--- /dev/null
+import { Observable } from '../Observable';
+import { Subscriber } from '../Subscriber';
+import { identity } from '../util/identity';
+import { SchedulerAction, SchedulerLike } from '../types';
+import { isScheduler } from '../util/isScheduler';
+
+export type ConditionFunc<S> = (state: S) => boolean;
+export type IterateFunc<S> = (state: S) => S;
+export type ResultFunc<S, T> = (state: S) => T;
+
+interface SchedulerState<T, S> {
+ needIterate?: boolean;
+ state: S;
+ subscriber: Subscriber<T>;
+ condition?: ConditionFunc<S>;
+ iterate: IterateFunc<S>;
+ resultSelector: ResultFunc<S, T>;
+}
+
+export interface GenerateBaseOptions<S> {
+ /**
+ * Initial state.
+ */
+ initialState: S;
+ /**
+ * Condition function that accepts state and returns boolean.
+ * When it returns false, the generator stops.
+ * If not specified, a generator never stops.
+ */
+ condition?: ConditionFunc<S>;
+ /**
+ * Iterate function that accepts state and returns new state.
+ */
+ iterate: IterateFunc<S>;
+ /**
+ * SchedulerLike to use for generation process.
+ * By default, a generator starts immediately.
+ */
+ scheduler?: SchedulerLike;
+}
+
+export interface GenerateOptions<T, S> extends GenerateBaseOptions<S> {
+ /**
+ * Result selection function that accepts state and returns a value to emit.
+ */
+ resultSelector: ResultFunc<S, T>;
+}
+
+/**
+ * Generates an observable sequence by running a state-driven loop
+ * producing the sequence's elements, using the specified scheduler
+ * to send out observer messages.
+ *
+ * 
+ *
+ * @example <caption>Produces sequence of 0, 1, 2, ... 9, then completes.</caption>
+ * const res = generate(0, x => x < 10, x => x + 1, x => x);
+ *
+ * @example <caption>Using asap scheduler, produces sequence of 2, 3, 5, then completes.</caption>
+ * const res = generate(1, x => x < 5, x => x * 2, x => x + 1, asap);
+ *
+ * @see {@link from}
+ * @see {@link Observable}
+ *
+ * @param {S} initialState Initial state.
+ * @param {function (state: S): boolean} condition Condition to terminate generation (upon returning false).
+ * @param {function (state: S): S} iterate Iteration step function.
+ * @param {function (state: S): T} resultSelector Selector function for results produced in the sequence. (deprecated)
+ * @param {SchedulerLike} [scheduler] A {@link SchedulerLike} on which to run the generator loop. If not provided, defaults to emit immediately.
+ * @returns {Observable<T>} The generated sequence.
+ */
+ export function generate<T, S>(initialState: S,
+ condition: ConditionFunc<S>,
+ iterate: IterateFunc<S>,
+ resultSelector: ResultFunc<S, T>,
+ scheduler?: SchedulerLike): Observable<T>;
+
+/**
+ * Generates an Observable by running a state-driven loop
+ * that emits an element on each iteration.
+ *
+ * <span class="informal">Use it instead of nexting values in a for loop.</span>
+ *
+ * <img src="./img/generate.png" width="100%">
+ *
+ * `generate` allows you to create stream of values generated with a loop very similar to
+ * traditional for loop. First argument of `generate` is a beginning value. Second argument
+ * is a function that accepts this value and tests if some condition still holds. If it does,
+ * loop continues, if not, it stops. Third value is a function which takes previously defined
+ * value and modifies it in some way on each iteration. Note how these three parameters
+ * are direct equivalents of three expressions in regular for loop: first expression
+ * initializes some state (for example numeric index), second tests if loop can make next
+ * iteration (for example if index is lower than 10) and third states how defined value
+ * will be modified on every step (index will be incremented by one).
+ *
+ * Return value of a `generate` operator is an Observable that on each loop iteration
+ * emits a value. First, condition function is ran. If it returned true, Observable
+ * emits currently stored value (initial value at the first iteration) and then updates
+ * that value with iterate function. If at some point condition returned false, Observable
+ * completes at that moment.
+ *
+ * Optionally you can pass fourth parameter to `generate` - a result selector function which allows you
+ * to immediately map value that would normally be emitted by an Observable.
