from __future__ import annotations

from datetime import date, timedelta

from fastapi import HTTPException


def _add(d: date, days: int) -> date:
    return d + timedelta(days=days)


def _step(d: date, weekdays: list[int], direction: int) -> date:
    selected = set(weekdays)
    cursor = _add(d, direction)
    for _ in range(28):
        if cursor.weekday() in selected:
            return cursor
        cursor = _add(cursor, direction)
    raise HTTPException(400, "Не удалось найти тренировочный день")


def _on_or_after(d: date, weekdays: list[int]) -> date:
    if d.weekday() in set(weekdays):
        return d
    return _step(_add(d, -1), weekdays, 1)


def _order(week: int, day_index: int) -> int:
    return week * 10 + day_index


def _next_training(after: date, weekdays: list[int], taken: set[date]) -> date:
    value = _step(after, weekdays, 1)
    while value in taken:
        value = _step(value, weekdays, 1)
    return value


def _place(desired: date, previous: date | None, weekdays: list[int], taken: set[date]) -> date:
    value = desired
    if previous is not None and value <= previous:
        value = _next_training(previous, weekdays, taken)
    while value in taken:
        value = _next_training(value, weekdays, taken)
    return value


def plan_move(workouts: list, moved_id: int, new_date: date, weekdays: list[int]) -> dict[int, date]:
    moved = next((w for w in workouts if w.id == moved_id), None)
    if moved is None:
        raise HTTPException(404, "Тренировка не найдена")
    if moved.status == "completed":
        raise HTTPException(400, "Выполненную тренировку переносить нельзя")
    if new_date < date.today():
        raise HTTPException(400, "В закрытый период переносить нельзя")

    sorted_items = sorted(workouts, key=lambda w: (_order(w.week_number, w.day_index), w.id))
    completed = [w for w in sorted_items if w.status == "completed"]
    if any(w.scheduled_date == new_date for w in completed):
        raise HTTPException(400, "На эту дату уже есть выполненная тренировка")

    moved_order = _order(moved.week_number, moved.day_index)
    earlier = [w for w in completed if _order(w.week_number, w.day_index) < moved_order]
    later = [w for w in completed if _order(w.week_number, w.day_index) > moved_order]
    if earlier and new_date <= earlier[-1].scheduled_date:
        raise HTTPException(400, "Дата должна быть позже уже выполненной тренировки")
    if later and new_date >= later[0].scheduled_date:
        raise HTTPException(400, "Дата должна быть раньше уже выполненной следующей тренировки")

    taken = {w.scheduled_date for w in completed}
    assigned: dict[int, date] = {}
    index = 0
    while index < len(sorted_items):
        if sorted_items[index].status == "completed":
            index += 1
            continue
        start = index
        while index < len(sorted_items) and sorted_items[index].status != "completed":
            index += 1
        segment = sorted_items[start:index]
        prev_anchor = sorted_items[start - 1] if start > 0 else None
        next_anchor = sorted_items[index] if index < len(sorted_items) else None
        proposed = sorted(new_date if item.id == moved_id else item.scheduled_date for item in segment)
        dates: list[date] = []
        for raw in proposed:
            value = _place(raw, dates[-1] if dates else None, weekdays, taken)
            if prev_anchor is not None and value <= prev_anchor.scheduled_date:
                raise HTTPException(400, "Дата должна быть позже уже выполненной тренировки")
            if next_anchor is not None and value >= next_anchor.scheduled_date:
                raise HTTPException(400, "Дата должна быть раньше уже выполненной следующей тренировки")
            dates.append(value)
            taken.add(value)
        for item, value in zip(segment, dates):
            assigned[item.id] = value

    return assigned


def plan_weekday_change(workouts: list, weekdays: list[int], start_from: date) -> dict[int, date]:
    open_items = sorted(
        (w for w in workouts if w.status != "completed"),
        key=lambda w: _order(w.week_number, w.day_index),
    )
    taken = {w.scheduled_date for w in workouts if w.status == "completed"}
    assigned: dict[int, date] = {}
    cursor = start_from
    for item in open_items:
        date_value = _on_or_after(cursor, weekdays)
        while date_value in taken:
            date_value = _step(date_value, weekdays, 1)
        assigned[item.id] = date_value
        taken.add(date_value)
        cursor = _add(date_value, 1)
    return assigned