DavidBM/iterated-pipes

var utils = require('./utils');

module.exports = function sequential(iterator, callback) {
    if(typeof callback !== 'function'){
        throw new TypeError(utils.NO_FUNCTION_CALLBACK);
    }

    var item = iterator.next();

    if(item.done) {
        return Promise.resolve();
    }

    return new Promise((resolve, reject) => {
        var executionResult = executeIteration(callback, item, undefined, iterator);
        
        if(!utils.isPromise(executionResult)){
            return resolve(executionResult);
        }

        return executionResult
        .then(resolve)
        .catch(reject);
    });
};

function executeIteration (callback, item, lastValue, iterable){
    var returnedValue = callback(item.value, lastValue);

    //In case of not promises
    if(!utils.isPromise(returnedValue)){
        return nextIteration(callback, returnedValue, iterable);
    }

    //If we have a promise
    return returnedValue
    .then(lastValue => nextIteration(callback, lastValue, iterable));
}

function nextIteration(callback, lastValue, iterable){
    var nextItem = iterable.next();

    if(nextItem.done) {
        return lastValue;
    }

    return executeIteration(callback, nextItem, nextItem.value, iterable);
}