"""Workload calculation service.

Provides functionality to calculate and retrieve user workload data
including weekly load percentages, task allocations, and load level classification.
"""
from datetime import date, timedelta
from decimal import Decimal
from typing import List, Optional, Tuple

from sqlalchemy import func, and_
from sqlalchemy.orm import Session, joinedload

from app.models.user import User
from app.models.task import Task
from app.models.task_status import TaskStatus
from app.models.project import Project
from app.schemas.workload import (
    LoadLevel,
    UserWorkloadSummary,
    UserWorkloadDetail,
    TaskWorkloadInfo,
)


def get_week_bounds(d: date) -> Tuple[date, date]:
    """
    Get ISO week boundaries (Monday to Sunday).

    Args:
        d: Any date within the week

    Returns:
        Tuple of (week_start, week_end) where week_start is Monday
    """
    week_start = d - timedelta(days=d.weekday())
    week_end = week_start + timedelta(days=6)
    return week_start, week_end


def get_current_week_start() -> date:
    """Get the Monday of the current week."""
    return get_week_bounds(date.today())[0]


def get_current_week_bounds() -> Tuple[date, date]:
    """
    Get current week bounds for default views.

    On Sundays, extend the window to include the upcoming week so that
    "tomorrow" tasks are still visible in default views.
    """
    week_start, week_end = get_week_bounds(date.today())
    if date.today().weekday() == 6:
        week_end = week_end + timedelta(days=7)
    return week_start, week_end


def _extend_week_end_if_sunday(week_start: date, week_end: date) -> Tuple[date, date]:
    """Extend week window on Sunday to include upcoming week."""
    if date.today().weekday() == 6 and week_start == get_current_week_start():
        return week_start, week_end + timedelta(days=7)
    return week_start, week_end


def determine_load_level(load_percentage: Optional[Decimal]) -> LoadLevel:
    """
    Determine the load level based on percentage.

    Args:
        load_percentage: The calculated load percentage (None if capacity is 0)

    Returns:
        LoadLevel enum value
    """
    if load_percentage is None:
        return LoadLevel.UNAVAILABLE

    if load_percentage < 80:
        return LoadLevel.NORMAL
    elif load_percentage < 100:
        return LoadLevel.WARNING
    else:
        return LoadLevel.OVERLOADED


def calculate_load_percentage(
    allocated_hours: Decimal,
    capacity_hours: Decimal
) -> Optional[Decimal]:
    """
    Calculate load percentage avoiding division by zero.

    Args:
        allocated_hours: Total allocated hours
        capacity_hours: User's weekly capacity

    Returns:
        Load percentage or None if capacity is 0
    """
    if capacity_hours == 0:
        return None
    return (allocated_hours / capacity_hours * 100).quantize(Decimal("0.01"))


def get_user_tasks_in_week(
    db: Session,
    user_id: str,
    week_start: date,
    week_end: date,
) -> List[Task]:
    """
    Get all tasks assigned to a user with due_date in the specified week.
    Excludes tasks with is_done=True status.

    Args:
        db: Database session
        user_id: User ID
        week_start: Start of week (Monday)
        week_end: End of week (Sunday)

    Returns:
        List of Task objects
    """
    # Convert date to datetime for comparison
    from datetime import datetime
    week_start_dt = datetime.combine(week_start, datetime.min.time())
    week_end_dt = datetime.combine(week_end, datetime.max.time())

    return (
        db.query(Task)
        .join(Task.status, isouter=True)
        .join(Task.project)
        .filter(
            Task.assignee_id == user_id,
            Task.due_date >= week_start_dt,
            Task.due_date <= week_end_dt,
            # Exclude completed tasks
            (TaskStatus.is_done == False) | (Task.status_id == None)
        )
        .options(joinedload(Task.project), joinedload(Task.status))
        .all()
    )


def calculate_user_workload(
    db: Session,
    user: User,
    week_start: date,
) -> UserWorkloadSummary:
    """
    Calculate workload summary for a single user.

    Args:
        db: Database session
        user: User object
        week_start: Start of week (Monday)

    Returns:
        UserWorkloadSummary object
    """
    week_start, week_end = get_week_bounds(week_start)

    # Get tasks for this user in this week
    tasks = get_user_tasks_in_week(db, user.id, week_start, week_end)

    # Calculate allocated hours from original_estimate
    allocated_hours = Decimal("0")
    for task in tasks:
        if task.original_estimate:
            allocated_hours += task.original_estimate

    capacity_hours = Decimal(str(user.capacity)) if user.capacity is not None else Decimal("40")
    load_percentage = calculate_load_percentage(allocated_hours, capacity_hours)
    load_level = determine_load_level(load_percentage)

    return UserWorkloadSummary(
        user_id=user.id,
        user_name=user.name,
        department_id=user.department_id,
        department_name=user.department.name if user.department else None,
        capacity_hours=capacity_hours,
        allocated_hours=allocated_hours,
        load_percentage=load_percentage,
        load_level=load_level,
        task_count=len(tasks),
    )


def get_workload_heatmap(
    db: Session,
    week_start: Optional[date] = None,
    department_id: Optional[str] = None,
    user_ids: Optional[List[str]] = None,
    hide_empty: bool = True,
) -> List[UserWorkloadSummary]:
    """
    Get workload heatmap for multiple users.

