using BenchmarkDotNet.Attributes;
using MiscUtil;

namespace Recyclable.Collections.Benchmarks
{
	public delegate T Compare<T>(T x, T y);

	public readonly struct MyComparerReadOnlyStruct<T> : IComparer<T>
	{
		public int Compare(T? x, T? y) => Operator.Subtract(x, y) switch
		{
			> 0 => 1,
			< 0 => -1,
			_ => 0,
		};
	}

	public struct MyComparerStruct<T> : IComparer<T>
	{
		public int Compare(T? x, T? y) => Operator.Subtract(x, y) switch
		{
			> 0 => 1,
			< 0 => -1,
			_ => 0,
		};
	}

	public class MyComparer : IComparer<long>
	{
		public int Compare(long x, long y) => (x - y) switch
		{
			> 0 => 1,
			< 0 => -1,
			_ => 0,
		};
	}

	[MemoryDiagnoser]
	public class DelegateVsComparerBenchmark
	{
		private static readonly Comparer<long> _comparer = Comparer<long>.Default;

		private const int _objectCount = 1_000_000;
		private static readonly IEnumerable<long> _testObjects = Enumerable.Range(1, _objectCount).Select(x => (long)x);
		private static readonly IEnumerable<Func<long, long, int>> _testListOfFunctions = _testObjects.Select<long, Func<long, long, int>>(static x => new MyComparer().Compare);
		private static readonly IEnumerable<IComparer<long>> _testListOfComparers = _testObjects.Select(x => (IComparer<long>)new MyComparer());
		private static readonly IEnumerable<Compare<long>> _testListOfDelegates = _testObjects.Select(x => new Compare<long>((x, y) => new MyComparer().Compare(x, y)));
		private static readonly IEnumerable<Func<long, long, int>> _testListOfLocalFunctions = GetLocalFunctions(_testObjects);
		private static readonly IEnumerable<MyComparer> _testListOfClasses = _testObjects.Select(x => new MyComparer());
		private static readonly IEnumerable<MyComparerStruct<long>> _testListOfStructs = _testObjects.Select(x => new MyComparerStruct<long>());
		private static readonly IEnumerable<IComparer<long>> _testListOfBoxedStructs = _testObjects.Select(x => (IComparer<long>)new MyComparerStruct<long>());
		private static IEnumerable<TComparer> _testListOfUnboxedStructs<TComparer, TValue>() where TComparer : IComparer<TValue>, new()
		{
			foreach (var item in _testObjects)
			{
				yield return new TComparer();
			}
		}

		private static IEnumerable<Func<long, long, int>> GetLocalFunctions(IEnumerable<long> testObjects)
		{
			static int compareFunc(long x, long y)
			{
				return (x - y) switch
				{
					> 0 => 1,
					< 0 => -1,
					_ => 0
				};
			}

			foreach (var item in testObjects)
			{
				yield return compareFunc;
			}
		}

		private static void TestWithComparer(IComparer<long> comparer)
		{
			var testData = _testObjects.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length - 1; itemIdx++)
			{
				_ = comparer.Compare(testData[itemIdx], testData[itemIdx + 1]);
			}
		}

		[Benchmark(Baseline = true)]
		public void Comparer()
		{
			TestWithComparer(_comparer);
		}

		private static void TestWithFunc(Func<long, long, int> compareFunc)
		{
			var testData = _testObjects.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length - 1; itemIdx++)
			{
				_ = compareFunc(testData[itemIdx], testData[itemIdx + 1]);
			}
		}

		[Benchmark]
		public void Func()
		{
			TestWithFunc((x, y) => (x - y) switch
			{
				> 0 => 1,
				< 0 => -1,
				_ => 0
			});
		}

		[Benchmark]
		public void StaticFunc()
		{
			TestWithFunc(static (x, y) => (x - y) switch
					{
						> 0 => 1,
						< 0 => -1,
						_ => 0
					});
		}

		private static void TestWithDelegate<T>(Compare<long> compareFunc)
		{
			var testData = _testObjects.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length - 1; itemIdx++)
			{
				_ = compareFunc(testData[itemIdx], testData[itemIdx + 1]);
			}
		}

		[Benchmark]
		public void Delegate()
		{
			TestWithDelegate<long>((x, y) => (x - y) switch
			{
				> 0 => 1,
				< 0 => -1,
				_ => 0
			});
		}

		[Benchmark]
		public void ListOfFuncs()
		{
			const long x = 2, y = 5;
			var testData = _testListOfFunctions.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var compareFunc = testData[itemIdx];
				_ = compareFunc(x, y);
			}
		}

		[Benchmark]
		public void ListOfLocalFuncs()
		{
			const long x = 2, y = 5;
			var testData = _testListOfLocalFunctions.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var compareFunc = testData[itemIdx];
				_ = compareFunc(x, y);
			}
		}

		[Benchmark]
		public void ListOfComparers()
		{
			const long x = 2, y = 5;
			var testData = _testListOfComparers.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var comparer = testData[itemIdx];
				_ = comparer.Compare(x, y);
			}
		}

		[Benchmark]
		public void ListOfClasses()
		{
			const long x = 2, y = 5;
			var testData = _testListOfClasses.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var comparer = testData[itemIdx];
				_ = comparer.Compare(x, y);
			}
		}

		[Benchmark]
		public void ListOfStructs()
		{
			const long x = 2, y = 5;
			var testData = _testListOfStructs.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var comparer = testData[itemIdx];
				_ = comparer.Compare(x, y);
			}
		}

		[Benchmark]
		public void ListOfBoxedStructs()
		{
			const long x = 2, y = 5;
			var testData = _testListOfBoxedStructs.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var comparer = testData[itemIdx];
				_ = comparer.Compare(x, y);
			}
		}

		[Benchmark]
		public void ListOfUnboxedStructs()
		{
			const long x = 2, y = 5;
			var testData = _testListOfUnboxedStructs<MyComparerStruct<long>, long>().ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var comparer = testData[itemIdx];
				_ = comparer.Compare(x, y);
			}
		}

		[Benchmark]
		public void ListOfUnboxedReadOnlyStructs()
		{
			const long x = 2, y = 5;
			var testData = _testListOfUnboxedStructs<MyComparerReadOnlyStruct<long>, long>().ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var comparer = testData[itemIdx];
				_ = comparer.Compare(x, y);
			}
		}

		[Benchmark]
		public void ListOfDelegates()
		{
			const long x = 2, y = 5;
			var testData = _testListOfDelegates.ToArray();
			for (var itemIdx = 0; itemIdx < testData.Length; itemIdx++)
			{
				var compareDelegate = testData[itemIdx];
				_ = compareDelegate(x, y);
			}
		}
	}
}