+ *
+ * If you find three anonymous functions in `generate` call hard to read, you can provide
+ * single object to the operator instead. That object has properties: `initialState`,
+ * `condition`, `iterate` and `resultSelector`, which should have respective values that you
+ * would normally pass to `generate`. `resultSelector` is still optional, but that form
+ * of calling `generate` allows you to omit `condition` as well. If you omit it, that means
+ * condition always holds, so output Observable will never complete.
+ *
+ * Both forms of `generate` can optionally accept a scheduler. In case of multi-parameter call,
+ * scheduler simply comes as a last argument (no matter if there is resultSelector
+ * function or not). In case of single-parameter call, you can provide it as a
+ * `scheduler` property on object passed to the operator. In both cases scheduler decides when
+ * next iteration of the loop will happen and therefore when next value will be emitted
+ * by the Observable. For example to ensure that each value is pushed to the observer
+ * on separate task in event loop, you could use `async` scheduler. Note that
+ * by default (when no scheduler is passed) values are simply emitted synchronously.
+ *
+ *
+ * @example <caption>Use with condition and iterate functions.</caption>
+ * const generated = generate(0, x => x < 3, x => x + 1);
+ *
+ * generated.subscribe(
+ * value => console.log(value),
+ * err => {},
+ * () => console.log('Yo!')
+ * );
+ *
+ * // Logs:
+ * // 0
+ * // 1
+ * // 2
+ * // "Yo!"
+ *
+ *
+ * @example <caption>Use with condition, iterate and resultSelector functions.</caption>
+ * const generated = generate(0, x => x < 3, x => x + 1, x => x * 1000);
+ *
+ * generated.subscribe(
+ * value => console.log(value),
+ * err => {},
+ * () => console.log('Yo!')
+ * );
+ *
+ * // Logs:
+ * // 0
+ * // 1000
+ * // 2000
+ * // "Yo!"
+ *
+ *
+ * @example <caption>Use with options object.</caption>
+ * const generated = generate({
+ * initialState: 0,
+ * condition(value) { return value < 3; },
+ * iterate(value) { return value + 1; },
+ * resultSelector(value) { return value * 1000; }
+ * });
+ *
+ * generated.subscribe(
+ * value => console.log(value),
+ * err => {},
+ * () => console.log('Yo!')
+ * );
+ *
+ * // Logs:
+ * // 0
+ * // 1000
+ * // 2000
+ * // "Yo!"
+ *
+ * @example <caption>Use options object without condition function.</caption>
+ * const generated = generate({
+ * initialState: 0,
+ * iterate(value) { return value + 1; },
+ * resultSelector(value) { return value * 1000; }
+ * });
+ *
+ * generated.subscribe(
+ * value => console.log(value),
+ * err => {},
+ * () => console.log('Yo!') // This will never run.
+ * );
+ *
+ * // Logs:
+ * // 0
+ * // 1000
+ * // 2000
+ * // 3000
+ * // ...and never stops.
+ *
+ *
+ * @see {@link from}
+ * @see {@link index/Observable.create}
+ *
+ * @param {S} initialState Initial state.
+ * @param {function (state: S): boolean} condition Condition to terminate generation (upon returning false).
+ * @param {function (state: S): S} iterate Iteration step function.
+ * @param {function (state: S): T} [resultSelector] Selector function for results produced in the sequence.
+ * @param {Scheduler} [scheduler] A {@link Scheduler} on which to run the generator loop. If not provided, defaults to emitting immediately.
+ * @return {Observable<T>} The generated sequence.
+ */
+export function generate<S>(initialState: S,
+ condition: ConditionFunc<S>,
+ iterate: IterateFunc<S>,
+ scheduler?: SchedulerLike): Observable<S>;
+
+/**
+ * Generates an observable sequence by running a state-driven loop
+ * producing the sequence's elements, using the specified scheduler
+ * to send out observer messages.
+ * The overload accepts options object that might contain initial state, iterate,
+ * condition and scheduler.
+ *
+ * 
+ *
+ * @example <caption>Produces sequence of 0, 1, 2, ... 9, then completes.</caption>
+ * const res = generate({
+ * initialState: 0,
+ * condition: x => x < 10,
+ * iterate: x => x + 1,
+ * });
+ *
+ * @see {@link from}
+ * @see {@link Observable}
+ *
+ * @param {GenerateBaseOptions<S>} options Object that must contain initialState, iterate and might contain condition and scheduler.
+ * @returns {Observable<S>} The generated sequence.
