixtures.ClassroomAndLab(desks: 16, computers: 12);
        var teachers = new[] { Fixtures.Teacher("inf", "Informatics") };

        var table = TimetablePlanner.Build(_catalog, map, classes, teachers);

        Assert.DoesNotContain(table.Lessons, lesson => lesson.Subject == "Informatics");
        Assert.Contains(table.Uncovered, row => row.ClassId == "y5A" && row.Subject == "Informatics" && row.Hours == 1);
    }

    [Fact]
    public void SubjectWithoutATeacher_IsUncoveredAndLeavesAGap()
    {
        var classes = new[] { Fixtures.Class(0, year: 5, pupils: 16) };
        var map = Fixtures.ClassroomsAndGym(1);
        var teachers = new[] { Fixtures.Teacher("pe", "PhysicalEducation") };

        var table = TimetablePlanner.Build(_catalog, map, classes, teachers);

        Assert.DoesNotContain(table.Lessons, lesson => lesson.Subject == "Mathematics");
        Assert.Contains(table.Uncovered, row => row.ClassId == "y5A" && row.Subject == "Mathematics" && row.Hours == 5);
        Assert.Equal(3, table.Lessons.Count(lesson => lesson.Subject == "PhysicalEducation"));
    }

    [Fact]
    public void LockedLesson_SurvivesHiringAnotherTeacher()
    {
        var classes = new[] { Fixtures.Class(0, year: 5, pupils: 16) };
        var map = Fixtures.ClassroomsAndGym(1);
        var first = TimetablePlanner.Build(
            _catalog,
            map,
            classes,
            [Fixtures.Teacher("t1", "Mathematics")]);

        var pinned = first.Lessons.First(lesson => lesson.Subject == "Mathematics");
        var locked = pinned with { Locked = true };

        var rebuilt = TimetablePlanner.Build(
            _catalog,
            map,
            classes,
            [Fixtures.Teacher("t1", "Mathematics"), Fixtures.Teacher("t2", "Mathematics")],
            [locked]);

        Assert.Contains(
            rebuilt.Lessons,
            lesson =>
                lesson.ClassId == locked.ClassId
                && lesson.Subject == locked.Subject
                && lesson.TeacherId == locked.TeacherId
                && lesson.RoomId == locked.RoomId
                && lesson.Day == locked.Day
                && lesson.Period == locked.Period
                && lesson.Locked);
    }

    [Fact]
    public void SameInputs_YieldTheSameTable()
    {
        var classes = Enumerable.Range(1, 11).Select(year => Fixtures.Class(year - 1, year, pupils: 16)).ToArray();
        var map = Fixtures.ClassroomsAndGym(11);
        var teachers = new[]
        {
            Fixtures.Teacher("pe", "PhysicalEducation"),
            Fixtures.Teacher("math", "Mathematics"),
        };

        var a = TimetablePlanner.Build(_catalog, map, classes, teachers);
        var b = TimetablePlanner.Build(_catalog, map, classes, teachers);

        Assert.Equal(Snapshot(a), Snapshot(b));
    }

    /// <summary>
    /// The four bans alone allowed a legal but unusable week. Taking the first free slot day by
    /// day gave a full school 77 lessons on Monday and 16 on Friday, with three foreign-language
    /// lessons back to back. These are the numbers a timetable is judged by, so they are asserted.
    /// </summary>
    [Fact]
    public void AWeek_IsSpreadAcrossDaysAndSubjectsDoNotRunInBlocks()
    {
        var catalog = Fixtures.Catalog();
        var map = Fixtures.ClassroomsAndGym(11);
        var classes = Enumerable.Range(0, 11).Select(index => Fixtures.Class(index, index + 1, 16)).ToArray();
        var teachers = catalog.Subjects.Values
            .Where(subject => !subject.Abstract)
            .SelectMany(subject => Enumerable
                .Range(0, 3)
                .Select(copy => Fixtures.Teacher($"t{subject.DefName}{copy}", subject.DefName)))
            .ToArray();

        var table = TimetablePlanner.Build(catalog, map, classes, teachers);

        var perDay = Enumerable.Range(0, 5).Select(day => table.Lessons.Count(lesson => lesson.Day == day)).ToArray();
        Assert.All(perDay, count => Assert.True(count > 0, $"a school day is empty: {string.Join("/", perDay)}"));
        Assert.True(
            perDay.Max() <= perDay.Min() * 1.5,
            $"the week is lopsided: {string.Join("/", perDay)}");

        // Spread as evenly as the curriculum allows, not "never twice a day": primary school is
        // twenty hours over five days, so four a day is the best that exists.
        foreach (var group in table.Lessons.GroupBy(lesson => (lesson.ClassId, lesson.Subject)))
        {
            var bySubjectDay = Enumerable
                .Range(0, 5)
                .Select(day => group.Count(lesson => lesson.Day == day))
                .ToArray();

            // Two, not one: the day order is a preference, and a busy room or teacher can still
            // push an hour onto a day that already has the subject. Before the fix the same
            // measurement read 5/5/5/0/0.
            Assert.True(
                bySubjectDay.Max() - bySubjectDay.Min() <= 2,
                $"{group.Key.ClassId} has {group.Key.Subject} bunched into days: {string.Join("/", bySubjectDay)}");
        }
    }

    private static string Snapshot(Timetable table) =>
        string.Join(
            '\n',
            table.Lessons.Select(lesson =>
                $"{lesson.Day}/{lesson.Period} {lesson.ClassId} {lesson.Subject} {lesson.TeacherId} {lesson.RoomId} {(lesson.Locked ? "L" : "")}")
            .Concat(table.Uncovered.Select(row => $"U {row.ClassId} {row.Subject} {row.Hours}")));
}