Added a basic ping command

Signed-off-by: Louis Vallat <louis@louis-vallat.xyz>

src/main/java/xyz/vallat/louis/MovieQuoteBot.java

@@ -4,15 +4,27 @@ import discord4j.core.DiscordClientBuilder;
 import discord4j.core.GatewayDiscordClient;
 import discord4j.core.event.domain.lifecycle.ReadyEvent;
 import discord4j.core.event.domain.message.MessageCreateEvent;
-import discord4j.core.object.entity.Message;
 import discord4j.core.object.entity.User;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import xyz.vallat.louis.commands.Command;
+import xyz.vallat.louis.commands.Ping;
+
+import java.util.HashMap;
+import java.util.Map;
 
 public class MovieQuoteBot {
 
     public static final String DISCORD_TOKEN_ENVIRONMENT = "DISCORD_TOKEN";
+    public static final String PREFIX = "!";
     private static final Logger logger = LoggerFactory.getLogger(MovieQuoteBot.class.getCanonicalName());
+    private static final Map<String, Command> commands = new HashMap<>();
+
+    static {
+        commands.put("ping", new Ping());
+    }
 
     public static void main(String[] args) {
         if (System.getenv(DISCORD_TOKEN_ENVIRONMENT) == null && args.length == 0) {
@@ -31,6 +43,14 @@ public class MovieQuoteBot {
                     logger.info("Logged in as {}#{}.", self.getUsername(), self.getDiscriminator());
                 });
 
+        client.getEventDispatcher().on(MessageCreateEvent.class)
+                .flatMap(event -> Mono.just(event.getMessage().getContent())
+                        .flatMap(content -> Flux.fromIterable(commands.entrySet())
+                                .filter(entry -> content.startsWith(PREFIX + entry.getKey()))
+                                .flatMap(entry -> entry.getValue().execute(event))
+                                .next()))
+                .subscribe();
+
         client.onDisconnect().block();
     }
 

src/main/java/xyz/vallat/louis/commands/Command.java

@@ -0,0 +1,9 @@
+package xyz.vallat.louis.commands;
+
+import discord4j.core.event.domain.message.MessageCreateEvent;
+import reactor.core.publisher.Mono;
+
+public interface Command {
+
+    Mono<Void> execute(MessageCreateEvent event);
+}

src/main/java/xyz/vallat/louis/commands/Ping.java

@@ -0,0 +1,14 @@
+package xyz.vallat.louis.commands;
+
+import discord4j.core.event.domain.message.MessageCreateEvent;
+import reactor.core.publisher.Mono;
+
+public class Ping implements Command {
+
+    @Override
+    public Mono<Void> execute(MessageCreateEvent event) {
+        return event.getMessage().getChannel()
+                .flatMap(channel -> channel.createMessage("Pong!"))
+                .then();
+    }
+}