most.js

/** @license MIT License (c) copyright 2010-2016 original author or authors */
/** @author Brian Cavalier */
/** @author John Hann */

var Stream = require('./lib/Stream');
var base = require('@most/prelude');
var core = require('./lib/source/core');
var from = require('./lib/source/from').from;
var periodic = require('./lib/source/periodic').periodic;
var symbolObservable = require('symbol-observable').default;

/**
 * Core stream type
 * @type {Stream}
 */
exports.Stream = Stream;

// Add of and empty to constructor for fantasy-land compat
exports.of       = Stream.of    = core.of;
exports.just     = core.of; // easier ES6 import alias
exports.empty    = Stream.empty = core.empty;
exports.never    = core.never;
exports.from     = from;
exports.periodic = periodic;

//-----------------------------------------------------------------------
// Draft ES Observable proposal interop
// https://github.com/zenparsing/es-observable

var subscribe = require('./lib/observable/subscribe').subscribe;

Stream.prototype.subscribe = function(subscriber) {
	return subscribe(subscriber, this);
};

Stream.prototype[symbolObservable] = function() {
	return this;
};

//-----------------------------------------------------------------------
// Fluent adapter

var thru = require('./lib/combinator/thru').thru;

/**
 * Adapt a functional stream transform to fluent style.
 * It applies f to the this stream object
 * @param  {function(s: Stream): Stream} f function that
 * receives the stream itself and must return a new stream
 * @return {Stream}
 */
Stream.prototype.thru = function(f) {
	return thru(f, this);
}

//-----------------------------------------------------------------------
// Adapting other sources

var events = require('./lib/source/fromEvent');

/**
 * Create a stream of events from the supplied EventTarget or EventEmitter
 * @param {String} event event name
 * @param {EventTarget|EventEmitter} source EventTarget or EventEmitter. The source
 *  must support either addEventListener/removeEventListener (w3c EventTarget:
 *  http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventTarget),
 *  or addListener/removeListener (node EventEmitter: http://nodejs.org/api/events.html)
 * @returns {Stream} stream of events of the specified type from the source
 */
exports.fromEvent = events.fromEvent;

//-----------------------------------------------------------------------
// Observing

var observe = require('./lib/combinator/observe');

exports.observe = observe.observe;
exports.forEach = observe.observe;
exports.drain   = observe.drain;

/**
 * Process all the events in the stream
 * @returns {Promise} promise that fulfills when the stream ends, or rejects
 *  if the stream fails with an unhandled error.
 */
Stream.prototype.observe = Stream.prototype.forEach = function(f) {
	return observe.observe(f, this);
};

/**
 * Consume all events in the stream, without providing a function to process each.
 * This causes a stream to become active and begin emitting events, and is useful
 * in cases where all processing has been setup upstream via other combinators, and
 * there is no need to process the terminal events.
 * @returns {Promise} promise that fulfills when the stream ends, or rejects
 *  if the stream fails with an unhandled error.
 */
Stream.prototype.drain = function() {
	return observe.drain(this);
};

//-------------------------------------------------------

var loop = require('./lib/combinator/loop').loop;

exports.loop = loop;

/**
 * Generalized feedback loop. Call a stepper function for each event. The stepper
 * will be called with 2 params: the current seed and the an event value.  It must
 * return a new { seed, value } pair. The `seed` will be fed back into the next
 * invocation of stepper, and the `value` will be propagated as the event value.
 * @param {function(seed:*, value:*):{seed:*, value:*}} stepper loop step function
 * @param {*} seed initial seed value passed to first stepper call
 * @returns {Stream} new stream whose values are the `value` field of the objects
 * returned by the stepper
 */
Stream.prototype.loop = function(stepper, seed) {
	return loop(stepper, seed, this);
};

//-------------------------------------------------------

var accumulate = require('./lib/combinator/accumulate');

exports.scan   = accumulate.scan;
exports.reduce = accumulate.reduce;

/**
 * Create a stream containing successive reduce results of applying f to
 * the previous reduce result and the current stream item.
 * @param {function(result:*, x:*):*} f reducer function
 * @param {*} initial initial value
 * @returns {Stream} new stream containing successive reduce results
 */
Stream.prototype.scan = function(f, initial) {
	return accumulate.scan(f, initial, this);
};

