using System.Globalization;
using System.Text;

namespace IRCTokens;

public static class TagEscape
{
    private static readonly string[] TagUnescaped = ["\\", " ", ";", "\r", "\n"];
    private static readonly string[] TagEscaped = [@"\\", "\\s", "\\:", "\\r", "\\n"];

    /// <summary>Unescape ircv3 tag</summary>
    /// <param name="val">escaped string</param>
    /// <returns>unescaped string</returns>
    public static string Unescape(string val)
    {
        StringBuilder unescaped = new();

        var graphemeIterator = StringInfo.GetTextElementEnumerator(val);
        graphemeIterator.Reset();

        while (graphemeIterator.MoveNext())
        {
            var current = graphemeIterator.GetTextElement();

            if (current == @"\")
            {
                try
                {
                    graphemeIterator.MoveNext();
                    var next = graphemeIterator.GetTextElement();
                    var pair = current + next;
                    unescaped.Append(TagEscaped.Contains(pair)
                        ? TagUnescaped[Array.IndexOf(TagEscaped, pair)]
                        : next);
                }
                catch (InvalidOperationException)
                {
                    // ignored
                }
            }
            else
            {
                unescaped.Append(current);
            }
        }

        return unescaped.ToString();
    }

    /// <summary>Escape strings for use in ircv3 tags</summary>
    /// <param name="val">string to escape</param>
    /// <returns>escaped string</returns>
    public static string Escape(string val)
    {
        StringBuilder sb = new(val);
        for (var i = 0; i < TagUnescaped.Length; ++i)
        {
            sb.Replace(TagUnescaped[i], TagEscaped[i]);
        }

        return sb.ToString();
    }
}