idgenerator.js

const emergencyIDLength = 4;
const maxAttempts = 10000;
// Extremely small likelihood of timing due to infinite loop out unless we are genuinely full.
// We have 36^4 = 1.6 million possible IDs.
const testID = "TEST";
const testDevice = "computer-id";

// No one should ever generate the testID except for testing purposes.
var usedEmergencyID = {
  testID: true
};
var deviceToEmergency = {};
// The archive is like deviceToEmergency, but is not deleted at the end, so that checking the status
// can be done after the emergency has ended.
var dToEArchive = {};

var emergencyToDevice = {};
var emergencyToStage = {};


function makeByDevice(deviceID) {
  const possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

  if (deviceID == testDevice) {
    console.log("Generating the test ID");
    emergencyID = testID;
    deviceToEmergency[deviceID] = emergencyID;
    dToEArchive[deviceID] = emergencyID;
    emergencyToDevice[emergencyID] = deviceID;
    return testID;
  }

  if (deviceToEmergency[deviceID]) {
    throw "Device already has an emergency";
  }

  var emergencyID;
  var called = 0;
  do {
    called += 1;
    emergencyID = "";
    for (var i = 0; i < emergencyIDLength; i++) {
      emergencyID += possible.charAt(Math.floor(Math.random() * possible.length));
    }
  } while (usedEmergencyID[emergencyID] && called < maxAttempts);

  if (called == maxAttempts) {
    throw "No unused IDs available.";
  }

  usedEmergencyID[emergencyID] = true;
  deviceToEmergency[deviceID] = emergencyID;
  dToEArchive[deviceID] = emergencyID;
  emergencyToDevice[emergencyID] = deviceID;
  return emergencyID;
}

function getEmergencyByDevice(deviceID) {
  emergencyID = deviceToEmergency[deviceID];
  if (!emergencyID) {
    throw "Getting undefined ID.";
  }
  return emergencyID;
}

function getEmergencyFromArchive(deviceID) {
  emergencyID = dToEArchive[deviceID];
  if (!emergencyID) {
    throw "Getting undefined ID from archive."
  }
  return emergencyID;
}

function setStageByEmergency(emergencyID, stage) {
  if (!emergencyToStage[emergencyID]) {
    emergencyToStage[emergencyID] = stage;
    return
  }
  currentStage = emergencyToStage[emergencyID];
  if (currentStage >= stage) {
    throw "Emergency " + emergencyID + " stage is being set out of order. Current stage: " +
      currentStage + ". New Stage: " + stage + ".";
  }
  emergencyToStage[emergencyID] = stage;
}


function endByEmergency(emergencyID) {
  // We don't free up usedEmergencyID because it has already been used and will never be used again.
  deviceID = emergencyToDevice[emergencyID];
  delete emergencyToDevice[emergencyID];
  delete deviceToEmergency[deviceID]
  delete emergencyToStage[emergencyID];
}

module.exports = {
  makeByDevice,
  getEmergencyByDevice,
  setStageByEmergency,
  endByEmergency,
  getEmergencyFromArchive
};