namespace QWERTYkez.Mensura.Tests
{
    public class CollectionsMultiplyExtensionsTest
    {
        private const double Tolerance = 1e-12;
        private static readonly Length scalarUnit = Length.Meter;            // 1000 mm
        private static readonly double scalarDouble = 2.0;

        // Коллекции единиц
        private static readonly Length[] unitsArray = [Length.Meter, Length._MilliMeter];
        private static readonly Length?[] nullableUnitsArray = [Length.Meter, null, Length._MilliMeter];
        private static readonly List<Length> unitsList = [Length.Meter, Length._MilliMeter];
        private static readonly List<Length?> nullableUnitsList = [Length.Meter, null, Length._MilliMeter];

        // Коллекции double
        private static readonly double[] doubleArray = [5.0, 3.0];
        private static readonly double?[] nullableDoubleArray = [5.0, null, 3.0];
        private static readonly List<double> doubleList = [5.0, 3.0];
        private static readonly List<double?> nullableDoubleList = [5.0, null, 3.0];

        // ====================== 1. T[] * double ======================
        [Fact]
        public void Mul_TArray_Double_Returns_TArray()
        {
            var result = unitsArray.Mul<Length>(scalarDouble);
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 * 2, (double)result[0], Tolerance);
            Assert.Equal(1 * 2, (double)result[1], Tolerance);
        }

        [Fact]
        public void Mul_TArray_Double_ByZero_Works()
        {
            var result = unitsArray.Mul<Length>(0.0);
            Assert.Equal(0, (double)result[0], Tolerance);
            Assert.Equal(0, (double)result[1], Tolerance);
        }

        // ====================== 2. T?[] * double ======================
        [Fact]
        public void Mul_NullableTArray_Double_Returns_NullableTArray()
        {
            var result = nullableUnitsArray.Mul<Length>(scalarDouble);
            Assert.Equal(3, result.Length);
            Assert.Equal(1000 * 2, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(1 * 2, (double)result[2]!, Tolerance);
        }

        // ====================== 3. double * T[] ======================
        [Fact]
        public void Mul_Double_TArray_Returns_TArray()
        {
            var result = scalarDouble.Mul<Length>(unitsArray);
            Assert.Equal(2, result.Length);
            Assert.Equal(2 * 1000, (double)result[0], Tolerance);
            Assert.Equal(2 * 1, (double)result[1], Tolerance);
        }

        // ====================== 4. double * T?[] ======================
        [Fact]
        public void Mul_Double_NullableTArray_Returns_NullableTArray()
        {
            var result = scalarDouble.Mul<Length>(nullableUnitsArray);
            Assert.Equal(3, result.Length);
            Assert.Equal(2 * 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(2 * 1, (double)result[2]!, Tolerance);
        }

        // ====================== 5. List<T> * double ======================
        [Fact]
        public void Mul_ListT_Double_Returns_ListT()
        {
            var result = unitsList.Mul<Length>(scalarDouble);
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 * 2, (double)result[0], Tolerance);
            Assert.Equal(1 * 2, (double)result[1], Tolerance);
        }

        // ====================== 6. List<T?> * double ======================
        [Fact]
        public void Mul_ListNullableT_Double_Returns_ListNullableT()
        {
            var result = nullableUnitsList.Mul<Length>(scalarDouble);
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 * 2, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(1 * 2, (double)result[2]!, Tolerance);
        }

        // ====================== 7. double * List<T> ======================
        [Fact]
        public void Mul_Double_ListT_Returns_ListT()
        {
            var result = scalarDouble.Mul<Length>(unitsList);
            Assert.Equal(2, result.Count);
            Assert.Equal(2 * 1000, (double)result[0], Tolerance);
            Assert.Equal(2 * 1, (double)result[1], Tolerance);
        }

        // ====================== 8. double * List<T?> ======================
        [Fact]
        public void Mul_Double_ListNullableT_Returns_ListNullableT()
        {
            var result = scalarDouble.Mul<Length>(nullableUnitsList);
            Assert.Equal(3, result.Count);
            Assert.Equal(2 * 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(2 * 1, (double)result[2]!, Tolerance);
        }

