# HG changeset patch
# User cin
# Date 2023-01-07 21:36:35
# Node ID fbe158a5752ad4d38382a265d9db5a402e4f1f01
# Parent  dd0b7cf0ce69501aca6e8c30f2ae4a1ca0540e21

added while, until methods to the observable interface.
added stateful producer

diff --git a/djx/src/main/ts/observable.ts b/djx/src/main/ts/observable.ts
--- a/djx/src/main/ts/observable.ts
+++ b/djx/src/main/ts/observable.ts
@@ -66,6 +66,8 @@ export interface Subscribable<T> {
 
 export type AccumulatorFn<T, A> = (acc: A, value: T) => A;
 
+export type OperatorFn<T, U> = (source: Observable<T>) => Producer<U>;
+
 /** The observable source of items. */
 export interface Observable<T> extends Subscribable<T> {
     /** Transforms elements of the sequence with the specified mapper
@@ -81,6 +83,17 @@ export interface Observable<T> extends S
      */
     filter(predicate: (value: T) => boolean): Observable<T>;
 
+    /** Completes the sequence once the condition is met.
+     * @param predicate The condition which should be met to complete the sequence
+     */
+    until(predicate: (value: T) => boolean): Observable<T>;
+
+    /** Keeps the sequence running while elements satisfy the condition.
+     * 
+     * @param predicate The condition which should be met to continue.
+     */
+    while(predicate: (value: T) => boolean): Observable<T>;
+
     /** Applies accumulator to each value in the sequence and
      * emits the accumulated value for each source element
      * 
@@ -102,13 +115,26 @@ export interface Observable<T> extends S
     /** Concatenates the specified sequences with this observable
      * 
      * @param seq sequences to concatenate with the current observable
+     * 
+     * The concatenation doesn't accumulate values from the specified sequences,
+     * The result of the concatenation is the new observable which will switch
+     * to the next observable after the previous one completes. Values emitted
+     * before the next observable being active are lost.
      */
     cat(...seq: Subscribable<T>[]): Observable<T>;
 
+
     /** Pipes the specified operator to produce the new observable
-     * @param op The operator which consumes this observable and produces a new one
+     * @param op The operator consumes this observable and produces a new one
+     * 
+     * The operator is a higher order function which takes a source observable
+     * and returns a producer for the new observable.
+     * 
+     * This function can be used to create a complex mapping between source and
+     * resulting observables. The operator may have a state (or a side effect)
+     * and can be connected to multiple observables.
      */
-    pipe<U>(op: (source: Observable<T>) => Producer<U>): Observable<U>;
+    pipe<U>(op: OperatorFn<T, U>): Observable<U>;
 
     /** Waits for the next event to occur and returns a promise for the next value
      * @param ct Cancellation token to 
@@ -142,6 +168,8 @@ const fuse = <T>(producer: Producer<T>) 
             void (0) :
             (done = true, cleanup(), fn(...args));
 
+    const _fin0 = () => done ? void (0) : (done = true, cleanup());
+
     const safeSink = {
         next: (value: T) => { !done && next(value); },
         error: _fin(error),
@@ -149,9 +177,7 @@ const fuse = <T>(producer: Producer<T>) 
         isClosed: () => done
     };
     cleanup = producer(safeSink) ?? noop;
-    return done ?
-        (cleanup(), noop) :
-        _fin(noop);
+    return done ? cleanup() : _fin0;
 };
 
 const _observe = <T>(producer: Producer<T>): Observable<T> => ({
@@ -173,6 +199,22 @@ const _observe = <T>(producer: Producer<
         })
     ),
 
+    until: predicate => _observe(({ next, complete, ...rest }) =>
+        producer({
+            next: v => predicate(v) ? complete() : next(v),
+            complete,
+            ...rest
+        })
+    ),
+
+    while: predicate => _observe(({ next, complete, ...rest }) =>
+        producer({
+            next: v => predicate(v) ? next(v) : complete(),
+            complete,
+            ...rest
+        })
+    ),
+
     scan: <A>(...args: [AccumulatorFn<T, A>, A] | [AccumulatorFn<T, T>]) => _observe<T | A>(({ next, ...rest }) => {
         if (args.length === 1) {
             const [accumulator] = args;
@@ -293,7 +335,10 @@ export const streamArray = <T>(items: T[
 );
 
 export const streamPromise = <T>(promise: PromiseLike<T>) => observe<T>(
-    ({next, error, complete}) => void promise.then(v => (next(v), complete()), error)
+    ({ next, error, complete }) => void promise.then(
+        v => (next(v), complete()),
+        error
+    )
 );
 
 export const of = <T>(...items: T[]) => _observe<T>(
@@ -303,4 +348,90 @@ export const of = <T>(...items: T[]) => 
     )
 );
 
