// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.Linq;
using System.Runtime.CompilerServices;
using CommunityToolkit.HighPerformance.Enumerables;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace CommunityToolkit.HighPerformance.UnitTests;

[TestClass]
public class Test_Span2DT
{
    [TestMethod]
    public void Test_Span2DT_Empty()
    {
        // Like in the tests for Memory2D<T>, here we validate a number of empty spans
        Span2D<int> empty1 = default;

        Assert.IsTrue(empty1.IsEmpty);
        Assert.AreEqual(empty1.Length, 0);
        Assert.AreEqual(empty1.Width, 0);
        Assert.AreEqual(empty1.Height, 0);

        Span2D<string> empty2 = Span2D<string>.Empty;

        Assert.IsTrue(empty2.IsEmpty);
        Assert.AreEqual(empty2.Length, 0);
        Assert.AreEqual(empty2.Width, 0);
        Assert.AreEqual(empty2.Height, 0);

        Span2D<int> empty3 = new int[4, 0];

        Assert.IsTrue(empty3.IsEmpty);
        Assert.AreEqual(empty3.Length, 0);
        Assert.AreEqual(empty3.Width, 0);
        Assert.AreEqual(empty3.Height, 4);

        Span2D<int> empty4 = new int[0, 7];

        Assert.IsTrue(empty4.IsEmpty);
        Assert.AreEqual(empty4.Length, 0);
        Assert.AreEqual(empty4.Width, 7);
        Assert.AreEqual(empty4.Height, 0);
    }

#if NET6_0_OR_GREATER
    [TestMethod]
    public unsafe void Test_Span2DT_RefConstructor()
    {
        Span<int> span = stackalloc[]
        {
            1,
            2,
            3,
            4,
            5,
            6
        };

        // Test for a Span2D<T> instance created from a target reference. This is only supported
        // on runtimes with fast Span<T> support (as we need the API to power this with just a ref).
        Span2D<int> span2d = Span2D<int>.DangerousCreate(ref span[0], 2, 3, 0);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 6);
        Assert.AreEqual(span2d.Width, 3);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 0] = 99;
        span2d[1, 2] = 101;

        // Validate that those values were mapped to the right spot in the target span
        Assert.AreEqual(span[0], 99);
        Assert.AreEqual(span[5], 101);

        // A few cases with invalid indices
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => Span2D<int>.DangerousCreate(ref Unsafe.AsRef<int>(null), -1, 0, 0));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => Span2D<int>.DangerousCreate(ref Unsafe.AsRef<int>(null), 1, -2, 0));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => Span2D<int>.DangerousCreate(ref Unsafe.AsRef<int>(null), 1, 0, -5));
    }
#endif

    [TestMethod]
    public unsafe void Test_Span2DT_PtrConstructor()
    {
        int* ptr = stackalloc[]
        {
            1,
            2,
            3,
            4,
            5,
            6
        };

        // Same as above, but creating a Span2D<T> from a raw pointer
        Span2D<int> span2d = new(ptr, 2, 3, 0);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 6);
        Assert.AreEqual(span2d.Width, 3);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 0] = 99;
        span2d[1, 2] = 101;

        Assert.AreEqual(ptr[0], 99);
        Assert.AreEqual(ptr[5], 101);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>((void*)0, -1, 0, 0));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>((void*)0, 1, -2, 0));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>((void*)0, 1, 0, -5));
        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<string>((void*)0, 2, 2, 0));
    }

    [TestMethod]
    public void Test_Span2DT_Array1DConstructor()
    {
        int[] array =
        {
            1, 2, 3, 4, 5, 6
        };

        // Same as above, but wrapping a 1D array with data in row-major order
        Span2D<int> span2d = new(array, 1, 2, 2, 1);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 4);
        Assert.AreEqual(span2d.Width, 2);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 0] = 99;
        span2d[1, 1] = 101;

        Assert.AreEqual(array[1], 99);
        Assert.AreEqual(array[5], 101);

