using System;
using System.Collections.Generic;
using System.Linq;
using QWERTYkez.Mensura.Units;
using QWERTYkez.Mensura.Extensions;
using Xunit;

namespace QWERTYkez.Mensura.Tests
{
    public class CollectionsPlusExtensionsTests
    {
        private const double Tolerance = 1e-12;
        private static readonly Length scalarUnit = Length.Meter;            // 1000 mm
        private static readonly double scalarDouble = 500.0;                 // прибавляемое значение в мм

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

        // Коллекции double
        private static readonly double[] doubleArray = new double[] { 200.0, 300.0 };
        private static readonly double?[] nullableDoubleArray = new double?[] { 200.0, null, 300.0 };
        private static readonly List<double> doubleList = new List<double> { 200.0, 300.0 };
        private static readonly List<double?> nullableDoubleList = new List<double?> { 200.0, null, 300.0 };

        // ====================== 1. T[] + double ======================
        [Fact]
        public void Plus_TArray_Double_Returns_TArray()
        {
            var result = unitsArray.Plus<Length>(scalarDouble);
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 + 500, (double)result[0], Tolerance);
            Assert.Equal(1 + 500, (double)result[1], Tolerance);
        }

        // ====================== 2. T?[] + double ======================
        [Fact]
        public void Plus_NullableTArray_Double_Returns_NullableTArray()
        {
            var result = nullableUnitsArray.Plus<Length>(scalarDouble);
            Assert.Equal(3, result.Length);
            Assert.Equal(1000 + 500, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // null + число = null
            Assert.Equal(1 + 500, (double)result[2]!, Tolerance);
        }

        // ====================== 3. double + T[] ======================
        [Fact]
        public void Plus_Double_TArray_Returns_TArray()
        {
            var result = scalarDouble.Plus<Length>(unitsArray);
            Assert.Equal(2, result.Length);
            Assert.Equal(500 + 1000, (double)result[0], Tolerance);
            Assert.Equal(500 + 1, (double)result[1], Tolerance);
        }

        // ====================== 4. double + T?[] ======================
        [Fact]
        public void Plus_Double_NullableTArray_Returns_NullableTArray()
        {
            var result = scalarDouble.Plus<Length>(nullableUnitsArray);
            Assert.Equal(3, result.Length);
            Assert.Equal(500 + 1000, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // число + null = null
            Assert.Equal(500 + 1, (double)result[2]!, Tolerance);
        }

        // ====================== 5. List<T> + double ======================
        [Fact]
        public void Plus_ListT_Double_Returns_ListT()
        {
            var result = unitsList.Plus<Length>(scalarDouble);
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 + 500, (double)result[0], Tolerance);
            Assert.Equal(1 + 500, (double)result[1], Tolerance);
        }

        // ====================== 6. List<T?> + double ======================
        [Fact]
        public void Plus_ListNullableT_Double_Returns_ListNullableT()
        {
            var result = nullableUnitsList.Plus<Length>(scalarDouble);
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 + 500, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // null + число = null
            Assert.Equal(1 + 500, (double)result[2]!, Tolerance);
        }

        // ====================== 7. double + List<T> ======================
        [Fact]
        public void Plus_Double_ListT_Returns_ListT()
        {
            var result = scalarDouble.Plus<Length>(unitsList);
            Assert.Equal(2, result.Count);
            Assert.Equal(500 + 1000, (double)result[0], Tolerance);
            Assert.Equal(500 + 1, (double)result[1], Tolerance);
        }

        // ====================== 8. double + List<T?> ======================
        [Fact]
        public void Plus_Double_ListNullableT_Returns_ListNullableT()
        {
            var result = scalarDouble.Plus<Length>(nullableUnitsList);
            Assert.Equal(3, result.Count);
            Assert.Equal(500 + 1000, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // число + null = null
            Assert.Equal(500 + 1, (double)result[2]!, Tolerance);
        }

        // ====================== 9. IReadOnlyCollection<T> + double (Span) ======================
        [Fact]
        public void Plus_IReadOnlyCollectionT_Double_Span()
        {
            Span<Length> dest = new Length[2];
            ((IReadOnlyCollection<Length>)unitsArray).Plus<Length>(scalarDouble, dest);
            Assert.Equal(1000 + 500, (double)dest[0], Tolerance);
            Assert.Equal(1 + 500, (double)dest[1], Tolerance);
        }

        // ====================== 10. IReadOnlyCollection<T?> + double (Span) ======================
        [Fact]
        public void Plus_IReadOnlyCollectionNullableT_Double_Span()
        {
            Span<Length?> dest = new Length?[3];
            ((IReadOnlyCollection<Length?>)nullableUnitsArray).Plus<Length>(scalarDouble, dest);
            Assert.Equal(1000 + 500, (double)dest[0]!, Tolerance);
            Assert.Null(dest[1]);                     // null + число = null
            Assert.Equal(1 + 500, (double)dest[2]!, Tolerance);
        }

        // ====================== 11. double + IReadOnlyCollection<T> (Span) ======================
        [Fact]
        public void Plus_Double_IReadOnlyCollectionT_Span()
        {
            Span<Length> dest = new Length[2];
            scalarDouble.Plus<Length>((IReadOnlyCollection<Length>)unitsArray, dest);
            Assert.Equal(500 + 1000, (double)dest[0], Tolerance);
            Assert.Equal(500 + 1, (double)dest[1], Tolerance);
        }

