issue-56 pause process implementation

src/processes/adapter/pause.ts

@@ -0,0 +1,33 @@
+import { Scroller } from '../../scroller';
+import { BaseAdapterProcessFactory, AdapterProcess, ProcessStatus } from '../misc/index';
+
+export default class Pause extends BaseAdapterProcessFactory(AdapterProcess.pause) {
+
+  static run(scroller: Scroller, options?: { resume: boolean }): void {
+    const resume = !!options?.resume;
+
+    if (!resume) {
+      if (!scroller.state.paused.get()) {
+        scroller.state.paused.set(true);
+        scroller.logger.log('pause scroller');
+      } else {
+        scroller.logger.log('pause scroller (cancelled)');
+      }
+      return;
+    }
+
+    if (!scroller.state.paused.get()) {
+      scroller.logger.log('resume scroller (cancelled)');
+      return;
+    }
+
+    scroller.state.paused.set(false);
+    scroller.logger.log('resume scroller');
+
+    scroller.workflow.call({
+      process: AdapterProcess.pause,
+      status: ProcessStatus.done
+    });
+  }
+
+}

src/processes/index.ts

@@ -9,6 +9,7 @@ import UserClip from './adapter/clip';
 import Insert from './adapter/insert';
 import Replace from './adapter/replace';
 import Update from './adapter/update';
+import Pause from './adapter/pause';
 import Fix from './adapter/fix';
 import Start from './start';
 import PreFetch from './preFetch';
@@ -24,7 +25,7 @@ import { CommonProcess, AdapterProcess, ProcessStatus } from './misc/enums';
 
 export {
   Init, Scroll,
-  Reset, Reload, Append, Check, Remove, UserClip, Insert, Replace, Update, Fix,
+  Reset, Reload, Append, Check, Remove, UserClip, Insert, Replace, Update, Pause, Fix,
   Start, PreFetch, Fetch, PostFetch, Render, PreClip, Clip, Adjust, End,
   CommonProcess, AdapterProcess, ProcessStatus,
 };

src/workflow-transducer.ts

@@ -13,6 +13,7 @@ import {
   Insert,
   Replace,
   Update,
+  Pause,
   Fix,
   Start,
   PreFetch,
@@ -131,6 +132,14 @@ export const runStateMachine = ({
         run(Init)(process);
       }
       break;
+    case AdapterProcess.pause:
+      if (status === Status.start) {
+        run(Pause)(options);
+      }
+      if (status === Status.done) {
+        run(Init)(process);
+      }
+      break;
     case AdapterProcess.fix:
       if (status === Status.start) {
         run(Fix)(options);

src/workflow.ts

@@ -2,7 +2,7 @@ import { Scroller } from './scroller';
 import { runStateMachine } from './workflow-transducer';
 import { Reactive } from './classes/reactive';
 import { Item } from './classes/item';
-import { CommonProcess, ProcessStatus as Status, } from './processes/index';
+import { AdapterProcess, CommonProcess, ProcessStatus as Status, } from './processes/index';
 import { WORKFLOW, validate } from './inputs/index';
 import {
   WorkflowParams,
@@ -100,6 +100,11 @@ export class Workflow<ItemData = unknown> {
       return;
     }
     const { process, status } = processSubject;
+    // if the scroller is paused, any process other than "pause" and "reset" should be blocked
+    if (this.scroller.state.paused.get() && process !== AdapterProcess.pause && process !== AdapterProcess.reset) {
+      this.scroller.logger.log('scroller is paused: ' + process + ' process is ignored');
+      return;
+    }
     if (process && process.startsWith('adapter') && status !== Status.next) {
       this.adapterRun$.set(processSubject);
     }