using UnityEngine;

namespace Cielonos.MainGame.Inventory
{
    /// <summary>
    /// 提供基于 Luck 和 Curse 的通用随机结果。
    /// 返回值始终位于 0 到 1 之间；具体含义由调用者自行映射。
    /// </summary>
    public static class Randomizer
    {
        private const float MinimumValue = 0f;
        private const float MaximumValue = 1f;
        private const float BiasScale = 0.5f;
        private const float GoodChanceRange = 0.45f;
        private const float RegularStandardDeviation = 0.165f;
        private const float ExtremeStandardDeviation = 0.06f;
        private const float ExtremeGoodMean = 0.9f;
        private const float ExtremeBadMean = 0.1f;
        private const int MaximumNormalRollAttempts = 4;

        /// <summary>
        /// 获取一个不受属性影响的基础随机值。
        /// </summary>
        public static float Roll01()
        {
            return Random.Range(MinimumValue, MaximumValue);
        }

        /// <summary>
        /// 根据 Luck 和 Curse 获取一个表示结果好坏的随机值。
        /// 0 表示最坏结果，1 表示最好结果；两项属性均为 0 时使用中心为 0.5 的正态分布。
        /// </summary>
        public static float RollLuckCurse01(float luck, float curse)
        {
            GetDistributionParameters(luck, curse, out float bias, out float goodChance, out float extremeWeight);

            if (Random.value < extremeWeight)
            {
                float mean = Random.value < goodChance ? ExtremeGoodMean : ExtremeBadMean;
                return RollTruncatedNormal(mean, ExtremeStandardDeviation);
            }

            return RollTruncatedNormal(0.5f + 0.25f * bias, RegularStandardDeviation);
        }

        private static void GetDistributionParameters(float luck, float curse, out float bias, out float goodChance,
            out float extremeWeight)
        {
            float normalizedLuck = Mathf.Clamp01(luck / 100f);
            float normalizedCurse = Mathf.Clamp01(curse / 100f);
            bias = HyperbolicTangent((normalizedLuck - normalizedCurse) / BiasScale);
            goodChance = 0.5f + GoodChanceRange * bias;
            extremeWeight = normalizedLuck * normalizedCurse;
        }

        /// <summary>
        /// Unity 的 Mathf 未提供 Tanh，因此通过指数定义计算双曲正切。
        /// </summary>
        private static float HyperbolicTangent(float value)
        {
            float exponent = Mathf.Exp(2f * value);
            return (exponent - 1f) / (exponent + 1f);
        }

        private static float RollTruncatedNormal(float mean, float standardDeviation)
        {
            for (int attempt = 0; attempt < MaximumNormalRollAttempts; attempt++)
            {
                float value = mean + RollStandardNormal() * standardDeviation;
                if (value > MinimumValue && value < MaximumValue) return value;
            }

            return Mathf.Clamp(mean + RollStandardNormal() * standardDeviation, MinimumValue, MaximumValue);
        }

        private static float RollStandardNormal()
        {
            float u1 = Mathf.Max(Random.value, float.Epsilon);
            float u2 = Random.value;
            return Mathf.Sqrt(-2f * Mathf.Log(u1)) * Mathf.Cos(2f * Mathf.PI * u2);
        }
    }
}