#region Copyright notice and license

// Protocol Buffers - Google's data interchange format
// Copyright 2015 Google Inc.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#endregion

using System;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using NUnit.Framework;

namespace Google.Protobuf.Collections;

public class UnsafeCollectionOperationsTest
{
    [Test]
    public void NullFieldAsSpanValueType()
    {
        RepeatedField<int> field = null;
        Assert.Throws<ArgumentNullException>(() => UnsafeCollectionOperations.AsSpan(field));
    }

    [Test]
    public void NullFieldAsSpanClass()
    {
        RepeatedField<object> field = null;
        Assert.Throws<ArgumentNullException>(() => UnsafeCollectionOperations.AsSpan(field));
    }

    [Test]
    public void FieldAsSpanValueType()
    {
        var field = new RepeatedField<int>();
        foreach (var length in Enumerable.Range(0, 36))
        {
            field.Clear();
            ValidateContentEquality(field, UnsafeCollectionOperations.AsSpan(field));

            for (var i = 0; i < length; i++)
            {
                field.Add(i);
            }

            ValidateContentEquality(field, UnsafeCollectionOperations.AsSpan(field));

            field.Add(length + 1);
            ValidateContentEquality(field, UnsafeCollectionOperations.AsSpan(field));
        }

        static void ValidateContentEquality(RepeatedField<int> field, Span<int> span)
        {
            Assert.AreEqual(field.Count, span.Length);

            for (var i = 0; i < span.Length; i++)
            {
                Assert.AreEqual(field[i], span[i]);
            }
        }
    }

    [Test]
    public void FieldAsSpanClass()
    {
        var field = new RepeatedField<IntAsObject>();
        foreach (var length in Enumerable.Range(0, 36))
        {
            field.Clear();
            ValidateContentEquality(field, UnsafeCollectionOperations.AsSpan(field));

            for (var i = 0; i < length; i++)
            {
                field.Add(new IntAsObject { Value = i });
            }

            ValidateContentEquality(field, UnsafeCollectionOperations.AsSpan(field));

            field.Add(new IntAsObject { Value = length + 1 });
            ValidateContentEquality(field, UnsafeCollectionOperations.AsSpan(field));
        }

        static void ValidateContentEquality(
            RepeatedField<IntAsObject> field,
            Span<IntAsObject> span)
        {
            Assert.AreEqual(field.Count, span.Length);

            for (var i = 0; i < span.Length; i++)
            {
                Assert.AreEqual(field[i].Value, span[i].Value);
            }
        }
    }

    [Test]
    public void FieldAsSpanLinkBreaksOnResize()
    {
        var field = new RepeatedField<int>();

        for (var i = 0; i < 8; i++)
        {
            field.Add(i);
        }

        var span = UnsafeCollectionOperations.AsSpan(field);

        var startCapacity = field.Capacity;
        var startCount = field.Count;
        Assert.AreEqual(startCount, startCapacity);
        Assert.AreEqual(startCount, span.Length);

        for (var i = 0; i < span.Length; i++)
        {
            span[i]++;
            Assert.AreEqual(field[i], span[i]);

            field[i]++;
            Assert.AreEqual(field[i], span[i]);
        }

        // Resize to break link between Span and RepeatedField
        field.Add(11);

        Assert.AreNotEqual(startCapacity, field.Capacity);
        Assert.AreNotEqual(startCount, field.Count);
        Assert.AreEqual(startCount, span.Length);

        for (var i = 0; i < span.Length; i++)
        {
            span[i] += 2;
            Assert.AreNotEqual(field[i], span[i]);

            field[i] += 3;
            Assert.AreNotEqual(field[i], span[i]);
        }
    }

    [Test]
    public void FieldSetCount()
    {
        RepeatedField<int> field = null;
        Assert.Throws<ArgumentNullException>(() => UnsafeCollectionOperations.SetCount(field, 3));

        field = new RepeatedField<int>();
        Assert.Throws<ArgumentOutOfRangeException>(()
            => UnsafeCollectionOperations.SetCount(field, -1));

        UnsafeCollectionOperations.SetCount(field, 5);
        Assert.AreEqual(5, field.Count);

        field = new RepeatedField<int> { 1, 2, 3, 4, 5 };
        ref var intRef = ref MemoryMarshal.GetReference(UnsafeCollectionOperations.AsSpan(field));

        // make sure that size decrease preserves content
        UnsafeCollectionOperations.SetCount(field, 3);
        Assert.AreEqual(3, field.Count);
        Assert.Throws<ArgumentOutOfRangeException>(() => field[3] = 42);
        var span = UnsafeCollectionOperations.AsSpan(field);
        SequenceEqual(span, new[] { 1, 2, 3 });
        Assert.True(Unsafe.AreSame(ref intRef, ref MemoryMarshal.GetReference(span)));

        // make sure that size increase preserves content and doesn't clear
        UnsafeCollectionOperations.SetCount(field, 5);
        span = UnsafeCollectionOperations.AsSpan(field);
        // .NET Framework always clears values. .NET 6+ only clears references.
        var expected =
#if NET5_0_OR_GREATER
            new[] { 1, 2, 3, 4, 5 };
#else
            new[] { 1, 2, 3, 0, 0 };
#endif
        SequenceEqual(span, expected);
        Assert.True(Unsafe.AreSame(ref intRef, ref MemoryMarshal.GetReference(span)));

        // make sure that reallocations preserve content
        var newCount = field.Capacity * 2;
        UnsafeCollectionOperations.SetCount(field, newCount);
        Assert.AreEqual(newCount, field.Count);
        span = UnsafeCollectionOperations.AsSpan(field);
        SequenceEqual(span.Slice(0, 3), new[] { 1, 2, 3 });
        Assert.True(!Unsafe.AreSame(ref intRef, ref MemoryMarshal.GetReference(span)));

        RepeatedField<string> listReference = new() { "a", "b", "c", "d", "e" };
        var listSpan = UnsafeCollectionOperations.AsSpan(listReference);
        ref var stringRef = ref MemoryMarshal.GetReference(listSpan);
        UnsafeCollectionOperations.SetCount(listReference, 3);

        // verify that reference types aren't cleared
        listSpan = UnsafeCollectionOperations.AsSpan(listReference);
        SequenceEqual(listSpan, new[] { "a", "b", "c" });
        Assert.True(Unsafe.AreSame(ref stringRef, ref MemoryMarshal.GetReference(listSpan)));
        UnsafeCollectionOperations.SetCount(listReference, 5);

        // verify that removed reference types are cleared
        listSpan = UnsafeCollectionOperations.AsSpan(listReference);
        SequenceEqual(listSpan, new[] { "a", "b", "c", null, null });
        Assert.True(Unsafe.AreSame(ref stringRef, ref MemoryMarshal.GetReference(listSpan)));
    }

    private static void SequenceEqual<T>(Span<T> span, Span<T> expected)
    {
        Assert.AreEqual(expected.Length, span.Length);
        for (var i = 0; i < expected.Length; i++)
        {
            Assert.AreEqual(expected[i], span[i]);
        }
    }

    private class IntAsObject
    {
        public int Value;
    }
}