From cbce03d550293d63ba13aa785a92773e4372043d Mon Sep 17 00:00:00 2001
From: Nick Exton <NExton@sypaq.com.au>
Date: Wed, 8 Nov 2023 17:04:35 +1100
Subject: [PATCH] GCS_MAVLink: Add FLIGHT_INFORMATION message

---
 libraries/GCS_MAVLink/GCS.h          |  7 ++++
 libraries/GCS_MAVLink/GCS_Common.cpp | 55 ++++++++++++++++++++++++++++
 libraries/GCS_MAVLink/ap_message.h   |  1 +
 3 files changed, 63 insertions(+)

diff --git a/libraries/GCS_MAVLink/GCS.h b/libraries/GCS_MAVLink/GCS.h
index 71725275b3e9ed..5af6e0c1672fbc 100644
--- a/libraries/GCS_MAVLink/GCS.h
+++ b/libraries/GCS_MAVLink/GCS.h
@@ -402,6 +402,13 @@ class GCS_MAVLINK
     void send_uavionix_adsb_out_status() const;
     void send_autopilot_state_for_gimbal_device() const;
 
+    struct {
+        MAV_LANDED_STATE last_landed_state;
+        uint64_t takeoff_time_us;
+    } flight_info;
+
+    void send_flight_information();
+
     // lock a channel, preventing use by MAVLink
     void lock(bool _lock) {
         _locked = _lock;
diff --git a/libraries/GCS_MAVLink/GCS_Common.cpp b/libraries/GCS_MAVLink/GCS_Common.cpp
index 61daff9dc3d299..f3b49273e7de16 100644
--- a/libraries/GCS_MAVLink/GCS_Common.cpp
+++ b/libraries/GCS_MAVLink/GCS_Common.cpp
@@ -5964,6 +5964,56 @@ void GCS_MAVLINK::send_autopilot_state_for_gimbal_device() const
 #endif  // AP_AHRS_ENABLED
 }
 
+void GCS_MAVLINK::send_flight_information()
+{
+    const uint32_t time_boot_us = AP_HAL::millis64();
+
+    // This field is misnamed as `arming_time_utc` in MAVLink. However, it is
+    // not a UTC time, it is the microseconds since boot.
+    const uint64_t arm_time_us = AP::arming().arm_time_us();
+
+    const MAV_LANDED_STATE current_landed_state = landed_state();
+    if (flight_info.last_landed_state != current_landed_state) {
+        switch (current_landed_state) {
+            case MAV_LANDED_STATE_IN_AIR:
+            case MAV_LANDED_STATE_TAKEOFF:
+            case MAV_LANDED_STATE_LANDING: {
+                if (!flight_info.takeoff_time_us) {
+                    flight_info.takeoff_time_us = time_boot_us;
+                }
+                break;
+            }
+
+            case MAV_LANDED_STATE_ON_GROUND: {
+                flight_info.takeoff_time_us = 0;
+                break;
+            }
+
+            case MAV_LANDED_STATE_UNDEFINED:
+            case MAV_LANDED_STATE_ENUM_END: {
+                break;
+            }
+        }
+
+        flight_info.last_landed_state = current_landed_state;
+    }
+
+    // This field is misnamed as `takeoff_time_utc` in MAVLink. However, it is
+    // not a UTC time, it is the microseconds since boot.
+    uint64_t takeoff_time_us = flight_info.takeoff_time_us;
+
+    // This field is misnamed as `flight_uuid` in MAVLink.
+    const uint64_t flight_number = 0;
+
+    mavlink_msg_flight_information_send(
+        chan,
+        time_boot_us,
+        arm_time_us,
+        takeoff_time_us,
+        flight_number
+    );
+}
+
 void GCS_MAVLINK::send_received_message_deprecation_warning(const char * message)
 {
     // we're not expecting very many of these ever, so a tiny bit of
@@ -6395,6 +6445,11 @@ bool GCS_MAVLINK::try_send_message(const enum ap_message id)
         break;
 #endif
 
+    case MSG_FLIGHT_INFORMATION:
+        CHECK_PAYLOAD_SIZE(FLIGHT_INFORMATION);
+        send_flight_information();
+        break;
+
     default:
         // try_send_message must always at some stage return true for
         // a message, or we will attempt to infinitely retry the
diff --git a/libraries/GCS_MAVLink/ap_message.h b/libraries/GCS_MAVLink/ap_message.h
index 4923317266025c..8d1f3d6133a1ac 100644
--- a/libraries/GCS_MAVLink/ap_message.h
+++ b/libraries/GCS_MAVLink/ap_message.h
@@ -97,5 +97,6 @@ enum ap_message : uint8_t {
 #if AP_MAVLINK_MSG_HIGHRES_IMU_ENABLED
     MSG_HIGHRES_IMU,
 #endif
+    MSG_FLIGHT_INFORMATION,
     MSG_LAST // MSG_LAST must be the last entry in this enum
 };