Misaki.HighPerformance/Misaki.HighPerformance.LowLevel/Collections/FixedString.tt

<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ assembly name="System.Core" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ output extension=".cs" #>
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;

namespace Misaki.HighPerformance.LowLevel.Collections;

<# for (int i = 32; i <= 4096; i *= 2) { #>
/// <summary>
/// Represents a stack allocated fixed-size UTF-8 encoded string of length <#= i #> bytes.
/// </summary>
/// <remarks>
/// This struct is designed to hold data on the stack. Every copy of this struct causes a copy of the underlying data.
/// If you need a heap allocated fixed-size UTF-8 encoded string of length <#= i #> bytes, consider using <see cref="Misaki.HighPerformance.Unsafe.Buffer.FixedString<#= i #>"/>.
/// </remarks>
[StructLayout(LayoutKind.Sequential, Size = <#= i #>)]
public unsafe struct FixedString<#= i #>
{
    private ushort _length;
    private fixed byte _buffer[<#= i - 2 #>];

    public readonly ushort Length => _length;
    public string Value
    {
        get
        {
            fixed (byte* bufferPtr = _buffer)
            {
                return Encoding.UTF8.GetString(bufferPtr, _length);
            }
        }
        set
        {
            if (string.IsNullOrEmpty(value))
            {
                _length = 0;
                return;
            }

            var maxBytes = Encoding.UTF8.GetByteCount(value);
            if (maxBytes > <#= i - 2 #>)
            {
                throw new ArgumentException("Input string is too long to fit in FixedString<#= i #>.");
            }

            fixed (byte* bufferPtr = _buffer)
            {
                _length = (ushort)Encoding.UTF8.GetBytes(value, new Span<byte>(bufferPtr, <#= i - 2 #>));
            }
        }
    }

    public FixedString<#= i #>(ReadOnlySpan<char> input)
    {
        var maxBytes = Encoding.UTF8.GetByteCount(input);
        if (maxBytes > <#= i - 2 #>)
        {
            throw new ArgumentException("Input string is too long to fit in FixedString<#= i #>.");
        }

        fixed (char* inputPtr = input)
        fixed (byte* bufferPtr = _buffer)
        {
            var actualByteCount = Encoding.UTF8.GetBytes(inputPtr, input.Length, bufferPtr, <#= i - 2 #>);
            _length = (ushort)actualByteCount;
        }
    }

    public FixedString<#= i #>(string input)
        : this(input.AsSpan())
    {
    }

    public FixedString<#= i #>(char* input, ushort length)
        : this(new Span<char>(input, length))
    {
    }

    public FixedString<#= i #>(ReadOnlySpan<byte> input)
    {
        if (input.Length > <#= i - 2 #>)
        {
            throw new ArgumentException("Input byte array is too long to fit in FixedString<#= i #>.");
        }

        _length = (ushort)input.Length;

        fixed (byte* inputPtr = input)
        fixed (byte* bufferPtr = _buffer)
        {
            Unsafe.CopyBlockUnaligned(bufferPtr, inputPtr, _length);
        }
    }

    public FixedString<#= i #>(byte* input, ushort length)
        : this(new ReadOnlySpan<byte>(input, length))
    {
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public Span<byte> AsSpan()
    {
        fixed (byte* ptr = _buffer)
        {
            return new(ptr, _length);
        }
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public byte* GetUnsafePointer()
    {
        fixed (byte* ptr = _buffer)
        {
            return ptr;
        }
    }

    public override string ToString()
    {
        return Value;
    }
}

<# } #>