add coverpage to price calculation

models/printer.go

@@ -133,6 +133,11 @@ func (p *PrintJob) Execute() error {
 
 func (p *PrintJob) CalculatePrintCosts() (float64, error) {
 	pageCount := utils.CountPagesAtPath(p.ShopItem.Pdf)
+
+	if pageCount == 0 {
+		return 0, fmt.Errorf("Cant calculate price, pdf seems to be empty")
+	}
+
 	printMode := GetPrintMode(p.ShopItem.PrintMode)
 
 	//Get actual pagecount depending on printmode
@@ -154,7 +159,15 @@ func (p *PrintJob) CalculatePrintCosts() (float64, error) {
 	if p.IsColored() {
 		partCost = 0.0478
 	}
-	printingCosts := float64(actualPageCount) * p.PaperType.Price
+
+	printingCosts := float64(actualPageCount-1) * p.PaperType.Price
+
+	if p.CoverPaperType != nil {
+		printingCosts += p.CoverPaperType.Price
+	} else {
+		printingCosts += p.PaperType.Price
+	}
+
 	printingCosts += float64(actualPageCount/2) * PPC
 	printingCosts += partCost * float64(actualPageCount)