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FA-66391 / Airline fare rule evaluation / Open access

Month-end departures lose the end-of-month extension · case 01

Departing 28 February with a one-month maximum expires 28 March instead of 31 March.

Verified by executionVariant 1 · 12 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The target day is always clamped from the departure day, ignoring the month-end rule.

VERIFIED REPAIR

Map a departure on the last day of its month to the last day of the target month.

Unsuccessful approach: Treating any day from the 28th as month-end extends ordinary 28th-30th departures.

Case contract

Input {'depart','return' ISO dates,'rule':{'sat_night','min_days','max_months'}}. Saturday-night rule: return on or after the Sunday following the first Saturday on or after departure. Min stay: return - depart >= min_days. Max stay: return <= departure date plus max_months calendar months; a month-end departure maps to the target month end, otherwise day clamps to month length. Return failed rule names in order SAT, MIN, MAX.

Why this case matters

Stay restrictions mix weekday logic and calendar-month arithmetic with month-end and year-rollover rules.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    d = datetime.date.fromisoformat(x['depart'])
    r = datetime.date.fromisoformat(x['return'])
    rule = x['rule']
    fails = []
    if rule['sat_night']:
        sun = d + datetime.timedelta(days=(5 - d.weekday()) % 7 + 1)
        if r < sun: fails.append('SAT')
    if (r - d).days < rule['min_days']: fails.append('MIN')
    mo = d.month - 1 + rule['max_months']
    y, mo = d.year + mo // 12, mo % 12 + 1
    last = calendar.monthrange(y, mo)[1]
    eom = d.day == calendar.monthrange(d.year, d.month)[1]
    lim = datetime.date(y, mo, min(d.day, last))
    if r > lim: fails.append('MAX')
    return fails
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-08', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-30', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-30', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-11', 'return': '2028-01-10', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, []], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-14', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, []], ['sampled case 1', {'depart': '2029-08-19', 'return': '2029-08-28', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 2}}, []], ['sampled case 2', {'depart': '2028-06-13', 'return': '2028-12-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 12}}, []], ['sampled case 3', {'depart': '2028-04-16', 'return': '2028-08-20', 'rule': {'sat_night': False, 'min_days': 1, 'max_months': 1}}, ['MAX']]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-09', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-31', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-31', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-12', 'return': '2028-01-12', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, []], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-15', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, []], ['sampled case 1', {'depart': '2029-07-11', 'return': '2029-07-23', 'rule': {'sat_night': True, 'min_days': 7, 'max_months': 12}}, []], ['sampled case 2', {'depart': '2029-06-25', 'return': '2029-12-12', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 2}}, ['MAX']], ['sampled case 3', {'depart': '2029-02-02', 'return': '2030-02-22', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 6}}, ['MAX']]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-10', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-29', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-29', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-13', 'return': '2028-01-14', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-16', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2027-10-05', 'return': '2027-10-14', 'rule': {'sat_night': True, 'min_days': 3, 'max_months': 6}}, []], ['sampled case 2', {'depart': '2028-04-06', 'return': '2028-10-12', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 11}}, []], ['sampled case 3', {'depart': '2027-11-12', 'return': '2027-11-21', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 2}}, []]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-11', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-30', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-30', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-14', 'return': '2028-01-16', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-17', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2027-06-01', 'return': '2027-06-09', 'rule': {'sat_night': True, 'min_days': 7, 'max_months': 1}}, []], ['sampled case 2', {'depart': '2028-03-04', 'return': '2028-06-07', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 6}}, []], ['sampled case 3', {'depart': '2029-03-17', 'return': '2029-03-25', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 12}}, []]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-12', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-31', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-31', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-15', 'return': '2028-01-18', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-18', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2029-08-05', 'return': '2030-07-02', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 11}}, []], ['sampled case 2', {'depart': '2028-05-10', 'return': '2028-05-12', 'rule': {'sat_night': False, 'min_days': 2, 'max_months': 11}}, []], ['sampled case 3', {'depart': '2027-09-03', 'return': '2027-09-03', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 6}}, ['SAT']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
Sunday departure next-day return['SAT']['SAT']Passed
Saturday departure Sunday return[][]Passed
Friday out Saturday back['SAT']['SAT']Passed
month-end max stay['MAX'][]Failed
the 28th is not month end['MAX']['MAX']Passed
Jan 31 plus one month[][]Passed
year rollover max stay[][]Passed
exact minimum stay[][]Passed
December twelve months[][]Passed
sampled case 1[][]Passed
sampled case 2[][]Passed
sampled case 3['MAX']['MAX']Passed

