stats: Support fetching StreamCount based on stream_id.

As a preliminary step for including graphs of StreamCount data in our
analytics pages, add API support for fetching the chart data.

Care is taken to limit access to streams that the current user has
access to, which isn't necessary in similar views where the current
user is a server administrator by assumption.

Fixes part of #19653.

Co-authored-by: Tim Abbott <tabbott@zulip.com>

analytics/tests/test_stats_views.py

@@ -6,7 +6,7 @@ from typing_extensions import override
 
 from analytics.lib.counts import COUNT_STATS, CountStat
 from analytics.lib.time_utils import time_range
-from analytics.models import FillState, RealmCount, UserCount
+from analytics.models import FillState, RealmCount, StreamCount, UserCount
 from analytics.views.stats import rewrite_client_arrays, sort_by_totals, sort_client_labels
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.lib.timestamp import ceiling_to_day, ceiling_to_hour, datetime_to_timestamp
@@ -74,6 +74,7 @@ class TestGetChartData(ZulipTestCase):
         super().setUp()
         self.realm = get_realm("zulip")
         self.user = self.example_user("hamlet")
+        self.stream_id = self.get_stream_id(self.get_streams(self.user)[0])
         self.login_user(self.user)
         self.end_times_hour = [
             ceiling_to_hour(self.realm.date_created) + timedelta(hours=i) for i in range(4)
@@ -116,6 +117,17 @@ class TestGetChartData(ZulipTestCase):
             )
             for i, subgroup in enumerate(user_subgroups)
         )
+        StreamCount.objects.bulk_create(
+            StreamCount(
+                property=stat.property,
+                subgroup=subgroup,
+                end_time=insert_time,
+                value=100 + i,
+                stream_id=self.stream_id,
+                realm=self.realm,
+            )
+            for i, subgroup in enumerate(realm_subgroups)
+        )
         FillState.objects.create(property=stat.property, end_time=fill_time, state=FillState.DONE)
 
     def test_number_of_humans(self) -> None:
@@ -252,6 +264,49 @@ class TestGetChartData(ZulipTestCase):
             },
         )
 
+    def test_messages_sent_by_stream(self) -> None:
+        stat = COUNT_STATS["messages_in_stream:is_bot:day"]
+        self.insert_data(stat, ["true", "false"], [])
+
+        result = self.client_get(
+            f"/json/analytics/chart_data/stream/{self.stream_id}",
+            {
+                "chart_name": "messages_sent_by_stream",
+            },
+        )
+        data = self.assert_json_success(result)
+        self.assertEqual(
+            data,
+            {
+                "msg": "",
+                "end_times": [datetime_to_timestamp(dt) for dt in self.end_times_day],
+                "frequency": CountStat.DAY,
+                "everyone": {"bot": self.data(100), "human": self.data(101)},
+                "display_order": None,
+                "result": "success",
+            },
+        )
+
+        result = self.api_get(
+            self.example_user("polonius"),
+            f"/api/v1/analytics/chart_data/stream/{self.stream_id}",
+            {
+                "chart_name": "messages_sent_by_stream",
+            },
+        )
+        self.assert_json_error(result, "Not allowed for guest users")
+
+        # Verify we correctly forbid access to stats of streams in other realms.
+        result = self.api_get(
+            self.mit_user("sipbtest"),
+            f"/api/v1/analytics/chart_data/stream/{self.stream_id}",
+            {
+                "chart_name": "messages_sent_by_stream",
+            },
+            subdomain="zephyr",
+        )
+        self.assert_json_error(result, "Invalid stream ID")
+
     def test_include_empty_subgroups(self) -> None:
         FillState.objects.create(
             property="realm_active_humans::day",