using System;

using System.Collections.Generic;

public class Program

{

    private static Dictionary<string, string> emojis = new Dictionary<string, string>

    {

        {":panda_face:", "<img src=\"/images/emoji/unicode/1f43c.png\" />"}

    };

​

    private static byte[] emojiParts = new byte[3] { (byte)':', (byte)'_', (byte)':' };

    private static byte[] invalidEmojiParts = new byte[3] { (byte)'_', (byte)':', (byte)'_' };

    private static List<(int startIndex, int endIndex, string match)> matches = new List<(int, int, string)>();

    public static void Main()

    {

        Console.WriteLine("Bio Builder");

        string test = "blahh blahh blahh :panda_face:";

        ParseBio(test);

    }

    public static string ParseBio(string bio)

    {

        //if (bio.Contains(emojis[":panda_face:"]))

        //{

        //  bio = bio.Replace(":panda_face:", emojis[":panda_face:"]);

        //}

        var match = "";

        var startIndex = -1;

        // Find first : then look for _ followed by :

        var p = 0;

        for (var i = 0; i < bio.Length; i++)

        {           

            if (bio[i] == emojiParts[p])

            {

                if(p == 0) {

                    // Start of a matching set

                    startIndex = i;

                    match = "";

                    match += bio[i];

                } else {

                    // Add next match

                    match += bio[i];

                }

                p++;

            }

            else if (bio[i] == invalidEmojiParts[p])

            {

                // Start over

                match = "";

                p = 0;

            } else if(p > 0) {

                // We are iterating over a match but it doesn't match

                match += bio[i];

            }

​

            if (p == emojiParts.Length)

            {               

                var endIndex = i;

                matches.Add((startIndex, endIndex, match));

                // Start over

                p = 0;

            }

        }

​

        Console.WriteLine($"Matches: {matches.Count}");

        foreach(var m in matches){

            Console.WriteLine($"{m.startIndex} {m.endIndex} \t {m.match}");

            if(emojis.ContainsKey(m.Item3)){

                var tag = emojis.GetValueOrDefault(m.Item3);

                var length = m.Item3.Length;

                var index = m.Item1;

                bio = string.Create(bio.Length - length + tag.Length, (bio, index, length, tag),

                        (span, state) =>

                        {

                            state.bio.AsSpan().Slice(0, state.index).CopyTo(span);

                            state.tag.AsSpan().CopyTo(span.Slice(state.index));

                            state.bio.AsSpan().Slice(state.index + state.length).CopyTo(span.Slice(state.index + state.tag.Length));

                        });             

            }

        }

​

        Console.WriteLine($"bio: {bio}");

        return bio;

    }   

}