handle input json in formats other than utf8

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -15,6 +16,9 @@ import (
 	"time"
 
 	"github.com/xuri/excelize/v2"
+	"golang.org/x/text/encoding/unicode"
+	"golang.org/x/text/transform"
+	"golang.org/x/text/unicode/norm"
 )
 
 type Input struct {
@@ -232,7 +236,7 @@ func AvgChart(f *excelize.File, worksheetName string, location string, avgCpuCol
 		chartSeries = append(chartSeries, thisChartSeries)
 	}
 
-	if err := f.AddChart("Report", location, &excelize.Chart{
+	chart := excelize.Chart{
 		Type:   excelize.Line,
 		Series: chartSeries,
 		Format: excelize.GraphicOptions{
@@ -278,14 +282,19 @@ func AvgChart(f *excelize.File, worksheetName string, location string, avgCpuCol
 			Font: excelize.Font{
 				Color: "000000",
 			},
-			Maximum: &yMaxValue,
-			Minimum: &yMinValue,
 		},
 		Dimension: excelize.ChartDimension{
 			Height: 500,
 			Width:  800,
 		},
-	}); err != nil {
+	}
+
+	if yMaxValue > 0 || yMinValue > 0 {
+		chart.YAxis.Maximum = &yMaxValue
+		chart.YAxis.Minimum = &yMinValue
+	}
+
+	if err := f.AddChart("Report", location, &chart); err != nil {
 		fmt.Printf("Error adding chart to workbook %s at location %s: %s\n", worksheetName, location, err)
 		return
 	}
@@ -293,6 +302,7 @@ func AvgChart(f *excelize.File, worksheetName string, location string, avgCpuCol
 
 func main() {
 	var err error
+	var data Input
 
 	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")
@@ -322,9 +332,19 @@ func main() {
 	}
 	defer file.Close()
 
-	byteValue, _ := io.ReadAll(file)
-	var data Input
-	if err := json.Unmarshal(byteValue, &data); err != nil {
+	byteValue, err := io.ReadAll(file)
+	if err != nil {
+		log.Fatalf("Failed to read input json: %v", err)
+	}
+
+	// Detect encoding and convert to UTF-8 if necessary
+	utf8Data, err := ensureUTF8(byteValue)
+	if err != nil {
+		fmt.Printf("Error ensuring UTF-8 encoding: %v\n", err)
+		return
+	}
+
+	if err := json.Unmarshal(utf8Data, &data); err != nil {
 		fmt.Printf("Error reading json input: %s\n", err)
 		os.Exit(1)
 	}
@@ -366,6 +386,44 @@ func sortDates(dates []string) error {
 	return nil
 }
 
+// ensureUTF8 checks if the data is UTF-8, and if not, converts it to UTF-8.
+// It also removes BOM from UTF-8 if present.
+func ensureUTF8(data []byte) ([]byte, error) {
+	// Detect and strip UTF-8 BOM if present
+	if hasUTF8BOM(data) {
+		data = stripUTF8BOM(data)
+	}
+
+	// If data is already UTF-8 (without BOM), return as is
+	if isUTF8(data) {
+		return data, nil
+	}
+
+	// Detect and decode UTF-16 (either UTF-16LE or UTF-16BE)
+	decoder := unicode.UTF16(unicode.LittleEndian, unicode.UseBOM).NewDecoder()
+	utf8Data, _, err := transform.Bytes(decoder, data)
+	if err != nil {
+		return nil, fmt.Errorf("error converting to UTF-8: %v", err)
+	}
+
+	return utf8Data, nil
+}
+
+// isUTF8 checks if the byte slice is already encoded in UTF-8
+func isUTF8(data []byte) bool {
+	return bytes.Equal(data, norm.NFC.Bytes(data)) // UTF-8 normalization check
+}
+
+// hasUTF8BOM checks if the data has a UTF-8 BOM
+func hasUTF8BOM(data []byte) bool {
+	return len(data) >= 3 && data[0] == 0xEF && data[1] == 0xBB && data[2] == 0xBF
+}
+
+// stripUTF8BOM removes the UTF-8 BOM if it exists
+func stripUTF8BOM(data []byte) []byte {
+	return data[3:]
+}
+
 func fetchValue(value interface{}) {
 	switch value.(type) {
 	case string: