nv-view 0.1.0

//! Epoch policy trait and default implementation.

use nv_core::{AffineTransform2D, Duration};

use crate::camera_motion::CameraMotionState;
use crate::provider::MotionReport;
use crate::validity::DegradationReason;
use crate::view_state::ViewState;

/// Decision returned by an [`EpochPolicy`] when camera motion is detected.
#[derive(Clone, Debug)]
pub enum EpochDecision {
    /// No temporal state change. View is continuous despite motion.
    Continue,

    /// Degrade context validity but keep the current epoch.
    Degrade { reason: DegradationReason },

    /// Degrade, but also apply a compensation transform to existing
    /// track positions so they align with the new view.
    Compensate {
        reason: DegradationReason,
        transform: AffineTransform2D,
    },

    /// Full segmentation: increment epoch, close trajectory segments,
    /// notify stages.
    Segment,
}

/// Context passed to [`EpochPolicy::decide`].
pub struct EpochPolicyContext<'a> {
    /// The view state from the previous frame.
    pub previous_view: &'a ViewState,
    /// The motion report for the current frame.
    pub current_report: &'a MotionReport,
    /// The computed motion state for the current frame.
    pub motion_state: CameraMotionState,
    /// How long the camera has been in the current motion state.
    pub state_duration: Duration,
}

/// User-implementable trait: controls the response to detected camera motion.
///
/// The library ships [`DefaultEpochPolicy`] for common threshold-based decisions.
/// Users with complex PTZ deployments can implement custom policies.
pub trait EpochPolicy: Send + Sync + 'static {
    /// Decide what to do in response to detected camera motion.
    fn decide(&self, ctx: &EpochPolicyContext<'_>) -> EpochDecision;
}

/// Default epoch policy based on configurable thresholds.
///
/// Covers the common case: large PTZ jumps → segment, small motions → degrade,
/// high-confidence transforms → compensate.
#[derive(Debug, Clone)]
pub struct DefaultEpochPolicy {
    /// Pan/tilt delta (degrees) above which a PTZ move triggers `Segment`.
    /// Below this, triggers `Degrade`. Default: `15.0`.
    pub segment_angle_threshold: f32,

    /// Zoom ratio change above which a zoom move triggers `Segment`.
    /// Default: `0.3`.
    pub segment_zoom_threshold: f32,

    /// Inferred-motion displacement (normalized coords) above which
    /// triggers `Segment`. Default: `0.25`.
    pub segment_displacement_threshold: f32,

    /// Minimum confidence for a `Compensate` decision (instead of `Segment`)
    /// when a transform is available. Default: `0.8`.
    pub compensate_min_confidence: f32,

    /// If `true`, small motions below segment thresholds produce `Degrade`
    /// instead of `Continue`. Default: `true`.
    pub degrade_on_small_motion: bool,

    /// Minimum PTZ telemetry delta (degrees for pan/tilt, ratio for zoom)
    /// below which changes are treated as sensor noise and ignored.
    /// Prevents floating-point jitter from triggering spurious `Degrade`
    /// events when the camera is at rest. Default: `0.01`.
    pub ptz_deadband: f32,
}

impl Default for DefaultEpochPolicy {
    fn default() -> Self {
        Self {
            segment_angle_threshold: 15.0,
            segment_zoom_threshold: 0.3,
            segment_displacement_threshold: 0.25,
            compensate_min_confidence: 0.8,
            degrade_on_small_motion: true,
            ptz_deadband: 0.01,
        }
    }
}

impl EpochPolicy for DefaultEpochPolicy {
    fn decide(&self, ctx: &EpochPolicyContext<'_>) -> EpochDecision {
        // A preset recall is always a full discontinuity.
        for event in &ctx.current_report.ptz_events {
            if matches!(event, crate::ptz::PtzEvent::PresetRecall { .. }) {
                return EpochDecision::Segment;
            }
        }

        // Check PTZ telemetry for large moves.
        if let (Some(prev_ptz), Some(curr_ptz)) = (
            ctx.previous_view.ptz.as_ref(),
            ctx.current_report.ptz.as_ref(),
        ) {
            let pan_delta = angular_delta(curr_ptz.pan, prev_ptz.pan);
            let tilt_delta = angular_delta(curr_ptz.tilt, prev_ptz.tilt);
            let zoom_delta = (curr_ptz.zoom - prev_ptz.zoom).abs();

            if pan_delta > self.segment_angle_threshold
                || tilt_delta > self.segment_angle_threshold
                || zoom_delta > self.segment_zoom_threshold
            {
                // Check if compensation is possible.
                if let Some(ref transform) = ctx.current_report.frame_transform
                    && transform.confidence >= self.compensate_min_confidence
                {
                    return EpochDecision::Compensate {
                        reason: DegradationReason::PtzMoving,
                        transform: transform.transform,
                    };
                }
                return EpochDecision::Segment;
            }

            if self.degrade_on_small_motion
                && (pan_delta > self.ptz_deadband
                    || tilt_delta > self.ptz_deadband
                    || zoom_delta > self.ptz_deadband)
            {
                return EpochDecision::Degrade {
                    reason: DegradationReason::PtzMoving,
                };
            }
        }

