Makes all output messages consistent

Since the panic() function provides overwhelming messages available
for developers but meaningless to users, the way to deal with error
output is simplified.

There are two panic()'s that are fixed:

* The one in parseArbitraryDateWithYear() function.
  This function is the possible endpoint of adding a todo or editing
  dues.  Instead of calling panic(), now it outputs the specific
  parsing error, and then terminate itself by os.Exit().

* The one in formatDue() function
  This function is responsible for parsing the due information of a
  given todo.  If the todos being added previously have passed the
  checking, then there is no reason that a due fails the format
  check here, except for the corruption of the todo file.

2 files changed, 14 insertions, 4 deletions

diff --git a/todolist/formatter.go b/todolist/formatter.go
index b259f6a..db4aa4b 100644
--- a/todolist/formatter.go
+++ b/todolist/formatter.go
@@ -62,7 +62,9 @@ func (f *Formatter) formatDue(due string) string {
 	dueTime, err := time.Parse("2006-01-02", due)
 
 	if err != nil {
-		panic(err)
+		fmt.Println(err)
+		fmt.Println("This may due to the corruption of .todos.json file.")
+		os.Exit(-1)
 	}
 
 	if isToday(dueTime) {
diff --git a/todolist/parser.go b/todolist/parser.go
index 767785b..b16dccb 100644
--- a/todolist/parser.go
+++ b/todolist/parser.go
@@ -2,6 +2,7 @@ package todolist
 
 import (
 	"fmt"
+	"os"
 	"regexp"
 	"strconv"
 	"strings"
@@ -109,14 +110,21 @@ func (p *Parser) parseArbitraryDate(_date string, pivot time.Time) string {
 
 func (p *Parser) parseArbitraryDateWithYear(_date string, year int) time.Time {
 	res := strings.Join([]string{_date, strconv.Itoa(year)}, " ")
-	if date, err := time.Parse("Jan 2 2006", res); err == nil {
+	var date time.Time
+	var err1 error
+	var err2 error
+	if date, err1 = time.Parse("Jan 2 2006", res); err1 == nil {
 		return date
 	}
 
-	if date, err := time.Parse("2 Jan 2006", res); err == nil {
+	if date, err2 = time.Parse("2 Jan 2006", res); err2 == nil {
 		return date
 	}
-	panic(fmt.Errorf("Could not parse the date you gave me: '%s'", _date))
+	fmt.Printf("Could not parse the date you gave me: %s\n", _date)
+	fmt.Println(err1)
+	fmt.Println(err2)
+	os.Exit(-1)
+	return time.Now()
 }
 
 func (p *Parser) monday(day time.Time) string {