t1

/*
There is an array of functions (the exact number of them is unknown),
all of them will return promise.
Write a solution that all promises would be resolved sequentially
without using async await
 */

const fn1 = () => new Promise((resolve) => {
  setTimeout(() => resolve(1), 1000);
});

const fn2 = () => new Promise((resolve) => {
  setTimeout(() => resolve(2), 1000);
});

const fn3 = () => new Promise((resolve) => {
  setTimeout(() => resolve(3), 1000);
});


// Iterable
// function consistently(fns) {
//   if(fns.length === 0) return Promise.resolve(0);

//   let stack = [fns[0]()]

//   for(let i = 1 ;i < fns.length; i++){
//     const currFn = fns[i];

//     stack.push( stack[i-1]
//         .then(r1 => currFn()
//           .then(r2 => r1 + r2))
//     )
//   }

//   return stack[stack.length - 1]
// }


// Recursive
function consistently(fns) {
  if(fns.length === 0) return Promise.resolve(0);

  const [fn, ...otherFns] = fns

  return fn()
      .then(res => consistently(otherFns)
        .then(allRes => allRes + res))
}



consistently([fn1, fn2, fn3]).then((sum) => console.log(sum));