"""Discord delivery — currently just the daily "most unusual right now" post.

A once-daily message to a Discord channel via an **incoming webhook** (a single
secret URL; no bot, no gateway, no persistent process). It rides the notifier
daemon like the homepage feed refresh does, so it inherits the single-leader
invariant and costs no new infrastructure. Entirely optional: with no webhook
configured, everything here no-ops.

The message is built from the same `data/homepage.json` feed the homepage renders
(homepage.build/refresh), so the Discord post and the site always agree.
"""
from __future__ import annotations

import datetime
import os

import httpx

import homepage

# The webhook URL IS the credential — env only, never the repo. Unset => disabled.
WEBHOOK_URL = os.environ.get("THERMOGRAPH_DISCORD_WEBHOOK", "").strip()

# How many cities the daily post lists.
POST_LIMIT = 8

# Embed accent: warm when the top anomaly is hot, cool when it's cold.
_HOT = 0xE8663B
_COLD = 0x4393C3

_TIMEOUT = httpx.Timeout(10.0)


def enabled() -> bool:
    return bool(WEBHOOK_URL)


def _f_c(value) -> str:
    """A Fahrenheit reading as '104°F (40°C)' — Discord's audience is global, so
    the post carries both, even though the site picks one per city."""
    if value is None:
        return "—"
    f = round(value)
    c = round((value - 32) * 5 / 9)
    return f"{f}°F ({c}°C)"


def _line(card: dict) -> str:
    """One city's line in the post."""
    display = card.get("display") or card.get("name") or "—"
    metric = (card.get("metric_label") or "").lower() or "reading"
    val = _f_c(card.get("value"))
    normal = _f_c(card.get("normal")) if card.get("normal") is not None else None
    pct = card.get("pct_label") or ""
    grade = card.get("grade_label") or card.get("grade") or ""
    tag = " · ".join(p for p in (pct, grade) if p)
    when = f" ({card['date_label']})" if card.get("date_label") else ""
    normal_txt = f", normal {normal}" if normal else ""
    return f"**{display}**: {metric} {val}{normal_txt}{when}" + (f" · {tag}" if tag else "")


def build_embed(feed: dict) -> dict:
    """A Discord rich embed for the day's most unusual cities, or raise ValueError
    if the feed has nothing to show."""
    ranked = (feed or {}).get("ranked") or []
    if not ranked:
        raise ValueError("empty feed")
    top = ranked[:POST_LIMIT]
    color = _COLD if top[0].get("tail") == "cold" else _HOT
    date_s = feed.get("date") or datetime.date.today().isoformat()
    description = "\n".join(_line(c) for c in top)
    embed = {
        "title": "🌡️ Most unusual weather right now",
        "description": description,
        "url": "https://thermograph.org/",
        "color": color,
        "footer": {"text": "thermograph.org · every day graded against ~45 years of local history"},
    }
    # ISO8601 timestamp from the feed's build time, when available.
    gen = feed.get("generated_at")
    if gen:
        embed["timestamp"] = datetime.datetime.fromtimestamp(
            float(gen), tz=datetime.timezone.utc
        ).isoformat()
    else:
        embed["footer"]["text"] += f" · {date_s}"
    return embed


def post_daily_feed(feed: dict | None = None) -> bool:
    """Post the daily feed to the configured webhook. Best-effort: returns True on
    a 2xx, False otherwise (disabled, empty/stale feed, or any HTTP error) and
    never raises — a Discord failure must not disturb the notifier pass."""
    if not enabled():
        return False
    if feed is None:
        feed = homepage.load()
    if not feed or homepage.is_stale(feed):
        return False
    try:
        embed = build_embed(feed)
    except ValueError:
        return False
    payload = {
        "username": "Thermograph",
        "avatar_url": "https://thermograph.org/logo.png?v=3",
        "embeds": [embed],
    }
    try:
        resp = httpx.post(WEBHOOK_URL, json=payload, timeout=_TIMEOUT)
        return 200 <= resp.status_code < 300
    except Exception:  # noqa: BLE001 - best-effort side channel
        return False