oops i need to commit this too

lib/util/template-parameters.js

@@ -0,0 +1,51 @@
+import {regExpEscape} from './regexp.js';
+
+/**
+ * Created a RegExp that matches an existing empty template parameter with the
+ * given name.
+ */
+const existingEmptyParameterRegExp = paramName =>
+	new RegExp(`^( *\\| *${regExpEscape(paramName)}( *)=) *$`, 'm');
+
+/**
+ * Sets the value of an existing empty parameter.
+ * @param {string} pageContent
+ * @param {string} paramName
+ * @param {string} value
+ * @returns {string | null}
+ */
+export function setEmptyParameter (pageContent, paramName, value) {
+	const regexp = existingEmptyParameterRegExp(paramName)
+	if (pageContent.match(regexp)) {
+		return pageContent.replace(regexp, `$1$2${value}`);
+	}
+	return null;
+}
+
+/**
+ * Creates a RegExp that matches an existing template parameter with the given
+ * name.
+ */
+const existingParameterRegExp = paramName =>
+	new RegExp(`^( *)\\|( *)${regExpEscape(paramName)}( *)=( *).*$`, 'm');
+
+/**
+ * Inserts a new parameter before or after an existing parameter.
+ * @param {string} pageContent
+ * @param {string} existingParamName
+ * @param {'before' | 'after'} location
+ * @param {string} newParamName
+ * @param {string} value
+ * @returns {string | null}
+ */
+export function addParameterBesideExistingParameter (pageContent, newParamName, value, location, existingParamName) {
+	let regexp = existingParameterRegExp(existingParamName);
+	if (pageContent.match(regexp)) {
+		let newParameterPattern = `$1|$2${newParamName}$3=$4${value}`;
+		return pageContent.replace(
+			regexp,
+			location === 'before' ? `${newParameterPattern}\n$&` : `$&\n${newParameterPattern}`
+		);
+	}
+	return null;
+}