# How Bridges Work 10, Exercise 3: what does a maintenance plan cost?
# Use the maintenance plan of the chapter (interval in years, cost of each event in
# thousand pounds, all illustrative). (a) For a 50-year life print the number of
# events and total cost for each element, and each element's share of the total.
# (b) Change the coating renewal interval from 25 years to 40 years and the cable
# interior inspection from every 10 years to every 5, and print the new
# total. (c) Which element dominates the budget, and which change matters most?
PLAN = {
    "bearings and expansion joints": (2, 15),
    "coating condition survey": (5, 40),
    "coating renewal": (25, 3000),
    "cable interior inspection": (10, 1200),
    "scour survey of piers": (1, 20),
    "fatigue-prone details": (6, 100),
}

def schedule(years, plan):
    return {name: (years // every, (years // every) * cost) for name, (every, cost) in plan.items()}

def total(plan):
    return sum(c for _, c in schedule(50, plan).values())

base = total(PLAN)
for name, (count, cost) in schedule(50, PLAN).items():
    print(f"{name:32} {count:3} {cost:6} {100 * cost / base:5.1f}%")
print("total", base)

plan_b = dict(PLAN)
plan_b["coating renewal"] = (40, 3000)
plan_b["cable interior inspection"] = (5, 1200)
print("changed total", total(plan_b))

only_coating = dict(PLAN)
only_coating["coating renewal"] = (40, 3000)
only_cable = dict(PLAN)
only_cable["cable interior inspection"] = (5, 1200)
print("coating only", total(only_coating) - base, "cable only", total(only_cable) - base)

# Output when run:
# bearings and expansion joints     25    375   2.6%
# coating condition survey          10    400   2.7%
# coating renewal                    2   6000  41.2%
# cable interior inspection          5   6000  41.2%
# scour survey of piers             50   1000   6.9%
# fatigue-prone details              8    800   5.5%
# total 14575
# changed total 17575
# coating only -3000 cable only 6000
#
# Columns: element, number of events in 50 years, cost (thousand pounds), share
# of the total. Two elements take 41.2% each: coating renewal (2 events, 6,000)
# and cable interior inspection (5 events, 6,000); together they are over 80% of
# the 14,575 thousand total. Stretching the coating renewal from every 25 to
# every 40 years means only one event in 50 years and saves 3,000; inspecting
# the cables every 5 years instead of 10 adds 6,000. Doing both gives 17,575.
# The cable inspection interval matters most, the biggest single swing, and
# the interval for a hidden element is a safety decision as well as a cost. All the numbers
# are illustrative, and the schedule ignores inflation and the extra cost of
# repairs found by inspections.