        // The first check fails due to the array covariance test mentioned in the Memory2D<T> tests.
        // The others just validate a number of cases with invalid arguments (eg. out of range).
        _ = Assert.ThrowsException<ArrayTypeMismatchException>(() => new Span2D<object>(new string[1], 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, -99, 1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 0, -10, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 0, 1, 1, -1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 0, 1, -100, 1));
        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<int>(array, 0, 10, 1, 120));
    }

    [TestMethod]
    public void Test_Span2DT_Array2DConstructor_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but directly wrapping a 2D array
        Span2D<int> span2d = new(array);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 6);
        Assert.AreEqual(span2d.Width, 3);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 1] = 99;
        span2d[1, 2] = 101;

        Assert.AreEqual(array[0, 1], 99);
        Assert.AreEqual(array[1, 2], 101);

        _ = Assert.ThrowsException<ArrayTypeMismatchException>(() => new Span2D<object>(new string[1, 2]));
    }

    [TestMethod]
    public void Test_Span2DT_Array2DConstructor_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but with a custom slicing over the target 2D array
        Span2D<int> span2d = new(array, 0, 1, 2, 2);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 4);
        Assert.AreEqual(span2d.Width, 2);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 0] = 99;
        span2d[1, 1] = 101;

        Assert.AreEqual(array[0, 1], 99);
        Assert.AreEqual(array[1, 2], 101);

        _ = Assert.ThrowsException<ArrayTypeMismatchException>(() => new Span2D<object>(new string[1, 2], 0, 0, 2, 2));
    }

    [TestMethod]
    public void Test_Span2DT_Array3DConstructor_1()
    {
        int[,,] array =
        {
            {
                { 1, 2, 3 },
                { 4, 5, 6 }
            },
            {
                { 10, 20, 30 },
                { 40, 50, 60 }
            }
        };

        // Here we wrap a layer in a 3D array instead, the rest is the same
        Span2D<int> span2d = new(array, 1);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 6);
        Assert.AreEqual(span2d.Width, 3);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 1] = 99;
        span2d[1, 2] = 101;

        Assert.AreEqual(span2d[0, 0], 10);
        Assert.AreEqual(array[1, 0, 1], 99);
        Assert.AreEqual(array[1, 1, 2], 101);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, -1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 20));
    }

    [TestMethod]
    public void Test_Span2DT_Array3DConstructor_2()
    {
        int[,,] array =
        {
            {
                { 1, 2, 3 },
                { 4, 5, 6 }
            },
            {
                { 10, 20, 30 },
                { 40, 50, 60 }
            }
        };

        // Same as above, but also slicing a target 2D area in the 3D array layer
        Span2D<int> span2d = new(array, 1, 0, 1, 2, 2);

        Assert.IsFalse(span2d.IsEmpty);
        Assert.AreEqual(span2d.Length, 4);
        Assert.AreEqual(span2d.Width, 2);
        Assert.AreEqual(span2d.Height, 2);

        span2d[0, 1] = 99;
        span2d[1, 1] = 101;

        Assert.AreEqual(span2d[0, 0], 20);
        Assert.AreEqual(array[1, 0, 2], 99);
        Assert.AreEqual(array[1, 1, 2], 101);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, -1, 1, 1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 1, -1, 1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 1, 1, -1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 1, 1, 1, -1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 1, 1, 1, 1, -1));
    }

    [TestMethod]
    public void Test_Span2DT_FillAndClear_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Tests for the Fill and Clear APIs for Span2D<T>. These should fill
        // or clear the entire wrapped 2D array (just like eg. Span<T>.Fill).
        Span2D<int> span2d = new(array);

        span2d.Fill(42);

        Assert.IsTrue(array.Cast<int>().All(n => n == 42));

        span2d.Clear();

        Assert.IsTrue(array.Cast<int>().All(n => n == 0));
    }

    [TestMethod]
    public void Test_Span2DT_Fill_Empty()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but with an initial slicing as well to ensure
        // these method work correctly with different internal offsets
        Span2D<int> span2d = new(array, 0, 0, 0, 0);

        span2d.Fill(42);

        CollectionAssert.AreEqual(array, array);

        span2d.Clear();

