ts: Convert resolved_topic.js to TypeScript.

web/shared/src/resolved_topic.ts

@@ -0,0 +1,45 @@
+/** The canonical form of the resolved-topic prefix. */
+export const RESOLVED_TOPIC_PREFIX = "✔ ";
+
+/**
+ * Pattern for an arbitrary resolved-topic prefix.
+ *
+ * These always begin with the canonical prefix, but can go on longer.
+ */
+// The class has the same characters as RESOLVED_TOPIC_PREFIX.
+// It's designed to remove a weird "✔ ✔✔ " prefix, if present.
+// Compare maybe_send_resolve_topic_notifications in zerver/actions/message_edit.py.
+const RESOLVED_TOPIC_PREFIX_RE = /^✔ [ ✔]*/;
+
+export function is_resolved(topic_name: string): boolean {
+    return topic_name.startsWith(RESOLVED_TOPIC_PREFIX);
+}
+
+export function resolve_name(topic_name: string): string {
+    return RESOLVED_TOPIC_PREFIX + topic_name;
+}
+
+/**
+ * The un-resolved form of this topic name.
+ *
+ * If the topic is already not a resolved topic, this is the identity.
+ */
+export function unresolve_name(topic_name: string): string {
+    return topic_name.replace(RESOLVED_TOPIC_PREFIX_RE, "");
+}
+
+/**
+ * Split the topic name for display, into a "resolved" prefix and remainder.
+ *
+ * The prefix is always the canonical resolved-topic prefix, or empty.
+ *
+ * This function is injective: different topics never produce the same
+ * result, even when `unresolve_name` would give the same result.  That's a
+ * property we want when listing topics in the UI, so that we don't end up
+ * showing what look like several identical topics.
+ */
+export function display_parts(topic_name: string): [string, string] {
+    return is_resolved(topic_name)
+        ? [RESOLVED_TOPIC_PREFIX, topic_name.slice(RESOLVED_TOPIC_PREFIX.length)]
+        : ["", topic_name];
+}