using System.Runtime.CompilerServices;
using Jint.Native;

namespace Jint.Pooling;

/// <summary>
/// Cache reusable <see cref="JsValue" /> array instances as we allocate them a lot.
/// </summary>
internal sealed class JsValueArrayPool
{
    private const int PoolSize = 15;
    private readonly ObjectPool<JsValue[]> _poolArray1;
    private readonly ObjectPool<JsValue[]> _poolArray2;
    private readonly ObjectPool<JsValue[]> _poolArray3;

    public JsValueArrayPool()
    {
        _poolArray1 = new ObjectPool<JsValue[]>(Factory1, PoolSize);
        _poolArray2 = new ObjectPool<JsValue[]>(Factory2, PoolSize);
        _poolArray3 = new ObjectPool<JsValue[]>(Factory3, PoolSize);
    }

    private static JsValue[] Factory1()
    {
        return new JsValue[1];
    }

    private static JsValue[] Factory2()
    {
        return new JsValue[2];
    }

    private static JsValue[] Factory3()
    {
        return new JsValue[3];
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public JsValue[] RentArray(int size)
    {
        if (size == 0)
        {
            return [];
        }
        if (size == 1)
        {
            return _poolArray1.Allocate();
        }
        if (size == 2)
        {
            return _poolArray2.Allocate();
        }
        if (size == 3)
        {
            return _poolArray3.Allocate();
        }

        return new JsValue[size];
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public void ReturnArray(JsValue[] array)
    {
        // Ensure that the array contents are cleared
        // to allow garbage collecting the values of the
        // array if possible. Only the array itself
        // should be cached.
        if (array.Length == 1)
        {
            array[0] = null!;
            _poolArray1.Free(array);
        }
        else if (array.Length == 2)
        {
            array[0] = null!;
            array[1] = null!;
            _poolArray2.Free(array);
        }
        else if (array.Length == 3)
        {
            array[0] = null!;
            array[1] = null!;
            array[2] = null!;
            _poolArray3.Free(array);
        }
    }
}