"""Domain entity: LeaveWish.

A family's intent to be home for N weeks inside a window of ONE year
(e.g. "6 weeks in the summer of 2028"). Renamed and extended from
`BreakPeriod` (see PLANNING_ENGINE_SPEC.md §2.1).

**One row = one occurrence.** A wish the user asked to repeat every year is
*materialised* by `LeaveWishService` into one row per year, all sharing a
`series_id`; a genuinely one-off wish has `series_id = None`. There is no
`recurrence` field any more — a row either stands alone or belongs to a
series, and either way it describes exactly one year's window.

That materialisation is what makes per-year divergence possible: Easter (and
therefore the planner's "shift this window onto the red days" advice) moves
from year to year, so every year needs its own editable row to carry its own
offset. Editing one year touches one row; editing "every year" re-projects
the whole series from the edited row.

The window is still stored as month/day integers plus `first_year` (the year
the window starts in) rather than two dates — that is the existing column
layout, and it keeps the wrap rule ("end sorts before start" => the end lands
in `first_year + 1`, e.g. Jullov 12-20 -> 01-07) expressible without a custom
SQLite type.
"""

import calendar
from dataclasses import dataclass
from datetime import date, datetime, timedelta
from uuid import UUID


def _shift_to_weekday(naive: date, target_weekday: int) -> date:
    """Nearest date to `naive` whose `weekday()` is `target_weekday`.

    Weekdays repeat every 7 days, so the shift is always in [-3, +3] days —
    built with `timedelta`, never by mutating month/day ints (Feb 29 and
    month-end would misbehave otherwise). Ties can't actually arise (7 is
    odd, so no naive date is equidistant between two candidates), but the
    comparison key resolves one in favour of the earlier date regardless, to
    stay defensive.
    """
    forward = (target_weekday - naive.weekday()) % 7  # 0..6, shift going forward
    shift = min((forward, forward - 7), key=lambda d: (abs(d), d))
    return naive + timedelta(days=shift)


def clamped_date(year: int, month: int, day: int) -> date:
    """`date(year, month, day)`, with `day` clamped to the month's real length.

    Only Feb 29 in a non-leap year can actually trigger the clamp for a
    stored window (the service's `_validate_month_day` already rejects
    month/day pairs that are not a real date in a leap year). A wish anchored
    on Feb 29 used to raise `ValueError` out of the allocator the first time
    it recurred into a non-leap year; clamping to Feb 28 is the only sane
    answer for a whole-day planner and never changes any other date.
    """
    return date(year, month, min(day, calendar.monthrange(year, month)[1]))


def window_wraps_month_day(start_month: int, start_day: int, end_month: int, end_day: int) -> bool:
    """Whether (end_month, end_day) sorts before (start_month, start_day)."""
    return (end_month, end_day) < (start_month, start_day)


def project_window(
    *,
    start_month: int,
    start_day: int,
    end_month: int,
    end_day: int,
    anchor_year: int,
    year: int,
    window_mode: str,
) -> tuple[date, date]:
    """The concrete window an anchor occurrence projects onto `year`.

    This is the materialisation step: it is called ONCE per year, by
    `LeaveWishService`, and the result is written into that year's own row.
    Nothing re-derives it at read time — `LeaveWish.window()` just reads the
    dates back off the row.

    Both `window_mode`s describe a week-based habit, not a literal month/day:
    someone who is off Mon-Sun this year means Mon-Sun again next year, even
    though the naive month/day anchor isn't a Monday every year (the reported
    bug: 2026-10-05..10-11, Mon-Sun, naively recurred to 2027-10-05..10-11,
    which is Tue-Mon). So for any `year` other than `anchor_year`, the naive
    `date(year, start_month, start_day)` is snapped to the nearest date
    carrying the anchor's *start weekday* (ties resolve to the earlier date
    — see `_shift_to_weekday`), and the end date is re-derived by holding the
    anchor window's day-*span* fixed rather than re-anchoring
    end_month/end_day. `anchor_year` itself is unshifted.

    For `window_mode == 'fixed'` the span being held fixed IS the placement:
    the result is the exact dates the family is home. For `window_mode ==
    'flexible'` (§10.2) the result is still a BOUNDING RANGE the allocator
    searches inside, not a placement — but the range itself must keep its
    weekday alignment year over year, or a week-shaped bound (e.g. Mon-Sun)
    degenerates into an arbitrary weekday every other year, which is exactly
    as wrong for a search bound as for a fixed placement (a week-shaped bound
    should stay week-shaped). The snap never changes the bound's *length* —
    only `_shift_to_weekday`'s ±3-day slide of the start, with the same
    day-span held fixed — so the search space `resolve_flexible_window`
    explores never shrinks. `window_mode` is otherwise unused here; kept as a
    parameter because both modes now take the identical snap path and every
    caller already has the value at hand — removing it would just make call
    sites pass a value nobody reads.
    """
    wraps = window_wraps_month_day(start_month, start_day, end_month, end_day)
    naive_start = clamped_date(year, start_month, start_day)
    naive_end = clamped_date(year + 1 if wraps else year, end_month, end_day)

    if year == anchor_year:
        return naive_start, naive_end

    anchor_start = clamped_date(anchor_year, start_month, start_day)
    anchor_end = clamped_date(anchor_year + 1 if wraps else anchor_year, end_month, end_day)
    span = anchor_end - anchor_start

    start = _shift_to_weekday(naive_start, anchor_start.weekday())
    return start, start + span


@dataclass
class LeaveWish:
    """One year's intent to be home for N weeks inside a window."""

