add command line flags

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"flag"
 	"fmt"
 	"io"
 	"log"
@@ -239,6 +240,10 @@ func AvgChart(f *excelize.File, worksheetName string, location string, avgCpuCol
 func main() {
 	var err error
 
+	inputFile := flag.String("input", "input.json", "The filename from which to load historical data")
+	outputFile := flag.String("output", "book1.xlsx", "The filename to use when writing excel workbook")
+	flag.Parse()
+
 	// Create the workbook
 	f := excelize.NewFile()
 	defer func() {
@@ -252,7 +257,7 @@ func main() {
 	}
 
 	// Load the JSON data from file
-	file, err := os.Open("input.json")
+	file, err := os.Open(*inputFile)
 	if err != nil {
 		log.Fatalf("Failed to open input.json: %v", err)
 	}
@@ -271,7 +276,7 @@ func main() {
 	GenerateCharts(f, data.Tracking.VmCount, "VM Count", "N60")
 
 	// Save workbook
-	if err := f.SaveAs("Book1.xlsx"); err != nil {
+	if err := f.SaveAs(*outputFile); err != nil {
 		fmt.Println(err)
 	}
 }