using System;

using System.Text;

using System.Globalization;

using System.Collections.Generic;

​

public static class ColumnNameUtilsV2

{

    private const string Escape = "x_";

​

    public static string EncodeColumnName(string input)

    {

        if (input == "")

        {

            return input;

        }

​

        var data = input.ToLowerInvariant();

​

        // If the string is a CrateDB reserved keyword then escape first character and return

        if (Reserved.Contains(data))

        {

            return Escape + ((int)(byte)data[0]).ToString("X2") + data.Substring(1);

        }

        // Escape escape sequences

        data = data.Replace(Escape, Escape + ((int)(byte)Escape[0]).ToString("X2") + Escape.Substring(1), StringComparison.InvariantCultureIgnoreCase);

​

        if (data[0] == '_')

        {

            data = Escape + ((int)(byte)data[0]).ToString("X2") + data.Substring(1);

        }

​

        var utf8Bytes = Encoding.UTF8.GetBytes(data);

​

        var result = new StringBuilder(data.Length);

​

        // Escape illegal characters

        foreach (var b in utf8Bytes)

        {

            char c = (char)b;

            if (c is >= 'a' and <= 'z' or >= 'A' and <= 'Z' or >= '0' and <= '9' or '_')

            {

                result.Append(c);

            }

            else

            {

                result.Append(Escape).Append(((int)b).ToString("X2"));

            }

        }

​

        return result.ToString();

    }

​

    public static string DecodeColumnName(string input)

    {

        if (input == "")

        {

            return input;

        }

​

        var data = Encoding.UTF8.GetBytes(input.ToLowerInvariant());

        var result = new byte[data.Length];

        int j = 0;

        for (int i = 0; i < data.Length - 1; i++)

        {

            if ((char)data[i] == char.ToLower(Escape[0]) && (char)data[i + 1] == char.ToLower(Escape[1]))

            {

                _ = byte.TryParse(input.AsSpan(i + 2, 2), NumberStyles.HexNumber, null, out var byteValue);

                result[j++] = byteValue;

                i += 3;

            }

            else

            {

                result[j++] = data[i];

            }

        }

​

        result[j++] = data[^1];

​

        return Encoding.UTF8.GetString(result.AsSpan(0, j));

    }

    public static void Main()

    {

        var str = "geo_ox_n";

        var encoded = ColumnNameUtilsV2.EncodeColumnName(str);

        var decoded = ColumnNameUtilsV2.DecodeColumnName(encoded);

        Console.WriteLine("escape:  " + Escape);

        Console.WriteLine("input:   " + str);

        Console.WriteLine("encoded: " + encoded);

        Console.WriteLine("decoded: " + decoded);

    }

​

    private static readonly HashSet<string> Reserved = new(){

        "add", "all", "alter", "and", "any", "array", "as", "asc", "between", "by", "called", "case", "cast", "column",

        "constraint", "costs", "create", "cross", "current_date", "current_schema", "current_time", "current_timestamp",

        "current_user", "default", "delete", "deny", "desc", "describe", "directory", "distinct", "drop", "else", "end",

        "escape", "except", "exists", "extract", "false", "first", "for", "from", "full", "function", "grant", "group",

        "having", "if", "in", "index", "inner", "input", "insert", "intersect", "into", "is", "join", "last", "left",

        "like", "limit", "match", "natural", "not", "null", "nulls", "object", "offset", "on", "or", "order", "outer",

        "persistent", "recursive", "reset", "returns", "revoke", "right", "select", "session_user", "set", "some",

        "stratify", "table", "then", "transient", "true", "try_cast", "unbounded", "union", "update", "user", "using",

        "when", "where", "with",

    };

}