PluralKit/PluralKit.Bot/Proxy/ProxyMatcher.cs

using NodaTime;

using PluralKit.Core;

namespace PluralKit.Bot;

public class ProxyMatcher
{
    private static readonly char AutoproxyEscapeCharacter = '\\';
    public static readonly Duration DefaultLatchExpiryTime = Duration.FromHours(6);

    private readonly IClock _clock;
    private readonly ProxyTagParser _parser;

    public ProxyMatcher(ProxyTagParser parser, IClock clock)
    {
        _parser = parser;
        _clock = clock;
    }

    public bool TryMatch(MessageContext ctx, IReadOnlyCollection<ProxyMember> members, out ProxyMatch match,
                         string messageContent,
                         bool hasAttachments, bool allowAutoproxy)
    {
        if (TryMatchTags(members, messageContent, hasAttachments, out match)) return true;
        if (allowAutoproxy && TryMatchAutoproxy(ctx, members, messageContent, out match)) return true;
        return false;
    }

    private bool TryMatchTags(IReadOnlyCollection<ProxyMember> members, string messageContent, bool hasAttachments,
                              out ProxyMatch match)
    {
        if (!_parser.TryMatch(members, messageContent, out match)) return false;

        // Edge case: If we got a match with blank inner text, we'd normally just send w/ attachments
        // However, if there are no attachments, the user probably intended something else, so we "un-match" and proceed to autoproxy
        return hasAttachments || match.Content.Trim().Length > 0;
    }

    private bool TryMatchAutoproxy(MessageContext ctx, IReadOnlyCollection<ProxyMember> members,
                                   string messageContent,
                                   out ProxyMatch match)
    {
        match = default;

        // Skip autoproxy match if we hit the escape character
        if (messageContent.StartsWith(AutoproxyEscapeCharacter))
            throw new ProxyService.ProxyChecksFailedException(
                "This message matches none of your proxy tags, and it was not autoproxied because it starts with a backslash (`\\`).");

        // Find the member we should autoproxy (null if none)
        var member = ctx.AutoproxyMode switch
        {
            AutoproxyMode.Member when ctx.AutoproxyMember != null =>
                members.FirstOrDefault(m => m.Id == ctx.AutoproxyMember),

            AutoproxyMode.Front when ctx.LastSwitchMembers.Length > 0 =>
                members.FirstOrDefault(m => m.Id == ctx.LastSwitchMembers[0]),

            AutoproxyMode.Latch when ctx.LastMessageMember != null =>
                members.FirstOrDefault(m => m.Id == ctx.LastMessageMember.Value),

            _ => null
        };
        // Throw an error if the member is null, message varies depending on autoproxy mode
        if (member == null)
        {
            if (ctx.AutoproxyMode == AutoproxyMode.Front)
                throw new ProxyService.ProxyChecksFailedException(
                    "You are using autoproxy front, but no members are currently registered as fronting. Please use `pk;switch <member>` to log a new switch.");
            if (ctx.AutoproxyMode == AutoproxyMode.Member)
                throw new ProxyService.ProxyChecksFailedException(
                    "You are using member-specific autoproxy with an invalid member. Was this member deleted?");
            if (ctx.AutoproxyMode == AutoproxyMode.Latch)
                throw new ProxyService.ProxyChecksFailedException(
                    "You are using autoproxy latch, but have not sent any messages yet in this server. Please send a message using proxy tags first.");
            throw new ProxyService.ProxyChecksFailedException(
                "This message matches none of your proxy tags and autoproxy is not enabled.");
        }

        if (ctx.AutoproxyMode != AutoproxyMode.Member && !member.AllowAutoproxy)
            throw new ProxyService.ProxyChecksFailedException(
                "This member has autoproxy disabled. To enable it, use `pk;m <member> autoproxy on`.");

        // Moved the IsLatchExpired() check to here, so that an expired latch and a latch without any previous messages throw different errors
        if (ctx.AutoproxyMode == AutoproxyMode.Latch && IsLatchExpired(ctx))
            throw new ProxyService.ProxyChecksFailedException(
                "Latch-mode autoproxy has timed out. Please send a new message using proxy tags.");

        match = new ProxyMatch
        {
            Content = messageContent,
            Member = member,

            // We're autoproxying, so not using any proxy tags here
            // we just find the first pair of tags (if any), otherwise null
            ProxyTags = member.ProxyTags.FirstOrDefault()
        };
        return true;
    }

    private bool IsLatchExpired(MessageContext ctx)
    {
        if (ctx.LastMessage == null) return true;
        if (ctx.LatchTimeout == 0) return false;

        var timeout = ctx.LatchTimeout.HasValue
            ? Duration.FromSeconds(ctx.LatchTimeout.Value)
            : DefaultLatchExpiryTime;

        var timestamp = DiscordUtils.SnowflakeToInstant(ctx.LastMessage.Value);
        return _clock.GetCurrentInstant() - timestamp > timeout;
    }
}