        // ====================== 9. IReadOnlyCollection<T> * double (Span) ======================
        [Fact]
        public void Mul_IReadOnlyCollectionT_Double_Span()
        {
            Span<Length> dest = new Length[2];
            ((IReadOnlyCollection<Length>)unitsArray).Mul<Length>(scalarDouble, dest);
            Assert.Equal(1000 * 2, (double)dest[0], Tolerance);
            Assert.Equal(1 * 2, (double)dest[1], Tolerance);
        }

        // ====================== 10. IReadOnlyCollection<T?> * double (Span) ======================
        [Fact]
        public void Mul_IReadOnlyCollectionNullableT_Double_Span()
        {
            Span<Length?> dest = new Length?[3];
            ((IReadOnlyCollection<Length?>)nullableUnitsArray).Mul<Length>(scalarDouble, dest);
            Assert.Equal(1000 * 2, (double)dest[0]!, Tolerance);
            Assert.Equal(0, (double)dest[1]!, Tolerance);
            Assert.Equal(1 * 2, (double)dest[2]!, Tolerance);
        }

        // ====================== 11. double * IReadOnlyCollection<T> (Span) ======================
        [Fact]
        public void Mul_Double_IReadOnlyCollectionT_Span()
        {
            Span<Length> dest = new Length[2];
            scalarDouble.Mul<Length>((IReadOnlyCollection<Length>)unitsArray, dest);
            Assert.Equal(2 * 1000, (double)dest[0], Tolerance);
            Assert.Equal(2 * 1, (double)dest[1], Tolerance);
        }

        // ====================== 12. double * IReadOnlyCollection<T?> (Span) ======================
        [Fact]
        public void Mul_Double_IReadOnlyCollectionNullableT_Span()
        {
            Span<Length?> dest = new Length?[3];
            scalarDouble.Mul<Length>((IReadOnlyCollection<Length?>)nullableUnitsArray, dest);
            Assert.Equal(2 * 1000, (double)dest[0]!, Tolerance);
            Assert.Equal(0, (double)dest[1]!, Tolerance);
            Assert.Equal(2 * 1, (double)dest[2]!, Tolerance);
        }

        // ====================== 13. IEnumerable<T> * double ======================
        [Fact]
        public void Mul_IEnumerableT_Double_Returns_IEnumerableT()
        {
            var result = ((IEnumerable<Length>)unitsArray).Mul<Length>(scalarDouble).ToList();
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 * 2, (double)result[0], Tolerance);
            Assert.Equal(1 * 2, (double)result[1], Tolerance);
        }

        // ====================== 14. IEnumerable<T?> * double ======================
        [Fact]
        public void Mul_IEnumerableNullableT_Double_Returns_IEnumerableNullableT()
        {
            var result = ((IEnumerable<Length?>)nullableUnitsArray).Mul<Length>(scalarDouble).ToList();
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 * 2, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(1 * 2, (double)result[2]!, Tolerance);
        }

        // ====================== 15. double * IEnumerable<T> ======================
        [Fact]
        public void Mul_Double_IEnumerableT_Returns_IEnumerableT()
        {
            var result = scalarDouble.Mul<Length>((IEnumerable<Length>)unitsArray).ToList();
            Assert.Equal(2, result.Count);
            Assert.Equal(2 * 1000, (double)result[0], Tolerance);
            Assert.Equal(2 * 1, (double)result[1], Tolerance);
        }

        // ====================== 16. double * IEnumerable<T?> ======================
        [Fact]
        public void Mul_Double_IEnumerableNullableT_Returns_IEnumerableNullableT()
        {
            var result = scalarDouble.Mul<Length>((IEnumerable<Length?>)nullableUnitsArray).ToList();
            Assert.Equal(3, result.Count);
            Assert.Equal(2 * 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(2 * 1, (double)result[2]!, Tolerance);
        }

        // ====================== 17. double[] * T ======================
        [Fact]
        public void Mul_DoubleArray_T_Returns_TArray()
        {
            var result = doubleArray.Mul(scalarUnit);
            Assert.Equal(2, result.Length);
            Assert.Equal(5 * 1000, (double)result[0], Tolerance);
            Assert.Equal(3 * 1000, (double)result[1], Tolerance);
        }

