using System;

namespace NightclubArcadia.Skills
{
    /// <summary>
    /// Pure check math. Exactly three modifier sources: rank, situational, state.
    /// No UnityEngine types. No side effects on PlayerSkills / VariableStorage / UI.
    /// </summary>
    public sealed class SkillCheckSystem
    {
        readonly SkillDatabase _database;
        readonly PlayerSkills _skills;
        readonly SkillStateModifiers _state;
        readonly IRollSource _rolls;

        public SkillCheckSystem(
            SkillDatabase database,
            PlayerSkills skills,
            SkillStateModifiers state,
            IRollSource rolls)
        {
            _database = database ?? throw new ArgumentNullException(nameof(database));
            _skills = skills ?? throw new ArgumentNullException(nameof(skills));
            _state = state ?? throw new ArgumentNullException(nameof(state));
            _rolls = rolls ?? throw new ArgumentNullException(nameof(rolls));
        }

        public SkillCheckResult Resolve(string skillId, int dc, int situationalMod)
        {
            skillId ??= string.Empty;

            string displayName;
            int rankMod;

            if (_database.TryGet(skillId, out var def) && def != null)
            {
                displayName = string.IsNullOrEmpty(def.DisplayName)
                    ? def.Id.ToUpperInvariant()
                    : def.DisplayName;
                rankMod = _skills.GetRank(skillId);
            }
            else
            {
                displayName = skillId.ToUpperInvariant();
                rankMod = 0;
            }

            var roll = _rolls.Roll(20);
            var stateMod = _state.TotalFor(skillId);
            var total = roll + rankMod + situationalMod + stateMod;

            bool success;
            SkillCheckDegree degree;

            if (roll == 1)
            {
                success = false;
                degree = SkillCheckDegree.CriticalFailure;
            }
            else if (roll == 20)
            {
                success = true;
                degree = SkillCheckDegree.CriticalSuccess;
            }
            else
            {
                success = total >= dc;
                degree = success ? SkillCheckDegree.Success : SkillCheckDegree.Failure;
            }

            return new SkillCheckResult(
                skillId,
                displayName,
                roll,
                rankMod,
                situationalMod,
                stateMod,
                total,
                dc,
                success,
                degree);
        }
    }
}