//! `mission_executor` — multirotor + fixed-wing FSMs, geofence, failsafe.
//!
//! AZ-648 lands the variant-aware state machine, the per-transition
//! retry budget, and the broadcast event stream. Subsequent tasks add:
//! - AZ-649 telemetry forwarding (wires real `Telemetry` from `mavlink_layer`)
//! - AZ-650 BIT F9
//! - AZ-651 lost-link ladder
//! - AZ-652 safety + resume + middle-waypoint insert
//!
//! The FSM core is variant-agnostic; per-variant transition tables in
//! [`internal::multirotor`] and [`internal::fixed_wing`] supply the
//! allowed state graph. Each transition is either:
//! - **Pure** — advances when its `Telemetry` guard returns `Ready`;
//!   no driver call is issued.
//! - **Action-bearing** — invokes [`MissionDriver`] (arm, takeoff,
//!   mission upload, set-auto, post-flight sync) and only advances on
//!   `Ok(())`. On `Err` the per-transition retry counter increments;
//!   on cap exhaustion the FSM moves to [`MissionState::Paused`] and
//!   health flips to red.

use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::time::Duration;

use serde::{Deserialize, Serialize};
use tokio::sync::{broadcast, watch, Mutex};
use tokio::task::JoinHandle;
use tokio::time::Instant;

use shared::error::{AutopilotError, Result};
use shared::health::ComponentHealth;
use shared::models::mission::{Coordinate, MissionItem, MissionWaypoint};

mod internal;

pub use internal::battery_thresholds::{
    BatteryAction, BatteryCommandIssuer, BatteryConfig, BatteryDriver, BatteryEvent,
    BatteryMonitor, BatteryMonitorHandle, BatteryOverride, MavlinkBatteryCommandIssuer,
    MAV_CMD_NAV_LAND,
};
pub use internal::bit::{
    BitController, BitControllerConfig, BitControllerHandle, BitDegradedAck, BitEvaluator,
    BitEvent, BitItem, BitItemStatus, BitOverall, BitReport, BitState,
};
pub use internal::bit_evaluators::{
    MapObjectsSyncedEvaluator, MissionLoadedEvaluator, StateDirFreeSpaceEvaluator,
    WallClockBoundEvaluator,
};
pub use internal::driver::{DriverError, MissionDriver};
pub use internal::geofence::{
    GeofenceCommandIssuer, GeofenceDriver, GeofenceEvent, GeofenceMonitor, GeofenceMonitorHandle,
    GeofenceVerdict, MavlinkGeofenceCommandIssuer,
};
pub use internal::lost_link::{
    LadderEvent, LadderInput, LadderOutput, LadderState, LostLinkCommandIssuer, LostLinkConfig,
    LostLinkDriver, LostLinkLadder, LostLinkLadderHandle, MavlinkCommandIssuer,
    MAV_CMD_NAV_RETURN_TO_LAUNCH,
};
pub use internal::middle_waypoint::{MiddleWaypointHint, MissionRePlanner};
pub use internal::post_flight::{MapObjectsDiffSource, MapObjectsPusher, PostFlightPusher};
pub use internal::safety_dispatch::SafetyDispatchHandle;
pub use internal::telemetry::{
    Consumer, DropCountingReceiver, MavlinkProjection, TelemetryForwarder,
};
pub use internal::types::{
    MissionState, StepOutcome, Telemetry, TransitionEvent, TransitionKey, Variant,
};

use internal::fsm::{step_one, FsmCore};

const NAME: &str = "mission_executor";

/// Default per-transition retry budget per AZ-648 §Non-Functional Requirements.
pub const DEFAULT_RETRY_CAP: u32 = 3;

/// Default tick interval. ≤10 ms p99 budget per AZ-648; we tick at 50 Hz
/// so each tick has ample headroom for one driver call.
pub const DEFAULT_TICK: Duration = Duration::from_millis(20);

/// FSM construction parameters.
#[derive(Debug, Clone)]
pub struct MissionExecutorConfig {
    pub variant: Variant,
    /// Multirotor only. Ignored for fixed-wing.
    pub takeoff_altitude_m: f32,
    /// Default = [`DEFAULT_RETRY_CAP`].
    pub retry_cap: u32,
    /// Default = [`DEFAULT_TICK`].
    pub tick_interval: Duration,
    /// Broadcast channel capacity for [`TransitionEvent`]. Consumers
    /// that lag past this fall behind and lose events; transitions
    /// themselves still happen.
    pub event_channel_capacity: usize,
}

impl MissionExecutorConfig {
    pub fn multirotor(takeoff_altitude_m: f32) -> Self {
        Self {
            variant: Variant::Multirotor,
            takeoff_altitude_m,
            retry_cap: DEFAULT_RETRY_CAP,
            tick_interval: DEFAULT_TICK,
            event_channel_capacity: 64,
        }
    }

    pub fn fixed_wing() -> Self {
        Self {
            variant: Variant::FixedWing,
            takeoff_altitude_m: 0.0,
            retry_cap: DEFAULT_RETRY_CAP,
            tick_interval: DEFAULT_TICK,
            event_channel_capacity: 64,
        }
    }
}

