"""Business logic for the Swedish calendar endpoint (röda dagar / klämdagar).

One service serves two UI surfaces (§3.4 shading the Kalender page, §3.8 the
per-year red-days list in Settings) from the same source data: the
`swedish_calendar.json` cache exposed via `app.utils.holidays`, merged with
the current workspace's `DayOverride`s (per §3.8's product decision) so the
UI can show what the app actually treats as free, not just the statutory
calendar.

No runtime external API calls (§6): everything here reads the pre-built
cache via `app.utils.holidays`. The requested window is clamped to the
cache's [min_year, max_year] (see `get_calendar_window`) and every lookup
uses `strict=True`, so this endpoint can never silently fall back to the
local `holidays` library for a year the cache doesn't cover — that fallback
only knows formal röda dagar (+ every Sunday), not de facto days or
klämdagar, and serving it unlabelled here previously caused a real bug
(Julafton/Nyårsafton/Midsommarafton silently reading as working days past
the cache's end).
"""

from __future__ import annotations

from dataclasses import dataclass
from datetime import date, timedelta
from typing import Literal
from uuid import UUID

from app.services.allocation_service import is_free_day
from app.services.day_override_service import DayOverrideService
from app.utils.errors import ValidationError
from app.utils.holidays import (
    cached_year_bounds,
    get_red_days,
    get_swedish_holidays,
    is_klamdag,
)

# Fixed page size per §3.8's product decision: paginate four years ahead at a
# time even though the full ~30-year cache is available.
MAX_WINDOW_YEARS = 4

DayType = Literal["red_day", "klamdag", "weekend", "working_day"]


@dataclass
class CalendarDay:
    """One day's calendar metadata, statutory + workspace override.

    `day_type` reuses the existing vocabulary from `app.utils.holidays` /
    `swedish_calendar.json` — no parallel taxonomy: a "red_day" is exactly
    what `get_red_days` returns (public/de_facto, exact-name matched so a
    holiday landing on a Sunday is never conflated with a bare weekend, see
    the module docstring on `app.utils.holidays`), "klamdag" mirrors the
    cache's `bridge_day` category (verified generic via `is_klamdag`), and
    "weekend"/"working_day" are the remaining ordinary cases.
    """

    date: date
    name: str | None
    day_type: DayType
    is_override: bool
    override_is_working_day: bool | None
    is_free: bool


@dataclass
class CalendarWindow:
    start_year: int
    end_year: int
    min_year: int | None
    max_year: int | None
    days: list[CalendarDay]


class CalendarService:
    def __init__(self, day_override_service: DayOverrideService) -> None:
        self._day_override_service = day_override_service

    async def get_calendar_window(
        self, workspace_id: UUID, start_year: int, years: int = MAX_WINDOW_YEARS
    ) -> CalendarWindow:
        """Return calendar-day metadata for `years` years starting at
        `start_year` (capped at `MAX_WINDOW_YEARS`), merged with the
        workspace's day overrides.

        Raises `ValidationError` for an out-of-range `years` or a
        `start_year` outside the cached year window (when the cache file
        is present at all).
        """
        if years < 1 or years > MAX_WINDOW_YEARS:
            raise ValidationError(f"years must be between 1 and {MAX_WINDOW_YEARS} (got {years})")

        bounds = cached_year_bounds()
        min_year, max_year = bounds if bounds is not None else (None, None)
        if min_year is not None and max_year is not None:
            if start_year < min_year or start_year > max_year:
                raise ValidationError(
                    f"start_year must be between {min_year} and {max_year} (got {start_year})"
                )

        end_year = start_year + years - 1
        if max_year is not None and end_year > max_year:
            # Clamp rather than 422: the response already carries min_year/
            # max_year for the UI's paging bounds, so the last page is
            # naturally shorter than `years` requested. `end_year` below
            # reports the ACTUAL clamped range — never a range not returned.
            end_year = max_year

        overrides = await self._day_override_service.get_effective_map(workspace_id)

        days: list[CalendarDay] = []
        for year in range(start_year, end_year + 1):
            # `strict=True`: after the clamp above, every `year` here is
            # guaranteed inside [min_year, max_year], so this must never hit
            # the live-`holidays` fallback. If it ever does, that's a bug in
            # the clamping above, not bad input — fail loudly (see
            # `app.utils.holidays.UncachedYearError`) rather than silently
            # serving degraded data for this endpoint (the actual bug this
            # guards against: years past the cache losing Julafton,
            # Nyårsafton, Midsommarafton).
            holidays_map = get_swedish_holidays(year, strict=True)
            red_days = get_red_days(year, strict=True)
            day = date(year, 1, 1)
            one_day = timedelta(days=1)
            while day.year == year:
                days.append(self._build_day(day, holidays_map, red_days, overrides))
                day += one_day

        return CalendarWindow(
            start_year=start_year,
            end_year=end_year,
            min_year=min_year,
            max_year=max_year,
            days=days,
        )

    @staticmethod
    def _build_day(
        day: date,
        holidays_map: dict[date, str],
        red_days: dict[date, str],
        overrides: dict[date, bool],
    ) -> CalendarDay:
        if day in red_days:
            day_type: DayType = "red_day"
        elif is_klamdag(day):
            day_type = "klamdag"
        elif day.weekday() >= 5:
            day_type = "weekend"
        else:
            day_type = "working_day"

        is_override = day in overrides
        override_is_working_day = overrides.get(day) if is_override else None

        return CalendarDay(
            date=day,
            name=red_days.get(day) if day_type == "red_day" else None,
            day_type=day_type,
            is_override=is_override,
            override_is_working_day=override_is_working_day,
            is_free=is_free_day(day, holidays_map, overrides),
        )