refactor(web): transcription cache needed for multitaps, no longer pr…

…ediction-only

common/web/input-processor/src/text/inputProcessor.ts

@@ -22,6 +22,7 @@ import {
   SystemStoreIDs,
   type TextTransform
 } from "@keymanapp/keyboard-processor";
+import { TranscriptionCache } from "../transcriptionCache.js";
 
 export default class InputProcessor {
   public static readonly DEFAULT_OPTIONS: ProcessorInitOptions = {
@@ -37,6 +38,8 @@ export default class InputProcessor {
   private kbdProcessor: KeyboardProcessor;
   private lngProcessor: LanguageProcessor;
 
+  private readonly contextCache = new TranscriptionCache();
+
   constructor(device: DeviceSpec, predictiveTextWorker: Worker, options?: ProcessorInitOptions) {
     if(!device) {
       throw new Error('device must be defined');
@@ -48,7 +51,7 @@ export default class InputProcessor {
 
     this.contextDevice = device;
     this.kbdProcessor = new KeyboardProcessor(device, options);
-    this.lngProcessor = new LanguageProcessor(predictiveTextWorker);
+    this.lngProcessor = new LanguageProcessor(predictiveTextWorker, this.contextCache);
   }
 
   public get languageProcessor(): LanguageProcessor {
@@ -215,6 +218,10 @@ export default class InputProcessor {
       ruleBehavior.triggersDefaultCommand = true;
     }
 
+    // Multitaps operate in part by referencing 'committed' Transcriptions to rewind
+    // the context as necessary.
+    this.contextCache.save(ruleBehavior.transcription);
+
     // The keyboard may want to take an action after all other keystroke processing is
     // finished, for example to switch layers. This action may not have any output
     // but may change system store or variable store values. Given this, we don't need to

common/web/input-processor/src/text/prediction/languageProcessor.ts

@@ -3,6 +3,7 @@ import { LMLayer } from "@keymanapp/lexical-model-layer/web";
 import { OutputTarget, Transcription, Mock } from "@keymanapp/keyboard-processor";
 import ContextWindow from "../contextWindow.js";
 import ModelSpec from "./modelSpec.js"
+import { TranscriptionCache } from "../../transcriptionCache.js";
 
 /**
  * Corresponds to the 'suggestionsready' LanguageProcessor event.
@@ -60,18 +61,18 @@ export default class LanguageProcessor extends EventEmitter<LanguageProcessorEve
   private configuration?: Configuration;
   private currentPromise?: Promise<Suggestion[]>;
 
-  private recentTranscriptions: Transcription[] = [];
+  private readonly recentTranscriptions: TranscriptionCache;
 
   private _mayPredict: boolean = true;
   private _mayCorrect: boolean = true;
 
   private _state: StateChangeEnum = 'inactive';
 
-  private static readonly TRANSCRIPTION_BUFFER: 10 = 10;
-
-  public constructor(predictiveTextWorker: Worker, supportsRightDeletions: boolean = false) {
+  public constructor(predictiveTextWorker: Worker, transcriptionCache: TranscriptionCache, supportsRightDeletions: boolean = false) {
     super();
 
+    this.recentTranscriptions = transcriptionCache;
+
     // Establishes KMW's platform 'capabilities', which limit the range of context a LMLayer
     // model may expect.
     let capabilities: Capabilities = {
@@ -357,11 +358,7 @@ export default class LanguageProcessor extends EventEmitter<LanguageProcessorEve
   }
 
   private recordTranscription(transcription: Transcription) {
-    this.recentTranscriptions.push(transcription);
-
-    if(this.recentTranscriptions.length > LanguageProcessor.TRANSCRIPTION_BUFFER) {
-      this.recentTranscriptions.splice(0, 1);
-    }
+    this.recentTranscriptions.save(transcription);
   }
 
   /**
@@ -372,11 +369,7 @@ export default class LanguageProcessor extends EventEmitter<LanguageProcessorEve
    * @returns The matching `Transcription`, or `null` none is found.
    */
   public getPredictionState(id: number): Transcription {
-    let match = this.recentTranscriptions.filter((t: Transcription) => {
-      return t.token == id;
-    })
-
-    return match.length == 0 ? null : match[0];
+    return this.recentTranscriptions.get(id);
   }
 
   public shutdown() {

common/web/input-processor/src/transcriptionCache.ts

@@ -0,0 +1,37 @@
+import { Transcription } from "@keymanapp/keyboard-processor";
+
+const TRANSCRIPTION_BUFFER_SIZE = 10;
+
+export class TranscriptionCache {
+  private readonly map = new Map<number, Transcription>();
+
+  public get(key: number) {
+    const value = this.map.get(key);
+
+    // Update the entry's 'age' / position in the keys() ordering.
+    if(value) {
+      this.save(value);
+    }
+
+    return value;
+  }
+
+  public save(value: Transcription) {
+    const key = value.token >= 0 ? value.token : -value.token;
+
+    // Resets the key's ordering in Map.keys.
+    this.map.delete(key);
+    this.map.set(key, value);
+
+    if(this.map.size > TRANSCRIPTION_BUFFER_SIZE) {
+      /* Deletes the oldest entry.  As per the specification of `Map.keys()`, the keys are in
+       * insertion order.  The earlier `map.delete` call resets a key's position in the list,
+       * ensuring index 0 corresponds to the entry least-recently referenced.
+       *
+       * See also:
+       * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/keys
+       */
+      this.map.delete(this.map.keys().next().value);
+    }
+  }
+}