const http = require("node:http");
const os = require("node:os");
const { execSync } = require("node:child_process");

const PORT = parseInt(process.env.PORT || "3001", 10);
const TOKEN = process.env.HEALTH_TOKEN;

if (!TOKEN) {
  console.warn("WARNING: HEALTH_TOKEN is not set. All requests will be rejected (fail-closed).");
}

function readProcStat() {
  try {
    const line = execSync("head -1 /proc/stat", { encoding: "utf-8" }).trim();
    const parts = line.split(/\s+/).slice(1).map(Number);
    const idle = parts[3] + parts[4];
    const total = parts.reduce((a, b) => a + b, 0);
    return { idle, total };
  } catch {
    return null;
  }
}

function getCpuPercent() {
  const t1 = readProcStat();
  if (!t1) return 0;
  const { idle: idle1, total: total1 } = t1;

  // Sample over 500ms
  execSync("sleep 0.5");

  const t2 = readProcStat();
  if (!t2) return 0;
  const dIdle = t2.idle - idle1;
  const dTotal = t2.total - total1;
  if (dTotal === 0) return 0;
  return Math.round((1 - dIdle / dTotal) * 100);
}

function getDisk() {
  try {
    // Alpine df doesn't support --output, use standard POSIX format
    const out = execSync("df -k /", { encoding: "utf-8" });
    const parts = out.trim().split("\n")[1].trim().split(/\s+/);
    // df -k columns: Filesystem, 1K-blocks, Used, Available, Use%, Mounted
    const totalGB = +(parseInt(parts[1], 10) / 1e6).toFixed(1);
    const usedGB = +(parseInt(parts[2], 10) / 1e6).toFixed(1);
    const freeGB = +(parseInt(parts[3], 10) / 1e6).toFixed(1);
    const usagePercent = totalGB > 0 ? Math.round((usedGB / totalGB) * 100) : 0;
    return { totalGB, usedGB, freeGB, usagePercent };
  } catch {
    return { totalGB: 0, usedGB: 0, freeGB: 0, usagePercent: 0 };
  }
}

function getHealth() {
  const cpus = os.cpus();
  const totalMem = os.totalmem();
  const freeMem = os.freemem();
  const usedMem = totalMem - freeMem;

  return {
    timestamp: new Date().toISOString(),
    hostname: os.hostname(),
    uptime: Math.floor(os.uptime()),
    cpu: {
      model: cpus[0]?.model?.trim() || "unknown",
      cores: cpus.length,
      loadAvg: os.loadavg().map((l) => +l.toFixed(2)),
      usagePercent: getCpuPercent(),
    },
    memory: {
      totalGB: +(totalMem / 1e9).toFixed(1),
      usedGB: +(usedMem / 1e9).toFixed(1),
      freeGB: +(freeMem / 1e9).toFixed(1),
      usagePercent: Math.round((usedMem / totalMem) * 100),
    },
    disk: getDisk(),
  };
}

const server = http.createServer((req, res) => {
  res.setHeader("Content-Type", "application/json");

  if (req.url !== "/health" || req.method !== "GET") {
    res.writeHead(404);
    res.end(JSON.stringify({ error: "Not found" }));
    return;
  }

  if (!TOKEN) {
    res.writeHead(401);
    res.end(JSON.stringify({ error: "HEALTH_TOKEN not configured" }));
    return;
  }

  const auth = req.headers["authorization"];
  if (auth !== `Bearer ${TOKEN}`) {
    res.writeHead(401);
    res.end(JSON.stringify({ error: "Unauthorized" }));
    return;
  }

  const data = getHealth();
  res.writeHead(200);
  res.end(JSON.stringify(data));
});

server.listen(PORT, () => {
  console.log(`vps-health-api listening on :${PORT}`);
});