/**
 * Reduce the stream to produce a single result.  Note that reducing an infinite
 * stream will return a Promise that never fulfills, but that may reject if an error
 * occurs.
 * @param {function(result:*, x:*):*} f reducer function
 * @param {*} initial optional initial value
 * @returns {Promise} promise for the file result of the reduce
 */
Stream.prototype.reduce = function(f, initial) {
	return accumulate.reduce(f, initial, this);
};

//-----------------------------------------------------------------------
// Building and extending

var unfold = require('./lib/source/unfold');
var iterate = require('./lib/source/iterate');
var generate = require('./lib/source/generate');
var build = require('./lib/combinator/build');

exports.unfold    = unfold.unfold;
exports.iterate   = iterate.iterate;
exports.generate  = generate.generate;
exports.concat    = build.concat;
exports.startWith = build.cons;

/**
 * @param {Stream} tail
 * @returns {Stream} new stream containing all items in this followed by
 *  all items in tail
 */
Stream.prototype.concat = function(tail) {
	return build.concat(this, tail);
};

/**
 * @param {*} x value to prepend
 * @returns {Stream} a new stream with x prepended
 */
Stream.prototype.startWith = function(x) {
	return build.cons(x, this);
};

//-----------------------------------------------------------------------
// Transforming

var transform = require('./lib/combinator/transform');
var applicative = require('./lib/combinator/applicative');

exports.map      = transform.map;
exports.constant = transform.constant;
exports.tap      = transform.tap;
exports.ap       = applicative.ap;

/**
 * Transform each value in the stream by applying f to each
 * @param {function(*):*} f mapping function
 * @returns {Stream} stream containing items transformed by f
 */
Stream.prototype.map = function(f) {
	return transform.map(f, this);
};

/**
 * Assume this stream contains functions, and apply each function to each item
 * in the provided stream.  This generates, in effect, a cross product.
 * @param {Stream} xs stream of items to which
 * @returns {Stream} stream containing the cross product of items
 */
Stream.prototype.ap = function(xs) {
	return applicative.ap(this, xs);
};

/**
 * Replace each value in the stream with x
 * @param {*} x
 * @returns {Stream} stream containing items replaced with x
 */
Stream.prototype.constant = function(x) {
	return transform.constant(x, this);
};

/**
 * Perform a side effect for each item in the stream
 * @param {function(x:*):*} f side effect to execute for each item. The
 *  return value will be discarded.
 * @returns {Stream} new stream containing the same items as this stream
 */
Stream.prototype.tap = function(f) {
	return transform.tap(f, this);
};

//-----------------------------------------------------------------------
// Transducer support

var transduce = require('./lib/combinator/transduce');

exports.transduce = transduce.transduce;

/**
 * Transform this stream by passing its events through a transducer.
 * @param  {function} transducer transducer function
 * @return {Stream} stream of events transformed by the transducer
 */
Stream.prototype.transduce = function(transducer) {
	return transduce.transduce(transducer, this);
};

//-----------------------------------------------------------------------
// FlatMapping

var flatMap = require('./lib/combinator/flatMap');

exports.flatMap = exports.chain = flatMap.flatMap;
exports.join    = flatMap.join;

/**
 * Map each value in the stream to a new stream, and merge it into the
 * returned outer stream. Event arrival times are preserved.
 * @param {function(x:*):Stream} f chaining function, must return a Stream
 * @returns {Stream} new stream containing all events from each stream returned by f
 */
Stream.prototype.flatMap = Stream.prototype.chain = function(f) {
	return flatMap.flatMap(f, this);
};

/**
 * Monadic join. Flatten a Stream<Stream<X>> to Stream<X> by merging inner
 * streams to the outer. Event arrival times are preserved.
 * @returns {Stream<X>} new stream containing all events of all inner streams
 */
Stream.prototype.join = function() {
	return flatMap.join(this);
};

var continueWith = require('./lib/combinator/continueWith').continueWith;

exports.continueWith = continueWith;
exports.flatMapEnd = continueWith;

