/*
 * Copyright (c) Gustave Monce and Contributors
 * 
 * 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.
 */
using System.Diagnostics.CodeAnalysis;

namespace Img2Ffu.Writer.Flashing
{
    public readonly struct ByteArrayKey
    {
        public readonly byte[] Bytes;
        private readonly int _hashCode;

        public override bool Equals(object obj)
        {
            ByteArrayKey other = (ByteArrayKey)obj;
            return Compare(Bytes, other.Bytes);
        }

        public override int GetHashCode()
        {
            return _hashCode;
        }

        private static int GetHashCode([NotNull] Memory<byte> bytes)
        {
            unchecked
            {
                int hash = 17;
                for (int i = 0; i < bytes.Length; i++)
                {
                    hash = (hash * 23) + bytes.Span[i];
                }
                return hash;
            }
        }

        public ByteArrayKey(byte[] bytes)
        {
            Bytes = bytes;
            _hashCode = GetHashCode(bytes);
        }

        public static ByteArrayKey Create(byte[] bytes)
        {
            return new ByteArrayKey(bytes);
        }

        public static unsafe bool Compare(byte[] a1, byte[] a2)
        {
            if (a1 == null || a2 == null || a1.Length != a2.Length)
            {
                return false;
            }

            fixed (byte* p1 = a1, p2 = a2)
            {
                byte* x1 = p1, x2 = p2;
                int l = a1.Length;
                for (int i = 0; i < l / 8; i++, x1 += 8, x2 += 8)
                {
                    if (*(long*)x1 != *(long*)x2)
                    {
                        return false;
                    }
                }

                if ((l & 4) != 0)
                {
                    if (*(int*)x1 != *(int*)x2)
                    {
                        return false;
                    }

                    x1 += 4;
                    x2 += 4;
                }
                if ((l & 2) != 0)
                {
                    if (*(short*)x1 != *(short*)x2)
                    {
                        return false;
                    }

                    x1 += 2;
                    x2 += 2;
                }
                if ((l & 1) != 0)
                {
                    if (*x1 != *x2)
                    {
                        return false;
                    }
                }

                return true;
            }
        }

        public static bool operator ==(ByteArrayKey left, ByteArrayKey right)
        {
            return left.Equals(right);
        }

        public static bool operator !=(ByteArrayKey left, ByteArrayKey right)
        {
            return !(left == right);
        }
    }
}