// PROGRAM SET UP

// Blocking code
function sleep(miliseconds) {
  var start = new Date().getTime();
  var expire = start + miliseconds
  while(new Date().getTime() < expire) {
  }
}

// Timeout function to simulate actual ASYNC function that is wrapped in promise
function timeoutPromise() {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      resolve()
    }, 0)
  })
}

// Program execution
console.log('Main context start')
asyncOperation()
  .then(() => {
    console.log('asyncOperation end')
  })
console.log('Main context end')

// Different scenarios for asyncOperation()
// ============== CASE 1 ============== //
async function asyncOperation() {
  timeoutPromise()
  sleep(5000)
  console.log('sleep completed')
}

// RESULT:
// 'Main context start'
// AFTER 5 SECONDS
// 'sleep completed'
// 'asyncOperation end'
// 'Main context end'

// Blocking code runs immediately after asyncOperation() is invoked, and blocks main context


// ============== CASE 2 ============== //
async function asyncOperation() {
  await timeoutPromise()
  sleep(5000)
  console.log('sleep completed')
}

// RESULT:
// 'Main context start'
// 'Main context end'
// AFTER 5 SECONDS
// 'sleep completed'
// 'asyncOperation end'

// Main context triggers asyncOperation(), does not wait, and proceeds to print 'main context end'
// Blocking code runs AFTER timeoutPromise() is completed (and so does not affect main context)
// Blocking code blocks asyncOperation(). asyncOperation() completes after sleeping 5 seconds

// Note:
await timeoutPromise()
sleep(5000)
console.log('sleep completed')

// is identical to
timeoutPromise().then(function() {
  sleep(5000)
  console.log('sleep completed')
})


// ============== CASE 3 ============== //
async function asyncOperation() {
  timeoutPromise()
  process.nextTick(function() {
    sleep(5000)
    console.log('sleep completed')
  })
}

// RESULT:
// 'Main context start'
// 'Main context end'
// AFTER 5 SECONDS
// 'sleep completed'
// 'asyncOperation end'

// Similar to CASE 1, but blocking code execution is deferred to next tick, and does not block main context


// ============== CASE 4 ============== //
async function asyncOperation() {
  await timeoutPromise()
  process.nextTick(function() {
    sleep(5000)
    console.log('sleep completed')
  })
}

// RESULT:
// 'Main context start'
// 'Main context end'
// 'asyncOperation end'
// AFTER 5 SECONDS
// 'sleep completed'