사용 가능 공간 조회 API 추가

src/main/java/com/kamco/cd/training/common/service/FormatStorage.java

@@ -0,0 +1,50 @@
+package com.kamco.cd.training.common.service;
+
+import java.nio.file.FileStore;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+public class FormatStorage {
+
+  private FormatStorage() {}
+
+  /** 디스크 사용량 조회 */
+  public static DiskUsage getDiskUsage(Path path) throws Exception {
+    FileStore store = Files.getFileStore(path);
+
+    long total = store.getTotalSpace();
+    long usable = store.getUsableSpace();
+
+    return new DiskUsage(path.toString(), total, usable);
+  }
+
+  /** 디스크 사용량 DTO */
+  public record DiskUsage(String path, long totalBytes, long usableBytes) {
+
+    public long usedBytes() {
+      return totalBytes - usableBytes;
+    }
+
+    public double usedPercent() {
+      return totalBytes == 0 ? 0.0 : (usedBytes() * 100.0) / totalBytes;
+    }
+
+    public String totalText() {
+      return formatStorageSize(totalBytes);
+    }
+
+    public String usableText() {
+      return formatStorageSize(usableBytes);
+    }
+
+    /** 저장공간을 사람이 읽기 좋은 단위로 변환 (GB / MB) */
+    private static String formatStorageSize(long bytes) {
+      double gb = bytes / 1024.0 / 1024 / 1024;
+      if (gb >= 1) {
+        return String.format("%.1f GB", gb);
+      }
+      double mb = bytes / 1024.0 / 1024;
+      return String.format("%.0f MB", mb);
+    }
+  }
+}