using QuestionsApi.Models;

namespace QuestionsApi.Services;

public static class DynamicDifficultyPolicy
{
    public const int MinimumElo = 600;
    public const int MaximumElo = 1800;
    public const int TargetOffset = 70;
    public static readonly IReadOnlyDictionary<string, int> TierElos =
        new Dictionary<string, int>(StringComparer.Ordinal)
        {
            ["foundation"] = 850,
            ["standard"] = 1050,
            ["advanced"] = 1250,
            ["expert"] = 1450
        };

    public static int EffectiveAbility(
        int overallElo,
        int categoryElo,
        DynamicObjectiveMastery? objective)
    {
        var bankAbility = (int)Math.Round((overallElo + categoryElo) / 2.0);
        if (objective is null || objective.Attempts <= 0)
            return Clamp(bankAbility);
        var objectiveWeight = Math.Min(0.8, objective.Attempts * 0.08);
        return Clamp((int)Math.Round(bankAbility * (1.0 - objectiveWeight) + objective.Elo * objectiveWeight));
    }

    public static int TargetFamilyElo(int effectiveAbility) => Clamp(effectiveAbility - TargetOffset);

    public static double ExpectedScore(int playerElo, int familyElo) =>
        1.0 / (1.0 + Math.Pow(10, (familyElo - playerElo) / 400.0));

    public static int LearnerDelta(int playerElo, int familyElo, bool correct, int attempts) =>
        (int)Math.Round((attempts < 5 ? 40 : 24)
            * ((correct ? 1.0 : 0.0) - ExpectedScore(playerElo, familyElo)));

    public static int FamilyDelta(int playerElo, int familyElo, bool correct, int attempts) =>
        (int)Math.Round((attempts < 20 ? 32 : 24)
            * (ExpectedScore(playerElo, familyElo) - (correct ? 1.0 : 0.0)));

    public static DynamicCaseFamily SelectFamily(
        IReadOnlyList<DynamicCaseFamily> families,
        IReadOnlyDictionary<string, DynamicFamilyRating> ratings,
        int targetElo,
        ISet<string> recentFamilyIds,
        int tieBreaker)
    {
        if (families.Count == 0) throw new InvalidOperationException("No case families are available.");
        var eligible = families.Where(value => !recentFamilyIds.Contains(value.Id)).ToList();
        if (eligible.Count == 0) eligible = families.ToList();
        var ranked = eligible
            .Select(value => new
            {
                Family = value,
                Elo = ratings.TryGetValue(value.Id, out var rating) ? rating.Elo : value.NominalElo
            })
            .OrderBy(value => Math.Abs(value.Elo - targetElo))
            .ThenBy(value => value.Family.Id, StringComparer.Ordinal)
            .ToList();
        var bestDistance = Math.Abs(ranked[0].Elo - targetElo);
        var tied = ranked.Where(value => Math.Abs(value.Elo - targetElo) == bestDistance).ToList();
        return tied[Math.Abs(tieBreaker) % tied.Count].Family;
    }

    public static int Clamp(int elo) => Math.Clamp(elo, MinimumElo, MaximumElo);
}