from datetime import datetime
from typing import Optional

from fastapi import APIRouter, Depends, HTTPException, Query
from pydantic import BaseModel
from sqlmodel import Session, col, func, select

from app.auth import get_current_user
from app.db import get_session
from app.api.v1.endpoints.notifications import send_push_to_all
from app.models.models import (
    Category,
    Currency,
    Transaction,
    TransactionCreate,
    TransactionRead,
    TransactionSource,
    TransactionUpdate,
)

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


def get_cycle_range(year: int, month: int) -> tuple[datetime, datetime]:
    """Return (start, end) for billing cycle: month/18 to month+1/18."""
    start = datetime(year, month, 18)
    if month == 12:
        end = datetime(year + 1, 1, 18)
    else:
        end = datetime(year, month + 1, 18)
    return start, end


class BillingCycle(BaseModel):
    year: int
    month: int
    label: str
    count: int
    total: float


def auto_categorize(merchant: str, session: Session) -> Optional[int]:
    categories = session.exec(select(Category)).all()
    merchant_lower = merchant.lower()
    for cat in categories:
        if cat.auto_match_patterns:
            patterns = [p.strip().lower() for p in cat.auto_match_patterns.split(",")]
            if any(p in merchant_lower for p in patterns if p):
                return cat.id
    return None


@router.get("/", response_model=list[TransactionRead])
def list_transactions(
    source: Optional[TransactionSource] = None,
    search: Optional[str] = None,
    category_id: Optional[int] = None,
    cycle_year: Optional[int] = None,
    cycle_month: Optional[int] = None,
    start_date: Optional[str] = None,
    end_date: Optional[str] = None,
    limit: int = Query(default=50, le=500),
    offset: int = 0,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    query = select(Transaction)
    if source:
        query = query.where(Transaction.source == source)
    if category_id:
        query = query.where(Transaction.category_id == category_id)
    if search:
        query = query.where(col(Transaction.merchant).ilike(f"%{search}%"))
    if cycle_year and cycle_month:
        start, end = get_cycle_range(cycle_year, cycle_month)
        query = query.where(Transaction.date >= start, Transaction.date < end)
    elif start_date and end_date:
        query = query.where(
            Transaction.date >= datetime.fromisoformat(start_date),
            Transaction.date < datetime.fromisoformat(end_date),
        )
    query = query.order_by(col(Transaction.date).desc()).offset(offset).limit(limit)
    return session.exec(query).all()


@router.get("/cycles", response_model=list[BillingCycle])
def list_billing_cycles(
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    """Return available billing cycles based on transaction dates."""
    # Get date range of all transactions
    result = session.exec(
        select(func.min(Transaction.date), func.max(Transaction.date))
    ).first()
    if not result or not result[0]:
        return []

    min_date, max_date = result

    cycles = []
    # Determine which cycle the min_date falls into
    if min_date.day < 18:
        # Falls in previous month's cycle
        if min_date.month == 1:
            y, m = min_date.year - 1, 12
        else:
            y, m = min_date.year, min_date.month - 1
    else:
        y, m = min_date.year, min_date.month

    while True:
        start, end = get_cycle_range(y, m)
        if start > max_date:
            break

        # Count transactions in this cycle
        count_result = session.exec(
            select(func.count(), func.coalesce(func.sum(Transaction.amount), 0)).where(
                Transaction.date >= start, Transaction.date < end
            )
        ).first()
        count = count_result[0] if count_result else 0
        total = float(count_result[1]) if count_result else 0.0

        if count > 0:
            month_names = [
                "", "Jan", "Feb", "Mar", "Apr", "May", "Jun",
                "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
            ]
            end_month = m + 1 if m < 12 else 1
            end_year = y if m < 12 else y + 1
            label = f"{month_names[m]} 18 - {month_names[end_month]} 18, {end_year}"
            cycles.append(BillingCycle(year=y, month=m, label=label, count=count, total=total))

        # Next month
        if m == 12:
            y, m = y + 1, 1
        else:
            m += 1

    return list(reversed(cycles))


@router.get("/recent", response_model=list[TransactionRead])
def recent_transactions(
    limit: int = Query(default=5, le=20),
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    query = (
        select(Transaction)
        .where(Transaction.source == TransactionSource.CREDIT_CARD)
        .order_by(col(Transaction.date).desc())
        .limit(limit)
    )
    return session.exec(query).all()


@router.post("/", response_model=TransactionRead, status_code=201)
def create_transaction(
    data: TransactionCreate,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    tx = Transaction.model_validate(data)
    # Duplicate detection by reference
    if tx.reference:
        existing = session.exec(
            select(Transaction).where(Transaction.reference == tx.reference)
        ).first()
        if existing:
            raise HTTPException(
                status_code=409,
                detail=f"Duplicate transaction: reference '{tx.reference}' already exists (id={existing.id})",
            )
    if tx.category_id is None:
        tx.category_id = auto_categorize(tx.merchant, session)
    session.add(tx)
    session.commit()
    session.refresh(tx)

    # Send push notification
    symbol = "₡" if tx.currency == Currency.CRC else tx.currency.value
    amount_str = f"{symbol}{tx.amount:,.0f}" if tx.currency == Currency.CRC else f"{symbol}{tx.amount:,.2f}"
    send_push_to_all(
        session,
        title=f"💳 {tx.merchant}",
        body=f"{amount_str} — {tx.bank.value} {tx.transaction_type.value.lower()}",
        url=f"/budget",
    )

    return tx


@router.patch("/{transaction_id}", response_model=TransactionRead)
def update_transaction(
    transaction_id: int,
    data: TransactionUpdate,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    tx = session.get(Transaction, transaction_id)
    if not tx:
        raise HTTPException(status_code=404, detail="Transaction not found")
    update_data = data.model_dump(exclude_unset=True)
    for key, value in update_data.items():
        setattr(tx, key, value)
    session.add(tx)
    session.commit()
    session.refresh(tx)
    return tx


@router.delete("/{transaction_id}", status_code=204)
def delete_transaction(
    transaction_id: int,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    tx = session.get(Transaction, transaction_id)
    if not tx:
        raise HTTPException(status_code=404, detail="Transaction not found")
    session.delete(tx)
    session.commit()