using System;
using Xunit;
using XWorld.Framework;

namespace XWorld.Framework.Tests
{
    public class DeterministicRandomTests
    {
        [Fact]
        public void SameSeed_ProducesIdenticalSequence()
        {
            var a = new DeterministicRandom(12345UL);
            var b = new DeterministicRandom(12345UL);
            for (int i = 0; i < 1000; i++)
                Assert.Equal(a.Next(100), b.Next(100));
        }

        [Fact]
        public void DifferentSeed_DivergesQuickly()
        {
            var a = new DeterministicRandom(1UL);
            var b = new DeterministicRandom(2UL);
            bool anyDiff = false;
            for (int i = 0; i < 20; i++)
                if (a.Next(1_000_000) != b.Next(1_000_000)) { anyDiff = true; break; }
            Assert.True(anyDiff);
        }

        [Fact]
        public void Next_StaysInRange()
        {
            var rng = new DeterministicRandom(999UL);
            for (int i = 0; i < 100_000; i++)
            {
                int v = rng.Next(7);
                Assert.InRange(v, 0, 6);
            }
        }

        [Fact]
        public void Next_One_AlwaysZero()
        {
            var rng = new DeterministicRandom(42UL);
            for (int i = 0; i < 100; i++)
                Assert.Equal(0, rng.Next(1));
        }

        [Theory]
        [InlineData(0)]
        [InlineData(-3)]
        public void Next_NonPositiveMax_Throws(int max)
        {
            var rng = new DeterministicRandom(42UL);
            Assert.Throws<ArgumentOutOfRangeException>((Action)(() => rng.Next(max)));
        }

        [Fact]
        public void State_SnapshotAndResume_ContinuesIdentically()
        {
            var rng = new DeterministicRandom(7UL);
            for (int i = 0; i < 10; i++) rng.Next(1000);
            ulong snapshot = rng.State;

            var resumed = new DeterministicRandom(snapshot);
            // 注意：State 是当前内部状态，用它重建后序列从"下一步"继续
            int[] fromOriginal = new int[5];
            int[] fromResumed = new int[5];
            for (int i = 0; i < 5; i++) fromOriginal[i] = rng.Next(1000);
            for (int i = 0; i < 5; i++) fromResumed[i] = resumed.Next(1000);
            Assert.Equal(fromOriginal, fromResumed);
        }
    }
}