"""
Fleet Calendar Service

Business logic for:
- Calculating unit availability on any given date
- Calibration status tracking (valid, expiring soon, expired)
- Job reservation management
- Conflict detection (calibration expires mid-job)
"""

from datetime import date, datetime, timedelta
from typing import Dict, List, Optional, Tuple
from sqlalchemy.orm import Session
from sqlalchemy import and_, or_

from backend.models import (
    RosterUnit, JobReservation, JobReservationUnit,
    UserPreferences, Project
)


def get_calibration_status(
    unit: RosterUnit,
    check_date: date,
    warning_days: int = 30
) -> str:
    """
    Determine calibration status for a unit on a specific date.

    Returns:
        "valid" - Calibration is good on this date
        "expiring_soon" - Within warning_days of expiry
        "expired" - Calibration has expired
        "needs_calibration" - No calibration date set
    """
    if not unit.last_calibrated:
        return "needs_calibration"

    # Calculate expiry date (1 year from last calibration)
    expiry_date = unit.last_calibrated + timedelta(days=365)

    if check_date >= expiry_date:
        return "expired"
    elif check_date >= expiry_date - timedelta(days=warning_days):
        return "expiring_soon"
    else:
        return "valid"


def get_unit_reservations_on_date(
    db: Session,
    unit_id: str,
    check_date: date
) -> List[JobReservation]:
    """Get all reservations that include this unit on the given date."""

    # Get reservation IDs that have this unit assigned
    assigned_reservation_ids = db.query(JobReservationUnit.reservation_id).filter(
        JobReservationUnit.unit_id == unit_id
    ).subquery()

    # Get reservations that:
    # 1. Have this unit assigned AND date is within range
    reservations = db.query(JobReservation).filter(
        JobReservation.id.in_(assigned_reservation_ids),
        JobReservation.start_date <= check_date,
        JobReservation.end_date >= check_date
    ).all()

    return reservations


def is_unit_available_on_date(
    db: Session,
    unit: RosterUnit,
    check_date: date,
    warning_days: int = 30
) -> Tuple[bool, str, Optional[str]]:
    """
    Check if a unit is available on a specific date.

    Returns:
        (is_available, status, reservation_name)
        - is_available: True if unit can be assigned to new work
        - status: "available", "reserved", "expired", "retired", "needs_calibration"
        - reservation_name: Name of blocking reservation (if any)
    """
    # Check if retired
    if unit.retired:
        return False, "retired", None

    # Check calibration status
    cal_status = get_calibration_status(unit, check_date, warning_days)
    if cal_status == "expired":
        return False, "expired", None
    if cal_status == "needs_calibration":
        return False, "needs_calibration", None

    # Check if already reserved
    reservations = get_unit_reservations_on_date(db, unit.id, check_date)
    if reservations:
        return False, "reserved", reservations[0].name

    # Unit is available (even if expiring soon - that's just a warning)
    return True, "available", None


def get_day_summary(
    db: Session,
    check_date: date,
    device_type: str = "seismograph"
) -> Dict:
    """
    Get a complete summary of fleet status for a specific day.

    Returns dict with:
        - available_units: List of available unit IDs with calibration info
        - reserved_units: List of reserved unit IDs with reservation info
        - expired_units: List of units with expired calibration
        - expiring_soon_units: List of units expiring within warning period
        - reservations: List of active reservations on this date
        - counts: Summary counts
    """
    # Get user preferences for warning days
    prefs = db.query(UserPreferences).filter_by(id=1).first()
    warning_days = prefs.calibration_warning_days if prefs else 30

