Allow the time formatting function return errors

src/statusscreen/SL.go

@@ -3,6 +3,7 @@ package statusscreen
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"github.com/olekukonko/tablewriter"
 	"io/ioutil"
@@ -71,10 +72,12 @@ func (sl *SL) GetOutput() string {
 	}
 
 	for _, v := range sl.lastResponse.ResponseData.Metros {
+		formattedTime, _ := sl.formatDisplayTime(v.ExpectedDateTime)
+
 		table.Append([]string{
 			v.LineNumber,
 			v.Destination,
-			sl.formatDisplayTime(v.ExpectedDateTime),
+			formattedTime,
 			v.TimeTabledDateTime[11:], // Remove YYYY-MM-DDT from the beginning of the string
 			v.ExpectedDateTime[11:],   // Remove YYYY-MM-DDT from the beginning of the string
 		})
@@ -117,7 +120,7 @@ func (sl *SL) getTimeTable() (SLResponse, error) {
 	return parsedResponse, nil
 }
 
-func (sl *SL) formatDisplayTime(expected string) string {
+func (sl *SL) formatDisplayTime(expected string) (string, error) {
 	myTimeZone, _ := time.Now().Zone()
 
 	then, err := time.Parse("2006-01-02T15:04:05 MST", expected+" "+myTimeZone)
@@ -127,13 +130,21 @@ func (sl *SL) formatDisplayTime(expected string) string {
 
 	timeLeft := time.Since(then).Seconds() * -1
 
+	// If time is less than zero
+	if timeLeft < 0 {
+		return "undefined", errors.New("Train is gone already")
+	}
+
+	// If time is less than one minute, show seconds
 	if timeLeft <= 60 && timeLeft > 0 {
-		return fmt.Sprintf("%d sec", int(timeLeft))
+		return fmt.Sprintf("%d sec", int(timeLeft)), nil
 	}
 
+	// If time is less than one hour, show minutes
 	if timeLeft <= 3600 && timeLeft > 0 {
-		return fmt.Sprintf("%d min", int(timeLeft)/60)
+		return fmt.Sprintf("%d min", int(timeLeft)/60), nil
 	}
 
-	return fmt.Sprintf("%02d:%02d:%02d", then.Hour(), then.Minute(), then.Second())
+	// Otherwise, just return a timestamp: HH:MM:SS
+	return fmt.Sprintf("%02d:%02d:%02d", then.Hour(), then.Minute(), then.Second()), nil
 }