namespace HSchool.People.Tests;

public class StaffingTests
{
    private const float Cap = 10_000f;

    /// <summary>
    /// Price of an hour times the hours carried, with one full rate as the floor: a hired person
    /// costs something even idle, and loading them past the rate costs more. The number of
    /// subjects does not enter into it — twenty hours are twenty hours.
    /// </summary>
    [Fact]
    public void MonthlyPay_IsHoursTimesTheHourlyAsk_WithAFullRateAsTheFloor()
    {
        var rules = Fixtures.Catalog().StaffingRules!;

        Assert.Equal(4_000f, Staffing.MonthlyBase(rules, 50f));
        Assert.Equal(4_000f, Staffing.MonthlyPay(rules, 50f, 0f));
        Assert.Equal(4_000f, Staffing.MonthlyPay(rules, 50f, 12f));
        Assert.Equal(4_000f, Staffing.MonthlyPay(rules, 50f, 20f));
        Assert.Equal(6_000f, Staffing.MonthlyPay(rules, 50f, 30f));
        Assert.Equal(7_200f, Staffing.MonthlyPay(rules, 50f, 36f));
    }

    [Fact]
    public void Hire_TwoPeopleAtThreeAndSevenThousand_RejectsTheThird()
    {
        var (catalog, map, roster, pool) = Fresh();
        var cheap = WithAsk(pool.Applicants[0], 37.5f);
        var expensive = WithAsk(pool.Applicants[1], 87.5f);
        var extra = WithAsk(pool.Applicants[2], 40f);
        pool = pool with { Applicants = [cheap, expensive, extra] };

        var first = Staffing.Hire(catalog, map, roster, pool, cheap.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(StaffingError.None, first.Error);
        Assert.Equal(3_000f, first.Payroll);

        var second = Staffing.Hire(catalog, map, first.Roster, first.Pool, expensive.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(StaffingError.None, second.Error);
        Assert.Equal(10_000f, second.Payroll);
        Assert.Equal(0f, second.Remaining);

        var third = Staffing.Hire(catalog, map, second.Roster, second.Pool, extra.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(StaffingError.PayrollExceeded, third.Error);
        Assert.Equal(10_000f, third.Payroll);
        Assert.True(third.Attempted > Cap);
        Assert.Equal(2, second.Roster.People.Count(person => person.IsStaff));
        Assert.DoesNotContain(third.Roster.People, person => person.Id == extra.Person.Id && person.IsStaff);
    }

    [Fact]
    public void UnassignSubject_LowersPayrollSoAnotherHireFits()
    {
        var (catalog, map, roster, pool) = Fresh();
        var first = WithAsk(pool.Applicants[0], 37.5f);
        var second = WithAsk(pool.Applicants[1], 50f);
        pool = pool with { Applicants = [first, second, .. pool.Applicants.Skip(2)] };

        var hired = Staffing.Hire(catalog, map, roster, pool, first.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(StaffingError.None, hired.Error);

        // Mathematics is 35 curriculum hours a week, Literature 21. At 37.5 an hour that is
        // 37.5 × 56 × 4 = 8 400 a month for one person — and no room left for a second.
        var loaded = hired;
        foreach (var subject in new[] { "Mathematics", "Literature" })
        {
            loaded = Staffing.AssignSubject(catalog, loaded.Roster, loaded.Pool, first.Person.Id, subject, Cap);
            Assert.Equal(StaffingError.None, loaded.Error);
        }

        Assert.Equal(8_400f, loaded.Payroll);

        var blocked = Staffing.Hire(catalog, map, loaded.Roster, loaded.Pool, second.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(StaffingError.PayrollExceeded, blocked.Error);

        var dropped = Staffing.UnassignSubject(catalog, loaded.Roster, loaded.Pool, first.Person.Id, "Literature", Cap);
        Assert.Equal(StaffingError.None, dropped.Error);
        Assert.Equal(5_250f, dropped.Payroll);

        var fitted = Staffing.Hire(catalog, map, dropped.Roster, dropped.Pool, second.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(StaffingError.None, fitted.Error);
        Assert.Equal(9_250f, fitted.Payroll);
    }

