using System;
    using System.Runtime.InteropServices;
    using System.Text;

    /// <summary>
    /// Quake uses a character set for its strings that is partially ASCII, but also partially nothing standard at all.
    /// Inside the main PAK file is a character atlas texture and in order to print text, each char value inside of a
    /// string is used to index a glyph in this atlas, which is then drawn to the screen.
    ///  
    /// Most strings received from Quake will work fine with the default ANSI charset marshaling, however some mods will
    /// define their own character sets and use byte values >127 to print special characters. This is where the ANSI
    /// marshaler breaks down, as these bytes are interpreted to signify multi-byte characters and result in a String
    /// conversion error. To remedy this, we define our own single-byte character set that reflects the default one from
    /// Quake and decode strings received from the engine by ourselves.
    /// </summary>
    public class QuakeTextMarshaler: ICustomMarshaler
    {
        private static QuakeTextMarshaler instance = null;

        private static readonly char[] CharacterTable =
        {
            '·', ' ', ' ', ' ', ' ', '·', ' ', ' ', ' ', ' ', '\n', ' ', ' ', ' ', '·', '·',
            '[', ']', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '·', ' ', ' ', ' ',
            ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/',
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?',
            '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
            'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_',
            '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
            'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', '←',
            '·', ' ', ' ', ' ', ' ', '·', ' ', ' ', ' ', ' ', '\n', ' ', ' ', ' ', '·', '·',
            '[', ']', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '·', ' ', ' ', ' ',
            ' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/',
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?',
            '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
            'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_',
            '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
            'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', '←',
        };
        
        public IntPtr MarshalManagedToNative(object managedObj)
        {
            if (managedObj == null)
                return IntPtr.Zero;

            if (!(managedObj is string str))
                throw new MarshalDirectiveException("QuakeTextMarshaler must be used on a string.");

            throw new NotImplementedException("QuakeTextMarshaler can only be used to decode text from Quake.");
        }

        public object MarshalNativeToManaged(IntPtr pNativeData)
        {
            byte b;
            
            var sb = new StringBuilder();
            while ((b = Marshal.ReadByte(pNativeData)) != 0)
            {
                sb.Append(CharacterTable[b]);
                pNativeData = IntPtr.Add(pNativeData, 1);
            }

            return sb.ToString();
        }

        public static string GetString(byte[] bytes)
        {
            var sb = new StringBuilder(bytes.Length);
            for (int i = 0; i < bytes.Length; ++i)
            {
                sb.Append(CharacterTable[bytes[i]]);
            }
            return sb.ToString();
        }
        
        public void CleanUpManagedData(object managedObj)
        {
        }

        public void CleanUpNativeData(IntPtr pNativeData)
        {
            // Free HGlobal memory if we decide to implement MarshalManagedToNative
        }

        public int GetNativeDataSize()
        {
            return -1;
        }

        public static ICustomMarshaler GetInstance(string cookie)
        {
            if (instance == null)
                return instance = new QuakeTextMarshaler();

            return instance;
        }
    }