# How Lighthouses Work 5, Exercise 1: classify a light from timed observations
# Each observation is a list of (state, seconds) for one full repeat of the pattern: L = light, D = dark.
def classify(segs):
    period = sum(d for _, d in segs)
    lights = [d for s, d in segs if s == "L"]
    darks = [d for s, d in segs if s == "D"]
    n = len(lights)
    if len(set(lights)) > 1:
        kind = "Mo"           # two clearly different durations of light
    elif n == 1:
        light, dark = lights[0], darks[0]
        if light == dark:
            kind = "Iso"
        elif light > dark:
            kind = "Oc"
        elif light >= 2:
            kind = "LFl"
        else:
            kind = "Fl"
    else:
        kind = "Fl(%d)" % n
    return kind, period

OBS = {
    "A": [("L", 1), ("D", 4)],
    "B": [("L", 3), ("D", 1)],
    "C": [("L", 2), ("D", 2)],
    "D": [("L", 1), ("D", 1), ("L", 1), ("D", 1), ("L", 1), ("D", 6)],
    "E": [("L", 1), ("D", 1), ("L", 3), ("D", 7)],
    "F": [("L", 3), ("D", 9)],
}
for name, segs in OBS.items():
    kind, period = classify(segs)
    light_share = sum(d for s, d in segs if s == "L") / period
    print(name, kind, period, "s", round(light_share, 2))
# Check against the rule for a single flash (darkness at least 3 times the flash)
flash, dark = 1, 4
print("A dark/flash ratio:", dark / flash, "ok" if dark >= 3 * flash else "too short")

# Output:
# A Fl 5 s 0.2
# B Oc 4 s 0.75
# C Iso 4 s 0.5
# D Fl(3) 11 s 0.27
# E Mo 12 s 0.33
# F LFl 12 s 0.25
# A dark/flash ratio: 4.0 ok
#
# The classifier uses the definitions in the Wikipedia article on light characteristics: equal light and dark
# is isophase, light longer than dark is occulting, a single light of 2 seconds or more is long flashing, several
# lights per period is a group flash, and two clearly different durations of light is Morse. A is a plain flash
# (Fl) every 5 s with 4 s of darkness, four times the flash, so it passes the "at least three times" rule. B is
# occulting (3 s of light, 1 s dark), C is isophase (2 s and 2 s), D is a group of three flashes every 11 s,
# E is Morse (a 1 s and a 3 s light, the pattern of the letter A) and F is a long flash. The classifier is crude:
# it ignores colour, sectors, the quick bands and the rules on darkness inside a group, and the timings are
# illustrative values chosen for this exercise, not those of any real light.