    /// <summary>
    /// Two teachers of one subject split its hours, so the second one costs a full rate and makes
    /// the first cheaper. That is the whole reason hiring another is not simply worse than loading
    /// the one you have.
    /// </summary>
    [Fact]
    public void TwoTeachersOfASubject_ShareItsHours()
    {
        var (catalog, map, roster, pool) = Fresh();
        var first = WithAsk(pool.Applicants[0], 50f);
        var second = WithAsk(pool.Applicants[1], 50f);
        pool = pool with { Applicants = [first, second, .. pool.Applicants.Skip(2)] };

        var one = Staffing.Hire(catalog, map, roster, pool, first.Person.Id, Staffing.TeacherPosition, 50_000f);
        one = Staffing.AssignSubject(catalog, one.Roster, one.Pool, first.Person.Id, "Mathematics", 50_000f);

        // All 35 hours on one person: 50 × 35 × 4.
        Assert.Equal(7_000f, one.Payroll);

        var two = Staffing.Hire(catalog, map, one.Roster, one.Pool, second.Person.Id, Staffing.TeacherPosition, 50_000f);
        two = Staffing.AssignSubject(catalog, two.Roster, two.Pool, second.Person.Id, "Mathematics", 50_000f);

        // 17.5 hours each, which is under a full rate, so both are paid the rate: 4 000 × 2.
        Assert.Equal(8_000f, two.Payroll);
        Assert.All(
            two.Roster.People.Where(person => person.IsStaff),
            person => Assert.Equal(17.5f, Staffing.WeeklyHours(catalog, two.Roster, person)));
    }

    /// <summary>
    /// Primary school is twenty hours a week for each of four classes. One teacher cannot carry
    /// eighty hours whatever the budget says, so the subject stays on the uncovered list until
    /// enough people share it.
    /// </summary>
    [Fact]
    public void SubjectNeedingMoreHoursThanOnePersonCarries_StaysUncovered()
    {
        var (catalog, map, roster, pool) = Fresh();
        var rules = catalog.StaffingRules!;
        Assert.Equal(80f, Staffing.SubjectHours(catalog, roster, "PrimarySchool"));
        Assert.True(80f > rules.MaxWeeklyHours);

        var outcome = new StaffingOutcome(StaffingError.None, roster, pool, 0, 0, 0, 0);
        for (var i = 0; i < 3; i++)
        {
            var applicant = outcome.Pool.Applicants[0];
            outcome = Staffing.Hire(catalog, map, outcome.Roster, outcome.Pool, applicant.Person.Id, Staffing.TeacherPosition, 500_000f);
            Assert.Equal(StaffingError.None, outcome.Error);
            outcome = Staffing.AssignSubject(catalog, outcome.Roster, outcome.Pool, applicant.Person.Id, "PrimarySchool", 500_000f);
            Assert.Equal(StaffingError.None, outcome.Error);

            var stillShort = 80f > (i + 1) * rules.MaxWeeklyHours;
            Assert.Equal(
                stillShort,
                Staffing.Uncovered(catalog, outcome.Roster).Any(subject => subject.DefName == "PrimarySchool"));
        }
    }

    [Fact]
    public void AssignSubject_ThatWouldExceedTheCap_IsRejected()
    {
        var (catalog, map, roster, pool) = Fresh();
        var applicant = WithAsk(pool.Applicants[0], 50f);
        pool = pool with { Applicants = [applicant, .. pool.Applicants.Skip(1)] };

        var hired = Staffing.Hire(catalog, map, roster, pool, applicant.Person.Id, Staffing.TeacherPosition, Cap);
        Assert.Equal(4_000f, hired.Payroll);

        // Mathematics is 35 hours: 50 × 35 × 4 = 7 000.
        var loaded = Staffing.AssignSubject(catalog, hired.Roster, hired.Pool, applicant.Person.Id, "Mathematics", Cap);
        Assert.Equal(StaffingError.None, loaded.Error);
        Assert.Equal(7_000f, loaded.Payroll);

        // Russian adds 28 more. 63 hours at 50 is 12 600 a month — past the 10 000 allocation.
        var rejected = Staffing.AssignSubject(catalog, loaded.Roster, loaded.Pool, applicant.Person.Id, "RussianLanguage", Cap);
        Assert.Equal(StaffingError.PayrollExceeded, rejected.Error);
        Assert.Equal(7_000f, rejected.Payroll);
        Assert.Equal(12_600f, rejected.Attempted);
        Assert.Equal(3_000f, rejected.Remaining);
        Assert.DoesNotContain(
            rejected.Roster.People.Single(person => person.Id == applicant.Person.Id).Subjects,
            name => name == "RussianLanguage");
    }