        CollectionAssert.AreEqual(array, array);
    }

    [TestMethod]
    public void Test_Span2DT_FillAndClear_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, just with different slicing to a target smaller 2D area
        Span2D<int> span2d = new(array, 0, 1, 2, 2);

        span2d.Fill(42);

        int[,] filled =
        {
            { 1, 42, 42 },
            { 4, 42, 42 }
        };

        CollectionAssert.AreEqual(array, filled);

        span2d.Clear();

        int[,] cleared =
        {
            { 1, 0, 0 },
            { 4, 0, 0 }
        };

        CollectionAssert.AreEqual(array, cleared);
    }

    [TestMethod]
    public void Test_Span2DT_CopyTo_Empty()
    {
        Span2D<int> span2d = Span2D<int>.Empty;

        int[] target = new int[0];

        // Copying an empty Span2D<T> to an empty array is just a no-op
        span2d.CopyTo(target);
    }

    [TestMethod]
    public void Test_Span2DT_CopyTo_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        int[] target = new int[array.Length];

        // Here we copy a Span2D<T> to a target Span<T> mapping an array.
        // This is valid, and the data will just be copied in row-major order.
        span2d.CopyTo(target);

        CollectionAssert.AreEqual(array, target);

        // Exception due to the target span being too small for the source Span2D<T> instance
        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<int>(array).CopyTo(Span<int>.Empty));
    }

    [TestMethod]
    public void Test_Span2DT_CopyTo_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but with different initial slicing
        Span2D<int> span2d = new(array, 0, 1, 2, 2);

        int[] target = new int[4];

        span2d.CopyTo(target);

        int[] expected = { 2, 3, 5, 6 };

        CollectionAssert.AreEqual(target, expected);

        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<int>(array).CopyTo(Span<int>.Empty));
        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<int>(array, 0, 1, 2, 2).CopyTo(Span<int>.Empty));
    }

    [TestMethod]
    public void Test_Span2DT_CopyTo2D_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        int[,] target = new int[2, 3];

        // Same as above, but copying to a target Span2D<T> instead. Note
        // that this method uses the implicit T[,] to Span2D<T> conversion.
        span2d.CopyTo(target);

        CollectionAssert.AreEqual(array, target);

        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<int>(array).CopyTo(Span2D<int>.Empty));
    }

    [TestMethod]
    public void Test_Span2DT_CopyTo2D_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but with extra initial slicing
        Span2D<int> span2d = new(array, 0, 1, 2, 2);

        int[,] target = new int[2, 2];

        span2d.CopyTo(target);

        int[,] expected =
        {
            { 2, 3 },
            { 5, 6 }
        };

        CollectionAssert.AreEqual(target, expected);

        _ = Assert.ThrowsException<ArgumentException>(() => new Span2D<int>(array).CopyTo(new Span2D<int>(target)));
    }

    [TestMethod]
    public void Test_Span2DT_TryCopyTo()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        int[] target = new int[array.Length];

        // Here we test the safe TryCopyTo method, which will fail gracefully
        Assert.IsTrue(span2d.TryCopyTo(target));
        Assert.IsFalse(span2d.TryCopyTo(Span<int>.Empty));

        int[] expected = { 1, 2, 3, 4, 5, 6 };

        CollectionAssert.AreEqual(target, expected);
    }

    [TestMethod]
    public void Test_Span2DT_TryCopyTo2D()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but copying to a 2D array with the safe TryCopyTo method
        Span2D<int> span2d = new(array);

        int[,] target = new int[2, 3];

        Assert.IsTrue(span2d.TryCopyTo(target));
        Assert.IsFalse(span2d.TryCopyTo(Span2D<int>.Empty));

        int[,] expected =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        CollectionAssert.AreEqual(target, expected);
    }

    [TestMethod]
    public unsafe void Test_Span2DT_GetPinnableReference()
    {
        // Here we test that a ref from an empty Span2D<T> returns a null ref
        Assert.IsTrue(Unsafe.AreSame(
            ref Unsafe.AsRef<int>(null),
            ref Span2D<int>.Empty.GetPinnableReference()));

        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        ref int r0 = ref span2d.GetPinnableReference();

        // Here we test that GetPinnableReference returns a ref to the first array element
        Assert.IsTrue(Unsafe.AreSame(ref r0, ref array[0, 0]));
    }

