Add irc.forEachChannelModeUpdate helper

lib/irc.js

@@ -571,3 +571,50 @@ export function getMessageLabel(msg) {
 
 	return null;
 }
+
+export function forEachChannelModeUpdate(msg, isupport, callback) {
+	let chanmodes = isupport.get("CHANMODES") || STD_CHANMODES;
+	let prefix = isupport.get("PREFIX") || "";
+
+	let typeByMode = new Map();
+	let [a, b, c, d] = chanmodes.split(",");
+	Array.from(a).forEach((mode) => typeByMode.set(mode, "A"));
+	Array.from(b).forEach((mode) => typeByMode.set(mode, "B"));
+	Array.from(c).forEach((mode) => typeByMode.set(mode, "C"));
+	Array.from(d).forEach((mode) => typeByMode.set(mode, "D"));
+	parseMembershipModes(prefix).forEach((membership) => typeByMode.set(membership.mode, "B"));
+
+	if (msg.command !== "MODE") {
+		throw new Error("Expected a MODE message");
+	}
+	let change = msg.params[1];
+	let args = msg.params.slice(2);
+
+	let plusMinus = null;
+	let j = 0;
+	for (let i = 0; i < change.length; i++) {
+		if (change[i] === "+" || change[i] === "-") {
+			plusMinus = change[i];
+			continue;
+		}
+		if (!plusMinus) {
+			throw new Error("malformed mode string: missing plus/minus");
+		}
+
+		let mode = change[i];
+		let add = plusMinus === "+";
+
+		let modeType = typeByMode.get(mode);
+		if (!modeType) {
+			continue;
+		}
+
+		let arg = null;
+		if (modeType === "A" || modeType === "B" || (modeType === "C" && add)) {
+			arg = args[j];
+			j++;
+		}
+
+		callback(mode, add, arg);
+	}
+}