# Exercise 2: choose a characteristic among neighbours, then identify lights from stopwatch readings.
NEIGHBOURS = {"Fl(2) W 10s": ("Fl", 2, 10), "Fl W 8s": ("Fl", 1, 8), "Oc W 6s": ("Oc", 1, 6)}
CANDIDATES = {"Fl(3) W 15s": ("Fl", 3, 15), "Fl W 10s": ("Fl", 1, 10), "Fl(2) W 12s": ("Fl", 2, 12),
              "Oc W 6s": ("Oc", 1, 6), "Fl W 3s": ("Fl", 1, 3), "Iso W 8s": ("Iso", 1, 8)}
FLASH_S = 1

def passes_rules(cls, n, period):
    if cls in ("Iso", "Oc"):
        return True
    if n == 1:
        return 2 <= period <= 15 and period - FLASH_S >= 3 * FLASH_S
    return period <= (20 if n == 2 else 30)

def confusable(a, b):
    return a[0] == b[0] and a[1] == b[1] and abs(a[2] - b[2]) < 3

# Part 1: test each candidate against the rules and the neighbours.
for name, c in CANDIDATES.items():
    clashes = [nb for nb, v in NEIGHBOURS.items() if confusable(c, v)]
    print(name, "| rules:", passes_rules(*c), "| clashes:", clashes or "none", "->", "ok" if passes_rules(*c) and not clashes else "reject")

# Part 2: identify a light from flash start times (seconds).
def identify(starts):
    gaps = [round(b - a, 1) for a, b in zip(starts, starts[1:])]
    if len(set(gaps)) == 1:
        return 1, gaps[0]
    long_gap = max(gaps)
    first = gaps.index(long_gap)
    second = gaps.index(long_gap, first + 1)
    return second - first, round(sum(gaps[first:second]), 1)

WATCHES = {
    "A": [1.0, 6.0, 11.0, 16.0, 21.0, 26.0],
    "B": [2.0, 4.0, 14.0, 16.0, 26.0, 28.0, 38.0],
    "C": [0.0, 2.0, 4.0, 15.0, 17.0, 19.0, 30.0],
}
for name, starts in WATCHES.items():
    n, period = identify(starts)
    print("watch", name, "-> flashes per group", n, "| period", period, "s")

# Part 3: the shortest watch that can show two full periods of the slowest candidate.
slowest = max(c[2] for c in CANDIDATES.values())
print("slowest candidate period:", slowest, "s; two full periods:", 2 * slowest, "s")
# Fl(3) W 15s | rules: True | clashes: none -> ok
# Fl W 10s | rules: True | clashes: ['Fl W 8s'] -> reject
# Fl(2) W 12s | rules: True | clashes: ['Fl(2) W 10s'] -> reject
# Oc W 6s | rules: True | clashes: ['Oc W 6s'] -> reject
# Fl W 3s | rules: False | clashes: none -> reject
# Iso W 8s | rules: True | clashes: none -> ok
# watch A -> flashes per group 1 | period 5.0 s
# watch B -> flashes per group 2 | period 12.0 s
# watch C -> flashes per group 3 | period 15.0 s
# slowest candidate period: 15 s; two full periods: 30 s