    [TestMethod]
    public unsafe void Test_Span2DT_DangerousGetReference()
    {
        // Same as above, but using DangerousGetReference instead (faster, no conditional check)
        Assert.IsTrue(Unsafe.AreSame(
            ref Unsafe.AsRef<int>(null),
            ref Span2D<int>.Empty.DangerousGetReference()));

        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        ref int r0 = ref span2d.DangerousGetReference();

        Assert.IsTrue(Unsafe.AreSame(ref r0, ref array[0, 0]));
    }

#if NET6_0_OR_GREATER
    [TestMethod]
    public unsafe void Test_Span2DT_Index_Indexer_1()
    {
        int[,] array = new int[4, 4];

        Span2D<int> span2d = new(array);

        ref int arrayRef = ref array[1, 3];
        ref int span2dRef = ref span2d[1, ^1];

        Assert.IsTrue(Unsafe.AreSame(ref arrayRef, ref span2dRef));
    }

    [TestMethod]
    public unsafe void Test_Span2DT_Index_Indexer_2()
    {
        int[,] array = new int[4, 4];

        Span2D<int> span2d = new(array);

        ref int arrayRef = ref array[2, 1];
        ref int span2dRef = ref span2d[^2, ^3];

        Assert.IsTrue(Unsafe.AreSame(ref arrayRef, ref span2dRef));
    }

    [TestMethod]
    [ExpectedException(typeof(IndexOutOfRangeException))]
    public unsafe void Test_Span2DT_Index_Indexer_Fail()
    {
        int[,] array = new int[4, 4];

        Span2D<int> span2d = new(array);

        ref int span2dRef = ref span2d[^6, 2];
    }

    [TestMethod]
    public unsafe void Test_Span2DT_Range_Indexer_1()
    {
        int[,] array = new int[4, 4];

        Span2D<int> span2d = new(array);
        Span2D<int> slice = span2d[1.., 1..];

        Assert.AreEqual(slice.Length, 9);
        Assert.IsTrue(Unsafe.AreSame(ref array[1, 1], ref slice[0, 0]));
        Assert.IsTrue(Unsafe.AreSame(ref array[3, 3], ref slice[2, 2]));
    }

    [TestMethod]
    public unsafe void Test_Span2DT_Range_Indexer_2()
    {
        int[,] array = new int[4, 4];

        Span2D<int> span2d = new(array);
        Span2D<int> slice = span2d[0..^2, 1..^1];

        Assert.AreEqual(slice.Length, 4);
        Assert.IsTrue(Unsafe.AreSame(ref array[0, 1], ref slice[0, 0]));
        Assert.IsTrue(Unsafe.AreSame(ref array[1, 2], ref slice[1, 1]));
    }

    [TestMethod]
    [ExpectedException(typeof(ArgumentOutOfRangeException))]
    public unsafe void Test_Span2DT_Range_Indexer_Fail()
    {
        int[,] array = new int[4, 4];

        Span2D<int> span2d = new(array);
        _ = span2d[0..6, 2..^1];

        Assert.Fail();
    }
#endif

    [TestMethod]
    public void Test_Span2DT_Slice_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Here we have a number of tests that just take an initial 2D array, create a Span2D<T>,
        // perform a number of slicing operations and then validate the parameters for the resulting
        // instances, and that the indexer works correctly and maps to the right original elements.
        Span2D<int> span2d = new(array);

        Span2D<int> slice1 = span2d.Slice(1, 1, 1, 2);

        Assert.AreEqual(slice1.Length, 2);
        Assert.AreEqual(slice1.Height, 1);
        Assert.AreEqual(slice1.Width, 2);
        Assert.AreEqual(slice1[0, 0], 5);
        Assert.AreEqual(slice1[0, 1], 6);

        Span2D<int> slice2 = span2d.Slice(0, 1, 2, 2);

        Assert.AreEqual(slice2.Length, 4);
        Assert.AreEqual(slice2.Height, 2);
        Assert.AreEqual(slice2.Width, 2);
        Assert.AreEqual(slice2[0, 0], 2);
        Assert.AreEqual(slice2[1, 0], 5);
        Assert.AreEqual(slice2[1, 1], 6);

