//! Portable board-support contract for Kaptan.
//!
//! This crate describes logical board identity, sensing capability and
//! outbound data-channel policy. It intentionally has no dependency on an MCU
//! family, peripheral access crate, RTIC, or a runtime framework.

#![no_std]

/// The vertical-sensing data a board support package makes available.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[repr(u8)]
pub enum VerticalSensingKind {
    /// No range or optical-flow data is supported.
    None,
    /// Range data is supported.
    Range,
    /// Coherent range and optical-flow data are supported.
    RangeAndOpticalFlow,
}

/// MAVLink endpoint identity selected by one board support package.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct MavlinkEndpoint {
    /// MAVLink system identifier.
    pub system_id: u8,
    /// MAVLink component identifier.
    pub component_id: u8,
}

/// Fixed outbound data-channel rates driven by a platform service timer.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct DataChannelRates {
    /// Frequency of the timer that calls the data-channel scheduler.
    pub service_hz: usize,
    /// Raw-IMU publication rate.
    pub raw_imu_hz: usize,
    /// Range publication rate. `None` means range is not published.
    pub range_hz: Option<usize>,
    /// Optical-flow publication rate. `None` means flow is not published.
    pub optical_flow_hz: Option<usize>,
    /// Link heartbeat publication rate.
    pub heartbeat_hz: usize,
}

/// Telemetry-only physical-sensor and outbound-data policy.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct TelemetryProfile {
    /// Supported physical vertical-sensing capability.
    pub vertical_sensing: VerticalSensingKind,
    /// Data-channel timer and publication rates.
    pub data_channel: DataChannelRates,
}

/// Exclusive build-time image selection.
///
/// `ExternalControlOnly` remains representable for an explicit validation
/// rejection rather than silently falling back to telemetry.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum BoardProfile {
    /// Physical-sensor telemetry image.
    TelemetryOnly(TelemetryProfile),
    /// Reserved and deliberately unimplemented production authority profile.
    ExternalControlOnly,
}

/// Static board identity and exclusive build-time image configuration.
///
/// The selected platform trait determines the MCU family. Keeping a free-form
/// MCU string here would duplicate that type-level fact without validating it.
///
/// TODO(configuration): board images currently receive this complete profile
/// at build time. Ground-station configuration must stage and validate a
/// whole profile (identity, sensor topology, link rates, actuator profile,
/// and calibration revision) before it is persisted. It must never apply
/// independent field updates or permit an active output while a profile is
/// staged, committed, or restored after power loss.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct BoardConfig {
    /// Stable board name used in build and diagnostic tooling.
    pub name: &'static str,
    /// MAVLink endpoint identity.
    pub mavlink: MavlinkEndpoint,
    /// Exactly one immutable image profile.
    pub profile: BoardProfile,
}

impl BoardConfig {
    /// Returns physical telemetry configuration only for a telemetry image.
    pub const fn telemetry(self) -> Option<TelemetryProfile> {
        match self.profile {
            BoardProfile::TelemetryOnly(profile) => Some(profile),
            BoardProfile::ExternalControlOnly => None,
        }
    }

    /// Validates the selected exclusive profile.
    pub const fn validate(self) -> Result<(), BoardConfigError> {
        match self.profile {
            BoardProfile::TelemetryOnly(profile) => Self::validate_telemetry(profile),
            BoardProfile::ExternalControlOnly => {
                // TODO(flight-config): replace this hard rejection only with a
                // complete runtime and atomic configuration activation. Required
                // inputs are vehicle geometry, calibrated sensors, actuator
                // limits, authenticated MAVLink-v2 authority, persistent replay
                // state, estimator/controller/allocator readiness, and a
                // verified output watchdog.
                Err(BoardConfigError::UnsupportedFlightProfile)
            }
        }
    }

    const fn validate_telemetry(profile: TelemetryProfile) -> Result<(), BoardConfigError> {
        let rates = profile.data_channel;
        if rates.service_hz == 0 {
            return Err(BoardConfigError::ZeroServiceFrequency);
        }
        if rates.raw_imu_hz == 0 || rates.heartbeat_hz == 0 {
            return Err(BoardConfigError::MissingRequiredDataChannel);
        }
        if rates.raw_imu_hz > rates.service_hz || rates.heartbeat_hz > rates.service_hz {
            return Err(BoardConfigError::RateExceedsServiceFrequency);
        }

