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ui/lib/message/variables.ts

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+import { JINJA_VAR_REGEX } from "./constant";
+import type { Message } from "./message";
+import { MessageRole } from "./types";
+
+/** A map of variable name → user-supplied value */
+export type VariableMap = Record<string, string>;
+
+/**
+ * Extract all unique Jinja2 variable names from a single string.
+ */
+export function extractVariablesFromText(text: string): string[] {
+	const vars = new Set<string>();
+	let match: RegExpExecArray | null;
+	// Reset lastIndex to be safe
+	JINJA_VAR_REGEX.lastIndex = 0;
+	while ((match = JINJA_VAR_REGEX.exec(text)) !== null) {
+		vars.add(match[1]);
+	}
+	return Array.from(vars);
+}
+
+/**
+ * Extract all unique Jinja2 variable names from an array of Messages.
+ * Scans content of every message (system, user, assistant, tool).
+ */
+export function extractVariablesFromMessages(messages: Message[]): string[] {
+	const vars = new Set<string>();
+	for (const msg of messages) {
+		if (msg.role === MessageRole.ASSISTANT || msg.role === MessageRole.TOOL) continue;
+		const content = msg.content;
+		if (!content) continue;
+		for (const v of extractVariablesFromText(content)) {
+			vars.add(v);
+		}
+	}
+	return Array.from(vars);
+}
+
+/**
+ * Replace Jinja2 variables in a string with values from the provided map.
+ * Variables without a value in the map are left untouched.
+ */
+export function replaceVariablesInText(text: string, variables: VariableMap): string {
+	return text.replace(JINJA_VAR_REGEX, (fullMatch, varName: string) => {
+		if (varName in variables && variables[varName] !== "") {
+			return variables[varName];
+		}
+		return fullMatch;
+	});
+}
+
+/**
+ * Create clones of messages with all Jinja2 variables replaced.
+ * Original messages are NOT mutated.
+ */
+export function replaceVariablesInMessages(messages: Message[], variables: VariableMap): Message[] {
+	// Fast path: nothing to replace
+	const hasVars = Object.values(variables).some((v) => v !== "");
+	if (!hasVars) return messages;
+
+	return messages.map((msg) => {
+		const content = msg.content;
+		if (!content || !JINJA_VAR_REGEX.test(content)) {
+			// Reset lastIndex after test
+			JINJA_VAR_REGEX.lastIndex = 0;
+			return msg;
+		}
+		JINJA_VAR_REGEX.lastIndex = 0;
+		const clone = msg.clone();
+		clone.content = replaceVariablesInText(content, variables);
+		return clone;
+	});
+}
+
+/**
+ * Merge existing variable values with a new set of variable names.
+ * - Keeps values for variables that still exist
+ * - Adds empty values for new variables
+ * - Drops variables that no longer exist in messages
+ */
+export function mergeVariables(currentVars: VariableMap, newVarNames: string[]): VariableMap {
+	const merged: VariableMap = {};
+	for (const name of newVarNames) {
+		merged[name] = currentVars[name] ?? "";
+	}
+	return merged;
+}