        // Some checks for invalid arguments
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(-1, 1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(1, -1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(1, 1, 1, -1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(1, 1, -1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(10, 1, 1, 1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(1, 12, 1, 12));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).Slice(1, 1, 55, 1));
    }

    [TestMethod]
    public void Test_Span2DT_Slice_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        // Same as above, but with some different slicing
        Span2D<int> slice1 = span2d.Slice(0, 0, 2, 2);

        Assert.AreEqual(slice1.Length, 4);
        Assert.AreEqual(slice1.Height, 2);
        Assert.AreEqual(slice1.Width, 2);
        Assert.AreEqual(slice1[0, 0], 1);
        Assert.AreEqual(slice1[1, 1], 5);

        Span2D<int> slice2 = slice1.Slice(1, 0, 1, 2);

        Assert.AreEqual(slice2.Length, 2);
        Assert.AreEqual(slice2.Height, 1);
        Assert.AreEqual(slice2.Width, 2);
        Assert.AreEqual(slice2[0, 0], 4);
        Assert.AreEqual(slice2[0, 1], 5);

        Span2D<int> slice3 = slice2.Slice(0, 1, 1, 1);

        Assert.AreEqual(slice3.Length, 1);
        Assert.AreEqual(slice3.Height, 1);
        Assert.AreEqual(slice3.Width, 1);
        Assert.AreEqual(slice3[0, 0], 5);
    }

#if NET6_0_OR_GREATER
    [TestMethod]
    public void Test_Span2DT_GetRowSpan()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        // Here we create a Span2D<T> from a 2D array and want to get a Span<T> from
        // a specific row. This is only supported on runtimes with fast Span<T> support
        // for the same reason mentioned in the Memory2D<T> tests (we need the Span<T>
        // constructor that only takes a target ref). Then we just get some references
        // to items in this span and compare them against references into the original
        // 2D array to ensure they match and point to the correct elements from there.
        Span<int> span = span2d.GetRowSpan(1);

        Assert.IsTrue(Unsafe.AreSame(
            ref span[0],
            ref array[1, 0]));
        Assert.IsTrue(Unsafe.AreSame(
            ref span[2],
            ref array[1, 2]));

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetRowSpan(-1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetRowSpan(5));
    }
#endif

    [TestMethod]
    public void Test_Span2DT_TryGetSpan_From1DArray_1()
    {
        int[] array = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

        Span2D<int> span2d = new(array, 3, 3);

        bool success = span2d.TryGetSpan(out Span<int> span);

        Assert.IsTrue(success);
        Assert.AreEqual(span.Length, span2d.Length);
        Assert.IsTrue(Unsafe.AreSame(ref array[0], ref span[0]));
    }

    [TestMethod]
    public void Test_Span2DT_TryGetSpan_From1DArray_2()
    {
        int[] array = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

        Span2D<int> span2d = new Span2D<int>(array, 3, 3).Slice(1, 0, 2, 3);

        bool success = span2d.TryGetSpan(out Span<int> span);

        Assert.IsTrue(success);
        Assert.AreEqual(span.Length, span2d.Length);
        Assert.IsTrue(Unsafe.AreSame(ref array[3], ref span[0]));
    }

    [TestMethod]
    public void Test_Span2DT_TryGetSpan_From1DArray_3()
    {
        int[] array = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

        Span2D<int> span2d = new Span2D<int>(array, 3, 3).Slice(0, 1, 3, 2);

        bool success = span2d.TryGetSpan(out Span<int> span);

        Assert.IsFalse(success);
        Assert.AreEqual(span.Length, 0);
    }

    // See https://github.com/CommunityToolkit/WindowsCommunityToolkit/issues/3947
    [TestMethod]
    public void Test_Span2DT_TryGetSpan_From1DArray_4()
    {
        int[] array = new int[128];
        Span2D<int> span2d = new(array, 8, 16);

        bool success = span2d.TryGetSpan(out Span<int> span);

        Assert.IsTrue(success);
        Assert.AreEqual(span.Length, span2d.Length);
        Assert.IsTrue(Unsafe.AreSame(ref array[0], ref span[0]));
    }