SHA-256 / a319167fe17cbd83d0209ba57b8e5502db19349e38137da90f1d58e3322891d0

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    d = datetime.date.fromisoformat(x['depart'])
    r = datetime.date.fromisoformat(x['return'])
    rule = x['rule']
    fails = []
    if rule['sat_night']:
        sun = d + datetime.timedelta(days=(5 - d.weekday()) % 7 + 1)
        if r < sun: fails.append('SAT')
    if (r - d).days < rule['min_days']: fails.append('MIN')
    mo = d.month - 1 + rule['max_months']
    y, mo = d.year + mo // 12, mo % 12 + 1
    last = calendar.monthrange(y, mo)[1]
    eom = d.day == calendar.monthrange(d.year, d.month)[1]
    lim = datetime.date(y, mo, last if d.day >= 28 else min(d.day, last))
    if r > lim: fails.append('MAX')
    return fails
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-08', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-30', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-30', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-11', 'return': '2028-01-10', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, []], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-14', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, []], ['sampled case 1', {'depart': '2029-08-19', 'return': '2029-08-28', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 2}}, []], ['sampled case 2', {'depart': '2028-06-13', 'return': '2028-12-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 12}}, []], ['sampled case 3', {'depart': '2028-04-16', 'return': '2028-08-20', 'rule': {'sat_night': False, 'min_days': 1, 'max_months': 1}}, ['MAX']]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-09', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-31', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-31', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-12', 'return': '2028-01-12', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, []], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-15', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, []], ['sampled case 1', {'depart': '2029-07-11', 'return': '2029-07-23', 'rule': {'sat_night': True, 'min_days': 7, 'max_months': 12}}, []], ['sampled case 2', {'depart': '2029-06-25', 'return': '2029-12-12', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 2}}, ['MAX']], ['sampled case 3', {'depart': '2029-02-02', 'return': '2030-02-22', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 6}}, ['MAX']]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-10', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-29', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-29', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-13', 'return': '2028-01-14', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-16', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2027-10-05', 'return': '2027-10-14', 'rule': {'sat_night': True, 'min_days': 3, 'max_months': 6}}, []], ['sampled case 2', {'depart': '2028-04-06', 'return': '2028-10-12', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 11}}, []], ['sampled case 3', {'depart': '2027-11-12', 'return': '2027-11-21', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 2}}, []]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-11', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-30', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-30', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-14', 'return': '2028-01-16', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-17', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2027-06-01', 'return': '2027-06-09', 'rule': {'sat_night': True, 'min_days': 7, 'max_months': 1}}, []], ['sampled case 2', {'depart': '2028-03-04', 'return': '2028-06-07', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 6}}, []], ['sampled case 3', {'depart': '2029-03-17', 'return': '2029-03-25', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 12}}, []]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-12', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-31', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-31', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-15', 'return': '2028-01-18', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-18', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2029-08-05', 'return': '2030-07-02', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 11}}, []], ['sampled case 2', {'depart': '2028-05-10', 'return': '2028-05-12', 'rule': {'sat_night': False, 'min_days': 2, 'max_months': 11}}, []], ['sampled case 3', {'depart': '2027-09-03', 'return': '2027-09-03', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 6}}, ['SAT']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
Sunday departure next-day return['SAT']['SAT']Passed
Saturday departure Sunday return[][]Passed
Friday out Saturday back['SAT']['SAT']Passed
month-end max stay[][]Passed
the 28th is not month end[]['MAX']Failed
Jan 31 plus one month[][]Passed
year rollover max stay[][]Passed
exact minimum stay[][]Passed
December twelve months[][]Passed
sampled case 1[][]Passed
sampled case 2[][]Passed
sampled case 3['MAX']['MAX']Passed