    # Get all non-retired units of the specified device type
    units = db.query(RosterUnit).filter(
        RosterUnit.device_type == device_type,
        RosterUnit.retired == False
    ).all()

    available_units = []
    reserved_units = []
    expired_units = []
    expiring_soon_units = []
    needs_calibration_units = []
    cal_expiring_today = []  # Units whose calibration expires ON this day

    for unit in units:
        is_avail, status, reservation_name = is_unit_available_on_date(
            db, unit, check_date, warning_days
        )

        cal_status = get_calibration_status(unit, check_date, warning_days)
        expiry_date = None
        if unit.last_calibrated:
            expiry_date = (unit.last_calibrated + timedelta(days=365)).isoformat()

        unit_info = {
            "id": unit.id,
            "last_calibrated": unit.last_calibrated.isoformat() if unit.last_calibrated else None,
            "expiry_date": expiry_date,
            "calibration_status": cal_status,
            "deployed": unit.deployed,
            "note": unit.note or ""
        }

        # Check if calibration expires ON this specific day
        if unit.last_calibrated:
            unit_expiry_date = unit.last_calibrated + timedelta(days=365)
            if unit_expiry_date == check_date:
                cal_expiring_today.append(unit_info)

        if status == "available":
            available_units.append(unit_info)
            if cal_status == "expiring_soon":
                expiring_soon_units.append(unit_info)
        elif status == "reserved":
            unit_info["reservation_name"] = reservation_name
            reserved_units.append(unit_info)
            if cal_status == "expiring_soon":
                expiring_soon_units.append(unit_info)
        elif status == "expired":
            expired_units.append(unit_info)
        elif status == "needs_calibration":
            needs_calibration_units.append(unit_info)

    # Get active reservations on this date
    reservations = db.query(JobReservation).filter(
        JobReservation.device_type == device_type,
        JobReservation.start_date <= check_date,
        JobReservation.end_date >= check_date
    ).all()

    reservation_list = []
    for res in reservations:
        # Count assigned units for this reservation
        assigned_count = db.query(JobReservationUnit).filter(
            JobReservationUnit.reservation_id == res.id
        ).count()

        reservation_list.append({
            "id": res.id,
            "name": res.name,
            "start_date": res.start_date.isoformat(),
            "end_date": res.end_date.isoformat(),
            "assignment_type": res.assignment_type,
            "quantity_needed": res.quantity_needed,
            "assigned_count": assigned_count,
            "color": res.color,
            "project_id": res.project_id
        })

    return {
        "date": check_date.isoformat(),
        "device_type": device_type,
        "available_units": available_units,
        "reserved_units": reserved_units,
        "expired_units": expired_units,
        "expiring_soon_units": expiring_soon_units,
        "needs_calibration_units": needs_calibration_units,
        "cal_expiring_today": cal_expiring_today,
        "reservations": reservation_list,
        "counts": {
            "available": len(available_units),
            "reserved": len(reserved_units),
            "expired": len(expired_units),
            "expiring_soon": len(expiring_soon_units),
            "needs_calibration": len(needs_calibration_units),
            "cal_expiring_today": len(cal_expiring_today),
            "total": len(units)
        }
    }


def get_calendar_year_data(
    db: Session,
    year: int,
    device_type: str = "seismograph"
) -> Dict:
    """
    Get calendar data for an entire year.

    For performance, this returns summary counts per day rather than
    full unit lists. Use get_day_summary() for detailed day data.
    """
    # Get user preferences
    prefs = db.query(UserPreferences).filter_by(id=1).first()
    warning_days = prefs.calibration_warning_days if prefs else 30

    # Get all units
    units = db.query(RosterUnit).filter(
        RosterUnit.device_type == device_type,
        RosterUnit.retired == False
    ).all()

    # Get all reservations that overlap with this year
    # Include TBD reservations (end_date is null) that started before year end
    year_start = date(year, 1, 1)
    year_end = date(year, 12, 31)

    reservations = db.query(JobReservation).filter(
        JobReservation.device_type == device_type,
        JobReservation.start_date <= year_end,
        or_(
            JobReservation.end_date >= year_start,
            JobReservation.end_date == None  # TBD reservations
        )
    ).all()

    # Get all unit assignments for these reservations
    reservation_ids = [r.id for r in reservations]
    assignments = db.query(JobReservationUnit).filter(
        JobReservationUnit.reservation_id.in_(reservation_ids)
    ).all() if reservation_ids else []