-export const empty = _observe<never>(({ complete }) => complete());
\ No newline at end of file
+export const empty = _observe<never>(({ complete }) => complete());
+
+/**
+ * Creates a mutable state and the observable for the stored value.
+ * 
+ * @param value The initial value for the state
+ * @returns an array of three elements `[observable, setter, getter]`
+ * 
+ * The returned observable keeps the actual value and will emit it as the next
+ * element each time a consumer subscribes the observable.
+ * 
+ * Calling the setter will update the stored value in the observable and notify
+ * all consumers.
+ */
+export const stateful = <T>(producer: Producer<T>): Producer<T> => {
+    const fusedProducer = fuse(producer);
+    type Status = "active" | "complete" | "error";
+
+    let lastValue: T;
+    let hasValue = false;
+    let status: Status = "active";
+    let lastError: unknown;
+    let subscribers: Sink<T>[] = [];
+
+    const sink: Sink<T> = {
+        isClosed: () => status !== "active",
+        complete: () => {
+            if (status === "active") {
+                status = "complete";
+                const _subscribers = subscribers;
+                subscribers = [];
+                _subscribers.forEach(s => s.complete());
+            }
+        },
+        error: e => {
+            if (status === "active") {
+                status = "error";
+                lastError = e;
+                const _subscribers = subscribers;
+                subscribers = [];
+                _subscribers.forEach(s => s.error(e));
+            }
+        },
+        next: v => {
+            if (status === "active") {
+                hasValue = true;
+                lastValue = v;
+                const _subscribers = subscribers;
+                _subscribers.forEach(s => s.next(v));
+            }
+        }
+    };
+
+    fusedProducer(sink);
+
+    return (s: Sink<T>) => {
+        const _subscribers = subscribers;
+        switch (status) {
+            case "active":
+                if (hasValue)
+                    s.next(lastValue); // if hasValue is true,
+                                       // lastValue has a valid value
+                subscribers.push(s);
+                return () => {
+                    if (_subscribers === subscribers) {
+                        const pos = subscribers.indexOf(s);
+                        if (pos >= 0)
+                            subscribers.splice(pos, 1);
+                    }
+                };
+            case "complete":
+                s.complete();
+                break;
+            case "error":
+                s.error(lastError);
+                break;
+        }
+    };
+};
+
+const subject = <T>(producer: Producer<T>): Producer<T> => {
+    const fusedProducer = fuse(producer);
+
+    return () => {
+
+    };
+};
\ No newline at end of file
diff --git a/djx/src/test/ts/plan.ts b/djx/src/test/ts/plan.ts
--- a/djx/src/test/ts/plan.ts
+++ b/djx/src/test/ts/plan.ts
@@ -1,2 +1,3 @@
 import "./declare-tests";
-import "./observable-tests";
\ No newline at end of file
+import "./observable-tests";
+import "./state-tests";
\ No newline at end of file
diff --git a/djx/src/test/ts/state-tests.ts b/djx/src/test/ts/state-tests.ts
new file mode 100644
--- /dev/null
+++ b/djx/src/test/ts/state-tests.ts
@@ -0,0 +1,27 @@
+import { observe, stateful } from "./observable";
+import * as t from "tap";
+
+interface CounterState {
+    count: number;
+
+    label: "low" | "mid" | "high"
+}
+
+let set: (v: CounterState) => void = () => void (0);
+const initial: CounterState = { count: 0, label: "low" };
+let value = initial;
+
+const obs = observe(stateful<CounterState>(({ next }) => {
+    next(initial);
+    set = next;
+}));
+
+set({ count: 10, label: "mid" });
+
+obs.subscribe({
+    next: v => value = v
+});
+
+t.equal(value.count, 10, "State should update");
+
+set({ count: 20, label: "high" });
diff --git a/playground/package-lock.json b/playground/package-lock.json
--- a/playground/package-lock.json
+++ b/playground/package-lock.json
@@ -30,7 +30,6 @@
         },
         "../djx/build/npm/package": {
             "name": "@implab/djx",
-            "version": "1.6.3",
             "dev": true,
             "license": "BSD-2-Clause",
             "peerDependencies": {