namespace AIStudio.Chat;

public static class StringExtensions
{
    /// <param name="text">The text.</param>
    extension(string text)
    {
        public string RemoveThinkTags()
        {
            const string OPEN_TAG = "<think>";
            const string CLOSE_TAG = "</think>";
            if (string.IsNullOrWhiteSpace(text) || !text.StartsWith(OPEN_TAG, StringComparison.Ordinal))
                return text;
        
            var endIndex = text.IndexOf(CLOSE_TAG, StringComparison.Ordinal);
            if (endIndex == -1)
                return string.Empty;
        
            return text[(endIndex + CLOSE_TAG.Length)..];
        }

        /// <summary>
        /// Shortens a text to the given number of characters, and marks the cut with three dots.
        /// </summary>
        /// <remarks>
        /// Never cuts between the two halves of a surrogate pair, which no JSON writer takes.<br/><br/>
        /// Takes and returns a string rather than a span on purpose: most texts are short enough, and
        /// those come back as the very same instance. Only a text which is cut costs one new string.
        /// </remarks>
        /// <param name="maxCharacters">How many characters of the text to keep at most, the dots not counted.</param>
        /// <returns>The text as it was when it is short enough, otherwise its beginning followed by three dots.</returns>
        public string Shorten(int maxCharacters)
        {
            if (text.Length <= maxCharacters)
                return text;

            var end = char.IsHighSurrogate(text[maxCharacters - 1]) ? maxCharacters - 1 : maxCharacters;
            return string.Concat(text.AsSpan(0, end).TrimEnd(), "...");
        }
    }
}