        // Check inferred displacement.
        if let CameraMotionState::Moving {
            displacement: Some(disp),
            ..
        } = &ctx.motion_state
        {
            if *disp > self.segment_displacement_threshold {
                if let Some(ref transform) = ctx.current_report.frame_transform
                    && transform.confidence >= self.compensate_min_confidence
                {
                    return EpochDecision::Compensate {
                        reason: DegradationReason::LargeJump,
                        transform: transform.transform,
                    };
                }
                return EpochDecision::Segment;
            }
            if self.degrade_on_small_motion && *disp > 0.0 {
                return EpochDecision::Degrade {
                    reason: DegradationReason::InferredMotionLowConfidence,
                };
            }
        }

        EpochDecision::Continue
    }
}

/// Compute the shortest angular delta between two angles in degrees,
/// correctly handling wraparound at the 0°/360° boundary.
fn angular_delta(a: f32, b: f32) -> f32 {
    let raw = (a - b).abs();
    raw.min(360.0 - raw)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::ptz::{PtzEvent, PtzTelemetry};
    use crate::transform::{GlobalTransformEstimate, TransformEstimationMethod};
    use crate::view_state::{ViewState, ViewVersion};
    use nv_core::MonotonicTs;

    fn stable_ctx<'a>(prev: &'a ViewState, report: &'a MotionReport) -> EpochPolicyContext<'a> {
        EpochPolicyContext {
            previous_view: prev,
            current_report: report,
            motion_state: CameraMotionState::Stable,
            state_duration: Duration::from_secs(10),
        }
    }

    fn moving_ctx<'a>(
        prev: &'a ViewState,
        report: &'a MotionReport,
        displacement: f32,
    ) -> EpochPolicyContext<'a> {
        EpochPolicyContext {
            previous_view: prev,
            current_report: report,
            motion_state: CameraMotionState::Moving {
                angular_velocity: None,
                displacement: Some(displacement),
            },
            state_duration: Duration::from_secs(1),
        }
    }

    // -- Continue --

    #[test]
    fn stable_camera_continues() {
        let policy = DefaultEpochPolicy::default();
        let prev = ViewState::fixed_initial();
        let report = MotionReport::default();
        let ctx = stable_ctx(&prev, &report);
        assert!(matches!(policy.decide(&ctx), EpochDecision::Continue));
    }

    // -- PTZ thresholds --

    #[test]
    fn large_ptz_pan_segments() {
        let policy = DefaultEpochPolicy::default();
        let mut prev = ViewState::observed_initial();
        prev.ptz = Some(PtzTelemetry {
            pan: 0.0,
            tilt: 0.0,
            zoom: 0.5,
            ts: MonotonicTs::from_nanos(0),
        });
        let report = MotionReport {
            ptz: Some(PtzTelemetry {
                pan: 20.0, // > 15.0 threshold
                tilt: 0.0,
                zoom: 0.5,
                ts: MonotonicTs::from_nanos(33_000_000),
            }),
            ..Default::default()
        };
        let ctx = stable_ctx(&prev, &report);
        assert!(matches!(policy.decide(&ctx), EpochDecision::Segment));
    }

    #[test]
    fn small_ptz_move_degrades() {
        let policy = DefaultEpochPolicy::default();
        let mut prev = ViewState::observed_initial();
        prev.ptz = Some(PtzTelemetry {
            pan: 0.0,
            tilt: 0.0,
            zoom: 0.5,
            ts: MonotonicTs::from_nanos(0),
        });
        let report = MotionReport {
            ptz: Some(PtzTelemetry {
                pan: 2.0, // < 15.0 threshold, > 0
                tilt: 0.0,
                zoom: 0.5,
                ts: MonotonicTs::from_nanos(33_000_000),
            }),
            ..Default::default()
        };
        let ctx = stable_ctx(&prev, &report);
        let d = policy.decide(&ctx);
        assert!(
            matches!(d, EpochDecision::Degrade { .. }),
            "small PTZ move should degrade, got: {d:?}"
        );
    }

