import json
import os
from datetime import date, timedelta
import calendar
from storage import load_json, save_json

DATA_DIR = os.environ.get("DATA_DIR", os.path.join(os.path.dirname(__file__), "data"))
BILLS_FILE = os.path.join(DATA_DIR, "bills.json")


def load_bills():
    return load_json(BILLS_FILE, [])


def save_bills(bills):
    save_json(BILLS_FILE, bills)


def get_week_label(day):
    if day <= 7:
        return "Week 1 (1–7)"
    elif day <= 14:
        return "Week 2 (8–14)"
    elif day <= 21:
        return "Week 3 (15–21)"
    else:
        return "Week 4 (22–end)"


def get_week_num(day):
    if day <= 7:
        return 1
    elif day <= 14:
        return 2
    elif day <= 21:
        return 3
    else:
        return 4


def bills_for_month(year, month):
    from datetime import datetime
    all_bills = load_bills()
    _, num_days = calendar.monthrange(year, month)
    result = []
    for b in all_bills:
        if not b.get("active", True):
            continue
        # Specific-date bills (BNPL payments)
        if b.get("due_date_str"):
            try:
                d = datetime.strptime(b["due_date_str"], "%Y-%m-%d").date()
                if d.year == year and d.month == month:
                    result.append({**b, "due_date": d, "due_day": d.day})
            except ValueError:
                pass
        # Recurring monthly bills
        elif b.get("due_day"):
            due_day = b["due_day"]
            if 1 <= due_day <= num_days:
                result.append({**b, "due_date": date(year, month, due_day)})
    return sorted(result, key=lambda x: x.get("due_day", 0))


def calendar_grid(year, month):
    _, num_days = calendar.monthrange(year, month)
    first_weekday = calendar.monthrange(year, month)[0]  # 0=Mon
    # Convert to Sun-first
    first_weekday = (first_weekday + 1) % 7

    days = []
    for _ in range(first_weekday):
        days.append(None)
    for d in range(1, num_days + 1):
        days.append(d)
    while len(days) % 7 != 0:
        days.append(None)

    return [days[i:i+7] for i in range(0, len(days), 7)]