import calendar
from bisect import bisect_right
from datetime import date, datetime, timedelta
from decimal import Decimal
from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
from fastapi import APIRouter, Depends
from sqlalchemy import select, func
from sqlalchemy.orm import Session

from database import get_db
from models import EggCollection, FlockHistory, FeedPurchase, OtherPurchase, User
from schemas import DashboardStats, BudgetStats, MonthlySummary
from auth import get_current_user

router = APIRouter(prefix="/api/stats", tags=["stats"])


def _today(user_timezone: str) -> date:
    try:
        return datetime.now(ZoneInfo(user_timezone)).date()
    except ZoneInfoNotFoundError:
        return date.today()


def _avg_per_hen_30d(db: Session, user_id: int, start_30d: date) -> float | None:
    flock_at_date = (
        select(FlockHistory.chicken_count)
        .where(FlockHistory.user_id == user_id)
        .where(FlockHistory.date <= EggCollection.date)
        .order_by(FlockHistory.date.desc())
        .limit(1)
        .correlate(EggCollection)
        .scalar_subquery()
    )

    rows = db.execute(
        select(EggCollection.eggs, flock_at_date.label('flock_count'))
        .where(EggCollection.user_id == user_id)
        .where(EggCollection.date >= start_30d)
    ).all()

    valid = [(r.eggs, r.flock_count) for r in rows if r.flock_count]
    if not valid:
        return None
    return round(sum(e / f for e, f in valid) / len(valid), 3)


def _current_flock(db: Session, user_id: int) -> int | None:
    row = db.scalars(
        select(FlockHistory)
        .where(FlockHistory.user_id == user_id)
        .order_by(FlockHistory.date.desc())
        .limit(1)
    ).first()
    return row.chicken_count if row else None


def _total_eggs(db: Session, user_id: int, start: date | None = None, end: date | None = None) -> int:
    q = select(func.coalesce(func.sum(EggCollection.eggs), 0)).where(EggCollection.user_id == user_id)
    if start:
        q = q.where(EggCollection.date >= start)
    if end:
        q = q.where(EggCollection.date <= end)
    return db.scalar(q)


def _total_feed_cost(db: Session, user_id: int, start: date | None = None, end: date | None = None):
    q = select(
        func.coalesce(func.sum(FeedPurchase.bags * FeedPurchase.price_per_bag), 0)
    ).where(FeedPurchase.user_id == user_id)
    if start:
        q = q.where(FeedPurchase.date >= start)
    if end:
        q = q.where(FeedPurchase.date <= end)
    return db.scalar(q)


def _total_other_cost(db: Session, user_id: int, start: date | None = None, end: date | None = None):
    q = select(func.coalesce(func.sum(OtherPurchase.total), 0)).where(OtherPurchase.user_id == user_id)
    if start:
        q = q.where(OtherPurchase.date >= start)
    if end:
        q = q.where(OtherPurchase.date <= end)
    return db.scalar(q)


@router.get("/dashboard", response_model=DashboardStats)
def dashboard_stats(
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    uid = current_user.id
    today     = _today(current_user.timezone)
    start_30d = today - timedelta(days=30)
    start_7d  = today - timedelta(days=7)

    total_alltime = _total_eggs(db, uid)
    total_30d     = _total_eggs(db, uid, start=start_30d)
    total_7d      = _total_eggs(db, uid, start=start_7d)
    flock         = _current_flock(db, uid)

    days_tracked = db.scalar(
        select(func.count(func.distinct(EggCollection.date)))
        .where(EggCollection.user_id == uid)
    )

    days_with_data_30d = db.scalar(
        select(func.count(func.distinct(EggCollection.date)))
        .where(EggCollection.user_id == uid)
        .where(EggCollection.date >= start_30d)
    )

    avg_per_day = round(total_30d / days_with_data_30d, 2) if days_with_data_30d else None
    avg_per_hen = _avg_per_hen_30d(db, uid, start_30d)

    return DashboardStats(
        current_flock=flock,
        total_eggs_alltime=total_alltime,
        total_eggs_30d=total_30d,
        total_eggs_7d=total_7d,
        avg_eggs_per_day_30d=avg_per_day,
        avg_eggs_per_hen_day_30d=avg_per_hen,
        days_tracked=days_tracked,
    )