    [TestMethod]
    public void Test_Span2DT_TryGetSpan_From2DArray_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        // This API tries to get a Span<T> for the entire contents of Span2D<T>.
        // This only works on runtimes if the underlying data is contiguous
        // and of a size that can fit into a single Span<T>. In this specific test,
        // this is not expected to work on .NET Standard 2.0 because it can't create a
        // Span<T> from a 2D array (reasons explained in the comments for the test above).
        bool success = span2d.TryGetSpan(out Span<int> span);

#if NETFRAMEWORK
        // Can't get a Span<T> over a T[,] array on .NET Standard 2.0
        Assert.IsFalse(success);
        Assert.AreEqual(span.Length, 0);
#else
        Assert.IsTrue(success);
        Assert.AreEqual(span.Length, span2d.Length);
#endif
    }

    [TestMethod]
    public void Test_Span2DT_TryGetSpan_From2DArray_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but this will always fail because we're creating
        // a Span2D<T> wrapping non contiguous data (the pitch is not 0).
        Span2D<int> span2d = new(array, 0, 0, 2, 2);

        bool success = span2d.TryGetSpan(out Span<int> span);

        Assert.IsFalse(success);
        Assert.IsTrue(span.IsEmpty);
    }

    [TestMethod]
    public void Test_Span2DT_ToArray_1()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Here we create a Span2D<T> and verify that ToArray() produces
        // a 2D array that is identical to the original one being wrapped.
        Span2D<int> span2d = new(array);

        int[,] copy = span2d.ToArray();

        Assert.AreEqual(copy.GetLength(0), array.GetLength(0));
        Assert.AreEqual(copy.GetLength(1), array.GetLength(1));

        CollectionAssert.AreEqual(array, copy);
    }

    [TestMethod]
    public void Test_Span2DT_ToArray_2()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but with extra initial slicing
        Span2D<int> span2d = new(array, 0, 0, 2, 2);

        int[,] copy = span2d.ToArray();

        Assert.AreEqual(copy.GetLength(0), 2);
        Assert.AreEqual(copy.GetLength(1), 2);

        int[,] expected =
        {
            { 1, 2 },
            { 4, 5 }
        };

        CollectionAssert.AreEqual(expected, copy);
    }

    [TestMethod]
    [ExpectedException(typeof(NotSupportedException))]
    public void Test_Span2DT_Equals()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        // Span2D<T>.Equals always throw (this mirrors the behavior of Span<T>.Equals)
        _ = span2d.Equals(null);
    }

    [TestMethod]
    [ExpectedException(typeof(NotSupportedException))]
    public void Test_Span2DT_GetHashCode()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        // Same as above, this always throws
        _ = span2d.GetHashCode();
    }

    [TestMethod]
    public void Test_Span2DT_ToString()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        Span2D<int> span2d = new(array);

        // Verify that we get the nicely formatted string
        string text = span2d.ToString();

        const string expected = "CommunityToolkit.HighPerformance.Span2D<System.Int32>[2, 3]";

        Assert.AreEqual(text, expected);
    }

    [TestMethod]
    public void Test_Span2DT_opEquals()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Create two Span2D<T> instances wrapping the same array with the same
        // parameters, and verify that the equality operators work correctly.
        Span2D<int> span2d_1 = new(array);
        Span2D<int> span2d_2 = new(array);

        Assert.IsTrue(span2d_1 == span2d_2);
        Assert.IsFalse(span2d_1 == Span2D<int>.Empty);
        Assert.IsTrue(Span2D<int>.Empty == Span2D<int>.Empty);

        // Same as above, but verify that a sliced span is not reported as equal
        Span2D<int> span2d_3 = new(array, 0, 0, 2, 2);

        Assert.IsFalse(span2d_1 == span2d_3);
        Assert.IsFalse(span2d_3 == Span2D<int>.Empty);
    }

    [TestMethod]
    public void Test_Span2DT_ImplicitCast()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Verify that an explicit constructor and the implicit conversion
        // operator generate an identical Span2D<T> instance from the array.
        Span2D<int> span2d_1 = array;
        Span2D<int> span2d_2 = new(array);

