add a --version switch, sort out duplicated block in index.js

Author: lornajane

index.js

@@ -1,26 +1,31 @@
 #!/usr/bin/env node
 import arg from 'arg'
+import fs from 'fs'
 import { overlayFiles } from './src/overlay.js'
 
 function showHelp () {
   console.log('Usage: overlayjs --openapi FILEPATH --overlay FILEPATH')
   console.log('    use --help to see this help')
 }
 
+// Function to read the version from package.json
+function showVersion () {
+  const packageJsonPath = './package.json'
+  const packageJson = JSON.parse(fs.readFileSync(packageJsonPath, 'utf8'))
+  console.log(packageJson.version)
+}
+
 try {
   const args = arg({
     '--openapi': String,
     '--overlay': String,
+    '--version': Boolean,
     '--help': Boolean
   })
 
-  if (args['--overlay'] && args['--openapi']) {
-    const openapiFile = args['--openapi']
-    const overlayFile = args['--overlay']
-    const spec = overlayFiles(openapiFile, overlayFile)
-    console.log(spec)
-  } else {
-    showHelp()
+  if (args['--version']) {
+    showVersion()
+    process.exit(0)
   }
 
   if (args['--overlay'] && args['--openapi']) {