        // ====================== 12. double + IReadOnlyCollection<T?> (Span) ======================
        [Fact]
        public void Plus_Double_IReadOnlyCollectionNullableT_Span()
        {
            Span<Length?> dest = new Length?[3];
            scalarDouble.Plus<Length>((IReadOnlyCollection<Length?>)nullableUnitsArray, dest);
            Assert.Equal(500 + 1000, (double)dest[0]!, Tolerance);
            Assert.Null(dest[1]);                     // число + null = null
            Assert.Equal(500 + 1, (double)dest[2]!, Tolerance);
        }

        // ====================== 13. IEnumerable<T> + double ======================
        [Fact]
        public void Plus_IEnumerableT_Double_Returns_IEnumerableT()
        {
            var result = ((IEnumerable<Length>)unitsArray).Plus<Length>(scalarDouble).ToList();
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 + 500, (double)result[0], Tolerance);
            Assert.Equal(1 + 500, (double)result[1], Tolerance);
        }

        // ====================== 14. IEnumerable<T?> + double ======================
        [Fact]
        public void Plus_IEnumerableNullableT_Double_Returns_IEnumerableNullableT()
        {
            var result = ((IEnumerable<Length?>)nullableUnitsArray).Plus<Length>(scalarDouble).ToList();
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 + 500, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // null + число = null
            Assert.Equal(1 + 500, (double)result[2]!, Tolerance);
        }

        // ====================== 15. double + IEnumerable<T> ======================
        [Fact]
        public void Plus_Double_IEnumerableT_Returns_IEnumerableT()
        {
            var result = scalarDouble.Plus<Length>((IEnumerable<Length>)unitsArray).ToList();
            Assert.Equal(2, result.Count);
            Assert.Equal(500 + 1000, (double)result[0], Tolerance);
            Assert.Equal(500 + 1, (double)result[1], Tolerance);
        }

        // ====================== 16. double + IEnumerable<T?> ======================
        [Fact]
        public void Plus_Double_IEnumerableNullableT_Returns_IEnumerableNullableT()
        {
            var result = scalarDouble.Plus<Length>((IEnumerable<Length?>)nullableUnitsArray).ToList();
            Assert.Equal(3, result.Count);
            Assert.Equal(500 + 1000, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // число + null = null
            Assert.Equal(500 + 1, (double)result[2]!, Tolerance);
        }

        // ====================== 17. double[] + T ======================
        [Fact]
        public void Plus_DoubleArray_T_Returns_TArray()
        {
            var result = doubleArray.Plus(scalarUnit);
            Assert.Equal(2, result.Length);
            Assert.Equal(200 + 1000, (double)result[0], Tolerance);
            Assert.Equal(300 + 1000, (double)result[1], Tolerance);
        }

        // ====================== 18. double?[] + T ======================
        [Fact]
        public void Plus_NullableDoubleArray_T_Returns_NullableTArray()
        {
            var result = nullableDoubleArray.Plus(scalarUnit);
            Assert.Equal(3, result.Length);
            Assert.Equal(200 + 1000, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // null + Length = null
            Assert.Equal(300 + 1000, (double)result[2]!, Tolerance);
        }

        // ====================== 19. T + double[] ======================
        [Fact]
        public void Plus_T_DoubleArray_Returns_TArray()
        {
            var result = scalarUnit.Plus(doubleArray);
            Assert.Equal(2, result.Length);
            Assert.Equal(1000 + 200, (double)result[0], Tolerance);
            Assert.Equal(1000 + 300, (double)result[1], Tolerance);
        }

        // ====================== 20. T + double?[] ======================
        [Fact]
        public void Plus_T_NullableDoubleArray_Returns_NullableTArray()
        {
            var result = scalarUnit.Plus(nullableDoubleArray);
            Assert.Equal(3, result.Length);
            Assert.Equal(1000 + 200, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // Length + null = null
            Assert.Equal(1000 + 300, (double)result[2]!, Tolerance);
        }

        // ====================== 21. List<double> + T ======================
        [Fact]
        public void Plus_ListDouble_T_Returns_ListT()
        {
            var result = doubleList.Plus(scalarUnit);
            Assert.Equal(2, result.Count);
            Assert.Equal(200 + 1000, (double)result[0], Tolerance);
            Assert.Equal(300 + 1000, (double)result[1], Tolerance);
        }

        // ====================== 22. List<double?> + T ======================
        [Fact]
        public void Plus_ListNullableDouble_T_Returns_ListNullableT()
        {
            var result = nullableDoubleList.Plus(scalarUnit);
            Assert.Equal(3, result.Count);
            Assert.Equal(200 + 1000, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // null + Length = null
            Assert.Equal(300 + 1000, (double)result[2]!, Tolerance);
        }

        // ====================== 23. T + List<double> ======================
        [Fact]
        public void Plus_T_ListDouble_Returns_ListT()
        {
            var result = scalarUnit.Plus(doubleList);
            Assert.Equal(2, result.Count);
            Assert.Equal(1000 + 200, (double)result[0], Tolerance);
            Assert.Equal(1000 + 300, (double)result[1], Tolerance);
        }

        // ====================== 24. T + List<double?> ======================
        [Fact]
        public void Plus_T_ListNullableDouble_Returns_ListNullableT()
        {
            var result = scalarUnit.Plus(nullableDoubleList);
            Assert.Equal(3, result.Count);
            Assert.Equal(1000 + 200, (double)result[0]!, Tolerance);
            Assert.Null(result[1]);                     // Length + null = null
            Assert.Equal(1000 + 300, (double)result[2]!, Tolerance);
        }

        // ====================== 25. T + T[] -> double[] ======================
        [Fact]
        public void Plus_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 Plus_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 Plus_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 Plus_NullArray_ReturnsNull()
        {
            Length[] nullArray = null;
            var result = nullArray.Plus<Length>(5.0);
            Assert.Null(result);
        }

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

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