//! Чистый FSM питания (B03, спека v0.3 §5). Без D-Bus/async/I/O — сервис исполняет `Action`.

use shturman_ipc::types::{IgnitionState, PowerSource, PowerState, ShutdownReason};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Phase {
    Abortable,
    Committed,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum State {
    Off,
    Accessory,
    Running,
    ShuttingDown {
        phase: Phase,
        reason: ShutdownReason,
    },
    Sleep,         // зарезервировано (полные sleep/wake — v1/v2)
    BatteryCutoff, // зарезервировано (long-park — v1/v2)
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Event {
    AccOn,
    AccOff,
    EngineOn,
    EngineOff,
    UnderVoltage,
    ThermalTrip,
    GraceExpired,
    ThermalCleared, // тепло вернулось в норму до PONR → abort thermal-shutdown (гейт reason==Thermal)
    FailsafeCut,    // MCU-авторитетный cut (зависший SoC / истёк hold-up) → off, необратимо
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Action {
    ShutdownImminent(ShutdownReason),
    ShutdownAborted,
    AccChanged(bool),
    StartGrace,
    Commit,
    Cut, // MCU снял питание (fail-safe) — сервис логирует + переходит в off
}

pub struct PowerFsm {
    state: State,
}

impl Default for PowerFsm {
    fn default() -> Self {
        Self {
            state: State::Running,
        }
    }
}

impl PowerFsm {
    pub fn new() -> Self {
        Self::default()
    }
    pub fn state(&self) -> State {
        self.state
    }

    /// D-Bus-проекция состояния (`PowerState`).
    pub fn power_state(&self) -> PowerState {
        match self.state {
            State::Off => PowerState::Off,
            State::Accessory => PowerState::Accessory,
            State::Running => PowerState::Running,
            State::ShuttingDown { .. } => PowerState::ShuttingDown,
            State::Sleep => PowerState::Sleep,
            State::BatteryCutoff => PowerState::BatteryCutoff,
        }
    }
    /// Ось зажигания (канон, B §1).
    pub fn ignition(&self) -> IgnitionState {
        match self.state {
            State::Running => IgnitionState::Running,
            State::Accessory => IgnitionState::Accessory,
            _ => IgnitionState::Off,
        }
    }
    /// Источник питания — сигнал потребителям «времени мало» при shutdown.
    pub fn source(&self) -> PowerSource {
        match self.state {
            State::ShuttingDown {
                reason: ShutdownReason::UnderVoltage,
                ..
            } => PowerSource::LowBattery,
            State::ShuttingDown { .. } => PowerSource::HoldupCap,
            _ => PowerSource::Vehicle12v,
        }
    }

    /// Шаг FSM. Возвращает действия для исполнения сервисом (спека §5).
    pub fn step(&mut self, ev: Event) -> Vec<Action> {
        use Event as E;
        use Phase::*;
        use State::*;
        match (self.state, ev) {
            (Off, E::AccOn) => {
                self.state = Accessory;
                vec![Action::AccChanged(true)]
            }
            (Accessory, E::EngineOn) => {
                self.state = Running;
                vec![]
            }
            (Running, E::EngineOff) => {
                self.state = Accessory;
                vec![]
            }
            // ACC-off: линия ACC сменилась (AccChanged) + старт shutdown.
            (Accessory | Running, E::AccOff) => {
                self.state = ShuttingDown {
                    phase: Abortable,
                    reason: ShutdownReason::AccOff,
                };
                vec![
                    Action::AccChanged(false),
                    Action::ShutdownImminent(ShutdownReason::AccOff),
                    Action::StartGrace,
                ]
            }
            // under-voltage/thermal: ACC не менялся → без AccChanged.
            (Accessory | Running, E::UnderVoltage) => {
                self.begin_shutdown(ShutdownReason::UnderVoltage)
            }
            (Accessory | Running, E::ThermalTrip) => self.begin_shutdown(ShutdownReason::Thermal),
            (
                ShuttingDown {
                    phase: Abortable, ..
                },
                E::AccOn,
            ) => {
                self.state = Running;
                vec![Action::ShutdownAborted, Action::AccChanged(true)]
            }
            (
                ShuttingDown {
                    phase: Abortable,
                    reason,
                },
                E::GraceExpired,
            ) => {
                self.state = ShuttingDown {
                    phase: Committed,
                    reason,
                };
                vec![Action::Commit]
            }
            // тепло вернулось до PONR → abort (только thermal-shutdown; ACC-off/under-voltage — no-op)
            (
                ShuttingDown {
                    phase: Abortable,
                    reason: ShutdownReason::Thermal,
                },
                E::ThermalCleared,
            ) => {
                self.state = Running;
                vec![Action::ShutdownAborted]
            }
            // MCU fail-safe cut → off из любого не-off (необратимо, MCU-авторитет)
            (Off, E::FailsafeCut) => vec![],
            (_, E::FailsafeCut) => {
                self.state = Off;
                vec![Action::Cut]
            }
            // committed/off/sleep/battery_cutoff + всё прочее — no-op (committed не abort-ится)
            _ => vec![],
        }
    }

    fn begin_shutdown(&mut self, reason: ShutdownReason) -> Vec<Action> {
        self.state = State::ShuttingDown {
            phase: Phase::Abortable,
            reason,
        };
        vec![Action::ShutdownImminent(reason), Action::StartGrace]
    }
}