        Assert.IsTrue(span2d_1 == span2d_2);
    }

    [TestMethod]
    public void Test_Span2DT_GetRow()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Get a target row and verify the contents match with our data
        RefEnumerable<int> enumerable = new Span2D<int>(array).GetRow(1);

        int[] expected = { 4, 5, 6 };

        CollectionAssert.AreEqual(enumerable.ToArray(), expected);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetRow(-1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetRow(2));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetRow(1000));
    }

    [TestMethod]
    public unsafe void Test_Span2DT_Pointer_GetRow()
    {
        int* array = stackalloc[]
        {
            1,
            2,
            3,
            4,
            5,
            6
        };

        // Same as above, but with a Span2D<T> wrapping a raw pointer
        RefEnumerable<int> enumerable = new Span2D<int>(array, 2, 3, 0).GetRow(1);

        int[] expected = { 4, 5, 6 };

        CollectionAssert.AreEqual(enumerable.ToArray(), expected);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 2, 3, 0).GetRow(-1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 2, 3, 0).GetRow(2));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 2, 3, 0).GetRow(1000));
    }

    [TestMethod]
    public void Test_Span2DT_GetColumn()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        // Same as above, but getting a column instead
        RefEnumerable<int> enumerable = new Span2D<int>(array).GetColumn(2);

        int[] expected = { 3, 6 };

        CollectionAssert.AreEqual(enumerable.ToArray(), expected);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetColumn(-1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetColumn(3));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array).GetColumn(1000));
    }

    [TestMethod]
    public unsafe void Test_Span2DT_Pointer_GetColumn()
    {
        int* array = stackalloc[]
        {
            1,
            2,
            3,
            4,
            5,
            6
        };

        // Same as above, but wrapping a raw pointer
        RefEnumerable<int> enumerable = new Span2D<int>(array, 2, 3, 0).GetColumn(2);

        int[] expected = { 3, 6 };

        CollectionAssert.AreEqual(enumerable.ToArray(), expected);

        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 2, 3, 0).GetColumn(-1));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 2, 3, 0).GetColumn(3));
        _ = Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Span2D<int>(array, 2, 3, 0).GetColumn(1000));
    }

    [TestMethod]
    public void Test_Span2DT_GetEnumerator()
    {
        int[,] array =
        {
            { 1, 2, 3 },
            { 4, 5, 6 }
        };

        int[] result = new int[4];
        int i = 0;

        // Here we want to test the Span2D<T> enumerator. We create a Span2D<T> instance over
        // a given section of the initial 2D array, then iterate over it and store the items
        // into a temporary array. We then just compare the contents to ensure they match.
        foreach (ref int item in new Span2D<int>(array, 0, 1, 2, 2))
        {
            // Check the reference to ensure it points to the right original item
            Assert.IsTrue(Unsafe.AreSame(
                ref array[i / 2, (i % 2) + 1],
                ref item));

            // Also store the value to compare it later (redundant, but just in case)
            result[i++] = item;
        }

        int[] expected = { 2, 3, 5, 6 };

        CollectionAssert.AreEqual(result, expected);
    }

    [TestMethod]
    public unsafe void Test_Span2DT_Pointer_GetEnumerator()
    {
        int* array = stackalloc[]
        {
            1,
            2,
            3,
            4,
            5,
            6
        };

        int[] result = new int[4];
        int i = 0;

        // Same test as above, but wrapping a raw pointer
        foreach (ref int item in new Span2D<int>(array + 1, 2, 2, 1))
        {
            // Check the reference again
            Assert.IsTrue(Unsafe.AreSame(
                ref Unsafe.AsRef<int>(&array[((i / 2) * 3) + (i % 2) + 1]),
                ref item));

            result[i++] = item;
        }

        int[] expected = { 2, 3, 5, 6 };

        CollectionAssert.AreEqual(result, expected);
    }

    [TestMethod]
    public void Test_Span2DT_GetEnumerator_Empty()
    {
        Span2D<int>.Enumerator enumerator = Span2D<int>.Empty.GetEnumerator();

        // Ensure that an enumerator from an empty Span2D<T> can't move next
        Assert.IsFalse(enumerator.MoveNext());
    }
}