/**
 * Map the end event to a new stream, and begin emitting its values.
 * @param {function(x:*):Stream} f function that receives the end event value,
 * and *must* return a new Stream to continue with.
 * @returns {Stream} new stream that emits all events from the original stream,
 * followed by all events from the stream returned by f.
 */
Stream.prototype.continueWith = Stream.prototype.flatMapEnd = function(f) {
	return continueWith(f, this);
};

var concatMap = require('./lib/combinator/concatMap').concatMap;

exports.concatMap = concatMap;

Stream.prototype.concatMap = function(f) {
	return concatMap(f, this);
};

//-----------------------------------------------------------------------
// Concurrent merging

var mergeConcurrently = require('./lib/combinator/mergeConcurrently');

exports.mergeConcurrently = mergeConcurrently.mergeConcurrently;

/**
 * Flatten a Stream<Stream<X>> to Stream<X> by merging inner
 * streams to the outer, limiting the number of inner streams that may
 * be active concurrently.
 * @param {number} concurrency at most this many inner streams will be
 *  allowed to be active concurrently.
 * @return {Stream<X>} new stream containing all events of all inner
 *  streams, with limited concurrency.
 */
Stream.prototype.mergeConcurrently = function(concurrency) {
	return mergeConcurrently.mergeConcurrently(concurrency, this);
};

//-----------------------------------------------------------------------
// Merging

var merge = require('./lib/combinator/merge');

exports.merge = merge.merge;
exports.mergeArray = merge.mergeArray;

/**
 * Merge this stream and all the provided streams
 * @returns {Stream} stream containing items from this stream and s in time
 * order.  If two events are simultaneous they will be merged in
 * arbitrary order.
 */
Stream.prototype.merge = function(/*...streams*/) {
	return merge.mergeArray(base.cons(this, arguments));
};

//-----------------------------------------------------------------------
// Combining

var combine = require('./lib/combinator/combine');

exports.combine = combine.combine;
exports.combineArray = combine.combineArray;

/**
 * Combine latest events from all input streams
 * @param {function(...events):*} f function to combine most recent events
 * @returns {Stream} stream containing the result of applying f to the most recent
 *  event of each input stream, whenever a new event arrives on any stream.
 */
Stream.prototype.combine = function(f /*, ...streams*/) {
	return combine.combineArray(f, base.replace(this, 0, arguments));
};

//-----------------------------------------------------------------------
// Sampling

var sample = require('./lib/combinator/sample');

exports.sample = sample.sample;
exports.sampleWith = sample.sampleWith;

/**
 * When an event arrives on sampler, emit the latest event value from stream.
 * @param {Stream} sampler stream of events at whose arrival time
 *  signal's latest value will be propagated
 * @returns {Stream} sampled stream of values
 */
Stream.prototype.sampleWith = function(sampler) {
	return sample.sampleWith(sampler, this);
};

/**
 * When an event arrives on this stream, emit the result of calling f with the latest
 * values of all streams being sampled
 * @param {function(...values):*} f function to apply to each set of sampled values
 * @returns {Stream} stream of sampled and transformed values
 */
Stream.prototype.sample = function(f /* ...streams */) {
	return sample.sampleArray(f, this, base.tail(arguments));
};

//-----------------------------------------------------------------------
// Zipping

var zip = require('./lib/combinator/zip');

exports.zip = zip.zip;

/**
 * Pair-wise combine items with those in s. Given 2 streams:
 * [1,2,3] zipWith f [4,5,6] -> [f(1,4),f(2,5),f(3,6)]
 * Note: zip causes fast streams to buffer and wait for slow streams.
 * @param {function(a:Stream, b:Stream, ...):*} f function to combine items
 * @returns {Stream} new stream containing pairs
 */
Stream.prototype.zip = function(f /*, ...streams*/) {
	return zip.zipArray(f, base.replace(this, 0, arguments));
};

//-----------------------------------------------------------------------
// Switching

var switchLatest = require('./lib/combinator/switch').switch;

exports.switch       = switchLatest;
exports.switchLatest = switchLatest;

