sort fields properly (#259)

describe.go

@@ -153,30 +153,30 @@ func DescribeFieldContainer(container FieldContainer, w io.Writer, filters ...Fi
 }
 
 func sortFieldIDs(fields map[string]field.Field) []string {
-	numericKeys := make([]int, 0)
-	nonNumericKeys := make([]string, 0)
-
-	for k := range fields {
-		if id, err := strconv.Atoi(k); err == nil {
-			numericKeys = append(numericKeys, id)
-		} else {
-			nonNumericKeys = append(nonNumericKeys, k)
-		}
-	}
-
-	// Sorting numeric and non-numeric keys separately
-	sort.Ints(numericKeys)
-	sort.Strings(nonNumericKeys)
-
 	keys := make([]string, 0, len(fields))
-
-	// Appending numeric keys first (as strings)
-	for _, key := range numericKeys {
-		keys = append(keys, strconv.Itoa(key))
+	for k := range fields {
+		keys = append(keys, k)
 	}
 
-	// Appending non-numeric keys
-	keys = append(keys, nonNumericKeys...)
+	sort.Slice(keys, func(i, j int) bool {
+		// check if both keys are numeric
+		ni, ei := strconv.Atoi(keys[i])
+		nj, ej := strconv.Atoi(keys[j])
+		if ei == nil && ej == nil {
+			// if both keys are numeric, compare as integers
+			return ni < nj
+		}
+		if ei == nil {
+			// if only i is numeric, it goes first
+			return true
+		}
+		if ej == nil {
+			// if only j is numeric, it goes first
+			return false
+		}
+		// if neither key is numeric, compare as strings
+		return keys[i] < keys[j]
+	})
 
 	return keys
 }

describe_test.go

@@ -2,11 +2,13 @@ package iso8583
 
 import (
 	"bytes"
+	"fmt"
 	"testing"
 
 	"github.com/moov-io/iso8583/encoding"
 	"github.com/moov-io/iso8583/field"
 	"github.com/moov-io/iso8583/prefix"
+	"github.com/moov-io/iso8583/sort"
 	"github.com/stretchr/testify/require"
 )
 
@@ -30,27 +32,64 @@ func TestDescribe(t *testing.T) {
 				Enc:         encoding.ASCII,
 				Pref:        prefix.ASCII.LL,
 			}),
+			3: field.NewComposite(&field.Spec{
+				Length:      6,
+				Description: "Processing Code",
+				Pref:        prefix.ASCII.Fixed,
+				Tag: &field.TagSpec{
+					Sort: sort.StringsByInt,
+				},
+				Subfields: map[string]field.Field{
+					"01": field.NewString(&field.Spec{
+						Length:      2,
+						Description: "Transaction Type",
+						Enc:         encoding.ASCII,
+						Pref:        prefix.ASCII.Fixed,
+					}),
+					"02": field.NewString(&field.Spec{
+						Length:      2,
+						Description: "From Account",
+						Enc:         encoding.ASCII,
+						Pref:        prefix.ASCII.Fixed,
+					}),
+					"03": field.NewString(&field.Spec{
+						Length:      2,
+						Description: "To Account",
+						Enc:         encoding.ASCII,
+						Pref:        prefix.ASCII.Fixed,
+					}),
+				},
+			}),
 		},
 	}
 
 	message := NewMessage(spec)
 	message.MTI("0100")
 	message.Field(2, "4242424242424242")
+	message.Field(3, "123456")
 	message.Pack() // to generate bitmap
 
 	out := bytes.NewBuffer([]byte{})
 	require.NotPanics(t, func() {
 		Describe(message, out, DoNotFilterFields()...)
 	})
 
+	fmt.Println(out.String())
+
 	expectedOutput := `ISO 8583 Message:
 MTI..........: 0100
-Bitmap HEX...: 4000000000000000
+Bitmap HEX...: 6000000000000000
 Bitmap bits..:
-    [1-8]01000000    [9-16]00000000   [17-24]00000000   [25-32]00000000
+    [1-8]01100000    [9-16]00000000   [17-24]00000000   [25-32]00000000
   [33-40]00000000   [41-48]00000000   [49-56]00000000   [57-64]00000000
 F0   Message Type Indicator..: 0100
 F2   Primary Account Number..: 4242424242424242
+F3   Processing Code SUBFIELDS:
+-------------------------------------------
+F01  Transaction Type..: 12
+F02  From Account......: 34
+F03  To Account........: 56
+------------------------------------------
 `
 	require.Equal(t, expectedOutput, out.String())
 }