// Legacy enums retained for AZ-651 / AZ-652 to consume. Not part of the
// AZ-648 surface but still publicly exported to keep the public crate
// API stable.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum FailsafeKind {
    LinkDegraded,
    LinkLost,
    LinkLostInFollow,
    BatteryRtl,
    BatteryHardFloor,
    GeofenceInclusion,
    GeofenceExclusion,
}

/// Top-level executor. Construct, then call [`MissionExecutor::run`]
/// to spawn the FSM task. The returned [`MissionExecutorHandle`] is
/// the read-side: state, health, transition event subscription.
pub struct MissionExecutor {
    config: MissionExecutorConfig,
}

impl MissionExecutor {
    pub fn new(config: MissionExecutorConfig) -> Self {
        Self { config }
    }

    /// Spawn the FSM driver. Returns a handle to read state and a join
    /// handle for the background task.
    ///
    /// `telemetry_rx` is a `watch::Receiver` so the producer (the
    /// `mavlink_layer` telemetry forwarder per AZ-649) can publish the
    /// latest snapshot without back-pressure. Each tick reads the
    /// current value; missed intermediate updates are intentionally
    /// dropped (the guards are level-triggered).
    pub fn run<D>(
        &self,
        driver: Arc<D>,
        mission: Vec<MissionWaypoint>,
        telemetry_rx: watch::Receiver<Telemetry>,
    ) -> (MissionExecutorHandle, JoinHandle<()>)
    where
        D: MissionDriver + 'static,
    {
        let (events_tx, _events_rx) = broadcast::channel(self.config.event_channel_capacity.max(1));
        let core = FsmCore::new(
            self.config.variant,
            self.config.retry_cap,
            mission,
            events_tx.clone(),
            self.config.takeoff_altitude_m,
        );
        let core = Arc::new(Mutex::new(core));

        let table: &'static [internal::fsm::Transition] = match self.config.variant {
            Variant::Multirotor => internal::multirotor::TABLE,
            Variant::FixedWing => internal::fixed_wing::TABLE,
        };

        let tick = self.config.tick_interval;
        let core_for_task = core.clone();
        let driver_for_task: Arc<dyn MissionDriver> = driver;
        let handle = MissionExecutorHandle {
            core: core.clone(),
            events_tx: events_tx.clone(),
            driver: driver_for_task.clone(),
            hard_floor_active: Arc::new(AtomicBool::new(false)),
        };

        let join = tokio::spawn(async move {
            run_loop(core_for_task, table, driver_for_task, telemetry_rx, tick).await;
        });

        (handle, join)
    }
}

async fn run_loop(
    core: Arc<Mutex<FsmCore>>,
    table: &'static [internal::fsm::Transition],
    driver: Arc<dyn MissionDriver>,
    mut telemetry_rx: watch::Receiver<Telemetry>,
    tick: Duration,
) {
    let mut ticker = tokio::time::interval_at(Instant::now() + tick, tick);
    ticker.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Skip);
    loop {
        ticker.tick().await;
        let telemetry = *telemetry_rx.borrow_and_update();
        let mut guard = core.lock().await;
        let outcome = step_one(&mut guard, table, &telemetry, driver.as_ref()).await;
        let terminal = matches!(
            outcome,
            StepOutcome::AlreadyDone | StepOutcome::Paused { .. }
        );
        drop(guard);
        if terminal {
            return;
        }
    }
}

/// Read-side handle. Clone-safe.
#[derive(Clone)]
pub struct MissionExecutorHandle {
    core: Arc<Mutex<FsmCore>>,
    events_tx: broadcast::Sender<TransitionEvent>,
    /// Driver used by [`insert_middle_waypoint`] and any other
    /// failsafe path that needs to issue a fresh mission upload.
    driver: Arc<dyn MissionDriver>,
    /// Set to `true` once the battery hard floor (15 % default) has
    /// fired. Latched: only the operator-level recovery flow can
    /// clear it. Drives `health()` → red while active.
    hard_floor_active: Arc<AtomicBool>,
}

impl MissionExecutorHandle {
    /// Current FSM state. Cheap (single mutex lock).
    pub async fn state(&self) -> MissionState {
        self.core.lock().await.state
    }

