refactor valid ticker validation checks

src/app.ts

@@ -1,34 +1,35 @@
-import { isMarketOpen, logError } from './utils';
+import { isMarketOpen, isValidMarketSymbol, logError } from './utils';
 import dotenv from 'dotenv';
 import { invokeWebhook } from './invoke_webhook';
 import { MarketSymbol } from './types';
 
 dotenv.config();
 
 const WEBHOOK_URL = process.env.WEBHOOK_URL;
-const TICKER: unknown = process.argv[2];
-const validTickers: MarketSymbol[] = ['usd-jpy', 'spy', 'spy-futures'];
+const TICKER: string | undefined = process.argv[2];
 
 if (!WEBHOOK_URL) {
   logError(new Error(`invalid webhook URL: ${WEBHOOK_URL}`));
   process.exit(1);
 }
 // If TICKER doesn't exist or it's not part of the valid ticker list, throw usage guide
-if (!(typeof TICKER === 'string' && validTickers.includes(TICKER))) {
+if (!isValidMarketSymbol(TICKER)) {
   logError(
     new Error(
       `Usage: npx ts-node src/app.js usd-jpy|spy|spy-futures - received ${TICKER}`
     )
   );
 }
+// TICKER is now guaranteed to be usd-jpy|spy|spy-futures
+const validatedTicker = TICKER as MarketSymbol;
 
 const date = new Date();
 const day = date.getDate();
 const month = date.getMonth() + 1;
 
 const marketStatus = isMarketOpen(new Date()) ? 'Market Open' : 'Market Closed';
 
-const metadata: Record<
+const symbolWebhookMetadata: Record<
   MarketSymbol,
   { title: string; description: string; filename: string }
 > = {
@@ -49,7 +50,7 @@ const metadata: Record<
   },
 };
 
-const marketSymbolMetaData = metadata[TICKER as MarketSymbol];
+const marketSymbolMetaData = symbolWebhookMetadata[validatedTicker];
 
-console.log('Invoking webhook for financial instrument:', TICKER);
+console.log('Invoking webhook for financial instrument:', validatedTicker);
 invokeWebhook(WEBHOOK_URL, marketSymbolMetaData);

src/invoke_webhook.ts

@@ -6,9 +6,14 @@ import FormData from 'form-data';
 // if we do not explicitly import FormData from "form-data"
 
 import axios from 'axios';
-import { MarketMetadata } from './types';
 import { isMarketOpen } from './utils';
 
+type MarketMetadata = {
+  title: string;
+  description: string;
+  filename: string;
+};
+
 export const invokeWebhook = async (
   URL: string,
   { title, description, filename }: MarketMetadata

src/types.d.ts

@@ -1 +1 @@
-type MarketSymbol = 'usd-jpy' | 'spy' | 'spy-futures';
+export type MarketSymbol = 'usd-jpy' | 'spy' | 'spy-futures';

src/utils.ts

@@ -1,3 +1,5 @@
+import { MarketSymbol } from 'types';
+
 export const isMarketOpen = (time: Date) =>
   time.getHours() < 5 ||
   (time.getHours() >= 22 && time.getMinutes() >= 30) ||
@@ -6,3 +8,6 @@ export const isMarketOpen = (time: Date) =>
 export const logError = (error: Error) => {
   console.error(error);
 };
+
+export const isValidMarketSymbol = (symbol: string): symbol is MarketSymbol =>
+  ['usd-jpy', 'spy', 'spy-futures'].includes(symbol);