@router.get("/monthly", response_model=list[MonthlySummary])
def monthly_stats(
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    uid = current_user.id
    MONTH_NAMES = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec']

    egg_rows = db.execute(
        select(
            func.year(EggCollection.date).label('year'),
            func.month(EggCollection.date).label('month'),
            func.sum(EggCollection.eggs).label('total_eggs'),
            func.count(EggCollection.date).label('days_logged'),
        )
        .where(EggCollection.user_id == uid)
        .group_by(func.year(EggCollection.date), func.month(EggCollection.date))
        .order_by(func.year(EggCollection.date).desc(), func.month(EggCollection.date).desc())
    ).all()

    if not egg_rows:
        return []

    feed_rows = db.execute(
        select(
            func.year(FeedPurchase.date).label('year'),
            func.month(FeedPurchase.date).label('month'),
            func.sum(FeedPurchase.bags * FeedPurchase.price_per_bag).label('feed_cost'),
        )
        .where(FeedPurchase.user_id == uid)
        .group_by(func.year(FeedPurchase.date), func.month(FeedPurchase.date))
    ).all()

    feed_map = {(r.year, r.month): r.feed_cost for r in feed_rows}

    other_rows = db.execute(
        select(
            func.year(OtherPurchase.date).label('year'),
            func.month(OtherPurchase.date).label('month'),
            func.sum(OtherPurchase.total).label('other_cost'),
        )
        .where(OtherPurchase.user_id == uid)
        .group_by(func.year(OtherPurchase.date), func.month(OtherPurchase.date))
    ).all()

    other_map = {(r.year, r.month): r.other_cost for r in other_rows}

    # Fetch all flock history once (ascending) to avoid N+1 per month
    flock_all = db.scalars(
        select(FlockHistory)
        .where(FlockHistory.user_id == uid)
        .order_by(FlockHistory.date)
    ).all()
    flock_dates  = [f.date for f in flock_all]
    flock_counts = [f.chicken_count for f in flock_all]

    def flock_at(month_end: date) -> int | None:
        idx = bisect_right(flock_dates, month_end) - 1
        return flock_counts[idx] if idx >= 0 else None

    results = []
    for row in egg_rows:
        y, m = int(row.year), int(row.month)
        month_end = date(y, m, calendar.monthrange(y, m)[1])
        flock = flock_at(month_end)

        total_eggs  = int(row.total_eggs)
        days_logged = int(row.days_logged)
        avg_per_day = round(total_eggs / days_logged, 2) if days_logged else None
        avg_per_hen = round(avg_per_day / flock, 3) if (avg_per_day and flock) else None

        raw_feed_cost  = feed_map.get((y, m))
        raw_other_cost = other_map.get((y, m))
        feed_cost  = round(raw_feed_cost,  2) if raw_feed_cost  else None
        other_cost = round(raw_other_cost, 2) if raw_other_cost else None

        total_cost = (raw_feed_cost or Decimal(0)) + (raw_other_cost or Decimal(0))
        cpe = round(total_cost / total_eggs, 4) if (total_cost and total_eggs) else None
        cpd = round(cpe * 12, 4) if cpe else None

        results.append(MonthlySummary(
            year=y,
            month=m,
            month_label=f"{MONTH_NAMES[m - 1]} {y}",
            total_eggs=total_eggs,
            days_logged=days_logged,
            avg_eggs_per_day=avg_per_day,
            flock_at_month_end=flock,
            avg_eggs_per_hen_per_day=avg_per_hen,
            feed_cost=feed_cost,
            other_cost=other_cost,
            cost_per_egg=cpe,
            cost_per_dozen=cpd,
        ))

    return results


@router.get("/budget", response_model=BudgetStats)
def budget_stats(
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    uid = current_user.id
    today     = _today(current_user.timezone)
    start_30d = today - timedelta(days=30)

    total_feed_cost      = _total_feed_cost(db, uid)
    total_feed_cost_30d  = _total_feed_cost(db, uid, start=start_30d)
    total_other_cost     = _total_other_cost(db, uid)
    total_other_cost_30d = _total_other_cost(db, uid, start=start_30d)
    total_eggs           = _total_eggs(db, uid)
    total_eggs_30d       = _total_eggs(db, uid, start=start_30d)

    def cost_per_egg(cost, eggs):
        if not eggs or not cost:
            return None
        return round(Decimal(str(cost)) / Decimal(eggs), 4)

    def cost_per_dozen(cpe):
        return round(cpe * 12, 4) if cpe else None

    combined_cost     = total_feed_cost + total_other_cost
    combined_cost_30d = total_feed_cost_30d + total_other_cost_30d

    cpe     = cost_per_egg(combined_cost, total_eggs)
    cpe_30d = cost_per_egg(combined_cost_30d, total_eggs_30d)

    return BudgetStats(
        total_feed_cost=round(Decimal(str(total_feed_cost)), 2) if total_feed_cost else None,
        total_feed_cost_30d=round(Decimal(str(total_feed_cost_30d)), 2) if total_feed_cost_30d else None,
        total_other_cost=round(Decimal(str(total_other_cost)), 2) if total_other_cost else None,
        total_other_cost_30d=round(Decimal(str(total_other_cost_30d)), 2) if total_other_cost_30d else None,
        total_eggs_alltime=total_eggs,
        total_eggs_30d=total_eggs_30d,
        cost_per_egg=cpe,
        cost_per_dozen=cost_per_dozen(cpe),
        cost_per_egg_30d=cpe_30d,
        cost_per_dozen_30d=cost_per_dozen(cpe_30d),
    )