    # Build a lookup: unit_id -> list of (start_date, end_date, reservation_name)
    # For TBD reservations, use estimated_end_date if available, or a far future date
    unit_reservations = {}
    for res in reservations:
        res_assignments = [a for a in assignments if a.reservation_id == res.id]
        for assignment in res_assignments:
            unit_id = assignment.unit_id
            # Use unit-specific dates if set, otherwise use reservation dates
            start_d = assignment.unit_start_date or res.start_date
            if assignment.unit_end_tbd or (assignment.unit_end_date is None and res.end_date_tbd):
                # TBD: use estimated date or far future for availability calculation
                end_d = res.estimated_end_date or date(year + 5, 12, 31)
            else:
                end_d = assignment.unit_end_date or res.end_date or date(year + 5, 12, 31)

            if unit_id not in unit_reservations:
                unit_reservations[unit_id] = []
            unit_reservations[unit_id].append((start_d, end_d, res.name))

    # Generate data for each month
    months_data = {}

    for month in range(1, 13):
        # Get first and last day of month
        first_day = date(year, month, 1)
        if month == 12:
            last_day = date(year, 12, 31)
        else:
            last_day = date(year, month + 1, 1) - timedelta(days=1)

        days_data = {}
        current_day = first_day

        while current_day <= last_day:
            available = 0
            reserved = 0
            expired = 0
            expiring_soon = 0
            needs_cal = 0
            cal_expiring_on_day = 0  # Units whose calibration expires ON this day
            cal_expired_on_day = 0   # Units whose calibration expired ON this day

            for unit in units:
                # Check calibration
                cal_status = get_calibration_status(unit, current_day, warning_days)

                # Check if calibration expires/expired ON this specific day
                if unit.last_calibrated:
                    unit_expiry = unit.last_calibrated + timedelta(days=365)
                    if unit_expiry == current_day:
                        cal_expiring_on_day += 1
                    # Check if expired yesterday (first day of being expired)
                    elif unit_expiry == current_day - timedelta(days=1):
                        cal_expired_on_day += 1

                if cal_status == "expired":
                    expired += 1
                    continue
                if cal_status == "needs_calibration":
                    needs_cal += 1
                    continue

                # Check if reserved
                is_reserved = False
                if unit.id in unit_reservations:
                    for start_d, end_d, _ in unit_reservations[unit.id]:
                        if start_d <= current_day <= end_d:
                            is_reserved = True
                            break

                if is_reserved:
                    reserved += 1
                else:
                    available += 1

                if cal_status == "expiring_soon":
                    expiring_soon += 1

            days_data[current_day.day] = {
                "available": available,
                "reserved": reserved,
                "expired": expired,
                "expiring_soon": expiring_soon,
                "needs_calibration": needs_cal,
                "cal_expiring_on_day": cal_expiring_on_day,
                "cal_expired_on_day": cal_expired_on_day
            }

            current_day += timedelta(days=1)

        months_data[month] = {
            "name": first_day.strftime("%B"),
            "short_name": first_day.strftime("%b"),
            "days": days_data,
            "first_weekday": first_day.weekday(),  # 0=Monday, 6=Sunday
            "num_days": last_day.day
        }

    # Also include reservation summary for the year
    reservation_list = []
    for res in reservations:
        assigned_count = len([a for a in assignments if a.reservation_id == res.id])
        reservation_list.append({
            "id": res.id,
            "name": res.name,
            "start_date": res.start_date.isoformat(),
            "end_date": res.end_date.isoformat(),
            "quantity_needed": res.quantity_needed,
            "assigned_count": assigned_count,
            "color": res.color
        })

    return {
        "year": year,
        "device_type": device_type,
        "months": months_data,
        "reservations": reservation_list,
        "total_units": len(units)
    }


def get_rolling_calendar_data(
    db: Session,
    start_year: int,
    start_month: int,
    device_type: str = "seismograph"
) -> Dict:
    """
    Get calendar data for 12 months starting from a specific month/year.

