"""
Demo Date Offset Utilities
Provides functions for adjusting dates during demo session cloning
to ensure all temporal data is relative to the demo session creation time
"""

from datetime import datetime, timezone, timedelta
from typing import Optional


# Base reference date for all demo seed data
# All seed scripts should use this as the "logical seed date"
BASE_REFERENCE_DATE = datetime(2025, 1, 15, 12, 0, 0, tzinfo=timezone.utc)


def adjust_date_for_demo(
    original_date: Optional[datetime],
    session_created_at: datetime,
    base_reference_date: datetime = BASE_REFERENCE_DATE
) -> Optional[datetime]:
    """
    Adjust a date from seed data to be relative to demo session creation time

    This ensures that demo data appears fresh and relevant regardless of when
    the demo session is created. For example, expiration dates that were "15 days
    from seed date" will become "15 days from session creation date".

    Args:
        original_date: The original date from the seed data (or None)
        session_created_at: When the demo session was created
        base_reference_date: The logical date when seed data was created (default: 2025-01-15)

    Returns:
        Adjusted date relative to session creation, or None if original_date was None

    Example:
        # Seed data created on 2025-01-15
        # Stock expiration: 2025-01-30 (15 days from seed date)
        # Demo session created: 2025-10-16
        # Result: 2025-10-31 (15 days from session date)

        >>> original = datetime(2025, 1, 30, 12, 0, tzinfo=timezone.utc)
        >>> session = datetime(2025, 10, 16, 10, 0, tzinfo=timezone.utc)
        >>> adjusted = adjust_date_for_demo(original, session)
        >>> print(adjusted)
        2025-10-31 10:00:00+00:00
    """
    if original_date is None:
        return None

    # Ensure timezone-aware datetimes
    if original_date.tzinfo is None:
        original_date = original_date.replace(tzinfo=timezone.utc)
    if session_created_at.tzinfo is None:
        session_created_at = session_created_at.replace(tzinfo=timezone.utc)
    if base_reference_date.tzinfo is None:
        base_reference_date = base_reference_date.replace(tzinfo=timezone.utc)

    # Calculate offset from base reference
    offset = original_date - base_reference_date

    # Apply offset to session creation date
    return session_created_at + offset


def adjust_date_relative_to_now(
    days_offset: int,
    hours_offset: int = 0,
    reference_time: Optional[datetime] = None
) -> datetime:
    """
    Create a date relative to now (or a reference time) with specified offset

    Useful for creating dates during cloning without needing to store seed dates.

    Args:
        days_offset: Number of days to add (negative for past dates)
        hours_offset: Number of hours to add (negative for past times)
        reference_time: Reference datetime (defaults to now)

    Returns:
        Calculated datetime

    Example:
        >>> # Create a date 7 days in the future
        >>> future = adjust_date_relative_to_now(days_offset=7)
        >>> # Create a date 3 days in the past
        >>> past = adjust_date_relative_to_now(days_offset=-3)
    """
    if reference_time is None:
        reference_time = datetime.now(timezone.utc)
    elif reference_time.tzinfo is None:
        reference_time = reference_time.replace(tzinfo=timezone.utc)

    return reference_time + timedelta(days=days_offset, hours=hours_offset)


def calculate_expiration_date(
    received_date: datetime,
    shelf_life_days: int
) -> datetime:
    """
    Calculate expiration date based on received date and shelf life

    Args:
        received_date: When the product was received
        shelf_life_days: Number of days until expiration

    Returns:
        Calculated expiration datetime
    """
    if received_date.tzinfo is None:
        received_date = received_date.replace(tzinfo=timezone.utc)

    return received_date + timedelta(days=shelf_life_days)


def get_days_until_expiration(
    expiration_date: datetime,
    reference_date: Optional[datetime] = None
) -> int:
    """
    Calculate number of days until expiration

    Args:
        expiration_date: The expiration datetime
        reference_date: Reference datetime (defaults to now)

    Returns:
        Number of days until expiration (negative if already expired)
    """
    if reference_date is None:
        reference_date = datetime.now(timezone.utc)
    elif reference_date.tzinfo is None:
        reference_date = reference_date.replace(tzinfo=timezone.utc)

    if expiration_date.tzinfo is None:
        expiration_date = expiration_date.replace(tzinfo=timezone.utc)

    delta = expiration_date - reference_date
    return delta.days


def is_expiring_soon(
    expiration_date: datetime,
    threshold_days: int = 3,
    reference_date: Optional[datetime] = None
) -> bool:
    """
    Check if a product is expiring soon

    Args:
        expiration_date: The expiration datetime
        threshold_days: Number of days to consider as "soon" (default: 3)
        reference_date: Reference datetime (defaults to now)

    Returns:
        True if expiring within threshold_days, False otherwise
    """
    days_until = get_days_until_expiration(expiration_date, reference_date)
    return 0 <= days_until <= threshold_days


def is_expired(
    expiration_date: datetime,
    reference_date: Optional[datetime] = None
) -> bool:
    """
    Check if a product is expired

    Args:
        expiration_date: The expiration datetime
        reference_date: Reference datetime (defaults to now)

    Returns:
        True if expired, False otherwise
    """
    days_until = get_days_until_expiration(expiration_date, reference_date)
    return days_until < 0


def adjust_multiple_dates(
    dates_dict: dict,
    session_created_at: datetime,
    base_reference_date: datetime = BASE_REFERENCE_DATE
) -> dict:
    """
    Adjust multiple dates in a dictionary

    Args:
        dates_dict: Dictionary with datetime values to adjust
        session_created_at: When the demo session was created
        base_reference_date: The logical date when seed data was created

    Returns:
        Dictionary with adjusted dates (preserves None values)

    Example:
        >>> dates = {
        ...     'expiration_date': datetime(2025, 1, 30, tzinfo=timezone.utc),
        ...     'received_date': datetime(2025, 1, 15, tzinfo=timezone.utc),
        ...     'optional_date': None
        ... }
        >>> session = datetime(2025, 10, 16, tzinfo=timezone.utc)
        >>> adjusted = adjust_multiple_dates(dates, session)
    """
    return {
        key: adjust_date_for_demo(value, session_created_at, base_reference_date)
        for key, value in dates_dict.items()
    }