/*************************************************************************
 * ModernUO                                                              *
 * Copyright 2019-2023 - ModernUO Development Team                       *
 * Email: hi@modernuo.com                                                *
 * File: TextEncoding.cs                                                 *
 *                                                                       *
 * This program is free software: you can redistribute it and/or modify  *
 * it under the terms of the GNU General Public License as published by  *
 * the Free Software Foundation, either version 3 of the License, or     *
 * (at your option) any later version.                                   *
 *                                                                       *
 * You should have received a copy of the GNU General Public License     *
 * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
 *************************************************************************/

using System;
using System.Runtime.CompilerServices;
using System.Text;

namespace Server.Text;

public static class TextEncoding
{
    private static Encoding m_UTF8, m_Unicode, m_UnicodeLE;

    public static Encoding UTF8 => m_UTF8 ??= new UTF8Encoding(false, false);
    public static Encoding Unicode => m_Unicode ??= new UnicodeEncoding(true, false, false);
    public static Encoding UnicodeLE => m_UnicodeLE ??= new UnicodeEncoding(false, false, false);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesAscii(this string str) => GetBytes(str, Encoding.ASCII);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesBigUni(this string str) => GetBytes(str, Unicode);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesLittleUni(this string str) => GetBytes(str, UnicodeLE);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesUtf8(this string str) => GetBytes(str, UTF8);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesAscii(this ReadOnlySpan<char> str) => GetBytes(str, Encoding.ASCII);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesBigUni(this ReadOnlySpan<char> str) => GetBytes(str, Unicode);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesLittleUni(this ReadOnlySpan<char> str) => GetBytes(str, UnicodeLE);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static byte[] GetBytesUtf8(this ReadOnlySpan<char> str) => GetBytes(str, UTF8);

    // Unlike the one built into the encoder, this avoids local init
    public static byte[] GetBytes(ReadOnlySpan<char> str, Encoding encoding)
    {
        if (str.Length == 0)
        {
            return Array.Empty<byte>();
        }

        var bytes = GC.AllocateUninitializedArray<byte>(encoding.GetByteCount(str));
        encoding.GetBytes(str, bytes);

        return bytes;
    }

    // Unlike the one built into the encoder, this avoids local init
    public static byte[] GetBytes(string str, Encoding encoding)
    {
        if (str.Length == 0)
        {
            return Array.Empty<byte>();
        }

        var bytes = GC.AllocateUninitializedArray<byte>(encoding.GetByteCount(str));
        encoding.GetBytes(str, 0, str.Length, bytes, 0);

        return bytes;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesAscii(this string str, Span<byte> buffer) => Encoding.ASCII.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesAscii(this ReadOnlySpan<char> str, Span<byte> buffer) => Encoding.ASCII.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesBigUni(this string str, Span<byte> buffer) => Unicode.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesBigUni(this ReadOnlySpan<char> str, Span<byte> buffer) => Unicode.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesLittleUni(this string str, Span<byte> buffer) => UnicodeLE.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesLittleUni(this ReadOnlySpan<char> str, Span<byte> buffer) => UnicodeLE.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesUtf8(this string str, Span<byte> buffer) => UTF8.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetBytesUtf8(this ReadOnlySpan<char> str, Span<byte> buffer) => UTF8.GetBytes(str, buffer);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static int GetByteLengthForEncoding(this Encoding encoding) =>
        encoding.BodyName switch
        {
            "utf-16BE" => 2,
            "utf-16"   => 2,
            "utf-32BE" => 3,
            "utf-32"   => 3,
            _          => 1
        };

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static bool IsSafeChar(ushort c) => c is >= 0x20 and < 0xFFFE;

    public static string GetString(ReadOnlySpan<byte> span, Encoding encoding, bool safeString = false)
    {
        string s = encoding.GetString(span);

        if (!safeString)
        {
            return s;
        }

        ReadOnlySpan<char> chars = s.AsSpan();

        using var sb = new ValueStringBuilder(stackalloc char[256]);
        var hasDoneAnyReplacements = false;

        for (int i = 0, last = 0; i < chars.Length; i++)
        {
            if (!IsSafeChar(chars[i]) && i == chars.Length - 1)
            {
                hasDoneAnyReplacements = true;
                sb.Append(chars.Slice(last, i - last));
                last = i + 1; // Skip the unsafe char
            }
        }

        return !hasDoneAnyReplacements ? s : sb.ToString();
    }
}