canic-core 0.95.1

//! Module: workflow::runtime::timer::control
//!
//! Responsibility: arbitrate one timer identity without platform side effects.
//! Does not own: task execution, IC timer handles, domain work, or persistence.
//! Boundary: the timer workflow applies these deterministic actions to TimerOps.

use thiserror::Error;

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(super) enum TimerRegistration {
    Unregistered,
    Scheduled { generation: u64, deadline_ns: u64 },
    Running { generation: u64 },
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum PendingCommand {
    Cancel { sequence: u64 },
    Schedule { sequence: u64, deadline_ns: u64 },
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(super) enum TimerControlAction {
    None,
    Arm { generation: u64, deadline_ns: u64 },
    Replace { generation: u64, deadline_ns: u64 },
    Clear,
    Disarm { cancelled: bool },
}

#[derive(Clone, Copy, Debug, Eq, Error, PartialEq)]
pub(super) enum TimerControlError {
    #[error("timer request sequence exhausted")]
    RequestSequenceExhausted,
    #[error("timer generation exhausted")]
    GenerationExhausted,
    #[error("timer completion does not own the running generation")]
    StaleCompletion,
}

#[derive(Debug)]
pub(super) struct TimerControl {
    generation: u64,
    request_sequence: u64,
    registration: TimerRegistration,
    pending: Option<PendingCommand>,
}

impl Default for TimerControl {
    fn default() -> Self {
        Self {
            generation: 0,
            request_sequence: 0,
            registration: TimerRegistration::Unregistered,
            pending: None,
        }
    }
}

impl TimerControl {
    pub(super) const fn generation(&self) -> u64 {
        self.generation
    }

    pub(super) const fn registration(&self) -> TimerRegistration {
        self.registration
    }

    pub(super) fn schedule(
        &mut self,
        deadline_ns: u64,
    ) -> Result<TimerControlAction, TimerControlError> {
        let sequence = self.next_request_sequence()?;

        match self.registration {
            TimerRegistration::Unregistered => {
                let generation = self.next_generation()?;
                self.request_sequence = sequence;
                self.generation = generation;
                self.registration = TimerRegistration::Scheduled {
                    generation,
                    deadline_ns,
                };
                Ok(TimerControlAction::Arm {
                    generation,
                    deadline_ns,
                })
            }
            TimerRegistration::Scheduled {
                deadline_ns: current_deadline,
                ..
            } if deadline_ns < current_deadline => {
                let generation = self.next_generation()?;
                self.request_sequence = sequence;
                self.generation = generation;
                self.registration = TimerRegistration::Scheduled {
                    generation,
                    deadline_ns,
                };
                Ok(TimerControlAction::Replace {
                    generation,
                    deadline_ns,
                })
            }
            TimerRegistration::Scheduled { .. } => {
                self.request_sequence = sequence;
                Ok(TimerControlAction::None)
            }
            TimerRegistration::Running { .. } => {
                self.request_sequence = sequence;
                self.pending = Some(match self.pending {
                    Some(PendingCommand::Schedule {
                        deadline_ns: current_deadline,
                        ..
                    }) => PendingCommand::Schedule {
                        sequence,
                        deadline_ns: current_deadline.min(deadline_ns),
                    },
                    Some(PendingCommand::Cancel { .. }) | None => PendingCommand::Schedule {
                        sequence,
                        deadline_ns,
                    },
                });
                Ok(TimerControlAction::None)
            }
        }
    }

    pub(super) fn cancel(&mut self) -> Result<TimerControlAction, TimerControlError> {
        let sequence = self.next_request_sequence()?;

        match self.registration {
            TimerRegistration::Unregistered => {
                self.request_sequence = sequence;
                Ok(TimerControlAction::None)
            }
            TimerRegistration::Scheduled { .. } => {
                let generation = self.next_generation()?;
                self.request_sequence = sequence;
                self.generation = generation;
                self.registration = TimerRegistration::Unregistered;
                self.pending = None;
                Ok(TimerControlAction::Clear)
            }
            TimerRegistration::Running { .. } => {
                self.request_sequence = sequence;
                self.pending = Some(PendingCommand::Cancel { sequence });
                Ok(TimerControlAction::None)
            }
        }
    }

    pub(super) const fn begin(&mut self, generation: u64) -> bool {
        match self.registration {
            TimerRegistration::Scheduled {
                generation: scheduled_generation,
                ..
            } if scheduled_generation == generation => {
                self.registration = TimerRegistration::Running { generation };
                true
            }
            TimerRegistration::Unregistered
            | TimerRegistration::Scheduled { .. }
            | TimerRegistration::Running { .. } => false,
        }
    }

    pub(super) fn complete(
        &mut self,
        generation: u64,
        directive_deadline_ns: Option<u64>,
    ) -> Result<TimerControlAction, TimerControlError> {
        if self.registration != (TimerRegistration::Running { generation }) {
            return Err(TimerControlError::StaleCompletion);
        }

        let pending = self.pending;
        let (deadline_ns, cancelled) = match pending {
            Some(PendingCommand::Cancel { .. }) => (None, true),
            Some(PendingCommand::Schedule { deadline_ns, .. }) => (
                Some(
                    directive_deadline_ns
                        .map_or(deadline_ns, |directive| directive.min(deadline_ns)),
                ),
                false,
            ),
            None => (directive_deadline_ns, false),
        };

        let next_generation = if deadline_ns.is_some() {
            Some(self.next_generation()?)
        } else {
            None
        };

