食品工場・飲食店のHACCP「毎日の冷蔵庫温度記録」を
紙バインダーから解放するIoTセンサーと3タップ衛生管理

#![forbid(unsafe_code)]

/// Temperature sample represented in milli-degrees Celsius (e.g., 4500 == 4.500 °C)
/// to guarantee deterministic integer arithmetic across edge sensors and servers.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ThermalSample {
    pub sensor_id: u32,
    pub timestamp_sec: u64,
    pub temp_milli_c: i32,
    pub corrective_action_code: u16,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ThermalAlertState {
    NominalWithinSpec,
    TransientDefrostOrDoorOpen { accumulated_degree_minutes: i64 },
    PredictiveBreachWarning { estimated_seconds_to_limit: u64 },
    CriticalSustainedExcursion { accumulated_degree_minutes: i64 },
}

/// Evaluates thermal drift and cumulative degree-minute exposure above `critical_limit_milli_c`.
pub fn evaluate_cold_chain_window(
    samples: &[ThermalSample],
    critical_limit_milli_c: i32,
    max_defrost_degree_minutes: i64,
) -> ThermalAlertState {
    if samples.len() < 2 {
        return ThermalAlertState::NominalWithinSpec;
    }

    let mut degree_minutes_milli: i64 = 0;
    for pair in samples.windows(2) {
        let dt_sec = pair[1].timestamp_sec.saturating_sub(pair[0].timestamp_sec) as i64;
        let excess_0 = (pair[0].temp_milli_c - critical_limit_milli_c).max(0) as i64;
        let excess_1 = (pair[1].temp_milli_c - critical_limit_milli_c).max(0) as i64;
        degree_minutes_milli += ((excess_0 + excess_1) * dt_sec) / 120;
    }

    let prev = samples[samples.len() - 2];
    let curr = samples[samples.len() - 1];
    let dt_sec = curr.timestamp_sec.saturating_sub(prev.timestamp_sec);
    let d_temp_milli = curr.temp_milli_c - prev.temp_milli_c;

    if curr.temp_milli_c > critical_limit_milli_c {
        if degree_minutes_milli > max_defrost_degree_minutes && d_temp_milli >= 0 {
            return ThermalAlertState::CriticalSustainedExcursion {
                accumulated_degree_minutes: degree_minutes_milli,
            };
        }
        return ThermalAlertState::TransientDefrostOrDoorOpen {
            accumulated_degree_minutes: degree_minutes_milli,
        };
    }

    // Predictive check: if temperature is rising rapidly toward critical limit
    if d_temp_milli > 0 && dt_sec > 0 {
        let margin_milli = (critical_limit_milli_c - curr.temp_milli_c).max(0) as u64;
        let est_sec = (margin_milli * dt_sec) / (d_temp_milli as u64);
        if est_sec <= 1500 {
            return ThermalAlertState::PredictiveBreachWarning {
                estimated_seconds_to_limit: est_sec,
            };
        }
    }

    ThermalAlertState::NominalWithinSpec
}

/// Computes a deterministic 64-bit FNV-1a chained audit digest over a sequence of HACCP samples.
pub fn compute_haccp_chain_digest(genesis_seed: u64, samples: &[ThermalSample]) -> u64 {
    const FNV_PRIME: u64 = 0x0000_0100_0000_01B3;
    let mut hash = genesis_seed ^ 0xcbf2_9ce4_8422_2325;

    for s in samples {
        let mut bytes = [0u8; 18];
        bytes[0..4].copy_from_slice(&s.sensor_id.to_le_bytes());
        bytes[4..12].copy_from_slice(&s.timestamp_sec.to_le_bytes());
        bytes[12..16].copy_from_slice(&s.temp_milli_c.to_le_bytes());
        bytes[16..18].copy_from_slice(&s.corrective_action_code.to_le_bytes());
        for &b in &bytes {
            hash ^= b as u64;
            hash = hash.wrapping_mul(FNV_PRIME);
        }
    }
    hash
}