    #[test]
    fn large_ptz_with_high_confidence_transform_compensates() {
        let policy = DefaultEpochPolicy::default();
        let mut prev = ViewState::observed_initial();
        prev.ptz = Some(PtzTelemetry {
            pan: 0.0,
            tilt: 0.0,
            zoom: 0.5,
            ts: MonotonicTs::from_nanos(0),
        });
        let report = MotionReport {
            ptz: Some(PtzTelemetry {
                pan: 20.0,
                tilt: 0.0,
                zoom: 0.5,
                ts: MonotonicTs::from_nanos(33_000_000),
            }),
            frame_transform: Some(GlobalTransformEstimate {
                transform: nv_core::AffineTransform2D::IDENTITY,
                confidence: 0.95, // > 0.8 threshold
                method: TransformEstimationMethod::FeatureMatching,
                computed_at: ViewVersion::INITIAL,
            }),
            ..Default::default()
        };
        let ctx = stable_ctx(&prev, &report);
        assert!(matches!(
            policy.decide(&ctx),
            EpochDecision::Compensate { .. }
        ));
    }

    // -- Inferred displacement thresholds --

    #[test]
    fn large_inferred_displacement_segments() {
        let policy = DefaultEpochPolicy::default();
        let prev = ViewState::observed_initial();
        let report = MotionReport::default();
        let ctx = moving_ctx(&prev, &report, 0.3); // > 0.25 threshold
        assert!(matches!(policy.decide(&ctx), EpochDecision::Segment));
    }

    #[test]
    fn small_inferred_displacement_degrades() {
        let policy = DefaultEpochPolicy::default();
        let prev = ViewState::observed_initial();
        let report = MotionReport::default();
        let ctx = moving_ctx(&prev, &report, 0.05); // > 0 but < 0.25
        let d = policy.decide(&ctx);
        assert!(
            matches!(d, EpochDecision::Degrade { .. }),
            "small displacement should degrade, got: {d:?}"
        );
    }

    // -- PTZ events --

    #[test]
    fn preset_recall_event_segments() {
        let policy = DefaultEpochPolicy::default();
        let prev = ViewState::observed_initial();
        let report = MotionReport {
            ptz_events: vec![PtzEvent::PresetRecall {
                preset_id: 3,
                ts: MonotonicTs::from_nanos(100_000),
            }],
            ..Default::default()
        };
        let ctx = stable_ctx(&prev, &report);
        assert!(
            matches!(policy.decide(&ctx), EpochDecision::Segment),
            "preset recall should force segment"
        );
    }

    #[test]
    fn move_start_event_alone_does_not_segment() {
        let policy = DefaultEpochPolicy::default();
        let prev = ViewState::observed_initial();
        let report = MotionReport {
            ptz_events: vec![PtzEvent::MoveStart {
                ts: MonotonicTs::from_nanos(100_000),
            }],
            ..Default::default()
        };
        let ctx = stable_ctx(&prev, &report);
        // MoveStart alone doesn't change telemetry or displacement,
        // so the policy falls through to Continue.
        assert!(matches!(policy.decide(&ctx), EpochDecision::Continue));
    }

    // -- Configuration --

    #[test]
    fn degrade_on_small_motion_can_be_disabled() {
        let policy = DefaultEpochPolicy {
            degrade_on_small_motion: false,
            ..DefaultEpochPolicy::default()
        };
        let prev = ViewState::observed_initial();
        let report = MotionReport::default();
        let ctx = moving_ctx(&prev, &report, 0.05);
        // With degrade disabled, small motion should continue.
        assert!(matches!(policy.decide(&ctx), EpochDecision::Continue));
    }

    #[test]
    fn ptz_jitter_within_deadband_continues() {
        let policy = DefaultEpochPolicy::default();
        let mut prev = ViewState::observed_initial();
        prev.ptz = Some(PtzTelemetry {
            pan: 10.0,
            tilt: 5.0,
            zoom: 0.5,
            ts: MonotonicTs::from_nanos(0),
        });
        let report = MotionReport {
            ptz: Some(PtzTelemetry {
                // Tiny jitter below the 0.01 deadband
                pan: 10.005,
                tilt: 5.003,
                zoom: 0.5002,
                ts: MonotonicTs::from_nanos(33_000_000),
            }),
            ..Default::default()
        };
        let ctx = stable_ctx(&prev, &report);
        assert!(
            matches!(policy.decide(&ctx), EpochDecision::Continue),
            "floating-point jitter within deadband should not degrade"
        );
    }
}