// api_v1/scanner/elevation.js


// ---------------------------------------------------------
// Provider 1: OpenElevation
// ---------------------------------------------------------
async function tryOpenElevation(lat, lon) {
  try {
    const url = `https://api.open-elevation.com/api/v1/lookup?locations=${lat},${lon}`;
    const res = await fetch(url, { timeout: 5000 });

    if (!res.ok) {
      console.log("OpenElevation status:", res.status);
      return null;
    }

    const text = await res.text();

    // Se non è JSON → errore HTML → fallback
    if (!text.startsWith('{')) {
      console.log("OpenElevation non-JSON:", text.slice(0, 60));
      return null;
    }

    const data = JSON.parse(text);
    return data?.results?.[0]?.elevation ?? null;

  } catch (err) {
    console.log("Errore OpenElevation:", err.message);
    return null;
  }
}

// ---------------------------------------------------------
// Provider 2: OpenTopoData (fallback)
// ---------------------------------------------------------
async function tryOpenTopoData(lat, lon) {
  try {
    const url = `https://api.opentopodata.org/v1/eudem25m?locations=${lat},${lon}`;
    const res = await fetch(url, { timeout: 5000 });

    if (!res.ok) {
      console.log("OpenTopoData status:", res.status);
      return null;
    }

    const text = await res.text();

    if (!text.startsWith('{')) {
      console.log("OpenTopoData non-JSON:", text.slice(0, 60));
      return null;
    }

    const data = JSON.parse(text);
    return data?.results?.[0]?.elevation ?? null;

  } catch (err) {
    console.log("Errore OpenTopoData:", err.message);
    return null;
  }
}

// ---------------------------------------------------------
// Funzione principale con fallback
// ---------------------------------------------------------
async function getElevation(lat, lon) {
  // 1️⃣ Prova OpenElevation
  const elev1 = await tryOpenElevation(lat, lon);
  if (elev1 !== null) return elev1;

  console.log("⚠️ OpenElevation fallito → uso OpenTopoData");

  // 2️⃣ Prova OpenTopoData
  const elev2 = await tryOpenTopoData(lat, lon);
  if (elev2 !== null) return elev2;

  console.log("❌ Nessun provider di elevazione disponibile");
  return null;
}

module.exports = getElevation;