SHA-256 / 4d48b4a8585750d4be357a153aee55c6e90a8ec528c74da859e4f6d72c0f71ae

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    d = datetime.date.fromisoformat(x['depart'])
    r = datetime.date.fromisoformat(x['return'])
    rule = x['rule']
    fails = []
    if rule['sat_night']:
        sun = d + datetime.timedelta(days=(5 - d.weekday()) % 7 + 1)
        if r < sun: fails.append('SAT')
    if (r - d).days < rule['min_days']: fails.append('MIN')
    mo = d.month - 1 + rule['max_months']
    y, mo = d.year + mo // 12, mo % 12 + 1
    last = calendar.monthrange(y, mo)[1]
    eom = d.day == calendar.monthrange(d.year, d.month)[1]
    lim = datetime.date(y, mo, last if eom else min(d.day, last))
    if r > lim: fails.append('MAX')
    return fails
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-08', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-30', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-30', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-11', 'return': '2028-01-10', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, []], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-14', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, []], ['sampled case 1', {'depart': '2029-08-19', 'return': '2029-08-28', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 2}}, []], ['sampled case 2', {'depart': '2028-06-13', 'return': '2028-12-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 12}}, []], ['sampled case 3', {'depart': '2028-04-16', 'return': '2028-08-20', 'rule': {'sat_night': False, 'min_days': 1, 'max_months': 1}}, ['MAX']]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-09', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-31', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-31', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-12', 'return': '2028-01-12', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, []], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-15', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, []], ['sampled case 1', {'depart': '2029-07-11', 'return': '2029-07-23', 'rule': {'sat_night': True, 'min_days': 7, 'max_months': 12}}, []], ['sampled case 2', {'depart': '2029-06-25', 'return': '2029-12-12', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 2}}, ['MAX']], ['sampled case 3', {'depart': '2029-02-02', 'return': '2030-02-22', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 6}}, ['MAX']]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-10', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-29', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-29', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-13', 'return': '2028-01-14', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-16', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2027-10-05', 'return': '2027-10-14', 'rule': {'sat_night': True, 'min_days': 3, 'max_months': 6}}, []], ['sampled case 2', {'depart': '2028-04-06', 'return': '2028-10-12', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 11}}, []], ['sampled case 3', {'depart': '2027-11-12', 'return': '2027-11-21', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 2}}, []]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-11', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-30', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-30', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-14', 'return': '2028-01-16', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-17', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2027-06-01', 'return': '2027-06-09', 'rule': {'sat_night': True, 'min_days': 7, 'max_months': 1}}, []], ['sampled case 2', {'depart': '2028-03-04', 'return': '2028-06-07', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 6}}, []], ['sampled case 3', {'depart': '2029-03-17', 'return': '2029-03-25', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 12}}, []]], [['Sunday departure next-day return', {'depart': '2027-03-07', 'return': '2027-03-12', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 1}}, ['SAT']], ['Saturday departure Sunday return', {'depart': '2027-03-13', 'return': '2027-03-14', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 1}}, []], ['Friday out Saturday back', {'depart': '2027-03-12', 'return': '2027-03-13', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 3}}, ['SAT']], ['month-end max stay', {'depart': '2027-02-28', 'return': '2027-03-31', 'rule': {'sat_night': False, 'min_days': 3, 'max_months': 1}}, []], ['the 28th is not month end', {'depart': '2027-04-28', 'return': '2027-05-31', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, ['MAX']], ['Jan 31 plus one month', {'depart': '2027-01-31', 'return': '2027-02-28', 'rule': {'sat_night': False, 'min_days': 0, 'max_months': 1}}, []], ['year rollover max stay', {'depart': '2027-11-15', 'return': '2028-01-18', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 2}}, ['MAX']], ['exact minimum stay', {'depart': '2027-06-01', 'return': '2027-06-08', 'rule': {'sat_night': False, 'min_days': 7, 'max_months': 12}}, []], ['December twelve months', {'depart': '2027-12-15', 'return': '2028-12-18', 'rule': {'sat_night': True, 'min_days': 2, 'max_months': 12}}, ['MAX']], ['sampled case 1', {'depart': '2029-08-05', 'return': '2030-07-02', 'rule': {'sat_night': True, 'min_days': 1, 'max_months': 11}}, []], ['sampled case 2', {'depart': '2028-05-10', 'return': '2028-05-12', 'rule': {'sat_night': False, 'min_days': 2, 'max_months': 11}}, []], ['sampled case 3', {'depart': '2027-09-03', 'return': '2027-09-03', 'rule': {'sat_night': True, 'min_days': 0, 'max_months': 6}}, ['SAT']]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
Sunday departure next-day return['SAT']['SAT']Passed
Saturday departure Sunday return[][]Passed
Friday out Saturday back['SAT']['SAT']Passed
month-end max stay[][]Passed
the 28th is not month end['MAX']['MAX']Passed
Jan 31 plus one month[][]Passed
year rollover max stay[][]Passed
exact minimum stay[][]Passed
December twelve months[][]Passed
sampled case 1[][]Passed
sampled case 2[][]Passed
sampled case 3['MAX']['MAX']Passed

SHA-256 / f556851a1161c802d280659c60ce9792da866069ec1c92478b63d34dbf93a60b

Verification & scope

A stipulated toy fare-rule contract with invented constants; it is not an ATPCO or carrier tariff implementation and makes no claim of industry-standard conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:47:43.209930+00:00.

Case digest / 40bee48e14c0d95a7614a43f37b80e6dd9010a919ed01a61caf2718e683619f9