// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics;
using System.Runtime.CompilerServices;

namespace System.Text.Encodings.Web
{
    /// <summary>
    /// A lookup map that maps individual ASCII chars to a single byte.
    /// Storing a 0 byte indicates that no mapping exists for this input.
    /// </summary>
    internal unsafe struct AsciiByteMap
    {
        private const int BufferSize = 128;
        private fixed byte Buffer[BufferSize];

        internal void InsertAsciiChar(char key, byte value)
        {
            Debug.Assert(key < BufferSize);
            Debug.Assert(value != 0);

            if (key < BufferSize)
            {
                Buffer[key] = value;
            }
        }

        /// <summary>
        /// Returns false if <paramref name="key"/> is non-ASCII or if it
        /// maps to a zero value.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal readonly bool TryLookup(Rune key, out byte value)
        {
            if (key.IsAscii)
            {
                byte entry = Buffer[(uint)key.Value];
                if (entry != 0)
                {
                    value = entry;
                    return true;
                }
            }

            value = default;
            return false;
        }
    }
}