const os = require("node:os");
const { execSync } = require("node:child_process");
const { setTimeout: delay } = require("node:timers/promises");

// Host metrics collection (CPU / memory / disk), extracted from index.js so the
// same code can be reused by the local workstation agent. Pure host probing:
// no HTTP, no config, no side effects — the caller owns the response shape.

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;
  }
}

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

  // Sample over 500ms without blocking the event loop, so other async work
  // (e.g. the Logto healthcheck) can run concurrently.
  await delay(500);

  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 };
  }
}

// Collect CPU, memory and disk into the `{ cpu, memory, disk }` slice of the
// /health payload. Awaiting getCpuPercent() first is deliberate: the 500ms
// sample is the only await here, so a caller running this inside a
// Promise.all() keeps its other work (the Logto check) fully concurrent.
// Everything else is cheap and synchronous.
async function collectMetrics() {
  const cpus = os.cpus();
  const totalMem = os.totalmem();
  const freeMem = os.freemem();
  const usedMem = totalMem - freeMem;

  const cpuUsagePercent = await getCpuPercent();

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

module.exports = { getCpuPercent, getDisk, collectMetrics };