    [Fact]
    public void Hire_ParentKeepsTheSameId_GeneratedJoinsTheRoster()
    {
        var catalog = Fixtures.Catalog();
        var map = Fixtures.VanillaMap();
        Roster? roster = null;
        Applicant? parent = null;
        Applicant? generated = null;
        ApplicantPool? pool = null;
        for (var seed = 1; seed <= 30 && pool is null; seed++)
        {
            var candidate = Fixtures.Generate(map, seed);
            var created = ApplicantPool.Create(catalog, candidate, seed, "Russia", Fixtures.AsOf);
            var rosterIds = candidate.People.Select(person => person.Id).ToHashSet(StringComparer.Ordinal);
            var parentHere = created.Applicants.FirstOrDefault(applicant => rosterIds.Contains(applicant.Person.Id));
            var generatedHere = created.Applicants.FirstOrDefault(applicant => applicant.Person.Id.StartsWith('a'));
            if (parentHere is not null && generatedHere is not null)
            {
                roster = candidate;
                pool = created;
                parent = parentHere;
                generated = generatedHere;
            }
        }

        Assert.NotNull(roster);
        Assert.NotNull(pool);
        Assert.NotNull(parent);
        Assert.NotNull(generated);

        var afterParent = Staffing.Hire(catalog, map, roster, pool, parent.Person.Id, Staffing.TeacherPosition, 50_000f);
        Assert.Equal(StaffingError.None, afterParent.Error);
        var staffParent = afterParent.Roster.People.Single(person => person.Id == parent.Person.Id);
        Assert.True(staffParent.IsParent);
        Assert.True(staffParent.IsStaff);
        Assert.Equal(1, afterParent.Roster.People.Count(person => person.Id == parent.Person.Id));
        Assert.DoesNotContain(afterParent.Pool.Applicants, applicant => applicant.Person.Id == parent.Person.Id);

        var afterGenerated = Staffing.Hire(catalog, map, afterParent.Roster, afterParent.Pool, generated.Person.Id, Staffing.TeacherPosition, 50_000f);
        Assert.Equal(StaffingError.None, afterGenerated.Error);
        Assert.Contains(afterGenerated.Roster.People, person => person.Id == generated.Person.Id && person.IsStaff && !person.IsParent);
        Assert.Contains(afterGenerated.Roster.Families, family => family.Id == generated.Person.FamilyId);

        var again = Staffing.Hire(catalog, map, afterGenerated.Roster, afterGenerated.Pool, parent.Person.Id, Staffing.TeacherPosition, 50_000f);
        Assert.Equal(StaffingError.AlreadyHired, again.Error);
    }

    [Fact]
    public void Uncovered_ListsSubjectsTaughtInExistingYearsWithoutATeacher()
    {
        var (catalog, map, roster, pool) = Fresh();
        var uncovered = Staffing.Uncovered(catalog, roster);
        Assert.Contains(uncovered, subject => subject.DefName == "PrimarySchool");
        Assert.Contains(uncovered, subject => subject.DefName == "Mathematics");
        Assert.Contains(uncovered, subject => subject.DefName == "PhysicalEducation");
        Assert.Equal(catalog.Subjects.Values.Count(subject => !subject.Abstract), uncovered.Count);

        var applicant = pool.Applicants[0];
        var hired = Staffing.Hire(catalog, map, roster, pool, applicant.Person.Id, Staffing.TeacherPosition, 100_000f);
        var assigned = Staffing.AssignSubject(catalog, hired.Roster, hired.Pool, applicant.Person.Id, "Mathematics", 100_000f);

        Assert.Equal(StaffingError.None, assigned.Error);
        Assert.DoesNotContain(Staffing.Uncovered(catalog, assigned.Roster), subject => subject.DefName == "Mathematics");
        Assert.Contains(Staffing.Uncovered(catalog, assigned.Roster), subject => subject.DefName == "PrimarySchool");
    }