        let Some(mut scheduled_hz) = rates.raw_imu_hz.checked_add(rates.heartbeat_hz) else {
            return Err(BoardConfigError::DataChannelOvercommitted);
        };
        if let Some(range_hz) = rates.range_hz {
            if range_hz == 0 || range_hz > rates.service_hz {
                return Err(BoardConfigError::RateExceedsServiceFrequency);
            }
            let Some(total) = scheduled_hz.checked_add(range_hz) else {
                return Err(BoardConfigError::DataChannelOvercommitted);
            };
            scheduled_hz = total;
        }
        if let Some(flow_hz) = rates.optical_flow_hz {
            if flow_hz == 0 || flow_hz > rates.service_hz {
                return Err(BoardConfigError::RateExceedsServiceFrequency);
            }
            let Some(total) = scheduled_hz.checked_add(flow_hz) else {
                return Err(BoardConfigError::DataChannelOvercommitted);
            };
            scheduled_hz = total;
        }
        if scheduled_hz > rates.service_hz {
            return Err(BoardConfigError::DataChannelOvercommitted);
        }

        let vertical_schedule_is_valid = match profile.vertical_sensing {
            VerticalSensingKind::None
                if rates.range_hz.is_none() && rates.optical_flow_hz.is_none() =>
            {
                true
            }
            VerticalSensingKind::Range
                if rates.range_hz.is_some() && rates.optical_flow_hz.is_none() =>
            {
                true
            }
            VerticalSensingKind::RangeAndOpticalFlow
                if rates.range_hz.is_some() && rates.optical_flow_hz.is_some() =>
            {
                true
            }
            _ => false,
        };
        if !vertical_schedule_is_valid {
            return Err(BoardConfigError::CapabilityDataChannelMismatch);
        }

        Ok(())
    }
}

/// Invalid board-support configuration.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum BoardConfigError {
    /// A data-channel schedule needs a nonzero service frequency.
    ZeroServiceFrequency,
    /// Raw IMU and heartbeat are mandatory on every flight board.
    MissingRequiredDataChannel,
    /// A configured stream is faster than its service timer.
    RateExceedsServiceFrequency,
    /// The schedule requests more than one frame per service tick.
    DataChannelOvercommitted,
    /// Declared vertical sensing and published streams disagree.
    CapabilityDataChannelMismatch,
    /// The selected operation profile has no complete runtime implementation.
    UnsupportedFlightProfile,
}

#[cfg(test)]
mod tests {
    use super::{
        BoardConfig, BoardConfigError, BoardProfile, DataChannelRates, MavlinkEndpoint,
        TelemetryProfile, VerticalSensingKind,
    };

    const BASE: BoardConfig = BoardConfig {
        name: "test",
        mavlink: MavlinkEndpoint {
            system_id: 1,
            component_id: 1,
        },
        profile: BoardProfile::TelemetryOnly(TelemetryProfile {
            vertical_sensing: VerticalSensingKind::RangeAndOpticalFlow,
            data_channel: DataChannelRates {
                service_hz: 100,
                raw_imu_hz: 20,
                range_hz: Some(20),
                optical_flow_hz: Some(20),
                heartbeat_hz: 2,
            },
        }),
    };

    #[test]
    fn accepts_a_schedulable_range_and_flow_board() {
        assert_eq!(BASE.validate(), Ok(()));
    }

    #[test]
    fn rejects_streams_that_exceed_the_service_budget() {
        let mut config = BASE;
        let BoardProfile::TelemetryOnly(profile) = &mut config.profile else {
            unreachable!();
        };
        profile.data_channel.optical_flow_hz = Some(80);

        assert_eq!(
            config.validate(),
            Err(BoardConfigError::DataChannelOvercommitted)
        );
    }

    #[test]
    fn rejects_capability_and_data_channel_mismatch() {
        let mut config = BASE;
        let BoardProfile::TelemetryOnly(profile) = &mut config.profile else {
            unreachable!();
        };
        profile.vertical_sensing = VerticalSensingKind::Range;

        assert_eq!(
            config.validate(),
            Err(BoardConfigError::CapabilityDataChannelMismatch)
        );
    }

    #[test]
    fn rejects_external_control_until_its_runtime_exists() {
        let mut config = BASE;
        config.profile = BoardProfile::ExternalControlOnly;

        assert_eq!(
            config.validate(),
            Err(BoardConfigError::UnsupportedFlightProfile)
        );
    }
}