PluralKit/PluralKit.Bot/Utils/DiscordUtils.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

using Myriad.Builders;
using Myriad.Extensions;
using Myriad.Gateway;
using Myriad.Rest;
using Myriad.Rest.Types;
using Myriad.Types;

using NodaTime;

using PluralKit.Core;

namespace PluralKit.Bot
{
    public static class DiscordUtils
    {
        public const uint Blue = 0x1f99d8;
        public const uint Green = 0x00cc78;
        public const uint Red = 0xef4b3d;
        public const uint Gray = 0x979c9f;
        
        private static readonly Regex USER_MENTION = new Regex("<@!?(\\d{17,19})>");
        private static readonly Regex ROLE_MENTION = new Regex("<@&(\\d{17,19})>");
        private static readonly Regex EVERYONE_HERE_MENTION = new Regex("@(everyone|here)");

        // Discord uses Khan Academy's simple-markdown library for parsing Markdown,
        // which uses the following regex for link detection: 
        // ^(https?:\/\/[^\s<]+[^<.,:;"')\]\s])
        // Source: https://raw.githubusercontent.com/DJScias/Discord-Datamining/master/2020/2020-07-10/47efb8681861cb7c5ffa.js @ line 20633
        // corresponding to: https://github.com/Khan/simple-markdown/blob/master/src/index.js#L1489
        // I added <? and >? at the start/end; they need to be handled specially later...
        private static readonly Regex UNBROKEN_LINK_REGEX = new Regex("<?(https?:\\/\\/[^\\s<]+[^<.,:;\"')\\]\\s])>?");
        
        public static string NameAndMention(this User user)
        {
            return $"{user.Username}#{user.Discriminator} ({user.Mention()})";
        }
        
        public static Instant SnowflakeToInstant(ulong snowflake) =>
            Instant.FromUtc(2015, 1, 1, 0, 0, 0) + Duration.FromMilliseconds(snowflake >> 22);

        public static ulong InstantToSnowflake(Instant time) =>
            (ulong) (time - Instant.FromUtc(2015, 1, 1, 0, 0, 0)).TotalMilliseconds << 22;
        
        public static async Task CreateReactionsBulk(this DiscordApiClient rest, Message msg, string[] reactions)
        {
            foreach (var reaction in reactions)
            {
                await rest.CreateReaction(msg.ChannelId, msg.Id, new() {Name = reaction});
            }
        }

        public static string WorkaroundForUrlBug(string input)
        {
            // Workaround for https://github.com/DSharpPlus/DSharpPlus/issues/565
            return input?.Replace("%20", "+");
        }
        
        public static uint? ToDiscordColor(this string color)
        {
            if (uint.TryParse(color, NumberStyles.HexNumber, null, out var colorInt))
                return colorInt;
            throw new ArgumentException($"Invalid color string '{color}'.");
        }

        public static bool HasMentionPrefix(string content, ref int argPos, out ulong mentionId)
        {
            mentionId = 0;

            // Roughly ported from Discord.Commands.MessageExtensions.HasMentionPrefix
            if (string.IsNullOrEmpty(content) || content.Length <= 3 || (content[0] != '<' || content[1] != '@'))
                return false;
            int num = content.IndexOf('>');
            if (num == -1 || content.Length < num + 2 || content[num + 1] != ' ' ||
                !TryParseMention(content.Substring(0, num + 1), out mentionId))
                return false;
            argPos = num + 2;
            return true;
        }

        public static bool TryParseMention(this string potentialMention, out ulong id)
        {
            if (ulong.TryParse(potentialMention, out id)) return true;

            var match = USER_MENTION.Match(potentialMention);
            if (match.Success && match.Index == 0 && match.Length == potentialMention.Length)
            {
                id = ulong.Parse(match.Groups[1].Value, NumberStyles.None, CultureInfo.InvariantCulture);
                return true;
            }

            return false;
        }

        public static AllowedMentions ParseMentions(this string input)
        {
            var users = USER_MENTION.Matches(input).Select(x => ulong.Parse(x.Groups[1].Value));
            var roles = ROLE_MENTION.Matches(input).Select(x => ulong.Parse(x.Groups[1].Value));
            var everyone = EVERYONE_HERE_MENTION.IsMatch(input);
            
            return new AllowedMentions
            {
                Users = users.Distinct().ToArray(),
                Roles = roles.Distinct().ToArray(),
                Parse = everyone ? new[] {AllowedMentions.ParseType.Everyone} : null
            };
        }

        public static AllowedMentions RemoveUnmentionableRoles(this AllowedMentions mentions, Guild guild)
        {
            return mentions with {
                Roles = mentions.Roles
                    ?.Where(id => guild.Roles.FirstOrDefault(r => r.Id == id)?.Mentionable == true)
                    .ToArray()
                };
        }

        public static string EscapeMarkdown(this string input)
        {
            Regex pattern = new Regex(@"[*_~>`(||)\\]", RegexOptions.Multiline);
            if (input != null) return pattern.Replace(input, @"\$&");
            else return input;
        }

        public static string EscapeBacktickPair(this string input)
        {
            if (input == null)
                return null;

            // Break all pairs of backticks by placing a ZWNBSP (U+FEFF) between them.
            // Run twice to catch any pairs that are created from the first pass
            var escaped = input
                .Replace("``", "`\ufeff`")
                .Replace("``", "`\ufeff`");

            // Escape the start/end of the string if necessary to better "connect" with other things
            if (escaped.StartsWith("`")) escaped = "\ufeff" + escaped;
            if (escaped.EndsWith("`")) escaped = escaped + "\ufeff";

            return escaped;
        }

        public static string AsCode(this string input)
        {
            // Inline code blocks started with two backticks need to end with two backticks
            // So, surrounding with two backticks, then escaping all backtick pairs makes it impossible(!) to "break out"
            return $"``{EscapeBacktickPair(input)}``";
        }
        
        public static EmbedBuilder WithSimpleLineContent(this EmbedBuilder eb, IEnumerable<string> lines)
        {
            static int CharacterLimit(int pageNumber) =>
                // First chunk goes in description (2048 chars), rest go in embed values (1000 chars)
                pageNumber == 0 ? 2048 : 1000;

            var linesWithEnding = lines.Select(l => $"{l}\n");
            var pages = StringUtils.JoinPages(linesWithEnding, CharacterLimit);

            // Add the first page to the embed description
            if (pages.Count > 0)
                eb.Description(pages[0]);

            // Add the rest to blank-named (\u200B) fields
            for (var i = 1; i < pages.Count; i++)
                eb.Field(new("\u200B", pages[i]));

            return eb;
        }

        public static string BreakLinkEmbeds(this string str) =>
            // Encases URLs in <brackets>
            UNBROKEN_LINK_REGEX.Replace(str, match =>
            {
                // Don't break already-broken links
                // The regex will include the brackets in the match, so we can check for their presence here
                if (match.Value.StartsWith("<") && match.Value.EndsWith(">"))
                    return match.Value;
                return $"<{match.Value}>";
            });

        public static string EventType(this IGatewayEvent evt) => 
            evt.GetType().Name.Replace("Event", "");
    }
}