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

    #[test]
    fn off_acc_on_to_accessory() {
        let mut f = PowerFsm { state: State::Off };
        assert_eq!(f.step(Event::AccOn), vec![Action::AccChanged(true)]);
        assert_eq!(f.state(), State::Accessory);
    }

    #[test]
    fn accessory_engine_on_to_running_and_back() {
        let mut f = PowerFsm {
            state: State::Accessory,
        };
        assert_eq!(f.step(Event::EngineOn), vec![]);
        assert_eq!(f.state(), State::Running);
        assert_eq!(f.step(Event::EngineOff), vec![]);
        assert_eq!(f.state(), State::Accessory);
    }

    #[test]
    fn acc_off_begins_abortable_shutdown() {
        let mut f = PowerFsm::new(); // Running
        assert_eq!(
            f.step(Event::AccOff),
            vec![
                Action::AccChanged(false),
                Action::ShutdownImminent(ShutdownReason::AccOff),
                Action::StartGrace
            ]
        );
        assert_eq!(f.power_state(), PowerState::ShuttingDown);
        assert_eq!(f.source(), PowerSource::HoldupCap);
    }

    #[test]
    fn under_voltage_reason_and_source() {
        let mut f = PowerFsm::new();
        let a = f.step(Event::UnderVoltage);
        assert_eq!(a[0], Action::ShutdownImminent(ShutdownReason::UnderVoltage));
        assert_eq!(f.source(), PowerSource::LowBattery);
    }

    #[test]
    fn abort_before_ponr() {
        let mut f = PowerFsm::new();
        f.step(Event::AccOff);
        assert_eq!(
            f.step(Event::AccOn),
            vec![Action::ShutdownAborted, Action::AccChanged(true)]
        );
        assert_eq!(f.state(), State::Running);
    }

    #[test]
    fn grace_expired_commits_and_is_irreversible() {
        let mut f = PowerFsm::new();
        f.step(Event::AccOff);
        assert_eq!(f.step(Event::GraceExpired), vec![Action::Commit]);
        assert_eq!(f.step(Event::AccOn), vec![]); // committed: abort игнорируется
        assert!(matches!(
            f.state(),
            State::ShuttingDown {
                phase: Phase::Committed,
                ..
            }
        ));
    }

    #[test]
    fn reserved_states_noop() {
        let mut f = PowerFsm {
            state: State::Sleep,
        };
        assert_eq!(f.step(Event::AccOn), vec![]);
        assert_eq!(f.state(), State::Sleep);
    }

    #[test]
    fn ignition_projection() {
        assert_eq!(
            PowerFsm {
                state: State::Running
            }
            .ignition(),
            IgnitionState::Running
        );
        assert_eq!(
            PowerFsm {
                state: State::Accessory
            }
            .ignition(),
            IgnitionState::Accessory
        );
        assert_eq!(
            PowerFsm { state: State::Off }.ignition(),
            IgnitionState::Off
        );
    }

    #[test]
    fn thermal_cleared_aborts_only_thermal_abortable() {
        let mut f = PowerFsm::new(); // Running
        f.step(Event::ThermalTrip); // → ShuttingDown{Abortable, Thermal}
        assert_eq!(f.step(Event::ThermalCleared), vec![Action::ShutdownAborted]);
        assert_eq!(f.state(), State::Running);

        // из ACC-off-shutdown ThermalCleared — no-op
        let mut g = PowerFsm::new();
        g.step(Event::AccOff);
        assert_eq!(g.step(Event::ThermalCleared), vec![]);
        assert_eq!(g.power_state(), PowerState::ShuttingDown);
    }

    #[test]
    fn failsafe_cut_forces_off_from_any_nonoff() {
        let mut f = PowerFsm::new(); // Running
        assert_eq!(f.step(Event::FailsafeCut), vec![Action::Cut]);
        assert_eq!(f.state(), State::Off);
        // из off — no-op
        assert_eq!(f.step(Event::FailsafeCut), vec![]);
        // даже из committed (необратимый shutdown) cut уводит в off
        let mut g = PowerFsm::new();
        g.step(Event::AccOff);
        g.step(Event::GraceExpired); // committed
        assert_eq!(g.step(Event::FailsafeCut), vec![Action::Cut]);
        assert_eq!(g.state(), State::Off);
    }
}