+ */
+export function generate<S>(options: GenerateBaseOptions<S>): Observable<S>;
+
+/**
+ * Generates an observable sequence by running a state-driven loop
+ * producing the sequence's elements, using the specified scheduler
+ * to send out observer messages.
+ * The overload accepts options object that might contain initial state, iterate,
+ * condition, result selector and scheduler.
+ *
+ * 
+ *
+ * @example <caption>Produces sequence of 0, 1, 2, ... 9, then completes.</caption>
+ * const res = generate({
+ * initialState: 0,
+ * condition: x => x < 10,
+ * iterate: x => x + 1,
+ * resultSelector: x => x,
+ * });
+ *
+ * @see {@link from}
+ * @see {@link Observable}
+ *
+ * @param {GenerateOptions<T, S>} options Object that must contain initialState, iterate, resultSelector and might contain condition and scheduler.
+ * @returns {Observable<T>} The generated sequence.
+ */
+export function generate<T, S>(options: GenerateOptions<T, S>): Observable<T>;
+
+export function generate<T, S>(initialStateOrOptions: S | GenerateOptions<T, S>,
+ condition?: ConditionFunc<S>,
+ iterate?: IterateFunc<S>,
+ resultSelectorOrObservable?: (ResultFunc<S, T>) | SchedulerLike,
+ scheduler?: SchedulerLike): Observable<T> {
+
+ let resultSelector: ResultFunc<S, T>;
+ let initialState: S;
+
+ if (arguments.length == 1) {
+ const options = initialStateOrOptions as GenerateOptions<T, S>;
+ initialState = options.initialState;
+ condition = options.condition;
+ iterate = options.iterate;
+ resultSelector = options.resultSelector || identity as ResultFunc<S, T>;
+ scheduler = options.scheduler;
+ } else if (resultSelectorOrObservable === undefined || isScheduler(resultSelectorOrObservable)) {
+ initialState = initialStateOrOptions as S;
+ resultSelector = identity as ResultFunc<S, T>;
+ scheduler = resultSelectorOrObservable as SchedulerLike;
+ } else {
+ initialState = initialStateOrOptions as S;
+ resultSelector = resultSelectorOrObservable as ResultFunc<S, T>;
+ }
+
+ return new Observable<T>(subscriber => {
+ let state = initialState;
+ if (scheduler) {
+ return scheduler.schedule<SchedulerState<T, S>>(dispatch, 0, {
+ subscriber,
+ iterate,
+ condition,
+ resultSelector,
+ state
+ });
+ }
+
+ do {
+ if (condition) {
+ let conditionResult: boolean;
+ try {
+ conditionResult = condition(state);
+ } catch (err) {
+ subscriber.error(err);
+ return undefined;
+ }
+ if (!conditionResult) {
+ subscriber.complete();
+ break;
+ }
+ }
+ let value: T;
+ try {
+ value = resultSelector(state);
+ } catch (err) {
+ subscriber.error(err);
+ return undefined;
+ }
+ subscriber.next(value);
+ if (subscriber.closed) {
+ break;
+ }
+ try {
+ state = iterate(state);
+ } catch (err) {
+ subscriber.error(err);
+ return undefined;
+ }
+ } while (true);
+
+ return undefined;
+ });
+}
+
+function dispatch<T, S>(this: SchedulerAction<SchedulerState<T, S>>, state: SchedulerState<T, S>) {
+ const { subscriber, condition } = state;
+ if (subscriber.closed) {
+ return undefined;
+ }
+ if (state.needIterate) {
+ try {
+ state.state = state.iterate(state.state);
+ } catch (err) {
+ subscriber.error(err);
+ return undefined;
+ }
+ } else {
+ state.needIterate = true;
+ }
+ if (condition) {
+ let conditionResult: boolean;
+ try {
+ conditionResult = condition(state.state);
+ } catch (err) {
+ subscriber.error(err);
+ return undefined;
+ }
+ if (!conditionResult) {
+ subscriber.complete();
+ return undefined;
+ }
+ if (subscriber.closed) {
+ return undefined;
+ }
+ }
+ let value: T;
+ try {
+ value = state.resultSelector(state.state);
+ } catch (err) {
+ subscriber.error(err);
+ return undefined;
+ }
+ if (subscriber.closed) {
+ return undefined;
+ }
+ subscriber.next(value);
+ if (subscriber.closed) {
+ return undefined;
+ }
+ return this.schedule(state);
+}
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