/**
 * Aggregator route for the Strommix-Live-Widget.
 *
 * Production + load come from **SMARD** (smard.de) — the canonical
 * German grid feed. Cross-border saldo + day-ahead prices come from
 * Energy-Charts (api.energy-charts.info) where SMARD has no convenient
 * single-call endpoint.
 *
 * Why split sources:
 *  - SMARD's `Erdgas` (filter 4069) is just natural gas. Energy-Charts'
 *    `Fossil gas` bundles natural gas + GuD + similar — values diverge
 *    by 2–3 GW. The audit user pointed at SMARD as ground truth.
 *  - SMARD has 15-min slot data with explicit timestamps; we align all
 *    filters to the same slot so every number on screen comes from one
 *    point in time.
 *  - Energy-Charts wins for cross-border + prices since SMARD's
 *    flow + price endpoints need extra plumbing we don't need here.
 *
 * Every value on the response carries its measurement timestamp so the
 * widget can render "Stand HH:MM" + "verzögert" hints when an upstream
 * lags.
 */

import type { RequestHandler } from "./$types";
import { env } from "$env/dynamic/public";
import type { StrommixResponse } from "$lib/strommix";
import { fetchSmardSnapshot } from "$lib/smard";

const CMS_BASE = (
  env.PUBLIC_CMS_URL ||
  import.meta.env.PUBLIC_CMS_URL ||
  "http://localhost:3000"
).replace(/\/$/, "");

type StrommixRaw = {
  wind_onshore_mw?: number | null;
  wind_offshore_mw?: number | null;
  solar_mw?: number | null;
  biomass_mw?: number | null;
  hydro_mw?: number | null;
  lignite_mw?: number | null;
  hard_coal_mw?: number | null;
  gas_mw?: number | null;
  nuclear_mw?: number | null;
  load_mw?: number | null;
  measured_at_unix?: number | null;
};

type CrossborderRaw = {
  flow_at_gw?: number | null;
  flow_be_gw?: number | null;
  flow_ch_gw?: number | null;
  flow_cz_gw?: number | null;
  flow_dk_gw?: number | null;
  flow_fr_gw?: number | null;
  flow_lu_gw?: number | null;
  flow_nl_gw?: number | null;
  flow_no_gw?: number | null;
  flow_pl_gw?: number | null;
  flow_se_gw?: number | null;
  measured_at_unix?: number | null;
};

function num(x: unknown): number {
  return typeof x === "number" && Number.isFinite(x) ? x : 0;
}

async function fetchOne<T>(
  collection: string,
  fetcher: typeof fetch
): Promise<{ data: T | null; stale: boolean }> {
  try {
    const res = await fetcher(`${CMS_BASE}/api/content/${collection}/current`, {
      signal: AbortSignal.timeout(8_000),
    });
    if (!res.ok) return { data: null, stale: false };
    const stale = res.headers.get("x-rustycms-external-stale") === "1";
    const data = (await res.json()) as T;
    return { data, stale };
  } catch {
    return { data: null, stale: false };
  }
}

type PriceArrayResp = {
  unix_seconds?: number[];
  price?: (number | null)[];
};

/**
 * Pick the day-ahead price slot whose start ≤ now. Energy-Charts
 * returns 96 slots covering the day; the last cell is typically a
 * future slot.
 */
async function fetchPriceAtNow(
  bzn: string,
  fetcher: typeof fetch
): Promise<{ price: number | null; slotUnix: number | null; stale: boolean }> {
  try {
    const res = await fetcher(
      `https://api.energy-charts.info/price?bzn=${encodeURIComponent(bzn)}`,
      { signal: AbortSignal.timeout(8_000) }
    );
    if (!res.ok) return { price: null, slotUnix: null, stale: false };
    const data = (await res.json()) as PriceArrayResp;
    const times = data.unix_seconds ?? [];
    const prices = data.price ?? [];
    if (times.length === 0 || prices.length === 0) {
      return { price: null, slotUnix: null, stale: false };
    }
    const nowSec = Math.floor(Date.now() / 1000);
    let pickIdx = -1;
    for (let i = 0; i < times.length; i++) {
      if (times[i] <= nowSec) pickIdx = i;
      else break;
    }
    if (pickIdx < 0) return { price: null, slotUnix: null, stale: false };
    const value = prices[pickIdx];
    return {
      price: typeof value === "number" && Number.isFinite(value) ? value : null,
      slotUnix: times[pickIdx] ?? null,
      stale: false,
    };
  } catch {
    return { price: null, slotUnix: null, stale: true };
  }
}

export const GET: RequestHandler = async ({ fetch }) => {
  const [smard, energyCharts, cross, priceDe, priceFr] = await Promise.all([
    fetchSmardSnapshot(fetch),
    // Energy-Charts via the CMS — used as per-field fallback when SMARD
    // returns null for a specific filter (notably load 410 when SMARD's
    // pipeline lags more than the production filters).
    fetchOne<StrommixRaw>("strommix_de", fetch),
    fetchOne<CrossborderRaw>("crossborder_de", fetch),
    fetchPriceAtNow("DE-LU", fetch),
    fetchPriceAtNow("FR", fetch),
  ]);

  const ec = energyCharts.data ?? {};