    /// Subscribe to the broadcast stream of [`TransitionEvent`]s.
    /// Each new subscriber starts from the next event published; past
    /// events are not replayed.
    pub fn subscribe(&self) -> broadcast::Receiver<TransitionEvent> {
        self.events_tx.subscribe()
    }

    /// Post-increment retry counter for the given transition.
    pub async fn retry_count(&self, key: TransitionKey) -> u32 {
        self.core.lock().await.retry_count(&key)
    }

    /// Reason the FSM paused, if it is paused.
    pub async fn paused_reason(&self) -> Option<String> {
        self.core.lock().await.paused_reason.clone()
    }

    /// `true` once the battery hard floor (15 % default) has fired.
    /// Drives `health()` → red until cleared via
    /// [`MissionExecutorHandle::clear_hard_floor`].
    pub fn hard_floor_active(&self) -> bool {
        self.hard_floor_active.load(Ordering::Relaxed)
    }

    /// Operator-acknowledged clear of the hard-floor latch. Intended
    /// for ground-test workflows where the battery has been swapped.
    pub fn clear_hard_floor(&self) {
        self.hard_floor_active.store(false, Ordering::Relaxed);
    }

    /// Aggregated health: red when paused or while the battery hard
    /// floor has fired, green when `Done`, yellow otherwise.
    pub async fn health(&self) -> ComponentHealth {
        if self.hard_floor_active() {
            return ComponentHealth::red(NAME, "battery hard floor active");
        }
        let guard = self.core.lock().await;
        match guard.state {
            MissionState::Paused => {
                let reason = guard
                    .paused_reason
                    .clone()
                    .unwrap_or_else(|| "paused".to_string());
                ComponentHealth::red(NAME, reason)
            }
            MissionState::Done => ComponentHealth::green(NAME).with_detail("mission complete"),
            other => ComponentHealth::yellow(NAME, format!("state={other:?}")),
        }
    }

    /// Insert a single middle waypoint immediately after the
    /// currently-active waypoint (or, if the mission has not started
    /// yet, at the head) and re-upload via the driver. Returns once
    /// the airframe has acknowledged the new mission. Strategic
    /// placement decisions (where in geographic space the new
    /// waypoint belongs) are owned by `scan_controller`; this entry
    /// point handles the **mechanics** of patch + re-upload only.
    pub async fn insert_middle_waypoint(&self, at: Coordinate) -> Result<()> {
        let hint = MiddleWaypointHint {
            at,
            // Insert after seq 0 so the airframe still treats seq 0
            // as the rejoin anchor. scan_controller will eventually
            // supply a richer hint via a follow-up surface.
            insert_after_seq: 0,
            label: None,
        };
        let current_mission: Vec<MissionWaypoint> = {
            let guard = self.core.lock().await;
            guard.mission.clone()
        };
        let planner = MissionRePlanner::new(self.driver.clone());
        let patched = planner
            .on_middle_waypoint(hint, &current_mission)
            .await
            .map_err(|e| AutopilotError::Internal(format!("middle-waypoint re-upload: {e}")))?;
        let mut guard = self.core.lock().await;
        guard.mission = patched;
        Ok(())
    }

    /// Apply a failsafe response immediately.
    ///
    /// All non-degraded variants short-circuit `MissionState::FlyMission`
    /// → `MissionState::Land`. The actual MAVLink command
    /// (`MAV_CMD_NAV_RETURN_TO_LAUNCH` or `MAV_CMD_NAV_LAND`) is
    /// issued by the dedicated driver for each failsafe family
    /// (`LostLinkDriver` for `LinkLost*`, `BatteryDriver` for
    /// `BatteryRtl` / `BatteryHardFloor`, `GeofenceDriver` for the
    /// geofence variants). The FSM transition recorded here is the
    /// autopilot's internal accounting of the abort; the airframe
    /// follows the command sent by the driver.
    ///
    /// Earlier states (`Disconnected`, `Connected`, `HealthOk`,
    /// `BitOk`, `Armed`, `TakeOff`, `MissionUploaded`) are NOT
    /// overridden: in those states the airframe's own failsafe and
    /// the driver's command are the right authority.
    ///
    /// Calling this while the FSM is already `Paused` is a no-op.
    pub async fn failsafe_trigger(&self, kind: FailsafeKind) -> Result<()> {
        match kind {
            FailsafeKind::LinkDegraded => {
                // Degraded is yellow-health-only; no transition needed.
                Ok(())
            }
            FailsafeKind::LinkLost
            | FailsafeKind::LinkLostInFollow
            | FailsafeKind::BatteryRtl
            | FailsafeKind::GeofenceInclusion
            | FailsafeKind::GeofenceExclusion => {
                self.transition_flymission_to_land().await;
                Ok(())
            }
            FailsafeKind::BatteryHardFloor => {
                self.hard_floor_active.store(true, Ordering::Relaxed);
                self.transition_flymission_to_land().await;
                Ok(())
            }
        }
    }

    async fn transition_flymission_to_land(&self) {
        let mut core = self.core.lock().await;
        if core.state == MissionState::FlyMission {
            let from = core.state;
            core.state = MissionState::Land;
            let _ = self.events_tx.send(TransitionEvent {
                variant: core.variant,
                from,
                to: MissionState::Land,
                at: chrono::Utc::now(),
                retry_count: 0,
            });
        }
    }

