namespace Amphora.UnitTests
{
    public class MinstdTests : UnitTestSharp.TestFixture
    {
        public class SeedCtorTests : UnitTestSharp.TestFixture
        {
            public void TenThousandthDrawFromSeedOneMatchesTheCppStandard()
            {
                var generator = new Minstd(1);
                ulong tenThousandth = 0;
                for (int i = 0; i < 10000; i++)
                {
                    tenThousandth = generator.NextUInt64() >> 33;
                }

                CheckEqual(1043618065UL, tenThousandth);
            }

            public void ReducesTheSeedModuloTheModulus()
            {
                var reduced = new Minstd(2147483648UL);
                var one = new Minstd(1);

                CheckEqual(one.NextUInt64(), reduced.NextUInt64());
            }

            public void ReplacesAZeroSeedWithOne()
            {
                var zero = new Minstd(0);
                var one = new Minstd(1);

                CheckEqual(one.NextUInt64(), zero.NextUInt64());
            }

            public void ReplacesAMultipleOfTheModulusWithOne()
            {
                var modulus = new Minstd(2147483647UL);
                var one = new Minstd(1);

                CheckEqual(one.NextUInt64(), modulus.NextUInt64());
            }
        }

        public class NextUInt64Tests : UnitTestSharp.TestFixture
        {
            public void PutsThe31BitStateAtTheTop()
            {
                var generator = new Minstd(1);

                CheckEqual(0x0000834e00000000UL, generator.NextUInt64());
                CheckEqual(0x21ac75e200000000UL, generator.NextUInt64());
                CheckEqual(0xc16f59b200000000UL, generator.NextUInt64());
                CheckEqual(0x756a185400000000UL, generator.NextUInt64());
            }
        }

        public class NextUInt32Tests : UnitTestSharp.TestFixture
        {
            public void ShiftsTheStateUpOneBit()
            {
                var generator = new Minstd(1);

                CheckEqual(0x0000834eU, generator.NextUInt32());
                CheckEqual(0x21ac75e2U, generator.NextUInt32());
                CheckEqual(0xc16f59b2U, generator.NextUInt32());
                CheckEqual(0x756a1854U, generator.NextUInt32());
            }
        }
    }
}