// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

namespace SixLabors.ImageSharp.Tests.TestUtilities.Tests;

public class SemaphoreReadMemoryStreamTests
{
    private readonly SemaphoreSlim continueSemaphore = new(0);
    private readonly SemaphoreSlim notifyWaitPositionReachedSemaphore = new(0);
    private readonly byte[] buffer = new byte[128];

    [Fact]
    public void Read_BeforeWaitLimit_ShouldFinish()
    {
        using Stream stream = this.CreateTestStream();
        int read = stream.Read(this.buffer);
        Assert.Equal(this.buffer.Length, read);
    }

    [Fact]
    public async Task ReadAsync_BeforeWaitLimit_ShouldFinish()
    {
        using Stream stream = this.CreateTestStream();
        int read = await stream.ReadAsync(this.buffer, 0, this.buffer.Length);
        Assert.Equal(this.buffer.Length, read);
    }

    [Fact]
    public async Task Read_AfterWaitLimit_ShouldPause()
    {
        using Stream stream = this.CreateTestStream();
        stream.Read(this.buffer);
        Assert.Equal(0, this.notifyWaitPositionReachedSemaphore.CurrentCount);

        Task readTask = Task.Factory.StartNew(
            () =>
            {
                stream.Read(this.buffer);
                stream.Read(this.buffer);
                stream.Read(this.buffer);
                stream.Read(this.buffer);
                stream.Read(this.buffer);
            },
            TaskCreationOptions.LongRunning);

        await Task.Delay(5);
        Assert.False(readTask.IsCompleted);
        await this.notifyWaitPositionReachedSemaphore.WaitAsync();
        await Task.Delay(5);
        Assert.False(readTask.IsCompleted);
        this.continueSemaphore.Release();
        await readTask;
    }

    [Fact]
    public async Task ReadAsync_AfterWaitLimit_ShouldPause()
    {
        using Stream stream = this.CreateTestStream();
        await stream.ReadAsync(this.buffer, 0, this.buffer.Length);

        Task readTask = Task.Factory.StartNew(
            async () =>
            {
                await stream.ReadAsync(this.buffer, 0, this.buffer.Length);
                await stream.ReadAsync(this.buffer, 0, this.buffer.Length);
                await stream.ReadAsync(this.buffer, 0, this.buffer.Length);
                await stream.ReadAsync(this.buffer, 0, this.buffer.Length);
                await stream.ReadAsync(this.buffer, 0, this.buffer.Length);
            },
            TaskCreationOptions.LongRunning);
        await Task.Delay(5);
        Assert.False(readTask.IsCompleted);
        await this.notifyWaitPositionReachedSemaphore.WaitAsync();
        await Task.Delay(5);
        Assert.False(readTask.IsCompleted);
        this.continueSemaphore.Release();
        await readTask;
    }

    private Stream CreateTestStream(int size = 1024, int waitAfterPosition = 256)
    {
        byte[] buffer = new byte[size];
        return new SemaphoreReadMemoryStream(buffer, waitAfterPosition, this.notifyWaitPositionReachedSemaphore, this.continueSemaphore);
    }
}