mcdiscordbot/MinecraftDiscordBot/Commands/CommandRouter.cs

using Discord.WebSocket;
using MinecraftDiscordBot.Services;
using System.Reflection;
using System.Text;

namespace MinecraftDiscordBot.Commands;

public abstract class CommandRouter : ICommandHandler<ResponseType> {
    public record struct HandlerStruct(HandleCommandDelegate<ResponseType> Delegate, CommandHandlerAttribute Attribute);
    private readonly Dictionary<string, HandlerStruct> _handlers = new();
    public abstract string HelpTextPrefix { get; }
    public CommandRouter() {
        foreach (var method in GetType().GetMethods())
            if (GetHandlerAttribute(method) is CommandHandlerAttribute attribute)
                try {
                    _handlers.Add(attribute.CommandName, new(method.CreateDelegate<HandleCommandDelegate<ResponseType>>(this), attribute));
                } catch (Exception) {
                    Program.LogWarning("CommandRouter", $"Could not add delegate for method {attribute.CommandName} in function {method.ReturnType} {method.Name}(...)!");
                    throw;
                }
    }

    [CommandHandler("help", HelpText = "Show this help information!")]
    public virtual Task<ResponseType> GetHelpText(SocketUserMessage message, string[] parameters, CancellationToken ct)
        => Task.FromResult(ResponseType.AsString(GenerateHelp()));
    private static CommandHandlerAttribute? GetHandlerAttribute(MethodInfo method)
        => method.GetCustomAttributes(typeof(CommandHandlerAttribute), true).OfType<CommandHandlerAttribute>().FirstOrDefault();
    public virtual Task<ResponseType> RootAnswer(SocketUserMessage message, CancellationToken ct) => GetHelpText(message, Array.Empty<string>(), ct);
    public abstract Task<ResponseType> FallbackHandler(SocketUserMessage message, string method, string[] parameters, CancellationToken ct);
    public Task<ResponseType> HandleCommand(SocketUserMessage message, string[] parameters, CancellationToken ct)
        => parameters is { Length: 0 }
            ? RootAnswer(message, ct)
            : _handlers.TryGetValue(parameters[0], out var handler)
                ? handler.Delegate(message, parameters[1..], ct)
                : FallbackHandler(message, parameters[0], parameters[1..], ct);
    private string GenerateHelp() {
        var sb = new StringBuilder();
        sb.Append("Command usage:");
        foreach (var (name, handler) in _handlers) {
            sb.Append($"\n{HelpTextPrefix}{name}");
            if (handler.Attribute.HelpText is string help)
                sb.Append($": {help}");
        }
        return sb.ToString();
    }
}