[MM-23264] Get channel member counts by group (#14068)

* MM-23264 Add api endpoint for get groups with members in channel

Add store tests

Add tests for api func

Gofmt

Apply changes from code review

* MM-23264 Make store layers

* MM-23264 Check read permission on channel member counts

* Trigger CI

api4/channel.go

@@ -44,6 +44,7 @@ func (api *API) InitChannel() {
 	api.BaseRoutes.Channel.Handle("/pinned", api.ApiSessionRequired(getPinnedPosts)).Methods("GET")
 	api.BaseRoutes.Channel.Handle("/timezones", api.ApiSessionRequired(getChannelMembersTimezones)).Methods("GET")
 	api.BaseRoutes.Channel.Handle("/members_minus_group_members", api.ApiSessionRequired(channelMembersMinusGroupMembers)).Methods("GET")
+	api.BaseRoutes.Channel.Handle("/member_counts_by_group", api.ApiSessionRequired(channelMemberCountsByGroup)).Methods("GET")
 
 	api.BaseRoutes.ChannelForUser.Handle("/unread", api.ApiSessionRequired(getChannelUnread)).Methods("GET")
 
@@ -1639,6 +1640,39 @@ func channelMembersMinusGroupMembers(c *Context, w http.ResponseWriter, r *http.
 	w.Write(b)
 }
 
+func channelMemberCountsByGroup(c *Context, w http.ResponseWriter, r *http.Request) {
+	if c.App.License() == nil {
+		c.Err = model.NewAppError("Api4.channelMemberCountsByGroup", "api.channel.channel_member_counts_by_group.license.error", nil, "", http.StatusNotImplemented)
+		return
+	}
+
+	c.RequireChannelId()
+	if c.Err != nil {
+		return
+	}
+
+	if !c.App.SessionHasPermissionToChannel(*c.App.Session(), c.Params.ChannelId, model.PERMISSION_READ_CHANNEL) {
+		c.SetPermissionError(model.PERMISSION_READ_CHANNEL)
+		return
+	}
+
+	includeTimezones := r.URL.Query().Get("include_timezones") == "true"
+
+	channelMemberCounts, err := c.App.Srv().Store.Channel().GetMemberCountsByGroup(c.Params.ChannelId, includeTimezones)
+	if err != nil {
+		c.Err = err
+		return
+	}
+
+	b, marshalErr := json.Marshal(channelMemberCounts)
+	if marshalErr != nil {
+		c.Err = model.NewAppError("Api4.channelMemberCountsByGroup", "api.marshal_error", nil, marshalErr.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	w.Write(b)
+}
+
 func getChannelModerations(c *Context, w http.ResponseWriter, r *http.Request) {
 	if c.App.License() == nil {
 		c.Err = model.NewAppError("Api4.GetChannelModerations", "api.channel.get_channel_moderations.license.error", nil, "", http.StatusNotImplemented)