#!/usr/bin/env python3
"""Navigation computer of the SS Probably Fine.

Usage: python3 nav.py DESTINATION
       python3 nav.py --list
       python3 nav.py --all
"""

import sys
from collections.abc import Iterator

# Distances between neighboring waypoints, in million km.
DISTANCES = {
    ("earth", "moon"): 0.4,
    ("earth", "gateway"): 0.4,
    ("gateway", "mars"): 225.0,
    ("gateway", "venus"): 41.0,
    ("mars", "phobos"): 0.01,
    ("mars", "deimos"): 0.02,
    ("venus", "mercury"): 48.0,
    ("mars", "ceres"): 265.0,
    ("gateway", "milliways"): 42.0,
    ("ceres", "vesta"): 96.0,
    ("ceres", "europa"): 399.0,
    ("europa", "io"): 0.25,
    ("europa", "ganymede"): 0.4,
    ("ganymede", "callisto"): 0.8,
    ("europa", "titan"): 655.0,
    ("titan", "enceladus"): 1.0,
    ("titan", "pluto"): 4387.0,
}

# Every route starts at Earth.
ROUTES = {
    "moon": ["earth", "moon"],
    "mars": ["earth", "gateway", "mars"],
    "venus": ["earth", "gateway", "venus"],
    "phobos": ["earth", "gateway", "mars", "phobos"],
    "deimos": ["earth", "gateway", "mars", "deimos"],
    "mercury": ["earth", "gateway", "venus", "mercury"],
    "ceres": ["earth", "gateway", "mars", "ceres"],
    "milliways": ["earth", "gateway", "milliways"],
    "vesta": ["earth", "gateway", "mars", "ceres", "vesta"],
    "europa": ["earth", "gateway", "mars", "ceres", "europa"],
    "io": ["earth", "gateway", "mars", "ceres", "europa", "io"],
    "ganymede": ["earth", "gateway", "mars", "ceres", "europa", "ganymede"],
    "callisto": ["earth", "gateway", "mars", "ceres", "europa", "ganymede", "callisto"],
    "titan": ["earth", "gateway", "mars", "ceres", "europa", "titan"],
    "enceladus": ["earth", "gateway", "mars", "ceres", "europa", "titan", "enceladus"],
    "pluto": ["earth", "gateway", "mars", "ceres", "europa", "titan", "pluto"],
}

NAMES = {
    "earth": "Earth",
    "moon": "Moon",
    "gateway": "Lunar Gateway",
    "mars": "Mars",
    "venus": "Venus",
    "phobos": "Phobos",
    "deimos": "Deimos",
    "mercury": "Mercury",
    "ceres": "Ceres",
    "milliways": "Restaurant at the End of the Universe",
    "vesta": "Vesta",
    "europa": "Europa",
    "io": "Io",
    "ganymede": "Ganymede",
    "callisto": "Callisto",
    "titan": "Titan",
    "enceladus": "Enceladus",
    "pluto": "Pluto",
}

CRUISE_SPEED = 0.87  # million km per day
FUEL_PER_MKM = 0.142  # tonnes of fuel per million km
LAUNCH_FUEL = 380.0  # tonnes of fuel to escape Earth's gravity


def distance(a: str, b: str) -> float:
    """Return the distance between two neighboring waypoints."""
    if (a, b) in DISTANCES:
        return DISTANCES[(a, b)]
    return DISTANCES[(b, a)]


def legs(route: list[str]) -> Iterator[tuple[str, str]]:
    """Yield the legs (pairs of consecutive waypoints) of a route."""
    for i in range(1, len(route) - 1):
        yield route[i], route[i + 1]


def plot_course(destination: str) -> tuple[list[str], float, float, float]:
    """Return route, distance, travel time (days) and fuel (t)."""
    route = ROUTES[destination]
    total = 0.0
    fuel = 0.0
    for start, end in legs(route):
        d = distance(start, end)
        total += d
        fuel += d * FUEL_PER_MKM
        if start == "earth":
            fuel += LAUNCH_FUEL
    return route, total, total / CRUISE_SPEED, fuel


def asteroid_route(belt: str) -> list[str]:
    """Return a route through the asteroid belt (currently: via Ceres)."""
    return ROUTES["ceres"] + [belt]


def print_plan(destination: str) -> None:
    """Print the flight plan for a destination."""
    route, total, days, fuel = plot_course(destination)
    print("Route: " + " -> ".join(NAMES[w] for w in route))
    print(f"Distance: {total:.1f} million km")
    print(f"Travel time: {round(days)} days")
    print(f"Fuel required: {round(fuel)} t")


def main() -> None:
    if len(sys.argv) != 2:
        sys.exit(__doc__)
    if sys.argv[1] == "--list":
        for key in sorted(ROUTES):
            print(f"{key:12} {NAMES[key]}")
        return
    if sys.argv[1] == "--all":
        for key in sorted(ROUTES):
            print_plan(key)
            print()
        return
    destination = sys.argv[1].lower()
    if destination not in ROUTES:
        known = ", ".join(sorted(ROUTES))
        sys.exit(f"Unknown destination: {destination} (known: {known})")
    print_plan(destination)


if __name__ == "__main__":
    main()