namespace QWERTYkez.Mensura.Tests
{
    public class CollectionsMinusExtensionsTest
    {
        private const double Tolerance = 1e-12;
        private static readonly Length scalarUnit = Length.Meter;            // 1000 mm
        private static readonly double scalarDouble = 1000.0;                // уменьшаемое/вычитаемое в мм

        // 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 = [500.0, 200.0];          // мм
        private static readonly double?[] nullableDoubleArray = [500.0, null, 200.0];
        private static readonly List<double> doubleList = [500.0, 200.0];
        private static readonly List<double?> nullableDoubleList = [500.0, null, 200.0];

        // ====================== 1. T[] - double (результат T[]) ======================
        [Fact]
        public void Minus_TArray_Double_Returns_TArray()
        {
            // units - subtrahend
            var result = unitsArray.Minus<Length>(scalarDouble);
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 - 1000, (double)result[0], Tolerance);
            Assert.Equal(1 - 1000, (double)result[1], Tolerance);
        }

        [Fact]
        public void Minus_TArray_Double_ByZero_Works()
        {
            var result = unitsArray.Minus<Length>(0.0);
            Assert.Equal(1000, (double)result[0], Tolerance);
            Assert.Equal(1, (double)result[1], Tolerance);
        }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        // ====================== 17. double[] - T ======================
        [Fact]
        public void Minus_DoubleArray_T_Returns_TArray()
        {
            var result = doubleArray.Minus(scalarUnit);
            Assert.Equal(2, result.Length);
            Assert.Equal(500 - 1000, (double)result[0], Tolerance);
            Assert.Equal(200 - 1000, (double)result[1], Tolerance);
        }

        // ====================== 18. double?[] - T ======================
        [Fact]
        public void Minus_NullableDoubleArray_T_Returns_NullableTArray()
        {
            var result = nullableDoubleArray.Minus(scalarUnit);
            Assert.Equal(3, result.Length);
            Assert.Equal(500 - 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0 - 1000, (double)result[1]!, Tolerance);
            Assert.Equal(200 - 1000, (double)result[2]!, Tolerance);
        }

        // ====================== 19. T - double[] ======================
        [Fact]
        public void Minus_T_DoubleArray_Returns_TArray()
        {
            var result = scalarUnit.Minus(doubleArray);
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 - 500, (double)result[0], Tolerance);
            Assert.Equal(1000 - 200, (double)result[1], Tolerance);
        }

        // ====================== 20. T - double?[] ======================
        [Fact]
        public void Minus_T_NullableDoubleArray_Returns_NullableTArray()
        {
            var result = scalarUnit.Minus(nullableDoubleArray);
            Assert.Equal(3, result.Length);
            Assert.Equal(1000 - 500, (double)result[0]!, Tolerance);
            Assert.Equal(1000 - 0, (double)result[1]!, Tolerance);
            Assert.Equal(1000 - 200, (double)result[2]!, Tolerance);
        }

        // ====================== 21. List<double> - T ======================
        [Fact]
        public void Minus_ListDouble_T_Returns_ListT()
        {
            var result = doubleList.Minus(scalarUnit);
            Assert.Equal(2, result.Count);
            Assert.Equal(500 - 1000, (double)result[0], Tolerance);
            Assert.Equal(200 - 1000, (double)result[1], Tolerance);
        }

        // ====================== 22. List<double?> - T ======================
        [Fact]
        public void Minus_ListNullableDouble_T_Returns_ListNullableT()
        {
            var result = nullableDoubleList.Minus(scalarUnit);
            Assert.Equal(3, result.Count);
            Assert.Equal(500 - 1000, (double)result[0]!, Tolerance);
            Assert.Equal(0 - 1000, (double)result[1]!, Tolerance);
            Assert.Equal(200 - 1000, (double)result[2]!, Tolerance);
        }

        // ====================== 23. T - List<double> ======================
        [Fact]
        public void Minus_T_ListDouble_Returns_ListT()
        {
            var result = scalarUnit.Minus(doubleList);
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 - 500, (double)result[0], Tolerance);
            Assert.Equal(1000 - 200, (double)result[1], Tolerance);
        }

        // ====================== 24. T - List<double?> ======================
        [Fact]
        public void Minus_T_ListNullableDouble_Returns_ListNullableT()
        {
            var result = scalarUnit.Minus(nullableDoubleList);
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 - 500, (double)result[0]!, Tolerance);
            Assert.Equal(1000 - 0, (double)result[1]!, Tolerance);
            Assert.Equal(1000 - 200, (double)result[2]!, Tolerance);
        }

        // ====================== 25. T - T[] -> double[] ======================
        [Fact]
        public void Minus_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, где результат double (без указания R)
        // Тестируем Minus<T>(T[] units, T subtrahend) – возвращает double[]
        [Fact]
        public void Minus_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 Minus_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);
        }

        // Проверка пустых коллекций
        [Fact]
        public void Minus_EmptyArray_ReturnsEmptyArray()
        {
            var empty = Array.Empty<Length>();
            var result = empty.Minus<Length>(5.0);
            Assert.Empty(result);
        }

        [Fact]
        public void Minus_NullArray_ReturnsNull()
        {
            Length[] nullArray = null!;
            var result = nullArray.Minus<Length>(5.0);
            Assert.Null(result);
        }

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