stream_data: Add get_invite_stream_data helper function.

This function unlike `invite_streams()` returns an array of objects having
various info (name, stream_id, invite_only, default_stream) related to
streams rather than an array of names of streams.

frontend_tests/node_tests/stream_data.js

@@ -745,3 +745,44 @@ run_test('edge_cases', () => {
     // just make sure we don't explode
     stream_data.sort_for_stream_settings(bad_stream_ids);
 });
+
+run_test('get_invite_stream_data', () => {
+    // add default stream
+    var orie = {
+        name: 'Orie',
+        stream_id: 320,
+        invite_only: false,
+        subscribed: true,
+    };
+
+    // clear all the data form stream_data, and people
+    stream_data.clear_subscriptions();
+    people.init();
+
+    stream_data.add_sub('Orie', orie);
+    stream_data.set_realm_default_streams([orie]);
+
+    var expected_list = [{
+        name: 'Orie',
+        stream_id: 320,
+        invite_only: false,
+        default_stream: true,
+    }];
+    assert.deepEqual(stream_data.get_invite_stream_data(), expected_list);
+
+    var inviter = {
+        name: 'Inviter',
+        stream_id: 25,
+        invite_only: true,
+        subscribed: true,
+    };
+    stream_data.add_sub('Inviter', inviter);
+
+    expected_list.push({
+        name: 'Inviter',
+        stream_id: 25,
+        invite_only: true,
+        default_stream: false,
+    });
+    assert.deepEqual(stream_data.get_invite_stream_data(), expected_list);
+});

static/js/stream_data.js

@@ -187,6 +187,30 @@ exports.subscribed_streams = function () {
     return _.pluck(exports.subscribed_subs(), 'name');
 };
 
+exports.get_invite_stream_data = function () {
+    var filter_stream_data = function (sub) {
+        return {
+            name: sub.name,
+            stream_id: sub.stream_id,
+            invite_only: sub.invite_only,
+            default_stream: stream_data.get_default_status(sub.name),
+        };
+    };
+    var invite_stream_data = _.map(stream_data.subscribed_subs(), filter_stream_data);
+    var default_stream_data = _.map(page_params.realm_default_streams, filter_stream_data);
+
+    // Since, union doesn't work on array of objects we are using filter
+    var is_included = {};
+    var streams = _.filter(default_stream_data.concat(invite_stream_data), function (sub) {
+        if (is_included[sub.name]) {
+            return false;
+        }
+        is_included[sub.name] = true;
+        return true;
+    });
+    return streams;
+};
+
 exports.invite_streams = function () {
     var invite_list = exports.subscribed_streams();
     var default_list = _.pluck(page_params.realm_default_streams, 'name');