fix: extension valid logic update

Author: Umjiseung

src/main/kotlin/gogo/gogostage/domain/image/application/ImageValidator.kt

@@ -8,16 +8,21 @@ import org.springframework.web.multipart.MultipartFile
 class ImageValidator {
 
     fun validImage(image: MultipartFile) {
-        val list = listOf("jpg", "png", "gif")
-        val splitFile = image.originalFilename.toString().split(".")
+        val allowedExtensions = listOf("jpg", "png", "gif")
+        val maxFileSize = 10 * 1024 * 1024 // 10MB
 
-        if(splitFile.size != 2)
-            throw StageException("Image Extension Invalid", 400)
+        val fileName = image.originalFilename ?: throw StageException("No file name", 400)
 
-        val extension = splitFile[1].lowercase()
+        val extension = fileName.substringAfterLast('.', missingDelimiterValue = "").lowercase()
 
-        if(list.none { it == extension })
+        if (extension.isBlank() || extension !in allowedExtensions) {
             throw StageException("Image Extension Invalid", 400)
+        }
+
+        if (image.size > maxFileSize) {
+            throw StageException("Image Size Exceeds 10MB", 400)
+        }
     }
 
+
 }