const ffi = require("ffi-napi");

// DWORD SetThreadExecutionState(EXECUTION_STATE esFlags);
const kernel32 = ffi.Library("kernel32", {
  SetThreadExecutionState: ["uint", ["uint"]],
});

// Flags from Win32 API
const ES_CONTINUOUS      = 0x80000000;
const ES_DISPLAY_REQUIRED = 0x00000002; // keep screen on
// Optional: const ES_SYSTEM_REQUIRED = 0x00000001; // keep system awake

function keepAwake() {
  const r = kernel32.SetThreadExecutionState(ES_CONTINUOUS | ES_DISPLAY_REQUIRED);
  if (r === 0) throw new Error("SetThreadExecutionState failed");
}

function clearAwake() {
  // Clears previous request for this thread
  kernel32.SetThreadExecutionState(ES_CONTINUOUS);
}

process.on("SIGINT", () => { clearAwake(); process.exit(0); });
process.on("exit", clearAwake);

keepAwake();
console.log("Display will be kept on. Press Ctrl+C to stop.");
setInterval(() => {}, 1 << 30);