  // Per-field fallback. SMARD value `null` = filter unavailable; we
  // reach for the Energy-Charts equivalent. SMARD `0` is preserved
  // (genuine night-time solar / decommissioned nuclear / etc).
  const pick = (smardVal: number | null | undefined, ecVal: number | null | undefined): number =>
    typeof smardVal === "number"
      ? smardVal
      : typeof ecVal === "number" && Number.isFinite(ecVal)
        ? ecVal
        : 0;

  const v = {
    lignite: pick(smard?.values.lignite, ec.lignite_mw),
    hardCoal: pick(smard?.values.hardCoal, ec.hard_coal_mw),
    gas: pick(smard?.values.gas, ec.gas_mw),
    nuclear: pick(smard?.values.nuclear, ec.nuclear_mw),
    windOnshore: pick(smard?.values.windOnshore, ec.wind_onshore_mw),
    windOffshore: pick(smard?.values.windOffshore, ec.wind_offshore_mw),
    solar: pick(smard?.values.solar, ec.solar_mw),
    hydro: pick(smard?.values.hydro, ec.hydro_mw),
    biomass: pick(smard?.values.biomass, ec.biomass_mw),
    load: pick(smard?.values.load, ec.load_mw),
  };

  // Track whether any field needed the Energy-Charts fallback so the
  // widget can attribute the source honestly.
  const usedFallback =
    !smard ||
    (Object.keys(v) as (keyof typeof v)[]).some(
      (k) => smard.values[k as keyof typeof smard.values] == null && (v[k] ?? 0) > 0
    );

  // Conventional, the way the widget label spells it: lignite + hard
  // coal + gas + nuclear. Pumped-storage + biomass + run-of-river
  // hydro are NOT included.
  const conventionalMw = v.lignite + v.hardCoal + v.gas + v.nuclear;
  const weatherRenewableMw = v.windOnshore + v.windOffshore + v.solar;

  const c = cross.data ?? {};
  const flowsByCountry: Record<string, number> = {
    AT: num(c.flow_at_gw),
    BE: num(c.flow_be_gw),
    CH: num(c.flow_ch_gw),
    CZ: num(c.flow_cz_gw),
    DK: num(c.flow_dk_gw),
    FR: num(c.flow_fr_gw),
    LU: num(c.flow_lu_gw),
    NL: num(c.flow_nl_gw),
    NO: num(c.flow_no_gw),
    PL: num(c.flow_pl_gw),
    SE: num(c.flow_se_gw),
  };
  const netFlowGw = Object.values(flowsByCountry).reduce((a, b) => a + b, 0);

  const body: StrommixResponse = {
    measuredAtUnix: smard?.measuredAtUnix ?? ec.measured_at_unix ?? null,
    dataSource: !smard ? "energy-charts" : usedFallback ? "smard+energy-charts" : "smard",
    windOnshoreMw: v.windOnshore,
    windOffshoreMw: v.windOffshore,
    solarMw: v.solar,
    biomassMw: v.biomass,
    hydroMw: v.hydro,
    ligniteMw: v.lignite,
    hardCoalMw: v.hardCoal,
    gasMw: v.gas,
    nuclearMw: v.nuclear,
    loadMw: v.load,
    weatherRenewableMw,
    conventionalMw,
    netFlowGw,
    crossborderMeasuredAtUnix: c.measured_at_unix ?? null,
    flowsByCountry,
    priceDeEurMwh: priceDe.price,
    priceFrEurMwh: priceFr.price,
    priceMeasuredAtUnix: priceDe.slotUnix,
    staleStrommix: smard == null && !energyCharts.data,
    staleCrossborder: cross.stale,
    stalePrice: priceDe.stale || priceFr.stale,
  };

  return new Response(JSON.stringify(body), {
    headers: {
      "content-type": "application/json",
      // 5 min ≈ SMARD update cadence. Browser/CDN hold the response that
      // long; SvelteKit re-fetches afterwards.
      "cache-control": "public, max-age=300, s-maxage=300",
    },
  });
};