        // ====================== 18. double?[] * T ======================
        [Fact]
        public void Mul_NullableDoubleArray_T_Returns_NullableTArray()
        {
            var result = nullableDoubleArray.Mul(scalarUnit);
            Assert.Equal(3, result.Length);
            Assert.Equal(5 * 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(3 * 1000, (double)result[2]!, Tolerance);
        }

        // ====================== 19. T * double[] ======================
        [Fact]
        public void Mul_T_DoubleArray_Returns_TArray()
        {
            var result = scalarUnit.Mul(doubleArray);
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 * 5, (double)result[0], Tolerance);
            Assert.Equal(1000 * 3, (double)result[1], Tolerance);
        }

        // ====================== 20. T * double?[] ======================
        [Fact]
        public void Mul_T_NullableDoubleArray_Returns_NullableTArray()
        {
            var result = scalarUnit.Mul(nullableDoubleArray);
            Assert.Equal(3, result.Length);
            Assert.Equal(1000 * 5, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(1000 * 3, (double)result[2]!, Tolerance);
        }

        // ====================== 21. List<double> * T ======================
        [Fact]
        public void Mul_ListDouble_T_Returns_ListT()
        {
            var result = doubleList.Mul(scalarUnit);
            Assert.Equal(2, result.Count);
            Assert.Equal(5 * 1000, (double)result[0], Tolerance);
            Assert.Equal(3 * 1000, (double)result[1], Tolerance);
        }

        // ====================== 22. List<double?> * T ======================
        [Fact]
        public void Mul_ListNullableDouble_T_Returns_ListNullableT()
        {
            var result = nullableDoubleList.Mul(scalarUnit);
            Assert.Equal(3, result.Count);
            Assert.Equal(5 * 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(3 * 1000, (double)result[2]!, Tolerance);
        }

        // ====================== 23. T * List<double> ======================
        [Fact]
        public void Mul_T_ListDouble_Returns_ListT()
        {
            var result = scalarUnit.Mul(doubleList);
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 * 5, (double)result[0], Tolerance);
            Assert.Equal(1000 * 3, (double)result[1], Tolerance);
        }

        // ====================== 24. T * List<double?> ======================
        [Fact]
        public void Mul_T_ListNullableDouble_Returns_ListNullableT()
        {
            var result = scalarUnit.Mul(nullableDoubleList);
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 * 5, (double)result[0]!, Tolerance);
            Assert.Equal(0, (double)result[1]!, Tolerance);
            Assert.Equal(1000 * 3, (double)result[2]!, Tolerance);
        }

        // ====================== 25. T * T[] -> double[] ======================
        [Fact]
        public void Mul_T_TArray_Returns_DoubleArray()
        {
            var result = scalarUnit * unitsArray;
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 * 1000, result[0]._Value, Tolerance);
            Assert.Equal(1000 * 1, result[1]._Value, Tolerance);
        }

        // Дополнительно: перегрузки с результатом double (без R)
        [Fact]
        public void Mul_TArray_T_Returns_DoubleArray()
        {
            var result = unitsArray * scalarUnit;
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 * 1000, result[0]._Value, Tolerance);
            Assert.Equal(1 * 1000, result[1]._Value, Tolerance);
        }

        [Fact]
        public void Mul_ListT_T_Returns_DoubleList()
        {
            var result = unitsList * scalarUnit;
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 * 1000, result[0]._Value, Tolerance);
            Assert.Equal(1 * 1000, result[1]._Value, Tolerance);
        }

        // ====================== Обработка null коллекций ======================
        [Fact]
        public void Mul_NullArray_ReturnsNull()
        {
            Length[] nullArray = null!;
            var result = nullArray.Mul<Length>(5.0);
            Assert.Null(result);
        }

        [Fact]
        public void Mul_NullList_ReturnsNull()
        {
            List<Length> nullList = null!;
            var result = nullList.Mul<Length>(5.0);
            Assert.Null(result);
        }

        [Fact]
        public void Mul_EmptyArray_ReturnsEmptyArray()
        {
            var empty = Array.Empty<Length>();
            var result = empty.Mul<Length>(5.0);
            Assert.Empty(result);
        }
    }
}