    /// Test-only back-door for forcing FSM state. The FSM normally
    /// advances through telemetry-gated transitions; integration
    /// tests that need to assert failsafe behaviour in a specific
    /// state use this rather than wiring a full transition harness.
    /// Not part of the production API.
    #[doc(hidden)]
    pub async fn force_state_for_tests(&self, state: MissionState) {
        let mut core = self.core.lock().await;
        core.state = state;
    }

    /// Pre-AZ-648 helper kept for callers that only need to validate a
    /// mission shape. The proper start path is [`MissionExecutor::run`].
    pub async fn start(&self, _mission: Vec<MissionItem>) -> Result<()> {
        Err(AutopilotError::NotImplemented(
            "mission_executor::start: use MissionExecutor::run (AZ-648)",
        ))
    }
}

trait HealthDetail {
    fn with_detail(self, detail: impl Into<String>) -> Self;
}

impl HealthDetail for ComponentHealth {
    fn with_detail(mut self, detail: impl Into<String>) -> Self {
        self.detail = Some(detail.into());
        self
    }
}

/// Spawn a task that subscribes to `mavlink_handle.subscribe_inbound()`
/// and republishes every telemetry-bearing message through
/// `forwarder`. Returns the task handle.
///
/// Non-telemetry MAVLink messages (mission protocol, command acks,
/// status text, etc.) are intentionally ignored — they are consumed
/// by other paths inside `mavlink_layer` (`send_command` demux,
/// `mission_client` pull, …).
///
/// `RecvError::Lagged(n)` on the inbound subscription is treated as
/// a hard drop on this side too: we log `n` skipped frames at warn
/// level (the forwarder doesn't even see them) and continue. The
/// forwarder's downstream channels are independent and unaffected.
pub fn spawn_mavlink_pump(
    mavlink_handle: mavlink_layer::MavlinkHandle,
    forwarder: Arc<TelemetryForwarder>,
) -> JoinHandle<()> {
    let mut rx = mavlink_handle.subscribe_inbound();
    tokio::spawn(async move {
        loop {
            match rx.recv().await {
                Ok(inbound) => {
                    if let Some(projection) = MavlinkProjection::from_mavlink(&inbound.message) {
                        forwarder.publish_from_mavlink(&projection);
                    }
                }
                Err(tokio::sync::broadcast::error::RecvError::Lagged(n)) => {
                    tracing::warn!(
                        skipped = n,
                        "mission_executor telemetry pump lagged on mavlink inbound stream"
                    );
                }
                Err(tokio::sync::broadcast::error::RecvError::Closed) => {
                    tracing::info!(
                        "mission_executor telemetry pump: mavlink inbound stream closed"
                    );
                    return;
                }
            }
        }
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use async_trait::async_trait;

    struct NeverCalledDriver;

    #[async_trait]
    impl MissionDriver for NeverCalledDriver {
        async fn arm(&self) -> std::result::Result<(), DriverError> {
            panic!("arm called");
        }
        async fn takeoff(&self, _altitude_m: f32) -> std::result::Result<(), DriverError> {
            panic!("takeoff called");
        }
        async fn upload_mission(
            &self,
            _items: &[MissionWaypoint],
        ) -> std::result::Result<(), DriverError> {
            panic!("upload_mission called");
        }
        async fn set_auto_mode(&self) -> std::result::Result<(), DriverError> {
            panic!("set_auto_mode called");
        }
        async fn post_flight_sync(&self) -> std::result::Result<(), DriverError> {
            panic!("post_flight_sync called");
        }
    }

    #[tokio::test]
    async fn handle_starts_in_disconnected_with_yellow_health() {
        // Arrange
        let exec = MissionExecutor::new(MissionExecutorConfig::multirotor(10.0));
        let (_tx, rx) = watch::channel(Telemetry::default());
        let driver = Arc::new(NeverCalledDriver);

        // Act
        let (handle, join) = exec.run(driver, vec![], rx);

        // Assert
        assert_eq!(handle.state().await, MissionState::Disconnected);
        let health = handle.health().await;
        assert_eq!(health.level, shared::health::HealthLevel::Yellow);

        // Cleanup
        join.abort();
    }
}