GCS_MAVLink: add support for more MISSION_CURRENT fields

- a state so someone can see if the mission is complete
 - total number of waypoints

libraries/GCS_MAVLink/GCS.h

@@ -323,6 +323,12 @@ public:
     // mission item index to be sent on queued msg, delayed or not
     uint16_t mission_item_reached_index = AP_MISSION_CMD_INDEX_NONE;
 
+    // generate a MISSION_STATE enumeration value for where the
+    // mission is up to:
+    MISSION_STATE mission_state(const class AP_Mission &mission) const;
+    // send a mission_current message for the supplied waypoint
+    void send_mission_current(const class AP_Mission &mission, uint16_t seq);
+
     // common send functions
     void send_heartbeat(void) const;
     void send_meminfo(void);

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -613,7 +613,46 @@ void GCS_MAVLINK::handle_mission_request(const mavlink_message_t &msg)
         prot->handle_mission_request(*this, packet, msg);
 }
 
+// returns a MISSION_STATE numeration value best describing out
+// current mission state.
+MISSION_STATE GCS_MAVLINK::mission_state(const AP_Mission &mission) const
+{
+    if (mission.num_commands() < 2) {  // 1 means just home is present
+        return MISSION_STATE_NO_MISSION;
+    }
+    switch (mission.state()) {
+    case AP_Mission::mission_state::MISSION_STOPPED:
+        return MISSION_STATE_NOT_STARTED;
+    case AP_Mission::mission_state::MISSION_RUNNING:
+        return MISSION_STATE_ACTIVE;
+    case AP_Mission::mission_state::MISSION_COMPLETE:
+        return MISSION_STATE_COMPLETE;
+    }
+
+    // compiler ensures we can't get here as no default case in above enumeration
+
+    return MISSION_STATE_UNKNOWN;
+}
+
 #if AP_MAVLINK_MISSION_SET_CURRENT_ENABLED
+void GCS_MAVLINK::send_mission_current(const class AP_Mission &mission, uint16_t seq)
+{
+    auto num_commands = mission.num_commands();
+    if (num_commands > 0) {
+        // exclude home location from the count; see message definition.
+        num_commands -= 1;
+    }
+
+    const uint8_t mission_mode = AP::vehicle()->current_mode_requires_mission() ? 1 : 0;
+
+    mavlink_msg_mission_current_send(
+        chan,
+        seq,
+        num_commands, // total
+        mission_state(mission), // mission_state
+        mission_mode);  // mission_mode
+}
+
 /*
   handle a MISSION_SET_CURRENT mavlink packet
 
@@ -642,7 +681,7 @@ void GCS_MAVLINK::handle_mission_set_current(AP_Mission &mission, const mavlink_
         // exactly that sequence number in it, even if ArduPilot never
         // actually holds that as a sequence number (e.g. packet.seq==0).
         if (HAVE_PAYLOAD_SPACE(chan, MISSION_CURRENT)) {
-            mavlink_msg_mission_current_send(chan, packet.seq);
+            send_mission_current(mission, packet.seq);
         } else {
             // schedule it for later:
             send_message(MSG_CURRENT_WAYPOINT);
@@ -5116,7 +5155,7 @@ bool GCS_MAVLINK::try_send_mission_message(const enum ap_message id)
         CHECK_PAYLOAD_SIZE(MISSION_CURRENT);
         AP_Mission *mission = AP::mission();
         if (mission != nullptr) {
-            mavlink_msg_mission_current_send(chan, mission->get_current_nav_index());
+            send_mission_current(*mission, mission->get_current_nav_index());
         }
         break;
     }