using HSchool.Content;

namespace HSchool.People;

public enum StaffingError
{
    None,
    UnknownSchool,
    UnknownApplicant,
    AlreadyHired,
    UnknownPosition,
    UnknownSubject,
    NotStaff,
    NotTeacher,
    AlreadyAssigned,
    SubjectNotAssigned,
    PayrollExceeded,
    NoOpening,
}

/// <summary>
/// A subject the school cannot actually teach, and how many more teachers would cover it.
/// </summary>
public sealed record UncoveredSubject(SubjectDef Subject, int Assigned, int TeachersShort)
{
    public string DefName => Subject.DefName;
}

public sealed record StaffingOutcome(
    StaffingError Error,
    Roster Roster,
    ApplicantPool Pool,
    float Allocated,
    float Payroll,
    float Remaining,
    float Attempted);

/// <summary>
/// Hire, subject assignment and the monthly payroll cap. Scale lives on <see cref="StaffingDef"/>;
/// the cap is supplied by the caller because it is a simulation option, not catalog data.
/// </summary>
public static class Staffing
{
    public const string TeacherPosition = "Teacher";

    public static StaffingOutcome UnknownSchool() =>
        Fail(StaffingError.UnknownSchool, new Roster([], [], []), ApplicantPool.Empty, allocated: 0, payroll: 0, attempted: 0);

    /// <summary>What one full rate costs at this price per hour — the floor under any hire.</summary>
    public static float MonthlyBase(StaffingDef rules, float hourlyAsk) =>
        Round(hourlyAsk * rules.BaseWeeklyHours * rules.WeeksPerMonth);

    /// <summary>
    /// Price of an hour times the hours actually carried, never below one full rate. A hired
    /// person costs something even with nothing assigned; loading them past the rate costs more.
    /// </summary>
    public static float MonthlyPay(StaffingDef rules, float hourlyAsk, float weeklyHours) =>
        Round(hourlyAsk * Math.Max(weeklyHours, rules.BaseWeeklyHours) * rules.WeeksPerMonth);

    /// <summary>
    /// Weekly hours this person carries: for every subject assigned to them, the curriculum hours
    /// of that subject across the classes that study it, split between everyone teaching it.
    ///
    /// Deliberately not capped at <see cref="StaffingDef.MaxWeeklyHours"/>. Refusing the
    /// assignment would deadlock — the first teacher of a subject always inherits all of its
    /// hours, so nobody could ever be the first. Capping what is paid would be worse: piling a
    /// seventh subject onto someone already at the cap would cost nothing, which is the loophole
    /// the hourly model exists to close. So the hours count in full, the money says so, and
    /// <see cref="Uncovered"/> is what reports that one person cannot really teach all of it.
    /// </summary>
    public static float WeeklyHours(DefCatalog catalog, Roster roster, Person person)
    {
        ArgumentNullException.ThrowIfNull(catalog);
        ArgumentNullException.ThrowIfNull(roster);
        ArgumentNullException.ThrowIfNull(person);

        if (person.Subjects.Count == 0)
        {
            return 0f;
        }

        var hours = 0f;
        foreach (var subject in person.Subjects)
        {
            hours += SubjectHours(catalog, roster, subject) / Math.Max(1, TeachersOf(roster, subject));
        }

        return hours;
    }

    /// <summary>Curriculum hours a subject needs each week across every class that studies it.</summary>
    public static float SubjectHours(DefCatalog catalog, Roster roster, string subject)
    {
        if (!catalog.Subjects.TryGetValue(subject, out var def) || def.Abstract)
        {
            return 0f;
        }

        var classes = 0;
        foreach (var schoolClass in roster.Classes)
        {
            if (schoolClass.Year >= def.Grades.Min && schoolClass.Year <= def.Grades.Max)
            {
                classes++;
            }
        }

        return def.HoursPerWeek * classes;
    }

    private static int TeachersOf(Roster roster, string subject)
    {
        var count = 0;
        foreach (var person in roster.People)
        {
            if (person.IsStaff && person.Subjects.Contains(subject, StringComparer.Ordinal))
            {
                count++;
            }
        }

        return count;
    }

    public static float Payroll(DefCatalog catalog, StaffingDef rules, Roster roster)
    {
        var total = 0f;
        foreach (var person in roster.People)
        {
            if (!person.IsStaff || person.HourlyWageAsk is not { } ask)
            {
                continue;
            }

            total += MonthlyPay(rules, ask, WeeklyHours(catalog, roster, person));
        }

        return Round(total);
    }

    /// <summary>
    /// How many people a subject needs at the weekly cap. Primary school on a vanilla map is
    /// eighty hours: one person cannot carry it, and the uncovered row has to say so.
    /// </summary>
    public static int TeachersToCover(float hours, float maxWeeklyHours)
    {
        if (hours <= 0f)
        {
            return 0;
        }

