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.

4 files changed, 44 insertions, 37 deletions

diff --git a/todolist/app.go b/todolist/app.go
index 24e2a61..ad02569 100644
--- a/todolist/app.go
+++ b/todolist/app.go
@@ -9,11 +9,16 @@ import (
 
 type App struct {
 	TodoStore Store
+	Printer   Printer
 	TodoList  *TodoList
 }
 
 func NewApp() *App {
-	app := &App{TodoList: &TodoList{}, TodoStore: NewFileStore()}
+	app := &App{
+		TodoList:  &TodoList{},
+		Printer:   NewScreenPrinter(),
+		TodoStore: NewFileStore(),
+	}
 	return app
 }
 
@@ -179,8 +184,7 @@ func (a *App) HandleNotes(input string) {
 	} else if parser.ParseShowNote(todo, input) {
 		groups := map[string][]*Todo{}
 		groups[""] = append(groups[""], todo)
-		formatter := NewFormatter(&GroupedTodos{Groups: groups})
-		formatter.Print(true)
+		a.Printer.Print(&GroupedTodos{Groups: groups}, false)
 		return
 	}
 	a.Save()
@@ -202,9 +206,8 @@ func (a *App) ListTodos(input string) {
 	filtered := NewFilter(a.TodoList.Todos()).Filter(input)
 	grouped := a.getGroups(input, filtered)
 
-	formatter := NewFormatter(grouped)
 	re, _ := regexp.Compile(`^ln`)
-	formatter.Print(re.MatchString(input))
+	a.Printer.Print(grouped, re.MatchString(input))
 }
 
 func (a *App) PrioritizeTodo(input string) {
diff --git a/todolist/printer.go b/todolist/printer.go
new file mode 100644
index 0000000..805cc6e
--- /dev/null
+++ b/todolist/printer.go
@@ -0,0 +1,5 @@
+package todolist
+
+type Printer interface {
+	Print(*GroupedTodos, bool)
+}
diff --git a/todolist/formatter.go b/todolist/screen_printer.go
index e7863db..eab0c39 100644
--- a/todolist/formatter.go
+++ b/todolist/screen_printer.go
@@ -13,30 +13,29 @@ import (
 	"github.com/fatih/color"
 )
 
-type Formatter struct {
-	GroupedTodos *GroupedTodos
-	Writer       *tabwriter.Writer
+type ScreenPrinter struct {
+	Writer *tabwriter.Writer
 }
 
-func NewFormatter(todos *GroupedTodos) *Formatter {
+func NewScreenPrinter() *ScreenPrinter {
 	w := new(tabwriter.Writer)
 	w.Init(os.Stdout, 0, 8, 0, '\t', 0)
-	formatter := &Formatter{GroupedTodos: todos, Writer: w}
+	formatter := &ScreenPrinter{Writer: w}
 	return formatter
 }
 
-func (f *Formatter) Print(printNotes bool) {
+func (f *ScreenPrinter) Print(groupedTodos *GroupedTodos, printNotes bool) {
 	cyan := color.New(color.FgCyan).SprintFunc()
 
 	var keys []string
-	for key := range f.GroupedTodos.Groups {
+	for key := range groupedTodos.Groups {
 		keys = append(keys, key)
 	}
 	sort.Strings(keys)
 
 	for _, key := range keys {
 		fmt.Fprintf(f.Writer, "\n %s\n", cyan(key))
-		for _, todo := range f.GroupedTodos.Groups[key] {
+		for _, todo := range groupedTodos.Groups[key] {
 			f.printTodo(todo)
 			if printNotes {
 				for nid, note := range todo.Notes {
@@ -49,7 +48,7 @@ func (f *Formatter) Print(printNotes bool) {
 	f.Writer.Flush()
 }
 
-func (f *Formatter) printTodo(todo *Todo) {
+func (f *ScreenPrinter) printTodo(todo *Todo) {
 	yellow := color.New(color.FgYellow)
 	if todo.IsPriority {
 		yellow.Add(color.Bold, color.Italic)
@@ -61,7 +60,7 @@ func (f *Formatter) printTodo(todo *Todo) {
 		f.formatSubject(todo.Subject, todo.IsPriority))
 }
 
-func (f *Formatter) formatDue(due string, isPriority bool) string {
+func (f *ScreenPrinter) formatDue(due string, isPriority bool) string {
 	blue := color.New(color.FgBlue)
 	red := color.New(color.FgRed)
 
@@ -92,27 +91,7 @@ func (f *Formatter) formatDue(due string, isPriority bool) string {
 	}
 }
 
-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)
-}
-
-func (f *Formatter) formatSubject(subject string, isPriority bool) string {
+func (f *ScreenPrinter) formatSubject(subject string, isPriority bool) string {
 
 	red := color.New(color.FgRed)
 	magenta := color.New(color.FgMagenta)
@@ -143,7 +122,7 @@ func (f *Formatter) formatSubject(subject string, isPriority bool) string {
 
 }
 
-func (f *Formatter) formatCompleted(completed bool) string {
+func (f *ScreenPrinter) formatCompleted(completed bool) string {
 	if completed {
 		return "[x]"
 	} else {
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)
+}