import csv
import io
import json
import os
from collections import defaultdict
from datetime import datetime
from decimal import Decimal
from zoneinfo import ZoneInfo

import boto3

from shared.db import current_week, get_orders, get_summary, put_summary

EASTERN = ZoneInfo("America/New_York")
_s3 = boto3.client("s3")
_lambda = boto3.client("lambda")


class DecimalEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, Decimal):
            return float(o)
        return super().default(o)


def lambda_handler(event, context):
    week = event.get("week", current_week())

    existing = get_summary(week)
    if existing:
        return {"status": "already_aggregated", "week": week}

    orders = get_orders(week)
    if not orders:
        return {"status": "no_orders", "week": week}

    summary = build_summary(orders, week)
    order_csv = build_order_summary_csv(summary)
    payroll_csv = build_payroll_csv(orders)

    bucket = os.environ["REPORTS_BUCKET"]
    order_csv_key = f"reports/{week}/order-summary.csv"
    payroll_csv_key = f"reports/{week}/payroll-deductions.csv"

    _s3.put_object(Bucket=bucket, Key=order_csv_key, Body=order_csv, ContentType="text/csv")
    _s3.put_object(Bucket=bucket, Key=payroll_csv_key, Body=payroll_csv, ContentType="text/csv")

    summary["order_csv_s3_key"] = order_csv_key
    summary["payroll_csv_s3_key"] = payroll_csv_key
    put_summary(week, summary)

    _lambda.invoke(
        FunctionName=os.environ["SLACK_NOTIFIER_ARN"],
        InvocationType="Event",
        Payload=json.dumps({"event": "orders_aggregated", "week": week}, cls=DecimalEncoder),
    )

    return {"status": "aggregated", "week": week, "total_employees": len(orders)}


def build_summary(orders: list[dict], week: str) -> dict:
    meal_totals = defaultdict(lambda: {"quantity": 0, "unit_price": 0})
    for order in orders:
        for item in order.get("items", []):
            name = item["name"]
            qty = int(item.get("quantity", 0))
            meal_totals[name]["quantity"] += qty
            meal_totals[name]["unit_price"] = float(item.get("price", 0))

    meals = []
    for name, data in sorted(meal_totals.items()):
        meals.append({
            "meal": name,
            "quantity": data["quantity"],
            "unit_price": data["unit_price"],
            "line_total": round(data["unit_price"] * data["quantity"], 2),
        })

    return {
        "week": week,
        "generated_at": datetime.now(EASTERN).isoformat(),
        "total_employees": len(orders),
        "total_meals": sum(m["quantity"] for m in meals),
        "grand_total": round(sum(m["line_total"] for m in meals), 2),
        "meals": meals,
    }


def build_order_summary_csv(summary: dict) -> str:
    buf = io.StringIO()
    writer = csv.writer(buf)
    writer.writerow(["Meal", "Quantity", "Unit Price", "Line Total"])
    for meal in summary["meals"]:
        writer.writerow([meal["meal"], meal["quantity"], f"${meal['unit_price']:.2f}", f"${meal['line_total']:.2f}"])
    writer.writerow([])
    writer.writerow(["TOTAL", summary["total_meals"], "", f"${summary['grand_total']:.2f}"])
    return buf.getvalue()


def build_payroll_csv(orders: list[dict]) -> str:
    buf = io.StringIO()
    writer = csv.writer(buf)
    writer.writerow(["Employee Name", "Employee Email", "Items Ordered", "Total Deduction"])
    for order in sorted(orders, key=lambda o: o["employee_name"]):
        items_str = "; ".join(
            f"{item['name']} x{int(item['quantity'])} (${float(item.get('subtotal', float(item.get('price', 0)) * int(item.get('quantity', 0)))):.2f})"
            for item in order.get("items", [])
        )
        writer.writerow([
            order["employee_name"],
            order["employee_email"],
            items_str,
            f"${float(order['total']):.2f}",
        ])
    return buf.getvalue()