FEATURE: Show notice if user can accept an answer (#175)

Implements a a notice that will show for old topics with no accepted
answers.

assets/javascripts/discourse/connectors/topic-navigation/no-answer.hbs

@@ -0,0 +1,6 @@
+{{#if show}}
+  {{#topic-navigation-popup}}
+    <h3>{{i18n "solved.no_answer.title"}}</h3>
+    <p>{{i18n "solved.no_answer.description"}}</p>
+  {{/topic-navigation-popup}}
+{{/if}}

assets/javascripts/discourse/connectors/topic-navigation/no-answer.js.es6

@@ -0,0 +1,40 @@
+import { later } from "@ember/runloop";
+
+// 7 days in milliseconds
+const MAX_DURATION_WITH_NO_ANSWER = 7 * 24 * 60 * 60 * 1000;
+
+export default {
+  setupComponent(args, component) {
+    component.set("show", false);
+
+    later(() => {
+      if (
+        !component.element ||
+        component.isDestroying ||
+        component.isDestroyed
+      ) {
+        return;
+      }
+
+      const topic = args.topic;
+      const currentUser = component.currentUser;
+
+      // show notice if:
+      // - user can accept answer
+      // - it does not have an accepted answer
+      // - topic is old
+      // - topic has at least one reply from another user that can be accepted
+      if (
+        !topic.accepted_answer &&
+        currentUser &&
+        topic.user_id === currentUser.id &&
+        moment() - moment(topic.created_at) > MAX_DURATION_WITH_NO_ANSWER &&
+        topic.postStream.posts.some(
+          (post) => post.user_id !== currentUser.id && post.can_accept_answer
+        )
+      ) {
+        component.set("show", true);
+      }
+    }, 2000);
+  },
+};

config/locales/client.en.yml

@@ -27,6 +27,10 @@ en:
       no_solved_topics_title: "You haven’t solved any topics yet"
       no_solved_topics_body: "When you provide a helpful reply to a topic, your reply might be selected as the solution by the topic owner or staff."
 
+      no_answer:
+        title: Has your question been answered?
+        description: "Highlight the answer and help others by using the solution button below the correct reply."
+
     topic_statuses:
       solved:
         help: "This topic has a solution"