feat(command): add CommandContext#commandPrefix (#157)

src/events/command-handler/CorePrefixedMessage.ts

@@ -11,24 +11,31 @@ export class CoreEvent extends Event<Events.PrefixedMessage> {
 	public run(message: Message, prefix: string | RegExp) {
 		const { client, stores } = this.context;
 		// Retrieve the command name and validate:
-		const trimLength = typeof prefix === 'string' ? prefix.length : prefix.exec(message.content)?.[0].length ?? 0;
-		const prefixLess = message.content.slice(trimLength).trim();
+		const commandPrefix = this.getCommandPrefix(message.content, prefix);
+		const prefixLess = message.content.slice(commandPrefix.length).trim();
+
+		// The character that separates the command name from the arguments, this will return -1 when '[p]command' is
+		// passed, and a non -1 value when '[p]command arg' is passed instead.
 		const spaceIndex = prefixLess.indexOf(' ');
-		const name = spaceIndex === -1 ? prefixLess : prefixLess.slice(0, spaceIndex);
-		if (!name) {
+		const commandName = spaceIndex === -1 ? prefixLess : prefixLess.slice(0, spaceIndex);
+		if (!commandName) {
 			client.emit(Events.UnknownCommandName, message, prefix);
 			return;
 		}
 
 		// Retrieve the command and validate:
-		const command = stores.get('commands').get(client.options.caseInsensitiveCommands ? name.toLowerCase() : name);
+		const command = stores.get('commands').get(client.options.caseInsensitiveCommands ? commandName.toLowerCase() : commandName);
 		if (!command) {
-			client.emit(Events.UnknownCommand, message, name, prefix);
+			client.emit(Events.UnknownCommand, message, commandName, prefix);
 			return;
 		}
 
 		// Run the last stage before running the command:
 		const parameters = spaceIndex === -1 ? '' : prefixLess.substr(spaceIndex + 1).trim();
-		client.emit(Events.PreCommandRun, { message, command, parameters, context: { commandName: name, prefix } });
+		client.emit(Events.PreCommandRun, { message, command, parameters, context: { commandName, commandPrefix, prefix } });
+	}
+
+	private getCommandPrefix(content: string, prefix: string | RegExp): string {
+		return typeof prefix === 'string' ? prefix : prefix.exec(content)![0];
 	}
 }

src/lib/structures/Command.ts

@@ -160,7 +160,12 @@ export interface CommandContext extends Record<PropertyKey, unknown> {
 	 */
 	prefix: string | RegExp;
 	/**
-	 * The alias used to run this command
+	 * The alias used to run this command.
 	 */
 	commandName: string;
+	/**
+	 * The matched prefix, this will always be the same as [[CommandContext.prefix]] if it was a string, otherwise it is
+	 * the result of doing `prefix.exec(content)[0]`.
+	 */
+	commandPrefix: string;
 }