back: add qver package to track qid versions

1 files changed, 29 insertions, 0 deletions

diff --git a/back/qver/update.go b/back/qver/update.go
new file mode 100644
index 0000000..afbe51c
--- /dev/null
+++ b/back/qver/update.go
@@ -0,0 +1,29 @@
+package qver
+
+import (
+	"os"
+	"time"
+)
+
+// An UpdateFunc updates the version and state variables. It is called
+// by Version.Get(). If there is an error, it should return the old
+// version and state along with the error.
+type UpdateFunc func(version uint32, state interface{}) (uint32, interface{}, error)
+
+// UpdateOnFileMod returns a state variable and an UpdateFunc that
+// bumps the version when a file or directory is modified. The return
+// values are to be passed to the Update() option.
+func UpdateOnFileMod(path string) (state interface{}, f UpdateFunc) {
+	return time.Now(), func(ver uint32, state interface{}) (uint32, interface{}, error) {
+		mtime := state.(time.Time)
+		info, err := os.Stat(path)
+		if err != nil {
+			return ver, mtime, err
+		}
+		if info.ModTime().After(mtime) {
+			mtime = info.ModTime()
+			ver++
+		}
+		return ver, mtime, err
+	}
+}