/**
 * Given a stream of streams, return a new stream that adopts the behavior
 * of the most recent inner stream.
 * @returns {Stream} switching stream
 */
Stream.prototype.switch = Stream.prototype.switchLatest = function() {
	return switchLatest(this);
};

//-----------------------------------------------------------------------
// Filtering

var filter = require('./lib/combinator/filter');

exports.filter          = filter.filter;
exports.skipRepeats     = exports.distinct   = filter.skipRepeats;
exports.skipRepeatsWith = exports.distinctBy = filter.skipRepeatsWith;

/**
 * Retain only items matching a predicate
 * stream:                           -12345678-
 * filter(x => x % 2 === 0, stream): --2-4-6-8-
 * @param {function(x:*):boolean} p filtering predicate called for each item
 * @returns {Stream} stream containing only items for which predicate returns truthy
 */
Stream.prototype.filter = function(p) {
	return filter.filter(p, this);
};

/**
 * Skip repeated events, using === to compare items
 * stream:           -abbcd-
 * distinct(stream): -ab-cd-
 * @returns {Stream} stream with no repeated events
 */
Stream.prototype.skipRepeats = function() {
	return filter.skipRepeats(this);
};

/**
 * Skip repeated events, using supplied equals function to compare items
 * @param {function(a:*, b:*):boolean} equals function to compare items
 * @returns {Stream} stream with no repeated events
 */
Stream.prototype.skipRepeatsWith = function(equals) {
	return filter.skipRepeatsWith(equals, this);
};

//-----------------------------------------------------------------------
// Slicing

var slice = require('./lib/combinator/slice');

exports.take      = slice.take;
exports.skip      = slice.skip;
exports.slice     = slice.slice;
exports.takeWhile = slice.takeWhile;
exports.skipWhile = slice.skipWhile;

/**
 * stream:          -abcd-
 * take(2, stream): -ab|
 * @param {Number} n take up to this many events
 * @returns {Stream} stream containing at most the first n items from this stream
 */
Stream.prototype.take = function(n) {
	return slice.take(n, this);
};

/**
 * stream:          -abcd->
 * skip(2, stream): ---cd->
 * @param {Number} n skip this many events
 * @returns {Stream} stream not containing the first n events
 */
Stream.prototype.skip = function(n) {
	return slice.skip(n, this);
};

/**
 * Slice a stream by event index. Equivalent to, but more efficient than
 * stream.take(end).skip(start);
 * NOTE: Negative start and end are not supported
 * @param {Number} start skip all events before the start index
 * @param {Number} end allow all events from the start index to the end index
 * @returns {Stream} stream containing items where start <= index < end
 */
Stream.prototype.slice = function(start, end) {
	return slice.slice(start, end, this);
};

/**
 * stream:                        -123451234->
 * takeWhile(x => x < 5, stream): -1234|
 * @param {function(x:*):boolean} p predicate
 * @returns {Stream} stream containing items up to, but not including, the
 * first item for which p returns falsy.
 */
Stream.prototype.takeWhile = function(p) {
	return slice.takeWhile(p, this);
};

/**
 * stream:                        -123451234->
 * skipWhile(x => x < 5, stream): -----51234->
 * @param {function(x:*):boolean} p predicate
 * @returns {Stream} stream containing items following *and including* the
 * first item for which p returns falsy.
 */
Stream.prototype.skipWhile = function(p) {
	return slice.skipWhile(p, this);
};

//-----------------------------------------------------------------------
// Time slicing

var timeslice = require('./lib/combinator/timeslice');

exports.until  = exports.takeUntil = timeslice.takeUntil;
exports.since  = exports.skipUntil = timeslice.skipUntil;
exports.during = timeslice.during;

/**
 * stream:                    -a-b-c-d-e-f-g->
 * signal:                    -------x
 * takeUntil(signal, stream): -a-b-c-|
 * @param {Stream} signal retain only events in stream before the first
 * event in signal
 * @returns {Stream} new stream containing only events that occur before
 * the first event in signal.
 */
Stream.prototype.until = Stream.prototype.takeUntil = function(signal) {
	return timeslice.takeUntil(signal, this);
};

