// Iterators example

const userNamesGroupedByLocation = {
  Tokio: [
    'Aiko',
    'Chizu',
    'Fushigi',
  ],
  'Buenos Aires': [
    'Santiago',
    'Valentina',
    'Lola',
  ],
  'Saint Petersburg': [
    'Sonja',
    'Dunja',
    'Iwan',
    'Tanja',
  ],
};

// We can't use arrow functions here because this wouldn't let us access the scope of the object ("this").
userNamesGroupedByLocation[Symbol.iterator] = function() {
  const cityKeys = Object.keys(this);
  let cityIndex = 0;
  let userIndex = 0;

  return {
    next: () => {
      // We already iterated over all cities
      if (cityIndex > cityKeys.length - 1) {
        return {
          value: undefined,
          done: true,
        };
      }

      const users = this[cityKeys[cityIndex]];
      const user = users[userIndex];
      

      const isLastUser = userIndex >= users.length - 1;
      if (isLastUser) {
        // Reset user index
        userIndex = 0;
        // Jump to next city
        cityIndex++
      } else {
        userIndex++;
      }

      return {
        done: false,
        value: user,        
      };
    },
  };
};

/*
const iterator = userNamesGroupedByLocation[Symbol.iterator]();

let state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);
state = iterator.next();
console.log(state.value, state.done);


for (let name of userNamesGroupedByLocation) {
 console.log('name', name);
}
*/

// Generator examples

function* nameGenerator() {
  yield 'Iwan';
  yield 'Aiko';
}

function* stringGenerator() {
  yield* nameGenerator();
  yield* ['one', 'two'];
  yield 'hi';
  yield 'hi';
  yield 'hi';
}

/*
const strings = stringGenerator();


console.log(strings.next());
console.log(strings.next());
console.log(strings.next());
console.log(strings.next());
console.log(strings.next());
console.log(strings.next());
console.log(strings.next());
*/

function* overrideValue() {
  const result = yield 'hi';
  console.log(result);
}

const overrideIterator = overrideValue();
overrideIterator.next();
overrideIterator.next('bye');


function* idGenerator() {
  let i = 0;
  while (true) {
    yield i++;
    console.log(i);
  }
}

/*
const ids = idGenerator();

console.log(ids.next().value);
console.log(ids.next().value);
console.log(ids.next().value);
console.log(ids.next().value);
console.log(ids.next().value);
*/

function* errorGenerator() {
  try {
    yield 'one';
    yield 'two';
  } catch(e) {
    console.error(e);
  }
}

const errorIterator = errorGenerator();

console.log(errorIterator.next()); 
console.log(errorIterator.throw('Bam!'));

// {value: 'one', done: false}
// Bam!
// {value: undefined, done: true}