/**
 * Fetches historical NWS storm-based warnings (SVR + TOR) from the Iowa
 * Environmental Mesonet (IEM) archive for WFO FWD (Fort Worth), which covers
 * Collin County and the Plano TX metro area.
 *
 * IEM SBW archive — free, no auth, GeoJSON polygons derived from NEXRAD.
 * https://mesonet.agron.iastate.edu/api/1/nws/sbw.geojson
 *
 * Response: array of storm events matching MOCK_STORM_EVENTS schema.
 * Cached 12 hours on Vercel edge — historical data rarely changes.
 */

const IEM_BASE = 'https://mesonet.agron.iastate.edu/api/1/nws/sbw.geojson';
const WFO = 'FWD'; // Fort Worth NWS office — covers Collin County / Plano TX

// Generous bounding box covering Plano, Allen, McKinney, Frisco, Richardson
const BBOX = { minLat: 32.85, maxLat: 33.40, minLon: -97.10, maxLon: -96.35 };

const IEM_HEADERS = {
    'User-Agent': 'LynkedUpPro-CRM/1.0 (admin@lynkedup.com)',
    Accept: 'application/geo+json',
};

function polygonIntersectsBBox(rawCoords) {
    return rawCoords.some(([lon, lat]) =>
        lat >= BBOX.minLat && lat <= BBOX.maxLat &&
        lon >= BBOX.minLon && lon <= BBOX.maxLon
    );
}

function derivedAreaName(rawCoords, phenomena) {
    const n = rawCoords.length;
    const centerLat = rawCoords.reduce((s, [, lat]) => s + lat, 0) / n;
    const centerLon = rawCoords.reduce((s, [lon]) => s + lon, 0) / n;

    let city;
    if      (centerLat > 33.22)                           city = 'McKinney';
    else if (centerLat > 33.16 && centerLon < -96.79)    city = 'Frisco';
    else if (centerLat > 33.16)                           city = 'N. Plano / Allen';
    else if (centerLat > 33.10)                           city = 'Allen';
    else if (centerLon < -96.84)                          city = 'Legacy Corridor';
    else if (centerLat > 33.04)                           city = 'Central Plano';
    else                                                   city = 'S. Plano';

    const evtLabel = phenomena === 'TO' ? 'Tornado Warning'
                   : phenomena === 'FF' ? 'Flash Flood Warning'
                   : 'Severe Thunderstorm';
    return `${city} — ${evtLabel}`;
}

function toStormEvent(feature, idx) {
    const p    = feature.properties || {};
    const geom = feature.geometry;
    if (!geom?.coordinates?.[0]) return null;

    const rawCoords = geom.coordinates[0]; // GeoJSON: [lon, lat]
    if (rawCoords.length < 3 || !polygonIntersectsBBox(rawCoords)) return null;

    // Swap to Leaflet [lat, lon] order
    const polygon = rawCoords.map(([lon, lat]) => [lat, lon]);

    const phenomena = p.phenomena || 'SV';
    const type = phenomena === 'TO' ? 'tornado'
               : phenomena === 'FF' ? 'flood'
               : 'hail';

    // area2163 = area in km² (EPSG:2163 equal-area projection). Use as severity proxy.
    const areaSqKm = parseFloat(p.area2163) || 0;
    const severity = phenomena === 'TO'  ? 'severe'
                   : areaSqKm > 900      ? 'severe'
                   : areaSqKm > 400      ? 'significant'
                   : areaSqKm > 120      ? 'moderate'
                   : 'trace';

    // Rough homes estimate: ~1200 homes/sq mile * 0.386 sq miles/km² ≈ 463 homes/km²
    const estimatedHomes = areaSqKm > 0
        ? Math.min(Math.round((areaSqKm * 463) / 50) * 50, 50000)
        : null;

    const issued = p.issued || p.expire || new Date().toISOString();

    return {
        id:             `IEM-${WFO}-${phenomena}-${p.eventid ?? idx}`,
        date:           issued,
        type,
        severity,
        maxHailSize:    null,
        areaName:       derivedAreaName(rawCoords, phenomena),
        county:         'Collin',
        estimatedHomes,
        description:    `${type === 'tornado' ? 'Tornado Warning' : type === 'flood' ? 'Flash Flood Warning' : 'Severe Thunderstorm Warning'} issued by NWS ${p.wfo || WFO}`,
        source:         'IEM/NWS',
        polygon,
    };
}

export default async function handler(req, res) {
    res.setHeader('Cache-Control', 's-maxage=43200, stale-while-revalidate=86400');
    res.setHeader('Access-Control-Allow-Origin', '*');

    if (req.method === 'OPTIONS') return res.status(200).end();
    if (req.method !== 'GET')    return res.status(405).json({ error: 'Method not allowed' });

    const months  = Math.min(parseInt(req.query.months ?? '36', 10), 36);
    const now     = new Date();
    const cutoff  = new Date(now.getTime() - months * 30.44 * 86400000);

    // Collect every calendar year between cutoff and now
    const years = new Set();
    for (let y = cutoff.getFullYear(); y <= now.getFullYear(); y++) years.add(y);

    // Fetch SV (Severe Thunderstorm) + TO (Tornado) per year in parallel
    const phenomena = ['SV', 'TO'];
    const fetches = [];
    for (const year of years) {
        for (const ph of phenomena) {
            const url = `${IEM_BASE}?wfo=${WFO}&year=${year}&phenomena=${ph}&significance=W`;
            fetches.push(
                fetch(url, { headers: IEM_HEADERS })
                    .then(r => r.ok ? r.json() : { features: [] })
                    .catch(() => ({ features: [] }))
            );
        }
    }

    try {
        const results  = await Promise.all(fetches);
        const features = results.flatMap(r => Array.isArray(r.features) ? r.features : []);

        const events = features
            .map((f, i) => toStormEvent(f, i))
            .filter(Boolean)
            .filter(e => {
                const d = new Date(e.date);
                return d >= cutoff && d <= now;
            })
            .sort((a, b) => new Date(b.date) - new Date(a.date))
            .slice(0, 150); // cap at 150 events

        return res.status(200).json(events);
    } catch (err) {
        console.error('[storm-polygons] fetch error:', err.message);
        return res.status(200).json([]);
    }
}