from datetime import datetime
from typing import Optional

from fastapi import APIRouter, Depends, HTTPException, Query
from fastapi.responses import Response as FastAPIResponse
from pydantic import BaseModel
from sqlalchemy import and_, or_
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,
    TransactionType,
    TransactionUpdate,
)

from app.services.budget_projection import (
    NOT_INSTALLMENT_ANCHOR,
    get_cycle_range,
    get_previous_cycle,
)
from app.services.csv_export import build_transactions_csv
from app.services.exchange_rate import get_converted_amount_expr
from app.services.installments import (
    DEFAULT_NUM_INSTALLMENTS,
    create_plan,
    is_tasa_cero_merchant,
    teardown_plan_for_anchor,
)

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


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,
    exclude_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 exclude_source:
        query = query.where(Transaction.source != exclude_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)
        prev_y, prev_m = get_previous_cycle(cycle_year, cycle_month)
        prev_start, prev_end = get_cycle_range(prev_y, prev_m)
        # Normal transactions in this cycle (not deferred) + deferred from previous cycle
        query = query.where(
            or_(
                and_(
                    Transaction.date >= start,
                    Transaction.date < end,
                    Transaction.deferred_to_next_cycle == False,  # noqa: E712
                ),
                and_(
                    Transaction.date >= prev_start,
                    Transaction.date < prev_end,
                    Transaction.deferred_to_next_cycle == True,  # noqa: E712
                ),
            )
        )
    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(), col(Transaction.id).desc()).offset(offset).limit(limit)
    return session.exec(query).all()


class BulkActionRequest(BaseModel):
    ids: list[int]
    action: str  # 'delete' | 'set_category' | 'set_deferred'
    category_id: Optional[int] = None  # for set_category (None clears)
    deferred: Optional[bool] = None  # for set_deferred


class BulkActionResponse(BaseModel):
    affected: int


@router.post("/bulk", response_model=BulkActionResponse)
def bulk_action(
    req: BulkActionRequest,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    """Apply one action to many transactions atomically (review 4.4)."""
    if not req.ids or len(req.ids) > 500:
        raise HTTPException(status_code=400, detail="ids must contain 1-500 entries")
    if req.action not in ("delete", "set_category", "set_deferred"):
        raise HTTPException(status_code=400, detail=f"Unknown action: {req.action}")
    if req.action == "set_deferred" and req.deferred is None:
        raise HTTPException(status_code=400, detail="deferred is required for set_deferred")
    if req.action == "set_category" and req.category_id is not None:
        if session.get(Category, req.category_id) is None:
            raise HTTPException(status_code=404, detail="Category not found")

    txs = session.exec(
        select(Transaction).where(col(Transaction.id).in_(req.ids))
    ).all()
    affected = 0
    for tx in txs:
        if req.action == "delete":
            teardown_plan_for_anchor(session, tx)
            session.delete(tx)
        elif req.action == "set_category":
            tx.category_id = req.category_id
            session.add(tx)
        elif req.action == "set_deferred":
            if tx.installment_plan_id:
                continue  # cuotas of a plan cannot be deferred
            tx.deferred_to_next_cycle = bool(req.deferred)
            session.add(tx)
        affected += 1
    session.commit()
    return {"affected": affected}


@router.get("/export")
def export_transactions_csv(
    source: Optional[TransactionSource] = None,
    transaction_type: Optional[TransactionType] = None,
    start_date: Optional[str] = None,
    end_date: Optional[str] = None,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    """Download transactions as CSV (filters optional). Cookie-authenticated,
    so a plain <a href> download works from the SPA."""
    csv_text = build_transactions_csv(
        session,
        source=source,
        transaction_type=transaction_type,
        start_date=datetime.fromisoformat(start_date) if start_date else None,
        end_date=datetime.fromisoformat(end_date) if end_date else None,
    )
    return FastAPIResponse(
        content=csv_text,
        media_type="text/csv; charset=utf-8",
        headers={
            "Content-Disposition": 'attachment; filename="wealthysmart-transactions.csv"'
        },
    )


@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
    amount_crc = get_converted_amount_expr(session)

    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(amount_crc), 0)).where(
                Transaction.date >= start,
                Transaction.date < end,
                NOT_INSTALLMENT_ANCHOR,
            )
        ).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(), col(Transaction.id).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)

    # Tasa Cero auto-detection: BAC prefixes financed purchases with "CC ".
    # Default 3 cuotas starting on the purchase date; editable afterwards via
    # /installment-plans.
    tasa_cero_note = ""
    if (
        tx.source == TransactionSource.CREDIT_CARD
        and tx.transaction_type == TransactionType.COMPRA
        and is_tasa_cero_merchant(tx.merchant)
    ):
        create_plan(session, tx, DEFAULT_NUM_INSTALLMENTS, tx.date)
        session.commit()
        session.refresh(tx)
        tasa_cero_note = f" — Tasa Cero {DEFAULT_NUM_INSTALLMENTS} cuotas"

    # Send push notification
    symbols = {Currency.CRC: "₡", Currency.USD: "$", Currency.EUR: "€"}
    symbol = symbols.get(tx.currency, tx.currency.value)
    amount_str = f"{symbol}{tx.amount:,.0f}" if tx.currency == Currency.CRC else f"{symbol}{tx.amount:,.2f}"
    is_income = tx.transaction_type in (TransactionType.DEPOSITO, TransactionType.SALARY)
    is_salary = tx.transaction_type == TransactionType.SALARY
    label = "salario" if is_salary else ("depósito" if is_income else tx.transaction_type.value.lower())
    send_push_to_all(
        session,
        title=f"{'🏦' if is_income else '💳'} {tx.merchant}",
        body=f"{amount_str} — {tx.bank.value} {label}{tasa_cero_note}",
        url="/salarios" if is_income else "/budget",
    )

    if is_salary:
        from app.services.savings_accrual import maybe_apply_monthly_savings
        maybe_apply_monthly_savings(session, tx)

    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)
    if update_data.get("deferred_to_next_cycle") is not None and tx.installment_plan_id:
        raise HTTPException(
            status_code=400,
            detail="Cuotas of an installment plan cannot be deferred",
        )
    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")
    teardown_plan_for_anchor(session, tx)
    session.delete(tx)
    session.commit()