add env validation utility

Author: stplasim

src/slack/app.ts

@@ -1,7 +1,8 @@
 import { App } from '@slack/bolt'
+import { requiredString } from '@utils/env.ts'
 
 export const app = new App({
-  token: process.env.SLACK_BOT_TOKEN,
-  appToken: process.env.SLACK_APP_TOKEN,
+  token: requiredString('SLACK_BOT_TOKEN'),
+  appToken: requiredString('SLACK_APP_TOKEN'),
   socketMode: true,
 })

src/utils/env.ts

@@ -0,0 +1,24 @@
+type EnvVarName = keyof typeof process.env
+
+export function requiredString(name: EnvVarName): string {
+  const value = process.env[name]
+  if (!value) {
+    throw new Error(`${name} is required`)
+  }
+
+  return value
+}
+
+export function positiveInt(name: EnvVarName, defaultValue: number): number {
+  const raw = process.env[name]
+  if (!raw) {
+    return defaultValue
+  }
+
+  const value = Number(raw)
+  if (!Number.isInteger(value) || value < 1) {
+    throw new Error(`${name} must be a positive integer`)
+  }
+
+  return value
+}