using System.Collections.Generic;
using NUnit.Framework;
using BaseGames.Core;

namespace BaseGames.Tests.EditMode.Core
{
    /// <summary>
    /// WeightedPick 加权随机取索引的共享原语测试。
    /// 该原语被敌人选招 / Boss 选招 / 战利品掉落共用，故对"绝不选中零权重项"等
    /// 确定性性质做强断言（多次采样），避免任一消费端出现选到不合格项的缺陷。
    /// </summary>
    public class WeightedPickTests
    {
        static List<float> W(params float[] w) => new List<float>(w);

        [Test]
        public void Null_ReturnsMinusOne()
        {
            Assert.AreEqual(-1, WeightedPick.Index(null));
        }

        [Test]
        public void Empty_ReturnsMinusOne()
        {
            Assert.AreEqual(-1, WeightedPick.Index(W()));
        }

        [Test]
        public void AllZero_ReturnsMinusOne()
        {
            Assert.AreEqual(-1, WeightedPick.Index(W(0f, 0f, 0f)));
        }

        [Test]
        public void AllNegative_ReturnsMinusOne()
        {
            // 负权重按 0 处理（非法输入不应造成负总和/错误索引）
            Assert.AreEqual(-1, WeightedPick.Index(W(-1f, -5f)));
        }

        [Test]
        public void SinglePositive_AlwaysThatIndex()
        {
            var w = W(0f, 3f, 0f);
            for (int i = 0; i < 50; i++)
                Assert.AreEqual(1, WeightedPick.Index(w));
        }

        [Test]
        public void NeverPicksZeroWeight()
        {
            // 索引 0/2 权重为 0，无论抽多少次都不该被选中
            var w = W(0f, 1f, 0f, 2f);
            for (int i = 0; i < 200; i++)
            {
                int idx = WeightedPick.Index(w);
                Assert.IsTrue(idx == 1 || idx == 3, $"选中了零权重索引 {idx}");
            }
        }

        [Test]
        public void NeverPicksNegativeWeight()
        {
            var w = W(-10f, 1f);
            for (int i = 0; i < 200; i++)
                Assert.AreEqual(1, WeightedPick.Index(w));
        }

        [Test]
        public void AllPositive_EveryIndexReachable()
        {
            // 等权重下，足够多次采样应覆盖所有索引（验证不会恒定只返回首个/末个）
            var w = W(1f, 1f, 1f);
            var seen = new HashSet<int>();
            for (int i = 0; i < 500; i++) seen.Add(WeightedPick.Index(w));
            CollectionAssert.AreEquivalent(new[] { 0, 1, 2 }, seen);
        }

        [Test]
        public void HeavyWeight_DominatesDistribution()
        {
            // 权重 99:1 时，重权重索引应占绝大多数（宽松阈值，避免随机性造成偶发失败）
            var w = W(99f, 1f);
            int heavy = 0;
            const int N = 1000;
            for (int i = 0; i < N; i++) if (WeightedPick.Index(w) == 0) heavy++;
            Assert.Greater(heavy, N * 0.9f, $"重权重仅被选中 {heavy}/{N} 次，分布不符合权重");
        }

        [Test]
        public void WorksWithArray()
        {
            // IReadOnlyList 契约：数组同样可用（消费端可复用缓存数组，免 GC）
            float[] w = { 0f, 5f };
            Assert.AreEqual(1, WeightedPick.Index(w));
        }
    }
}