/**
 * stream:                    -a-b-c-d-e-f-g->
 * signal:                    -------x
 * takeUntil(signal, stream): -------d-e-f-g->
 * @param {Stream} signal retain only events in stream at or after the first
 * event in signal
 * @returns {Stream} new stream containing only events that occur after
 * the first event in signal.
 */
Stream.prototype.since = Stream.prototype.skipUntil = function(signal) {
	return timeslice.skipUntil(signal, this);
};

/**
 * stream:                    -a-b-c-d-e-f-g->
 * timeWindow:                -----s
 * s:                               -----t
 * stream.during(timeWindow): -----c-d-e-|
 * @param {Stream<Stream>} timeWindow a stream whose first event (s) represents
 *  the window start time.  That event (s) is itself a stream whose first event (t)
 *  represents the window end time
 * @returns {Stream} new stream containing only events within the provided timespan
 */
Stream.prototype.during = function(timeWindow) {
	return timeslice.during(timeWindow, this);
};

//-----------------------------------------------------------------------
// Delaying

var delay = require('./lib/combinator/delay').delay;

exports.delay = delay;

/**
 * @param {Number} delayTime milliseconds to delay each item
 * @returns {Stream} new stream containing the same items, but delayed by ms
 */
Stream.prototype.delay = function(delayTime) {
	return delay(delayTime, this);
};

//-----------------------------------------------------------------------
// Getting event timestamp

var timestamp = require('./lib/combinator/timestamp').timestamp;

exports.timestamp = timestamp;

/**
 * Expose event timestamps into the stream. Turns a Stream<X> into
 * Stream<{time:t, value:X}>
 * @returns {Stream<{time:number, value:*}>}
 */
Stream.prototype.timestamp = function() {
	return timestamp(this);
};

//-----------------------------------------------------------------------
// Rate limiting

var limit = require('./lib/combinator/limit');

exports.throttle = limit.throttle;
exports.debounce = limit.debounce;

/**
 * Limit the rate of events
 * stream:              abcd----abcd----
 * throttle(2, stream): a-c-----a-c-----
 * @param {Number} period time to suppress events
 * @returns {Stream} new stream that skips events for throttle period
 */
Stream.prototype.throttle = function(period) {
	return limit.throttle(period, this);
};

/**
 * Wait for a burst of events to subside and emit only the last event in the burst
 * stream:              abcd----abcd----
 * debounce(2, stream): -----d-------d--
 * @param {Number} period events occuring more frequently than this
 *  on the provided scheduler will be suppressed
 * @returns {Stream} new debounced stream
 */
Stream.prototype.debounce = function(period) {
	return limit.debounce(period, this);
};

//-----------------------------------------------------------------------
// Awaiting Promises

var promises = require('./lib/combinator/promises');

exports.fromPromise = promises.fromPromise;
exports.await       = promises.awaitPromises;

/**
 * Await promises, turning a Stream<Promise<X>> into Stream<X>.  Preserves
 * event order, but timeshifts events based on promise resolution time.
 * @returns {Stream<X>} stream containing non-promise values
 */
Stream.prototype.await = function() {
	return promises.awaitPromises(this);
};

//-----------------------------------------------------------------------
// Error handling

var errors = require('./lib/combinator/errors');

exports.recoverWith  = errors.flatMapError;
exports.flatMapError = errors.flatMapError;
exports.throwError   = errors.throwError;

/**
 * If this stream encounters an error, recover and continue with items from stream
 * returned by f.
 * stream:                  -a-b-c-X-
 * f(X):                           d-e-f-g-
 * flatMapError(f, stream): -a-b-c-d-e-f-g-
 * @param {function(error:*):Stream} f function which returns a new stream
 * @returns {Stream} new stream which will recover from an error by calling f
 */
Stream.prototype.recoverWith = Stream.prototype.flatMapError = function(f) {
	return errors.flatMapError(f, this);
};

//-----------------------------------------------------------------------
// Multicasting

var multicast = require('@most/multicast').default;

exports.multicast = multicast;

/**
 * Transform the stream into multicast stream.  That means that many subscribers
 * to the stream will not cause multiple invocations of the internal machinery.
 * @returns {Stream} new stream which will multicast events to all observers.
 */
Stream.prototype.multicast = function() {
	return multicast(this);
};