extend technical indicator

src/DMA/DMA.ts

@@ -1,4 +1,5 @@
 import type {Big, BigSource} from '../index.js';
+import {TechnicalIndicator} from '../index.js';
 import type {Indicator} from '../Indicator.js';
 import type {FasterMovingAverage, MovingAverage} from '../MA/MovingAverage.js';
 import type {FasterMovingAverageTypes, MovingAverageTypes} from '../MA/MovingAverageTypes.js';
@@ -23,11 +24,12 @@ export interface FasterDMAResult {
  *
  * @see https://faculty.fuqua.duke.edu/~charvey/Teaching/BA453_2002/CCAM/CCAM.htm#_Toc2634228
  */
-export class DMA implements Indicator<DMAResult> {
+export class DMA extends TechnicalIndicator<DMAResult, BigSource> {
   public readonly short: MovingAverage;
   public readonly long: MovingAverage;
 
   constructor(short: number, long: number, Indicator: MovingAverageTypes = SMA) {
+    super();
     this.short = new Indicator(short);
     this.long = new Indicator(long);
   }

src/Indicator.ts

@@ -1,5 +1,5 @@
 import {NotEnoughDataError} from './error/index.js';
-import type {Big, BigSource} from './index.js';
+import {getLastFromForEach, type Big, type BigSource} from './index.js';
 
 export interface Indicator<Result = Big, Input = BigSource> {
   getResult(): Result;
@@ -13,6 +13,22 @@ export interface Indicator<Result = Big, Input = BigSource> {
   updates(input: Input[], replace: boolean): void | Result;
 }
 
+export abstract class TechnicalIndicator<Result, Input> implements Indicator<Result, Input> {
+  accessor isStable: boolean = false;
+
+  abstract getResult(): Result;
+
+  replace(input: Input) {
+    return this.update(input, true);
+  }
+
+  abstract update(input: Input, replace: boolean): void | Result;
+
+  updates(inputs: Input[], replace: boolean) {
+    return getLastFromForEach(inputs, input => this.update(input, replace));
+  }
+}
+
 /**
  * Tracks results of an indicator over time and memorizes the highest & lowest result.
  */