        if (maxWeeklyHours <= 0f)
        {
            return 1;
        }

        return (int)Math.Ceiling(hours / maxWeeklyHours);
    }

    /// <summary>
    /// Subjects the school cannot actually teach: nobody is assigned them, or the people who are
    /// cannot between them carry the curriculum hours. Both read the same way to a player — the
    /// lessons will not happen — so both belong in one list. <see cref="UncoveredSubject.TeachersShort"/>
    /// is how many more people it still needs.
    /// </summary>
    public static IReadOnlyList<UncoveredSubject> Uncovered(DefCatalog catalog, Roster roster)
    {
        var years = new HashSet<int>();
        foreach (var schoolClass in roster.Classes)
        {
            years.Add(schoolClass.Year);
        }

        var teachers = new Dictionary<string, int>(StringComparer.Ordinal);
        foreach (var person in roster.People)
        {
            if (!person.IsStaff)
            {
                continue;
            }

            foreach (var subject in person.Subjects)
            {
                teachers[subject] = teachers.TryGetValue(subject, out var count) ? count + 1 : 1;
            }
        }

        var cap = catalog.StaffingRules?.MaxWeeklyHours ?? 0f;
        var uncovered = new List<UncoveredSubject>();
        foreach (var subject in catalog.Subjects.Values)
        {
            if (subject.Abstract || !TouchesYears(subject, years))
            {
                continue;
            }

            var assigned = teachers.GetValueOrDefault(subject.DefName);
            var hours = SubjectHours(catalog, roster, subject.DefName);
            var needed = TeachersToCover(hours, cap);
            var shortfall = Math.Max(0, needed - assigned);
            if (shortfall > 0)
            {
                uncovered.Add(new UncoveredSubject(subject, assigned, shortfall));
            }
        }

        return uncovered;
    }

    public static StaffingOutcome Hire(
        DefCatalog catalog,
        MapLayout? map,
        Roster roster,
        ApplicantPool pool,
        string personId,
        string position,
        float allocated)
    {
        var rules = RequireRules(catalog);
        var payroll = Payroll(catalog, rules, roster);

        if (roster.People.Any(person => person.Id.Equals(personId, StringComparison.Ordinal) && person.IsStaff))
        {
            return Fail(StaffingError.AlreadyHired, roster, pool, allocated, payroll, payroll);
        }

        var applicant = pool.Applicants.FirstOrDefault(candidate => candidate.Person.Id.Equals(personId, StringComparison.Ordinal));
        if (applicant is null)
        {
            return Fail(StaffingError.UnknownApplicant, roster, pool, allocated, payroll, payroll);
        }

        if (!IsConcretePosition(catalog, position))
        {
            return Fail(StaffingError.UnknownPosition, roster, pool, allocated, payroll, payroll);
        }

        if (!TryWorkplace(catalog, map, roster, position, out var workplace))
        {
            return Fail(StaffingError.NoOpening, roster, pool, allocated, payroll, payroll);
        }

        var hired = applicant.Person with
        {
            IsStaff = true,
            Position = position,
            WorkplaceRoomId = workplace,
            HourlyWageAsk = applicant.HourlyWageAsk,
            Subjects = [],
        };

        // Priced on the resulting roster, not by adding one salary: hours are shared between the
        // teachers of a subject, so one person joining can change what the others cost.
        var nextRoster = UpsertStaff(roster, hired);
        var attempted = Payroll(catalog, rules, nextRoster);
        if (attempted > allocated)
        {
            return Fail(StaffingError.PayrollExceeded, roster, pool, allocated, payroll, attempted);
        }

        var nextPool = pool.Without(personId);
        return Ok(nextRoster, nextPool, allocated, attempted);
    }

    public static StaffingOutcome AssignSubject(
        DefCatalog catalog,
        Roster roster,
        ApplicantPool pool,
        string personId,
        string subject,
        float allocated)
    {
        var rules = RequireRules(catalog);
        var payroll = Payroll(catalog, rules, roster);
        var index = IndexOf(roster, personId);
        if (index < 0)
        {
            return Fail(StaffingError.NotStaff, roster, pool, allocated, payroll, payroll);
        }

        var person = roster.People[index];
        if (!person.IsStaff)
        {
            return Fail(StaffingError.NotStaff, roster, pool, allocated, payroll, payroll);
        }

        if (!TeacherPosition.Equals(person.Position, StringComparison.Ordinal))
        {
            return Fail(StaffingError.NotTeacher, roster, pool, allocated, payroll, payroll);
        }

        if (!IsConcreteSubject(catalog, subject))
        {
            return Fail(StaffingError.UnknownSubject, roster, pool, allocated, payroll, payroll);
        }

        if (person.Subjects.Contains(subject, StringComparer.Ordinal))
        {
            return Fail(StaffingError.AlreadyAssigned, roster, pool, allocated, payroll, payroll);
        }

