/* SPDX-License-Identifier: Apache-2.0
*
* The OpenSearch Contributors require contributions made to
* this file be licensed under the Apache-2.0 license or a
* compatible open source license.
*/
/*
* Modifications Copyright OpenSearch Contributors. See
* GitHub history for details.
*
*  Licensed to Elasticsearch B.V. under one or more contributor
*  license agreements. See the NOTICE file distributed with
*  this work for additional information regarding copyright
*  ownership. Elasticsearch B.V. licenses this file to you under
*  the Apache License, Version 2.0 (the "License"); you may
*  not use this file except in compliance with the License.
*  You may obtain a copy of the License at
*
* 	http://www.apache.org/licenses/LICENSE-2.0
*
*  Unless required by applicable law or agreed to in writing,
*  software distributed under the License is distributed on an
*  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
*  KIND, either express or implied.  See the License for the
*  specific language governing permissions and limitations
*  under the License.
*/

#region Utf8Json License https://github.com/neuecc/Utf8Json/blob/master/LICENSE
// MIT License
//
// Copyright (c) 2017 Yoshifumi Kawai
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
#endregion

using System;
using System.Runtime.CompilerServices;

namespace OpenSearch.Net.Utf8Json.Internal
{
	internal static class ByteArrayComparer
	{
		private static readonly bool Is32Bit = IntPtr.Size == 4;

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static int GetHashCode(byte[] bytes, int offset, int count)
		{
			if (Is32Bit)
				return unchecked((int)FarmHash.Hash32(bytes, offset, count));

			return unchecked((int)FarmHash.Hash64(bytes, offset, count));
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool Equals(byte[] xs, int xsOffset, int xsCount, byte[] ys) =>
			Equals(xs, xsOffset, xsCount, ys, 0, ys.Length);

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static unsafe bool Equals(byte[] xs, int xsOffset, int xsCount, byte[] ys, int ysOffset, int ysCount)
		{
			if (xs == null || ys == null || xsCount != ysCount)
				return false;

			if (xsCount == 0 && ysCount == 0)
				return true;

			fixed (byte* p1 = &xs[xsOffset])
			fixed (byte* p2 = &ys[ysOffset])
			{
				switch (xsCount)
				{
					case 0:
						return true;
					case 1:
						return *p1 == *p2;
					case 2:
						return *(short*)p1 == *(short*)p2;
					case 3:
						if (*p1 != *p2) return false;
						return *(short*)(p1 + 1) == *(short*)(p2 + 1);
					case 4:
						return *(int*)p1 == *(int*)p2;
					case 5:
						if (*p1 != *p2) return false;
						return *(int*)(p1 + 1) == *(int*)(p2 + 1);
					case 6:
						if (*(short*)p1 != *(short*)p2) return false;
						return *(int*)(p1 + 2) == *(int*)(p2 + 2);
					case 7:
						if (*p1 != *p2) return false;
						if (*(short*)(p1 + 1) != *(short*)(p2 + 1)) return false;
						return *(int*)(p1 + 3) == *(int*)(p2 + 3);
					default:
						{
							var x1 = p1;
							var x2 = p2;

							var xEnd = p1 + xsCount - 8;
							var yEnd = p2 + ysCount - 8;

							while (x1 < xEnd)
							{
								if (*(long*)x1 != *(long*)x2)
								{
									return false;
								}

								x1 += 8;
								x2 += 8;
							}

							return *(long*)xEnd == *(long*)yEnd;
						}
				}
			}
		}
	}
}