from datetime import datetime
from typing import Optional

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

from app.auth import get_current_user
from app.db import get_session
from app.models.models import Category, Transaction
from app.api.v1.endpoints.transactions import get_cycle_range

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


class CategorySpending(BaseModel):
    category_id: Optional[int]
    category_name: str
    total: float
    count: int
    percentage: float


class MonthlyTrend(BaseModel):
    year: int
    month: int
    label: str
    total_crc: float
    total_usd: float
    count: int


class DailySpending(BaseModel):
    date: str
    total: float
    count: int


@router.get("/by-category", response_model=list[CategorySpending])
def spending_by_category(
    cycle_year: Optional[int] = None,
    cycle_month: Optional[int] = None,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    query = (
        select(
            Transaction.category_id,
            func.sum(Transaction.amount).label("total"),
            func.count().label("count"),
        )
        .where(Transaction.transaction_type == "COMPRA")
        .group_by(Transaction.category_id)
    )

    if cycle_year and cycle_month:
        start, end = get_cycle_range(cycle_year, cycle_month)
        query = query.where(Transaction.date >= start, Transaction.date < end)

    rows = session.exec(query).all()

    grand_total = sum(r[1] for r in rows) or 1

    results = []
    for category_id, total, count in rows:
        cat_name = "Uncategorized"
        if category_id:
            cat = session.get(Category, category_id)
            if cat:
                cat_name = cat.name
        results.append(
            CategorySpending(
                category_id=category_id,
                category_name=cat_name,
                total=float(total),
                count=count,
                percentage=round(float(total) / grand_total * 100, 1),
            )
        )

    return sorted(results, key=lambda x: x.total, reverse=True)


@router.get("/monthly-trend", response_model=list[MonthlyTrend])
def monthly_trend(
    months: int = 6,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    """Monthly spending totals using billing cycle boundaries (18th-18th)."""
    now = datetime.now()
    results = []
    month_names = [
        "", "Jan", "Feb", "Mar", "Apr", "May", "Jun",
        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
    ]

    y, m = now.year, now.month
    for _ in range(months):
        start, end = get_cycle_range(y, m)

        row = session.exec(
            select(
                func.count(),
                func.coalesce(
                    func.sum(
                        func.case(
                            (Transaction.currency == "CRC", Transaction.amount),
                            else_=0,
                        )
                    ),
                    0,
                ),
                func.coalesce(
                    func.sum(
                        func.case(
                            (Transaction.currency == "USD", Transaction.amount),
                            else_=0,
                        )
                    ),
                    0,
                ),
            )
            .where(
                Transaction.transaction_type == "COMPRA",
                Transaction.date >= start,
                Transaction.date < end,
            )
        ).first()

        count = row[0] if row else 0
        total_crc = float(row[1]) if row else 0.0
        total_usd = float(row[2]) if row else 0.0

        end_month = m + 1 if m < 12 else 1
        label = f"{month_names[m]} - {month_names[end_month]}"

        results.append(
            MonthlyTrend(
                year=y,
                month=m,
                label=label,
                total_crc=total_crc,
                total_usd=total_usd,
                count=count,
            )
        )

        # Previous month
        if m == 1:
            y, m = y - 1, 12
        else:
            m -= 1

    return list(reversed(results))


@router.get("/daily-spending", response_model=list[DailySpending])
def daily_spending(
    cycle_year: Optional[int] = None,
    cycle_month: Optional[int] = None,
    session: Session = Depends(get_session),
    _user: str = Depends(get_current_user),
):
    query = (
        select(
            func.date(Transaction.date).label("day"),
            func.sum(Transaction.amount).label("total"),
            func.count().label("count"),
        )
        .where(Transaction.transaction_type == "COMPRA")
        .group_by(func.date(Transaction.date))
        .order_by(func.date(Transaction.date))
    )

    if cycle_year and cycle_month:
        start, end = get_cycle_range(cycle_year, cycle_month)
        query = query.where(Transaction.date >= start, Transaction.date < end)

    rows = session.exec(query).all()
    return [
        DailySpending(date=str(day), total=float(total), count=count)
        for day, total, count in rows
    ]