// Copyright (c) Six Labors.
// Licensed under the Apache License, Version 2.0.

using System;
using System.Threading;
using SixLabors.ImageSharp.Diagnostics;
using Xunit;

namespace SixLabors.ImageSharp.Tests
{
    public static class MemoryAllocatorValidator
    {
        private static readonly AsyncLocal<TestMemoryDiagnostics> LocalInstance = new();

        public static bool MonitoringAllocations => LocalInstance.Value != null;

        static MemoryAllocatorValidator()
        {
            MemoryDiagnostics.MemoryAllocated += MemoryDiagnostics_MemoryAllocated;
            MemoryDiagnostics.MemoryReleased += MemoryDiagnostics_MemoryReleased;
        }

        private static void MemoryDiagnostics_MemoryReleased()
        {
            TestMemoryDiagnostics backing = LocalInstance.Value;
            if (backing != null)
            {
                backing.TotalRemainingAllocated--;
            }
        }

        private static void MemoryDiagnostics_MemoryAllocated()
        {
            TestMemoryDiagnostics backing = LocalInstance.Value;
            if (backing != null)
            {
                backing.TotalAllocated++;
                backing.TotalRemainingAllocated++;
            }
        }

        public static TestMemoryDiagnostics MonitorAllocations()
        {
            var diag = new TestMemoryDiagnostics();
            LocalInstance.Value = diag;
            return diag;
        }

        public static void StopMonitoringAllocations() => LocalInstance.Value = null;

        public static void ValidateAllocations(int expectedAllocationCount = 0)
            => LocalInstance.Value?.Validate(expectedAllocationCount);

        public class TestMemoryDiagnostics : IDisposable
        {
            public int TotalAllocated { get; set; }

            public int TotalRemainingAllocated { get; set; }

            public void Validate(int expectedAllocationCount)
            {
                var count = this.TotalRemainingAllocated;
                var pass = expectedAllocationCount == count;
                Assert.True(pass, $"Expected a {expectedAllocationCount} undisposed buffers but found {count}");
            }

            public void Dispose()
            {
                this.Validate(0);
                if (LocalInstance.Value == this)
                {
                    StopMonitoringAllocations();
                }
            }
        }
    }
}