    id: UUID
    workspace_id: UUID
    child_id: UUID | None  # None = family-wide; set = tied to that child's pools
    name: str  # "Sommar", "Jullov" — persisted, possibly-translated display text

    # The window, stored as month/day ints anchored at `first_year`
    # (SQLite-friendly, no custom type). These are this occurrence's REAL
    # dates — including the weekday snap a repeating wish got when it was
    # materialised — not a pattern to be re-derived per year.
    window_start_month: int  # 1-12
    window_start_day: int  # 1-31
    window_end_month: int
    window_end_day: int

    target_weeks: int  # 6
    first_year: int  # the (single) year this occurrence's window starts in

    priority: int  # 1 = highest; drives best-effort fill order
    parent_mode: str  # 'either' | 'both' | 'specific'
    parent_personal_data_uuid: UUID | None  # required when parent_mode == 'specific'

    # PLANNING_ENGINE_SPEC.md §10.1 — 'fixed' (default): window_start_*/window_end_*
    # are the exact placement, as above. 'flexible': the SAME four fields instead
    # describe the BOUNDING RANGE the allocator searches inside for the
    # best-costing placement (e.g. "vår" = 03-01..05-31) — target_weeks is still
    # the wanted duration inside that range. Both modes get the same
    # per-year weekday snap at materialisation (`project_window`): a fixed
    # window's exact placement keeps its weekday, AND a flexible window's
    # bounding range keeps its weekday alignment (so a week-shaped bound
    # stays week-shaped every year) while its span — and so its search
    # space — stays exactly as wide as the anchor year's.
    window_mode: str = "fixed"  # 'fixed' | 'flexible'

    # Groups the per-year rows a repeating wish was materialised into. `None`
    # = a standalone, genuinely one-off occurrence. Every row of one series
    # shares this id; the service is the only writer, and it keeps the rows
    # of a series consistent (same name/parent/series bound, one row per year).
    series_id: UUID | None = None

    # SERIES-LEVEL intent, mirrored identically onto every row of a series:
    # the final anchor year the user asked for, or `None` = "until the child
    # turns 4" (the app's premise — see `AnalyticsService.get_days_left_at_age_4`).
    # Always `None` when `series_id is None`. Denormalised deliberately: the
    # UI reads the repeat-until control straight off whichever occurrence was
    # clicked, and re-materialising a series after an edit needs the intent,
    # not just the rows that happen to exist. `LeaveWishService` is the sole
    # writer and rewrites it across the series whenever it changes.
    last_year: int | None = None

    # §Decision A (co-leave, 2026-09-18 correction) — dubbeldagar are OPT-IN,
    # never automatic, even when `parent_mode == 'both'` and the child is
    # still inside the 15-month dubbeldagar window with quota left. Only set
    # when the user has explicitly requested them for this wish. NOTE: no
    # frontend exposes this yet -- the period editor's dubbeldag checkbox is
    # not built, and there is no `wantsDubbeldag` in the TS types, so today
    # the flag is only reachable through the API. When that UI lands it must
    # show the checkbox only where `WindowOutcome.dubbeldagar_legally_available`
    # says they legally could apply -- see allocation_service.py. Defaults to False so every
    # existing wish (and every wish that never opts in) gets the new
    # PL+vacation co-leave behaviour instead of dubbeldagar. Meaningless
    # outside `parent_mode == 'both'` -- `LeaveWishService._validate` rejects
    # setting it otherwise.
    wants_dubbeldag: bool = False

    # Provenance of `name`: when a wish is created from a preset (Sommar,
    # Jullov, Höstlov, ...) this holds the i18n message key that produced the
    # translated string stored in `name` (e.g. "wishEditor.presetSommar").
    # Nullable — free-typed names, and every row created before this field
    # existed, have no key and just show `name` verbatim. Cleared by
    # `LeaveWishService.update` the moment the user edits `name`, since a
    # user-typed name is no longer a preset label and must never silently
    # revert to one.
    name_message_key: str | None = None

    # A calendar-drawn period (e.g. dragging a band on the calendar UI) is not
    # a whole number of weeks. NULL (every row created before this field
    # existed, and any wish still specified in weeks) falls back to
    # `target_weeks * 7` — see `target_span_days()`.
    target_days: int | None = None

    created_at: datetime | None = None
    updated_at: datetime | None = None

    def target_span_days(self) -> int:
        """Wanted duration in days. `target_days` wins when set; otherwise weeks * 7."""
        return self.target_days if self.target_days is not None else self.target_weeks * 7

    def window_wraps(self) -> bool:
        """Whether (end_month, end_day) sorts before (start_month, start_day).

        A wrapping window (e.g. Jullov 12-20 -> 01-07) ends in the year *after*
        `first_year`.
        """
        return window_wraps_month_day(
            self.window_start_month,
            self.window_start_day,
            self.window_end_month,
            self.window_end_day,
        )

    def window(self) -> tuple[date, date]:
        """This occurrence's concrete (start_date, end_date), inclusive.

        A pure read of the stored fields — no recurrence projection, no
        weekday snapping. Whatever shifting this occurrence needed was applied
        once, at materialisation (`project_window`), and written into the row.

        If the window wraps, the end date lands in `first_year + 1` — which
        also means it spans two vacation-year budgets (see
        PLANNING_ENGINE_SPEC.md §3.2); callers that debit vacation must
        account for both years separately.
        """
        start = clamped_date(self.first_year, self.window_start_month, self.window_start_day)
        end_year = self.first_year + 1 if self.window_wraps() else self.first_year
        end = clamped_date(end_year, self.window_end_month, self.window_end_day)
        return start, end