    This supports the rolling calendar view where users can scroll through
    months one at a time, viewing any 12-month window.
    """
    # Get user preferences
    prefs = db.query(UserPreferences).filter_by(id=1).first()
    warning_days = prefs.calibration_warning_days if prefs else 30

    # Get all units
    units = db.query(RosterUnit).filter(
        RosterUnit.device_type == device_type,
        RosterUnit.retired == False
    ).all()

    # Calculate the date range for 12 months
    first_date = date(start_year, start_month, 1)
    # Calculate end date (12 months later)
    end_year = start_year + 1 if start_month == 1 else start_year
    end_month = 12 if start_month == 1 else start_month - 1
    if start_month == 1:
        end_year = start_year
        end_month = 12
    else:
        # 12 months from start_month means we end at start_month - 1 next year
        end_year = start_year + 1
        end_month = start_month - 1

    # Actually, simpler: go 11 months forward from start
    end_year = start_year + ((start_month + 10) // 12)
    end_month = ((start_month + 10) % 12) + 1
    if end_month == 12:
        last_date = date(end_year, 12, 31)
    else:
        last_date = date(end_year, end_month + 1, 1) - timedelta(days=1)

    # Get all reservations that overlap with this 12-month range
    reservations = db.query(JobReservation).filter(
        JobReservation.device_type == device_type,
        JobReservation.start_date <= last_date,
        or_(
            JobReservation.end_date >= first_date,
            JobReservation.end_date == None  # TBD reservations
        )
    ).all()

    # Get all unit assignments for these reservations
    reservation_ids = [r.id for r in reservations]
    assignments = db.query(JobReservationUnit).filter(
        JobReservationUnit.reservation_id.in_(reservation_ids)
    ).all() if reservation_ids else []

    # Build a lookup: unit_id -> list of (start_date, end_date, reservation_name)
    unit_reservations = {}
    for res in reservations:
        res_assignments = [a for a in assignments if a.reservation_id == res.id]
        for assignment in res_assignments:
            unit_id = assignment.unit_id
            start_d = assignment.unit_start_date or res.start_date
            if assignment.unit_end_tbd or (assignment.unit_end_date is None and res.end_date_tbd):
                end_d = res.estimated_end_date or date(start_year + 5, 12, 31)
            else:
                end_d = assignment.unit_end_date or res.end_date or date(start_year + 5, 12, 31)

            if unit_id not in unit_reservations:
                unit_reservations[unit_id] = []
            unit_reservations[unit_id].append((start_d, end_d, res.name))

    # Generate data for each of the 12 months
    months_data = []
    current_year = start_year
    current_month = start_month

    for i in range(12):
        # Calculate this month's year and month
        m_year = start_year + ((start_month - 1 + i) // 12)
        m_month = ((start_month - 1 + i) % 12) + 1

        first_day = date(m_year, m_month, 1)
        if m_month == 12:
            last_day = date(m_year, 12, 31)
        else:
            last_day = date(m_year, m_month + 1, 1) - timedelta(days=1)

        days_data = {}
        current_day = first_day

        while current_day <= last_day:
            available = 0
            reserved = 0
            expired = 0
            expiring_soon = 0
            needs_cal = 0
            cal_expiring_on_day = 0
            cal_expired_on_day = 0

            for unit in units:
                cal_status = get_calibration_status(unit, current_day, warning_days)

                if unit.last_calibrated:
                    unit_expiry = unit.last_calibrated + timedelta(days=365)
                    if unit_expiry == current_day:
                        cal_expiring_on_day += 1
                    elif unit_expiry == current_day - timedelta(days=1):
                        cal_expired_on_day += 1

                if cal_status == "expired":
                    expired += 1
                    continue
                if cal_status == "needs_calibration":
                    needs_cal += 1
                    continue

                is_reserved = False
                if unit.id in unit_reservations:
                    for start_d, end_d, _ in unit_reservations[unit.id]:
                        if start_d <= current_day <= end_d:
                            is_reserved = True
                            break

                if is_reserved:
                    reserved += 1
                else:
                    available += 1