        var ask = person.HourlyWageAsk ?? ApplicantPool.HourlyAsk(catalog, person);
        var nextSubjects = person.Subjects.Append(subject).ToArray();
        var nextRoster = Replace(roster, index, person with { HourlyWageAsk = ask, Subjects = nextSubjects });
        var attempted = Payroll(catalog, rules, nextRoster);
        if (attempted > allocated)
        {
            return Fail(StaffingError.PayrollExceeded, roster, pool, allocated, payroll, attempted);
        }

        return Ok(nextRoster, pool, allocated, attempted);
    }

    public static StaffingOutcome UnassignSubject(
        DefCatalog catalog,
        Roster roster,
        ApplicantPool pool,
        string personId,
        string subject,
        float allocated)
    {
        var rules = RequireRules(catalog);
        var payroll = Payroll(catalog, rules, roster);
        var index = IndexOf(roster, personId);
        if (index < 0)
        {
            return Fail(StaffingError.NotStaff, roster, pool, allocated, payroll, payroll);
        }

        var person = roster.People[index];
        if (!person.IsStaff)
        {
            return Fail(StaffingError.NotStaff, roster, pool, allocated, payroll, payroll);
        }

        if (!person.Subjects.Contains(subject, StringComparer.Ordinal))
        {
            return Fail(StaffingError.SubjectNotAssigned, roster, pool, allocated, payroll, payroll);
        }

        var nextSubjects = person.Subjects.Where(name => !name.Equals(subject, StringComparison.Ordinal)).ToArray();
        var nextRoster = Replace(roster, index, person with { Subjects = nextSubjects });
        return Ok(nextRoster, pool, allocated, Payroll(catalog, rules, nextRoster));
    }

    private static StaffingOutcome Ok(Roster roster, ApplicantPool pool, float allocated, float payroll) =>
        new(StaffingError.None, roster, pool, allocated, payroll, Remaining(allocated, payroll), payroll);

    private static StaffingOutcome Fail(
        StaffingError error,
        Roster roster,
        ApplicantPool pool,
        float allocated,
        float payroll,
        float attempted) =>
        new(error, roster, pool, allocated, payroll, Remaining(allocated, payroll), attempted);

    private static float Remaining(float allocated, float payroll) => Round(MathF.Max(0f, allocated - payroll));

    private static float Round(float value) => MathF.Round(value, 2);

    private static StaffingDef RequireRules(DefCatalog catalog) =>
        catalog.StaffingRules ?? throw new InvalidOperationException("The catalog has no StaffingDef.");

    private static bool IsConcretePosition(DefCatalog catalog, string position) =>
        catalog.Positions.TryGetValue(position, out var def) && !def.Abstract;

    private static bool IsConcreteSubject(DefCatalog catalog, string subject) =>
        catalog.Subjects.TryGetValue(subject, out var def) && !def.Abstract;

    private static bool TouchesYears(SubjectDef subject, HashSet<int> years)
    {
        for (var year = subject.Grades.Min; year <= subject.Grades.Max; year++)
        {
            if (years.Contains(year))
            {
                return true;
            }
        }

        return false;
    }

    private static bool TryWorkplace(
        DefCatalog catalog,
        MapLayout? map,
        Roster roster,
        string position,
        out string? workplace)
    {
        workplace = null;
        if (TeacherPosition.Equals(position, StringComparison.Ordinal))
        {
            return true;
        }

        if (map is null)
        {
            return false;
        }

        var taken = new HashSet<string>(StringComparer.Ordinal);
        foreach (var person in roster.People)
        {
            if (person.IsStaff
                && position.Equals(person.Position, StringComparison.Ordinal)
                && person.WorkplaceRoomId is { } roomId)
            {
                taken.Add(roomId);
            }
        }

        foreach (var opening in SchoolDemand.From(catalog, map).Staff)
        {
            if (opening.Position.Equals(position, StringComparison.Ordinal) && taken.Add(opening.RoomId))
            {
                workplace = opening.RoomId;
                return true;
            }
        }

        return false;
    }

    private static int IndexOf(Roster roster, string personId)
    {
        for (var i = 0; i < roster.People.Count; i++)
        {
            if (roster.People[i].Id.Equals(personId, StringComparison.Ordinal))
            {
                return i;
            }
        }

        return -1;
    }

    private static Roster Replace(Roster roster, int index, Person person)
    {
        var people = roster.People.ToArray();
        people[index] = person;
        return roster with { People = people };
    }

    private static Roster UpsertStaff(Roster roster, Person hired)
    {
        var index = IndexOf(roster, hired.Id);
        if (index >= 0)
        {
            return Replace(roster, index, hired);
        }

        var people = roster.People.Append(hired).ToArray();
        if (roster.Families.Any(family => family.Id.Equals(hired.FamilyId, StringComparison.Ordinal)))
        {
            return roster with { People = people };
        }

        var families = roster.Families.Append(new Family(hired.FamilyId, [hired.Id], [])).ToArray();
        return roster with { People = people, Families = families };
    }
}