subscriptions.trial-end

def trial_end(start_date: str, trial_days: int) -> TrialPeriod

@dataclass(frozen=True)
class TrialPeriod:
    """The trial's last free day and the day billing starts."""

    #: the last free day, inclusive; null when trialDays is 0
    last_trial_day: Optional[str]
    #: the day the first payment is taken: the day after the last free day
    first_charge_date: str

from fune.subscriptions.trial_end import trial_end  # subscriptions.trial-end@^1

from .dates_add_days import add_days  ← from dates.add-days ^1.0.0 · built alongside by fune
from .subscriptions_trial_end_types import TrialPeriod


def trial_end(start_date: str, trial_days: int) -> TrialPeriod:
    """The last free day and the first charge date of a trial of ``trial_days``
    days starting on ``start_date``. The start day counts as day one, so the
    last free day is start + trial_days - 1 and the charge is the day after it.
    """
    if isinstance(trial_days, bool) or not isinstance(trial_days, int):
        raise TypeError("trial days must be an integer, received %r" % (trial_days,))
    if trial_days < 0:
        raise ValueError("trial days must not be negative, received %d" % (trial_days,))
    # add_days validates the start date even when there is no trial, so a
    # malformed date never slips through as the "first charge date".
    first_charge_date = add_days(start_date, trial_days)
    last_trial_day = None if trial_days == 0 else add_days(start_date, trial_days - 1)
    return TrialPeriod(last_trial_day=last_trial_day, first_charge_date=first_charge_date)

Install

fune build

With that line in your source, in a Python project (language python in fune.project), fune build resolves it and its 1 dependency, pins them in fune.lock, downloads only the Python package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add subscriptions.trial-end

The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./subscriptions.trial-end-1.0.0-python.fune, or fetch it from a terminal with fune pull subscriptions.trial-end@1.0.0:python.

The whole function, every language, is one file too: subscriptions.trial-end-1.0.0.fune, 9,102 bytes, sha256 34e5fca082f1dd914bf792c858bd5b8e161ad3cf9dfe5681ace9b206478a7b3e. It installs into a project of any language.

# fune: before subscriptions.trial-end

# fune: after subscriptions.trial-end

# fune: replace dates.add-days in subscriptions.trial-end

# fune: step subscriptions.trial-end after <n|label>

More from the author

A trial of 0 days is no trial: lastTrialDay is null and the first charge is on the start date itself. A negative length is an error, as is an impossible start date (2026-02-30), which the dates.add-days kernel refuses to parse.

This works on calendar dates. A trial that starts at 23:59 in one time zone and is billed at midnight in another is a time-zone decision for the caller; convert to the billing account's local date first.

Files