From 31beb8b2c02f03ba4b31d9e5696e575ce84f0d42 Mon Sep 17 00:00:00 2001
From: Alex Yatskov <alex@foosoft.net>
Date: Tue, 12 Jan 2016 17:04:41 +0900
Subject: [PATCH] Don't copy unmodified files from source to dest

---
 file.go |  4 ++++
 util.go | 14 ++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/file.go b/file.go
index 719fd28..60c024b 100644
--- a/file.go
+++ b/file.go
@@ -39,6 +39,10 @@ type file struct {
 }
 
 func (f *file) export(dstPath string) error {
+	if f.reader == nil && fileCached(f.asset, dstPath) {
+		return nil
+	}
+
 	if err := os.MkdirAll(path.Dir(dstPath), 0755); err != nil {
 		return err
 	}
diff --git a/util.go b/util.go
index 12cbd58..18a032d 100644
--- a/util.go
+++ b/util.go
@@ -66,3 +66,17 @@ func scanDir(root string, files, dirs chan string) {
 		return nil
 	})
 }
+
+func fileCached(srcPath, dstPath string) bool {
+	srcStat, err := os.Stat(srcPath)
+	if err != nil {
+		return false
+	}
+
+	dstStat, err := os.Stat(dstPath)
+	if err != nil {
+		return false
+	}
+
+	return dstStat.ModTime().Unix() >= srcStat.ModTime().Unix()
+}