"""Lambda handler — posts the weekly on-call schedule and previous week's pay summary
to Slack every Monday at 7am ET."""

import logging
import os
from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

import boto3
from slack_sdk import WebClient

from src.blocks import build_pay_summary_blocks, build_week_schedule
from src.schedule import FALLBACK_EXTENSION, ShiftSchedule

logger = logging.getLogger()
logger.setLevel(logging.INFO)

EASTERN = ZoneInfo("America/New_York")

DAY_ORDER = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]


WEEKEND_DAYS = {"Saturday", "Sunday"}


def _add_shift_to_pay(schedule, breakdown, totals, date, day_name, shift_type="night"):
    """Resolve a shift and add it to the pay breakdown if assigned."""
    date_str = date.strftime("%Y-%m-%d")
    ext, name, source = schedule.resolve_shift(date_str, day_name, shift_type)

    if source == "available" or ext == FALLBACK_EXTENSION:
        return

    rate = schedule.get_shift_rate(ext)
    label_suffix = " (Day)" if shift_type == "day" else ""

    breakdown.append({
        "date": date_str,
        "date_label": date.strftime("%b %-d"),
        "day": f"{day_name[:3]}{label_suffix}",
        "name": name,
        "extension": ext,
        "rate": rate,
    })

    if name not in totals:
        totals[name] = {"shifts": 0, "total": 0.0, "extension": ext, "rate": rate}
    totals[name]["shifts"] += 1
    totals[name]["total"] += rate


def _calculate_weekly_pay(schedule: ShiftSchedule, week_start: datetime) -> dict:
    """Calculate pay for a Mon–Sun week. Returns pay record dict."""
    default_rate = schedule.get_shift_rate()
    breakdown = []
    totals = {}

    for i in range(7):
        date = week_start + timedelta(days=i)
        day_name = DAY_ORDER[i]

        # Weekend day shifts (8am–5pm)
        if day_name in WEEKEND_DAYS:
            _add_shift_to_pay(schedule, breakdown, totals, date, day_name, "day")

        # After-hours (night) shift
        _add_shift_to_pay(schedule, breakdown, totals, date, day_name, "night")

    return {
        "week_start": week_start.strftime("%Y-%m-%d"),
        "default_rate": str(default_rate),
        "breakdown": breakdown,
        "totals": totals,
    }


def handler(event, context):
    now = datetime.now(EASTERN)

    # DST guard — same pattern as the 3CX scheduler
    if now.hour != 7:
        logger.info("ET hour is %d, not 7am — skipping (wrong DST rule fired)", now.hour)
        return {"skipped": True}

    ssm = boto3.client("ssm")
    bot_token = ssm.get_parameter(
        Name=os.environ["SLACK_BOT_TOKEN_PARAM"], WithDecryption=True
    )["Parameter"]["Value"]
    channel_id = ssm.get_parameter(
        Name=os.environ["SHIFT_CHANNEL_PARAM"], WithDecryption=True
    )["Parameter"]["Value"]

    schedule = ShiftSchedule()
    slack = WebClient(token=bot_token)

    # --- Previous week's pay summary ---
    prev_monday = now - timedelta(days=7)
    prev_monday = prev_monday.replace(hour=0, minute=0, second=0, microsecond=0)
    pay_record = _calculate_weekly_pay(schedule, prev_monday)

    if pay_record["breakdown"]:
        week_key = prev_monday.strftime("%Y-%m-%d")
        schedule.save_pay_record(week_key, pay_record)

        prev_sunday = prev_monday + timedelta(days=6)
        week_label = f"{prev_monday.strftime('%b %-d')} to {prev_sunday.strftime('%b %-d')}"
        pay_blocks = build_pay_summary_blocks(
            week_label, pay_record["breakdown"], pay_record["totals"]
        )
        slack.chat_postMessage(
            channel=channel_id,
            blocks=pay_blocks,
            text=f"After-Hours Pay — {week_label}",
        )
        logger.info("Posted pay summary for week of %s", week_key)

    # --- Two-week schedule ---
    blocks = build_week_schedule(schedule, start_date=now)

    end_date = now + timedelta(days=13)
    slack.chat_postMessage(
        channel=channel_id,
        blocks=blocks,
        text=f"After-Hours Schedule — {now.strftime('%b %-d')} to {end_date.strftime('%b %-d')}",
    )

    logger.info("Posted weekly schedule to channel %s", channel_id)
    return {"posted": True, "channel": channel_id, "pay_calculated": bool(pay_record["breakdown"])}