Refactor the formatter to an interface and rename it

This change refactors the formatter to be an interface called Printer.
`NewApp` will use the functionality of `ScreenPrinter`,  which is what I
refactored the old `Formatter` class into.

There is a new class the implements the `Printer` interface called
`MemoryPrinter`, which will simply store the `groups` as they were
passed to it.  This will allow tests in `app_test.go` to become much
more powerful, since `App` no longer needs to be tightly coupled to
printing to the screen.

1 files changed, 20 insertions, 0 deletions

diff --git a/todolist/util.go b/todolist/util.go
index ff3dbba..6fa93f3 100644
--- a/todolist/util.go
+++ b/todolist/util.go
@@ -59,3 +59,23 @@ func pluralize(count int, singular, plural string) string {
 	}
 	return singular
 }
+
+func isToday(t time.Time) bool {
+	nowYear, nowMonth, nowDay := time.Now().Date()
+	timeYear, timeMonth, timeDay := t.Date()
+	return nowYear == timeYear &&
+		nowMonth == timeMonth &&
+		nowDay == timeDay
+}
+
+func isTomorrow(t time.Time) bool {
+	nowYear, nowMonth, nowDay := time.Now().AddDate(0, 0, 1).Date()
+	timeYear, timeMonth, timeDay := t.Date()
+	return nowYear == timeYear &&
+		nowMonth == timeMonth &&
+		nowDay == timeDay
+}
+
+func isPastDue(t time.Time) bool {
+	return time.Now().After(t)
+}