        self.pending = None;
        if let (Some(deadline_ns), Some(next_generation)) = (deadline_ns, next_generation) {
            self.generation = next_generation;
            self.registration = TimerRegistration::Scheduled {
                generation: next_generation,
                deadline_ns,
            };
            Ok(TimerControlAction::Arm {
                generation: next_generation,
                deadline_ns,
            })
        } else {
            self.registration = TimerRegistration::Unregistered;
            Ok(TimerControlAction::Disarm { cancelled })
        }
    }

    fn next_generation(&self) -> Result<u64, TimerControlError> {
        self.generation
            .checked_add(1)
            .ok_or(TimerControlError::GenerationExhausted)
    }

    fn next_request_sequence(&self) -> Result<u64, TimerControlError> {
        self.request_sequence
            .checked_add(1)
            .ok_or(TimerControlError::RequestSequenceExhausted)
    }
}

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

    fn arm(control: &mut TimerControl, deadline_ns: u64) -> u64 {
        let TimerControlAction::Arm { generation, .. } = control
            .schedule(deadline_ns)
            .expect("initial schedule should succeed")
        else {
            panic!("initial schedule should arm")
        };
        generation
    }

    #[test]
    fn duplicate_and_later_schedules_keep_one_earliest_handle() {
        let mut control = TimerControl::default();
        assert_eq!(arm(&mut control, 100), 1);
        assert_eq!(control.schedule(100), Ok(TimerControlAction::None));
        assert_eq!(control.schedule(200), Ok(TimerControlAction::None));
        assert_eq!(
            control.registration(),
            TimerRegistration::Scheduled {
                generation: 1,
                deadline_ns: 100
            }
        );
    }

    #[test]
    fn earlier_schedule_replaces_and_invalidates_the_old_generation() {
        let mut control = TimerControl::default();
        let old_generation = arm(&mut control, 100);
        assert_eq!(
            control.schedule(50),
            Ok(TimerControlAction::Replace {
                generation: 2,
                deadline_ns: 50
            })
        );
        assert!(!control.begin(old_generation));
        assert!(control.begin(2));
    }

    #[test]
    fn schedule_while_running_waits_and_survives_callback_stop() {
        let mut control = TimerControl::default();
        let generation = arm(&mut control, 100);
        assert!(control.begin(generation));
        assert_eq!(control.schedule(90), Ok(TimerControlAction::None));
        assert_eq!(
            control.complete(generation, None),
            Ok(TimerControlAction::Arm {
                generation: 2,
                deadline_ns: 90
            })
        );
    }

    #[test]
    fn running_schedules_merge_to_the_earliest_deadline() {
        let mut control = TimerControl::default();
        let generation = arm(&mut control, 100);
        assert!(control.begin(generation));
        assert_eq!(control.schedule(80), Ok(TimerControlAction::None));
        assert_eq!(control.schedule(70), Ok(TimerControlAction::None));
        assert_eq!(control.schedule(90), Ok(TimerControlAction::None));
        assert_eq!(
            control.complete(generation, Some(75)),
            Ok(TimerControlAction::Arm {
                generation: 2,
                deadline_ns: 70
            })
        );
    }

    #[test]
    fn later_cancel_suppresses_callback_rearm() {
        let mut control = TimerControl::default();
        let generation = arm(&mut control, 100);
        assert!(control.begin(generation));
        assert_eq!(control.schedule(80), Ok(TimerControlAction::None));
        assert_eq!(control.cancel(), Ok(TimerControlAction::None));
        assert_eq!(
            control.complete(generation, Some(75)),
            Ok(TimerControlAction::Disarm { cancelled: true })
        );
    }

    #[test]
    fn schedule_after_cancel_reenables_only_after_completion() {
        let mut control = TimerControl::default();
        let generation = arm(&mut control, 100);
        assert!(control.begin(generation));
        assert_eq!(control.cancel(), Ok(TimerControlAction::None));
        assert_eq!(control.schedule(90), Ok(TimerControlAction::None));
        assert_eq!(
            control.complete(generation, Some(95)),
            Ok(TimerControlAction::Arm {
                generation: 2,
                deadline_ns: 90
            })
        );
    }

    #[test]
    fn scheduled_cancel_invalidates_the_consumed_generation() {
        let mut control = TimerControl::default();
        let generation = arm(&mut control, 100);
        assert_eq!(control.cancel(), Ok(TimerControlAction::Clear));
        assert!(!control.begin(generation));
        assert_eq!(control.generation(), 2);
        assert_eq!(control.registration(), TimerRegistration::Unregistered);
    }

    #[test]
    fn exhausted_request_sequence_fails_without_mutating_registration() {
        let mut control = TimerControl {
            request_sequence: u64::MAX,
            ..TimerControl::default()
        };

        assert_eq!(
            control.schedule(100),
            Err(TimerControlError::RequestSequenceExhausted)
        );
        assert_eq!(control.registration(), TimerRegistration::Unregistered);
    }

    #[test]
    fn exhausted_generation_fails_without_replacing_the_current_handle() {
        let mut control = TimerControl {
            generation: u64::MAX,
            registration: TimerRegistration::Scheduled {
                generation: u64::MAX,
                deadline_ns: 100,
            },
            ..TimerControl::default()
        };

        assert_eq!(
            control.schedule(50),
            Err(TimerControlError::GenerationExhausted)
        );
        assert_eq!(
            control.registration(),
            TimerRegistration::Scheduled {
                generation: u64::MAX,
                deadline_ns: 100
            }
        );
    }
}