                if cal_status == "expiring_soon":
                    expiring_soon += 1

            days_data[current_day.day] = {
                "available": available,
                "reserved": reserved,
                "expired": expired,
                "expiring_soon": expiring_soon,
                "needs_calibration": needs_cal,
                "cal_expiring_on_day": cal_expiring_on_day,
                "cal_expired_on_day": cal_expired_on_day
            }

            current_day += timedelta(days=1)

        months_data.append({
            "year": m_year,
            "month": m_month,
            "name": first_day.strftime("%B"),
            "short_name": first_day.strftime("%b"),
            "year_short": first_day.strftime("%y"),
            "days": days_data,
            "first_weekday": first_day.weekday(),
            "num_days": last_day.day
        })

    return {
        "start_year": start_year,
        "start_month": start_month,
        "device_type": device_type,
        "months": months_data,
        "total_units": len(units)
    }


def check_calibration_conflicts(
    db: Session,
    reservation_id: str
) -> List[Dict]:
    """
    Check if any units assigned to a reservation will have their
    calibration expire during the reservation period.

    Returns list of conflicts with unit info and expiry date.
    """
    reservation = db.query(JobReservation).filter_by(id=reservation_id).first()
    if not reservation:
        return []

    # Get assigned units
    assigned = db.query(JobReservationUnit).filter_by(
        reservation_id=reservation_id
    ).all()

    conflicts = []
    for assignment in assigned:
        unit = db.query(RosterUnit).filter_by(id=assignment.unit_id).first()
        if not unit or not unit.last_calibrated:
            continue

        expiry_date = unit.last_calibrated + timedelta(days=365)

        # Check if expiry falls within reservation period
        if reservation.start_date < expiry_date <= reservation.end_date:
            conflicts.append({
                "unit_id": unit.id,
                "last_calibrated": unit.last_calibrated.isoformat(),
                "expiry_date": expiry_date.isoformat(),
                "reservation_name": reservation.name,
                "days_into_job": (expiry_date - reservation.start_date).days
            })

    return conflicts


def get_available_units_for_period(
    db: Session,
    start_date: date,
    end_date: date,
    device_type: str = "seismograph",
    exclude_reservation_id: Optional[str] = None
) -> List[Dict]:
    """
    Get units that are available for the entire specified period.

    A unit is available if:
    - Not retired
    - Calibration is valid through the end date
    - Not assigned to any other reservation that overlaps the period
    """
    prefs = db.query(UserPreferences).filter_by(id=1).first()
    warning_days = prefs.calibration_warning_days if prefs else 30

    units = db.query(RosterUnit).filter(
        RosterUnit.device_type == device_type,
        RosterUnit.retired == False
    ).all()

    # Get reservations that overlap with this period
    overlapping_reservations = db.query(JobReservation).filter(
        JobReservation.device_type == device_type,
        JobReservation.start_date <= end_date,
        JobReservation.end_date >= start_date
    )

    if exclude_reservation_id:
        overlapping_reservations = overlapping_reservations.filter(
            JobReservation.id != exclude_reservation_id
        )

    overlapping_reservations = overlapping_reservations.all()

    # Get all units assigned to overlapping reservations
    reserved_unit_ids = set()
    for res in overlapping_reservations:
        assigned = db.query(JobReservationUnit).filter_by(
            reservation_id=res.id
        ).all()
        for a in assigned:
            reserved_unit_ids.add(a.unit_id)

    available_units = []
    for unit in units:
        # Check if already reserved
        if unit.id in reserved_unit_ids:
            continue

        # Check calibration through end of period
        if not unit.last_calibrated:
            continue  # Needs calibration

        expiry_date = unit.last_calibrated + timedelta(days=365)
        if expiry_date <= end_date:
            continue  # Calibration expires during period

        cal_status = get_calibration_status(unit, end_date, warning_days)

        available_units.append({
            "id": unit.id,
            "last_calibrated": unit.last_calibrated.isoformat(),
            "expiry_date": expiry_date.isoformat(),
            "calibration_status": cal_status,
            "deployed": unit.deployed,
            "note": unit.note or ""
        })

    return available_units