// 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.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading;

namespace CommunityToolkit.HighPerformance;

/// <summary>
/// Helpers for working with the <see cref="SpinLock"/> type.
/// </summary>
public static class SpinLockExtensions
{
    /// <summary>
    /// Enters a specified <see cref="SpinLock"/> instance and returns a wrapper to use to release the lock.
    /// This extension should be used though a <see langword="using"/> block or statement:
    /// <code>
    /// SpinLock spinLock = new SpinLock();
    ///
    /// using (SpinLockExtensions.Enter(&amp;spinLock))
    /// {
    ///     // Thread-safe code here...
    /// }
    /// </code>
    /// The compiler will take care of releasing the SpinLock when the code goes out of that <see langword="using"/> scope.
    /// </summary>
    /// <param name="spinLock">A pointer to the target <see cref="SpinLock"/> to use</param>
    /// <returns>A wrapper type that will release <paramref name="spinLock"/> when its <see cref="System.IDisposable.Dispose"/> method is called.</returns>
    /// <remarks>The returned <see cref="UnsafeLock"/> value shouldn't be used directly: use this extension in a <see langword="using"/> block or statement.</remarks>
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static unsafe UnsafeLock Enter(SpinLock* spinLock)
    {
        return new(spinLock);
    }

    /// <summary>
    /// A <see langword="struct"/> that is used to enter and hold a <see cref="SpinLock"/> through a <see langword="using"/> block or statement.
    /// </summary>
    [EditorBrowsable(EditorBrowsableState.Never)]
    public readonly unsafe ref struct UnsafeLock
    {
        /// <summary>
        /// The <see cref="SpinLock"/>* pointer to the target <see cref="SpinLock"/> value to use.
        /// </summary>
        private readonly SpinLock* spinLock;

        /// <summary>
        /// A value indicating whether or not the lock is taken by this <see cref="Lock"/> instance.
        /// </summary>
        private readonly bool lockTaken;

        /// <summary>
        /// Initializes a new instance of the <see cref="UnsafeLock"/> struct.
        /// </summary>
        /// <param name="spinLock">The target <see cref="SpinLock"/> to use.</param>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public UnsafeLock(SpinLock* spinLock)
        {
            this.spinLock = spinLock;
            this.lockTaken = false;

            spinLock->Enter(ref this.lockTaken);
        }

        /// <summary>
        /// Implements the duck-typed <see cref="System.IDisposable.Dispose"/> method and releases the current <see cref="SpinLock"/> instance.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Dispose()
        {
            if (this.lockTaken)
            {
                this.spinLock->Exit();
            }
        }
    }

#if NETSTANDARD2_1_OR_GREATER
    /// <summary>
    /// Enters a specified <see cref="SpinLock"/> instance and returns a wrapper to use to release the lock.
    /// This extension should be used though a <see langword="using"/> block or statement:
    /// <code>
    /// SpinLock spinLock = new SpinLock();
    ///
    /// using (spinLock.Enter())
    /// {
    ///     // Thread-safe code here...
    /// }
    /// </code>
    /// The compiler will take care of releasing the SpinLock when the code goes out of that <see langword="using"/> scope.
    /// </summary>
    /// <param name="spinLock">The target <see cref="SpinLock"/> to use</param>
    /// <returns>A wrapper type that will release <paramref name="spinLock"/> when its <see cref="System.IDisposable.Dispose"/> method is called.</returns>
    /// <remarks>The returned <see cref="Lock"/> value shouldn't be used directly: use this extension in a <see langword="using"/> block or statement.</remarks>
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static Lock Enter(ref this SpinLock spinLock)
    {
        return new(ref spinLock);
    }
#else
    /// <summary>
    /// Enters a specified <see cref="SpinLock"/> instance and returns a wrapper to use to release the lock.
    /// This extension should be used though a <see langword="using"/> block or statement:
    /// <code>
    /// private SpinLock spinLock = new SpinLock();
    ///
    /// public void Foo()
    /// {
    ///     using (SpinLockExtensions.Enter(this, ref spinLock))
    ///     {
    ///         // Thread-safe code here...
    ///     }
    /// }
    /// </code>
    /// The compiler will take care of releasing the SpinLock when the code goes out of that <see langword="using"/> scope.
    /// </summary>
    /// <param name="owner">The owner <see cref="object"/> to create a portable reference for.</param>
    /// <param name="spinLock">The target <see cref="SpinLock"/> to use (it must be within <paramref name="owner"/>).</param>
    /// <returns>A wrapper type that will release <paramref name="spinLock"/> when its <see cref="System.IDisposable.Dispose"/> method is called.</returns>
    /// <remarks>The returned <see cref="Lock"/> value shouldn't be used directly: use this extension in a <see langword="using"/> block or statement.</remarks>
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static Lock Enter(object owner, ref SpinLock spinLock)
    {
        return new(owner, ref spinLock);
    }
#endif

    /// <summary>
    /// A <see langword="struct"/> that is used to enter and hold a <see cref="SpinLock"/> through a <see langword="using"/> block or statement.
    /// </summary>
    [EditorBrowsable(EditorBrowsableState.Never)]
    public readonly ref struct Lock
    {
        /// <summary>
        /// The <see cref="Ref{T}"/> instance pointing to the target <see cref="SpinLock"/> value to use.
        /// </summary>
        private readonly Ref<SpinLock> spinLock;

        /// <summary>
        /// A value indicating whether or not the lock is taken by this <see cref="Lock"/> instance.
        /// </summary>
        private readonly bool lockTaken;

#if NETSTANDARD2_1_OR_GREATER
        /// <summary>
        /// Initializes a new instance of the <see cref="Lock"/> struct.
        /// </summary>
        /// <param name="spinLock">The target <see cref="SpinLock"/> to use.</param>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public Lock(ref SpinLock spinLock)
        {
            this.spinLock = new Ref<SpinLock>(ref spinLock);
            this.lockTaken = false;

            spinLock.Enter(ref this.lockTaken);
        }
#else
        /// <summary>
        /// Initializes a new instance of the <see cref="Lock"/> struct.
        /// </summary>
        /// <param name="owner">The owner <see cref="object"/> to create a portable reference for.</param>
        /// <param name="spinLock">The target <see cref="SpinLock"/> to use (it must be within <paramref name="owner"/>).</param>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public Lock(object owner, ref SpinLock spinLock)
        {
            this.spinLock = new Ref<SpinLock>(owner, ref spinLock);
            this.lockTaken = false;

            spinLock.Enter(ref this.lockTaken);
        }
#endif

        /// <summary>
        /// Implements the duck-typed <see cref="System.IDisposable.Dispose"/> method and releases the current <see cref="SpinLock"/> instance.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Dispose()
        {
            if (this.lockTaken)
            {
                this.spinLock.Value.Exit();
            }
        }
    }
}