fix: Check long interval when using moving average crossover with EMA (#142)

Author: bennycode

src/DMA/DMA.test.ts

@@ -30,7 +30,7 @@ describe('DMA', () => {
   });
 
   describe('isStable', () => {
-    it('is dependant on the long interval', () => {
+    it('is dependant on the long interval (SMA)', () => {
       const dma = new DMA(3, 5);
       dma.update(40);
       dma.update(30);
@@ -40,6 +40,17 @@ describe('DMA', () => {
       dma.update(30);
       expect(dma.isStable).toBeTrue();
     });
+
+    it('is dependant on the long interval (EMA)', () => {
+      const dma = new DMA(3, 5, EMA);
+      dma.update(40);
+      dma.update(30);
+      dma.update(20);
+      expect(dma.isStable).toBeFalse();
+      dma.update(10);
+      dma.update(30);
+      expect(dma.isStable).toBeTrue();
+    });
   });
 
   describe('getResult', () => {

src/DMA/DMA.ts

@@ -7,21 +7,22 @@ export type DMAResult = {long: Big; short: Big};
 export class DMA {
   public readonly long: MovingAverage;
   public readonly short: MovingAverage;
+  private received: number = 0;
 
   constructor(short: number, long: number, Indicator: typeof EMA | typeof SMA = SMA) {
     this.short = new Indicator(short);
     this.long = new Indicator(long);
   }
 
   get isStable(): boolean {
-    return this.long.isStable;
+    return this.received >= this.long.interval;
   }
 
   update(_price: BigSource): void {
     const price = new Big(_price);
-
     this.short.update(price);
     this.long.update(price);
+    this.received += 1;
   }
 
   getResult(): DMAResult {