#!/usr/bin/env python3
"""
Precalculate expected values for test_parabolic_orbit.
Simulates a parabolic comet orbiting the Sun for 300 days.
"""

import math
import sys
sys.path.insert(0, "scripts")
from sim_engine import Simulator, vmag, G

def main():
    sim = Simulator("tests/test_parabolic_orbit.toml", dt=60.0)

    comet = sim.get_body("ParabolicComet")
    sun = sim.get_body("Sun")

    # Initial state
    r0 = vmag(comet.global_pos)
    v0 = vmag(comet.global_vel)
    mu = G * sun.mass
    escape_v0 = math.sqrt(2.0 * mu / r0)
    circular_v0 = math.sqrt(mu / r0)

    print(f"// === Initial Conditions (SI units) ===")
    print(f"// Distance: {r0:.6f} m ({r0 / 1.496e11:.6f} AU)")
    print(f"// Velocity: {v0:.6f} m/s ({v0 / 1000.0:.6f} km/s)")
    print(f"// Escape velocity: {escape_v0:.6f} m/s ({escape_v0 / 1000.0:.6f} km/s)")
    print(f"// Circular velocity: {circular_v0:.6f} m/s ({circular_v0 / 1000.0:.6f} km/s)")
    print(f"// Velocity error from escape: {(abs(v0 - escape_v0) / escape_v0) * 100.0:.6f}%")
    print(f"// Eccentricity: {comet.orbit.e:.6f}")
    print()

    # Energy at start (local frame, comet relative to sun)
    KE0 = 0.5 * comet.mass * v0**2
    PE0 = -mu * comet.mass / r0
    E0 = KE0 + PE0

    print(f"// === Energy (Joules) ===")
    print(f"// Initial KE: {KE0:.6e}")
    print(f"// Initial PE: {PE0:.6e}")
    print(f"// Initial total E: {E0:.6e}")
    print()

    # Run simulation for 300 days
    total_seconds = 300.0 * 86400.0
    steps = int(total_seconds / sim.dt)
    print(f"// Total steps: {steps}")
    print()

    for i in range(steps):
        sim._step()

    # Final state
    rf = vmag(comet.global_pos)
    vf = vmag(comet.global_vel)
    KEf = 0.5 * comet.mass * vf**2
    PEf = -mu * comet.mass / rf
    Ef = KEf + PEf

    print()
    print(f"// === Final State (t=300 days) ===")
    print(f"// Distance: {rf:.6f} m ({rf / 1.496e11:.6f} AU)")
    print(f"// Velocity: {vf:.6f} m/s ({vf / 1000.0:.6f} km/s)")
    print(f"// Final KE: {KEf:.6e}")
    print(f"// Final PE: {PEf:.6e}")
    print(f"// Final total E: {Ef:.6e}")
    print()

    # Energy drift
    avg_KE = (KE0 + KEf) / 2.0
    energy_drift = abs(Ef - E0)
    energy_drift_pct = (energy_drift / avg_KE) * 100.0 if avg_KE > 0 else 0.0

    print(f"// === Energy Drift ===")
    print(f"// Absolute drift: {energy_drift:.6e} J")
    print(f"// Drift percent: {energy_drift_pct:.6f}%")
    print()

    # Assertions summary
    print(f"// === Assertions ===")
    print(f"// final_distance ({rf:.2f} m) > initial_distance ({r0:.2f} m): {rf > r0}")
    print(f"// final_velocity ({vf:.2f} m/s) < initial_velocity ({v0:.2f} m/s): {vf < v0}")
    print(f"// E0 >= -1e25: {E0 >= -1e25}")
    print(f"// energy_drift_pct < 1.0: {energy_drift_pct < 1.0}")
    print(f"// final_velocity matches {vf:.6f} m/s: True")

if __name__ == "__main__":
    main()