yearmonth: extract to separate file

Config.go

@@ -4,13 +4,6 @@ import (
 	"time"
 )
 
-type YearMonth struct {
-	Year int
-
-	// time.Month is a 1-based month counting system
-	Month time.Month
-}
-
 type LogLocation struct {
 
 	// LogFilePath will be passed to time.Format().
@@ -37,7 +30,7 @@ func (this *LogSource) LatestDate() YearMonth {
 	// assume it's the last in the list (although it might not be)
 	end := this.FileLocation[len(this.FileLocation)-1].EndMonth
 	if end == nil {
-		return YearMonth{time.Now().Year(), time.Now().Month()}
+		return CurrentYearMonth()
 	} else {
 		return *end
 	}

YearMonth.go

@@ -0,0 +1,28 @@
+package archive
+
+import (
+	"time"
+)
+
+type YearMonth struct {
+	Year int
+
+	// time.Month is a 1-based month counting system
+	Month time.Month
+}
+
+func CurrentYearMonth() YearMonth {
+	return YearMonth{time.Now().Year(), time.Now().Month()}
+}
+
+func (ym YearMonth) Equals(other YearMonth) bool {
+	return ym.Year == other.Year && ym.Month == other.Month
+}
+
+func (ym YearMonth) Next() YearMonth {
+	if ym.Month == time.December {
+		return YearMonth{Year: ym.Year + 1, Month: time.January}
+	} else {
+		return YearMonth{Year: ym.Year, Month: ym.Month + 1}
+	}
+}