import numpy as np

def altitude_to_pressure(altitude_ft):
    """
    Convert altitude (feet) to pressure (mbar) using ISA model.
    Valid for troposphere (0-36,089 ft) and lower stratosphere (36,089-65,617 ft).
    """
    altitude_m = altitude_ft * 0.3048

    # Sea level constants
    P0 = 1013.25   # mbar
    T0 = 288.15    # K (15C)
    L = 0.0065     # K/m lapse rate (troposphere)
    g = 9.80665    # m/s2
    R = 287.058    # J/(kgK)

    # Tropopause
    h_trop = 11000  # m (36,089 ft)
    P_trop = P0 * (1 - L * h_trop / T0) ** (g / (R * L))
    T_trop = T0 - L * h_trop

    if altitude_m <= h_trop:
        # Troposphere: temperature decreasing with altitude
        P = P0 * (1 - L * altitude_m / T0) ** (g / (R * L))
    else:
        # Lower stratosphere: isothermal
        P = P_trop * np.exp(-g * (altitude_m - h_trop) / (R * T_trop))

    return P

# Test altitude points for DO-160 Cat B (commercial avionics)
DO160_CAT_B_ALTITUDES_FT = [0, 5000, 10000, 20000, 30000, 40000, 50000]
pressures = {alt: altitude_to_pressure(alt) for alt in DO160_CAT_B_ALTITUDES_FT}

for alt, p in pressures.items():
    print(f"{alt:6d} ft -> {p:7.1f} mbar")

class VacuumChamberController:
    def __init__(self, target_altitude_ft, chamber_volume_L=50):
        self.target_pressure_mbar = altitude_to_pressure(target_altitude_ft)
        self.chamber_volume = chamber_volume_L
        self.target_altitude = target_altitude_ft

    def control_step(self, current_pressure_mbar, dt=1.0):
        """
        PID control for vacuum pump and vent valve.
        Returns: pump_speed_pct (0-100), vent_valve_pct (0-100)
        """
        error = current_pressure_mbar - self.target_pressure_mbar

        if error > 50:
            # Far above target: full pump, closed vent
            return 100, 0
        elif error > 10:
            # Close to target: proportional pump
            pump_speed = min(100, error * 2)
            return pump_speed, 0
        elif error < -10:
            # Below target (overshot): open vent valve
            vent_pct = min(50, abs(error) * 2)
            return 0, vent_pct
        else:
            # Within +/-10 mbar: fine control
            pump_speed = max(0, error * 0.5)
            return pump_speed, 0

    def is_stable(self, pressure_history_mbar, window_s=60, 
                  tolerance_mbar=2.0):
        """Check if chamber has reached stable altitude simulation"""
        if len(pressure_history_mbar) < window_s:
            return False
        recent = pressure_history_mbar[-window_s:]
        return (max(recent) - min(recent)) <= tolerance_mbar

# Test logging per MIL-STD-810 Method 500.6
def log_test_data(timestamp, altitude_ft, chamber_pressure_mbar,
                  T_chamber, DUT_functional_status):
    return {
        'timestamp_utc': timestamp,
        'test_altitude_ft': altitude_ft,
        'target_pressure_mbar': altitude_to_pressure(altitude_ft),
        'actual_pressure_mbar': chamber_pressure_mbar,
        'pressure_error_mbar': chamber_pressure_mbar - altitude_to_pressure(altitude_ft),
        'chamber_temp_C': T_chamber,
        'DUT_status': DUT_functional_status,
        'standard': 'MIL-STD-810G Method 500.6 Procedure II'
    }