Don't fail to start up if there are no widgets defined

Signed-off-by: Chris Cummer <chriscummer@me.com>

_sample_configs/multi_config.yml

@@ -0,0 +1,3 @@
+configs:
+  - small_config.yml
+  - sample_config.yml

app/display.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"github.com/gdamore/tcell"
 	"github.com/olebedev/config"
 	"github.com/rivo/tview"
 	"github.com/wtfutil/wtf/utils"
@@ -9,24 +10,28 @@ import (
 
 // Display is the container for the onscreen representation of a WtfApp
 type Display struct {
-	Grid   *tview.Grid
-	config *config.Config
+	Grid *tview.Grid
+
+	bgColor tcell.Color
+	config  *config.Config
 }
 
 // NewDisplay creates and returns a Display
 func NewDisplay(widgets []wtf.Wtfable, config *config.Config) *Display {
 	display := Display{
-		Grid:   tview.NewGrid(),
-		config: config,
+		Grid: tview.NewGrid(),
+
+		bgColor: wtf.ColorFor("black"),
+		config:  config,
 	}
 
-	firstWidget := widgets[0]
-	display.Grid.SetBackgroundColor(
-		wtf.ColorFor(
-			firstWidget.CommonSettings().Colors.WidgetTheme.Background,
-		),
-	)
+	// Make sure we have some widgets before trying to get the first one
+	if len(widgets) > 0 {
+		firstWidget := widgets[0]
+		display.bgColor = wtf.ColorFor(firstWidget.CommonSettings().Colors.WidgetTheme.Background)
+	}
 
+	display.Grid.SetBackgroundColor(display.bgColor)
 	display.build(widgets)
 
 	return &display

app/wtf_app.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"errors"
 	"fmt"
 	"log"
 	"os"
@@ -60,12 +61,7 @@ func NewWtfApp(tviewApp *tview.Application, config *config.Config, configFilePat
 
 	wtfApp.validator.Validate(wtfApp.widgets)
 
-	firstWidget := wtfApp.widgets[0]
-	wtfApp.pages.Box.SetBackgroundColor(
-		wtf.ColorFor(
-			firstWidget.CommonSettings().Colors.WidgetTheme.Background,
-		),
-	)
+	wtfApp.setBackgroundColor()
 
 	wtfApp.TViewApp.SetInputCapture(wtfApp.keyboardIntercept)
 	wtfApp.TViewApp.SetRoot(wtfApp.pages, true)
@@ -75,6 +71,16 @@ func NewWtfApp(tviewApp *tview.Application, config *config.Config, configFilePat
 
 /* -------------------- Exported Functions -------------------- */
 
+// FirstWidget returns the first wiget in the set of widgets, or
+// an error if there are none
+func (wtfApp *WtfApp) FirstWidget() (wtf.Wtfable, error) {
+	if len(wtfApp.widgets) < 1 {
+		return nil, errors.New("cannot get first widget. no widgets defined")
+	}
+
+	return wtfApp.widgets[0], nil
+}
+
 // Run starts the underlying tview app
 func (wtfApp *WtfApp) Run() {
 	if err := wtfApp.TViewApp.Run(); err != nil {
@@ -99,6 +105,19 @@ func (wtfApp *WtfApp) Stop() {
 
 /* -------------------- Unexported Functions -------------------- */
 
+func (wtfApp *WtfApp) setBackgroundColor() {
+	var bgColor tcell.Color
+
+	firstWidget, err := wtfApp.FirstWidget()
+	if err != nil {
+		bgColor = wtf.ColorFor("black")
+	} else {
+		bgColor = wtf.ColorFor(firstWidget.CommonSettings().Colors.WidgetTheme.Background)
+	}
+
+	wtfApp.pages.Box.SetBackgroundColor(bgColor)
+}
+
 func (wtfApp *WtfApp) stopAllWidgets() {
 	for _, widget := range wtfApp.widgets {
 		widget.Stop()