    [Fact]
    public void PrimarySchool_OnVanillaMap_NeedsThreeTeachers_AndASecondDoesNotCloseIt()
    {
        var (catalog, map, roster, pool) = Fresh();
        var rules = catalog.StaffingRules!;
        Assert.Equal(80f, Staffing.SubjectHours(catalog, roster, "PrimarySchool"));
        Assert.Equal(3, Staffing.TeachersToCover(80f, rules.MaxWeeklyHours));

        var empty = Staffing.Uncovered(catalog, roster).Single(subject => subject.DefName == "PrimarySchool");
        Assert.Equal(3, empty.TeachersShort);

        var outcome = new StaffingOutcome(StaffingError.None, roster, pool, 0, 0, 0, 0);
        outcome = HireAndAssign(catalog, map, outcome, "PrimarySchool");
        Assert.Equal(2, Staffing.Uncovered(catalog, outcome.Roster).Single(subject => subject.DefName == "PrimarySchool").TeachersShort);

        outcome = HireAndAssign(catalog, map, outcome, "PrimarySchool");
        Assert.Equal(1, Staffing.Uncovered(catalog, outcome.Roster).Single(subject => subject.DefName == "PrimarySchool").TeachersShort);

        outcome = HireAndAssign(catalog, map, outcome, "PrimarySchool");
        Assert.DoesNotContain(Staffing.Uncovered(catalog, outcome.Roster), subject => subject.DefName == "PrimarySchool");
    }

    [Fact]
    public void PeopleJson_RoundTripsHiredStaffAndSubjects()
    {
        var (catalog, map, roster, pool) = Fresh();
        var applicant = pool.Applicants[0];
        var hired = Staffing.Hire(catalog, map, roster, pool, applicant.Person.Id, Staffing.TeacherPosition, 100_000f);
        var assigned = Staffing.AssignSubject(catalog, hired.Roster, hired.Pool, applicant.Person.Id, "Mathematics", 100_000f);
        Assert.Equal(StaffingError.None, assigned.Error);

        var json = RosterJson.Serialize(RosterDocument.From(Fixtures.SchoolSeed, assigned.Roster, assigned.Pool));
        var loaded = RosterJson.Parse(json);
        var person = loaded.People.Single(member => member.Id == applicant.Person.Id);

        Assert.True(person.IsStaff);
        Assert.Equal(Staffing.TeacherPosition, person.Position);
        Assert.Equal(applicant.HourlyWageAsk, person.HourlyWageAsk);
        Assert.Equal(["Mathematics"], person.Subjects);
        Assert.DoesNotContain(loaded.Applicants!.Applicants, candidate => candidate.Person.Id == applicant.Person.Id);
    }

    [Fact]
    public void Hire_UnknownApplicantAndUnknownPosition()
    {
        var (catalog, map, roster, pool) = Fresh();

        Assert.Equal(
            StaffingError.UnknownApplicant,
            Staffing.Hire(catalog, map, roster, pool, "nobody", Staffing.TeacherPosition, Cap).Error);
        Assert.Equal(
            StaffingError.UnknownPosition,
            Staffing.Hire(catalog, map, roster, pool, pool.Applicants[0].Person.Id, "Janitor", Cap).Error);
    }

    private static (DefCatalog Catalog, MapLayout Map, Roster Roster, ApplicantPool Pool) Fresh()
    {
        var catalog = Fixtures.Catalog();
        var map = Fixtures.VanillaMap();
        var roster = Fixtures.Generate(map);
        var pool = ApplicantPool.Create(catalog, roster, Fixtures.SchoolSeed, "Russia", Fixtures.AsOf);
        return (catalog, map, roster, pool);
    }

    private static StaffingOutcome HireAndAssign(
        DefCatalog catalog,
        MapLayout map,
        StaffingOutcome current,
        string subject)
    {
        var applicant = current.Pool.Applicants[0];
        var hired = Staffing.Hire(catalog, map, current.Roster, current.Pool, applicant.Person.Id, Staffing.TeacherPosition, 500_000f);
        Assert.Equal(StaffingError.None, hired.Error);
        var assigned = Staffing.AssignSubject(catalog, hired.Roster, hired.Pool, applicant.Person.Id, subject, 500_000f);
        Assert.Equal(StaffingError.None, assigned.Error);
        return assigned;
    }

    private static Applicant WithAsk(Applicant applicant, float hourlyAsk) =>
        applicant with { HourlyWageAsk = hourlyAsk };
}