namespace HSchool.People.Tests;

public class YearlyIntakeTests
{
    private static readonly DateTime September = new(2012, 9, 1, 0, 0, 0, DateTimeKind.Utc);

    [Fact]
    public void DatesBetween_SkipsAStartAlreadyOnFirstSeptember()
    {
        var start = new DateTime(2012, 9, 1, 0, 0, 0, DateTimeKind.Utc);
        Assert.Empty(YearlyIntake.DatesBetween(start, start.AddMinutes(1)));
        Assert.Equal(
            [new DateTime(2012, 9, 1, 0, 0, 0, DateTimeKind.Utc)],
            YearlyIntake.DatesBetween(new DateTime(2012, 4, 3, 6, 0, 0, DateTimeKind.Utc), start));
    }

    [Fact]
    public void FourClassrooms_GraduatesTheOldestYearNotEleventh()
    {
        var map = Fixtures.Classrooms(4);
        var catalog = Fixtures.Catalog();
        var before = Fixtures.Generate(map);
        Assert.Equal(4, before.Classes.Max(schoolClass => schoolClass.Year));
        Assert.DoesNotContain(before.Classes, schoolClass => schoolClass.Year == 11);

        var after = YearlyIntake.Apply(catalog, before, Fixtures.SchoolSeed, "Russia", September);
        var demand = SchoolDemand.From(catalog, map);

        Assert.True(RosterFit.Matches(after, demand));
        Assert.Equal(before.People.Count(person => person.IsStudent), after.People.Count(person => person.IsStudent));
        Assert.Equal(before.Classes.Sum(schoolClass => schoolClass.Capacity), after.Classes.Sum(schoolClass => schoolClass.Capacity));
        Assert.Equal(4, after.Classes.Max(schoolClass => schoolClass.Year));
        Assert.Contains(after.Classes, schoolClass => schoolClass.Year == 1);
        Assert.All(after.Classes, schoolClass => Assert.Equal(schoolClass.Capacity, schoolClass.PupilIds.Count));

        var graduated = before.Classes
            .Where(schoolClass => schoolClass.Year == 4)
            .SelectMany(schoolClass => schoolClass.PupilIds)
            .ToHashSet(StringComparer.Ordinal);
        Assert.All(graduated, id => Assert.DoesNotContain(after.People, person => person.Id == id));
    }

    [Fact]
    public void SameInputs_YieldTheSameIntake()
    {
        var map = Fixtures.Classrooms(4);
        var catalog = Fixtures.Catalog();
        var before = Fixtures.Generate(map);
        var a = Snapshot(YearlyIntake.Apply(catalog, before, Fixtures.SchoolSeed, "Russia", September));
        var b = Snapshot(YearlyIntake.Apply(catalog, before, Fixtures.SchoolSeed, "Russia", September));
        Assert.Equal(a, b);
    }

    [Fact]
    public void NewFirstYear_CanShareAFamilyWithAnOlderPupil()
    {
        var map = Fixtures.Classrooms(4);
        var catalog = Fixtures.Catalog();
        var before = Fixtures.Generate(map);
        var after = YearlyIntake.Apply(catalog, before, Fixtures.SchoolSeed, "Russia", September);
        var people = after.People.ToDictionary(person => person.Id, StringComparer.Ordinal);
        var yearOf = after.Classes.ToDictionary(schoolClass => schoolClass.Id, schoolClass => schoolClass.Year, StringComparer.Ordinal);

        Assert.Contains(after.Families, family =>
        {
            var years = family.ChildIds
                .Select(id => people[id])
                .Where(person => person.IsStudent && person.ClassId is not null)
                .Select(person => yearOf[person.ClassId!])
                .ToHashSet();
            return years.Contains(1) && years.Any(year => year > 1);
        });
    }

    [Fact]
    public void ParentsOfOnlyGraduates_LeaveUnlessTheyWorkHere()
    {
        var map = Fixtures.Classrooms(4);
        var catalog = Fixtures.Catalog();
        var before = Fixtures.Generate(map);
        var people = before.People.ToDictionary(person => person.Id, StringComparer.Ordinal);
        var graduating = before.Classes
            .Where(schoolClass => schoolClass.Year == 4)
            .SelectMany(schoolClass => schoolClass.PupilIds)
            .ToHashSet(StringComparer.Ordinal);

        var shouldLeave = new List<string>();
        var staffWhoStay = new List<string>();
        foreach (var family in before.Families)
        {
            if (family.ChildIds.Count == 0 || family.ChildIds.Any(id => !graduating.Contains(id)))
            {
                continue;
            }

            foreach (var parentId in family.ParentIds)
            {
                if (people[parentId].IsStaff)
                {
                    staffWhoStay.Add(parentId);
                }
                else
                {
                    shouldLeave.Add(parentId);
                }
            }
        }

        var after = YearlyIntake.Apply(catalog, before, Fixtures.SchoolSeed, "Russia", September);
        var afterIds = after.People.Select(person => person.Id).ToHashSet(StringComparer.Ordinal);
        Assert.NotEmpty(shouldLeave);
        Assert.All(shouldLeave, id => Assert.DoesNotContain(id, afterIds));
        Assert.All(staffWhoStay, id => Assert.Contains(id, afterIds));
        Assert.All(
            after.People.Where(person => staffWhoStay.Contains(person.Id)),
            person => Assert.False(person.IsParent));
    }

    private static string Snapshot(Roster roster) =>
        string.Join('\n', roster.People.Select(person =>
            $"{person.Id}|{person.FamilyId}|{person.IsStudent}|{person.IsStaff}|{person.IsParent}|{person.ClassId}|{person.Name.Full}|{Skills(person)}"));

    private static string Skills(Person person) =>
        string.Join(',', person.Skills.OrderBy(pair => pair.Key, StringComparer.Ordinal).Select(pair => $"{pair.Key}={pair.Value}"));
}