"""Expenses CSV reader and summary."""

import csv
from collections import defaultdict
from fastapi import APIRouter, Query

import sys
from pathlib import Path
sys.path.insert(0, str(Path(__file__).parent.parent))

from lib_bridge import EXPENSES_CSV

router = APIRouter(tags=["expenses"])


def _read_expenses() -> list[dict]:
    """Read all expenses from CSV."""
    if not EXPENSES_CSV.exists():
        return []
    with open(EXPENSES_CSV, "r", newline="") as f:
        return list(csv.DictReader(f))


@router.get("/expenses")
def list_expenses(month: str | None = Query(None, description="Filter by YYYY-MM")):
    """List expenses, optionally filtered by month."""
    expenses = _read_expenses()
    if month:
        expenses = [e for e in expenses if e.get("date", "").startswith(month)]
    return expenses


@router.get("/expenses/summary")
def expenses_summary(month: str | None = Query(None, description="Filter by YYYY-MM")):
    """Monthly total, count, top 10 vendors by amount."""
    expenses = _read_expenses()
    if month:
        expenses = [e for e in expenses if e.get("date", "").startswith(month)]

    if not expenses:
        return {"total": 0, "count": 0, "top_vendors": [], "month": month}

    total = 0.0
    vendor_totals = defaultdict(float)
    for e in expenses:
        try:
            amount = float(e.get("amount", 0))
        except (ValueError, TypeError):
            amount = 0.0
        total += amount
        vendor = e.get("vendor", "unknown")
        vendor_totals[vendor] += amount

    top_vendors = sorted(vendor_totals.items(), key=lambda x: x[1], reverse=True)[:10]

    return {
        "total": round(total, 2),
        "count": len(expenses),
        "top_vendors": [{"vendor": v, "amount": round(a, 2)} for v, a in top_vendors],
        "month": month,
    }