    Args:
        db: Database session
        week_start: Start of week (defaults to current week)
        department_id: Filter by department
        user_ids: Filter by specific user IDs
        hide_empty: If True, exclude users with no tasks (default: True)

    Returns:
        List of UserWorkloadSummary objects
    """
    from datetime import datetime
    from collections import defaultdict

    if week_start is None:
        week_start = get_current_week_start()

    # Normalize to week start (Monday)
    week_start = get_week_bounds(week_start)[0]
    week_start, week_end = get_week_bounds(week_start)
    week_start, week_end = _extend_week_end_if_sunday(week_start, week_end)

    # Build user query
    query = db.query(User).filter(User.is_active == True)

    if department_id:
        query = query.filter(User.department_id == department_id)

    if user_ids:
        query = query.filter(User.id.in_(user_ids))

    users = query.options(joinedload(User.department)).all()

    if not users:
        return []

    # Batch query: fetch all tasks for all users in one query
    user_id_list = [user.id for user in users]
    week_start_dt = datetime.combine(week_start, datetime.min.time())
    week_end_dt = datetime.combine(week_end, datetime.max.time())

    all_tasks = (
        db.query(Task)
        .join(Task.status, isouter=True)
        .filter(
            Task.assignee_id.in_(user_id_list),
            Task.due_date >= week_start_dt,
            Task.due_date <= week_end_dt,
            # Exclude completed tasks
            (TaskStatus.is_done == False) | (Task.status_id == None)
        )
        .all()
    )

    # Group tasks by assignee_id in memory
    tasks_by_user: dict = defaultdict(list)
    for task in all_tasks:
        tasks_by_user[task.assignee_id].append(task)

    # Calculate workload for each user using pre-fetched tasks
    results = []
    for user in users:
        user_tasks = tasks_by_user.get(user.id, [])

        # Calculate allocated hours from original_estimate
        allocated_hours = Decimal("0")
        for task in user_tasks:
            if task.original_estimate:
                allocated_hours += task.original_estimate

        capacity_hours = Decimal(str(user.capacity)) if user.capacity is not None else Decimal("40")
        load_percentage = calculate_load_percentage(allocated_hours, capacity_hours)
        load_level = determine_load_level(load_percentage)

        summary = UserWorkloadSummary(
            user_id=user.id,
            user_name=user.name,
            department_id=user.department_id,
            department_name=user.department.name if user.department else None,
            capacity_hours=capacity_hours,
            allocated_hours=allocated_hours,
            load_percentage=load_percentage,
            load_level=load_level,
            task_count=len(user_tasks),
        )
        results.append(summary)

    # Filter out users with no tasks if hide_empty is True
    if hide_empty:
        results = [r for r in results if r.task_count > 0]

    return results


def get_user_workload_detail(
    db: Session,
    user_id: str,
    week_start: Optional[date] = None,
) -> Optional[UserWorkloadDetail]:
    """
    Get detailed workload for a specific user including task list.

    Args:
        db: Database session
        user_id: User ID
        week_start: Start of week (defaults to current week)

    Returns:
        UserWorkloadDetail object or None if user not found
    """
    user = (
        db.query(User)
        .filter(User.id == user_id)
        .options(joinedload(User.department))
        .first()
    )

    if not user:
        return None

    if week_start is None:
        week_start = get_current_week_start()
    week_start = get_week_bounds(week_start)[0]
    week_start, week_end = get_week_bounds(week_start)
    week_start, week_end = _extend_week_end_if_sunday(week_start, week_end)

    # Get tasks
    tasks = get_user_tasks_in_week(db, user_id, week_start, week_end)

    # Calculate totals
    allocated_hours = Decimal("0")
    task_infos = []

    for task in tasks:
        if task.original_estimate:
            allocated_hours += task.original_estimate

        task_infos.append(TaskWorkloadInfo(
            task_id=task.id,
            title=task.title,
            project_id=task.project_id,
            project_name=task.project.title if task.project else "Unknown",
            due_date=task.due_date,
            original_estimate=task.original_estimate,
            status=task.status.name if task.status else None,
        ))

    capacity_hours = Decimal(str(user.capacity)) if user.capacity is not None else Decimal("40")
    load_percentage = calculate_load_percentage(allocated_hours, capacity_hours)
    load_level = determine_load_level(load_percentage)

    return UserWorkloadDetail(
        user_id=user.id,
        user_name=user.name,
        week_start=week_start,
        week_end=week_end,
        capacity_hours=capacity_hours,
        allocated_hours=allocated_hours,
        load_percentage=load_percentage,
        load_level=load_level,
        tasks=task_infos,
    )