feat: add IBM1047 ASCII compatibility when in FRB_COMPATIBILITY_MODE

Add support for IBM1047 EBCDIC encoding compatibility with IBM037 for the
three ASCII characters that differ between the encodings: [ ] ^

When FRB_COMPATIBILITY_MODE is enabled, converts IBM037 byte values to their
IBM1047 equivalents before decoding:
- 0xAD (Ý) -> 0xBA ([)
- 0xBD (¨) -> 0xBB (])
- 0x5F (¬) -> 0xB0 (^)

checkDetailAddendumA_test.go

@@ -187,7 +187,7 @@ func TestCDAddendumATruncationIndicatorFRB(t *testing.T) {
 	var e *FieldError
 	require.ErrorAs(t, err, &e)
 	require.Equal(t, "TruncationIndicator", e.FieldName)
-	t.Setenv(FRBCompatibilityMode, "")
+	t.Setenv(FRBCompatibilityMode, "true")
 	require.NoError(t, cdAddendumA.Validate())
 }
 
@@ -308,3 +308,57 @@ func TestStringFieldTrim(t *testing.T) {
 	cdAddendumA.ReturnLocationRoutingNumber = "12345678912345"
 	require.Len(t, cdAddendumA.ReturnLocationRoutingNumberField(), 9)
 }
+
+func TestParseCheckDetailAddendumA_BOFDAccountEBCDIC(t *testing.T) {
+	t.Setenv("FRB_COMPATIBILITY_MODE", "true")
+	line := "\xf2\xf6" + // Record Type 26
+		strings.Repeat("\xf1", 33) + // Fill with '1's
+		"@@@@@@@@@@@" + // Spaces
+		"\xad\x85\x94\x97\xa3\xa8\xbd" + // [empty] in IBM1047
+		strings.Repeat("@", 20) + // More spaces
+		"\xe8\xf2\xf0@@@@" // End padding
+	r := NewReader(strings.NewReader(line), ReadEbcdicEncodingOption())
+	r.line = line
+
+	clh := mockCashLetterHeader()
+	r.addCurrentCashLetter(NewCashLetter(clh))
+	bh := mockBundleHeader()
+	b := NewBundle(bh)
+	r.currentCashLetter.AddBundle(b)
+	r.addCurrentBundle(b)
+	cd := mockCheckDetail()
+	r.currentCashLetter.currentBundle.AddCheckDetail(cd)
+
+	err := r.parseCheckDetailAddendumA()
+	require.NoError(t, err)
+
+	record := r.currentCashLetter.currentBundle.GetChecks()[0].CheckDetailAddendumA[0]
+	require.Equal(t, "[empty]", record.BOFDAccountNumber)
+	t.Setenv("FRB_COMPATIBILITY_MODE", "")
+}
+
+func TestParseCheckDetailAddendumA_BOFDAccountEBCDIC_NoFlag(t *testing.T) {
+	t.Setenv("FRB_COMPATIBILITY_MODE", "false")
+	line := "\xf2\xf6" +
+		strings.Repeat("\xf1", 33) +
+		"@@@@@@@@@@@" +
+		"\xad\x85\x94\x97\xa3\xa8\xbd" +
+		strings.Repeat("@", 20) +
+		"\xe8\xf2\xf0@@@@"
+
+	r := NewReader(strings.NewReader(line), ReadEbcdicEncodingOption())
+	r.line = line
+
+	clh := mockCashLetterHeader()
+	r.addCurrentCashLetter(NewCashLetter(clh))
+	bh := mockBundleHeader()
+	b := NewBundle(bh)
+	r.currentCashLetter.AddBundle(b)
+	r.addCurrentBundle(b)
+	cd := mockCheckDetail()
+	r.currentCashLetter.currentBundle.AddCheckDetail(cd)
+
+	err := r.parseCheckDetailAddendumA()
+	require.Error(t, err, "Expected an error when FRB_COMPATIBILITY_MODE is false")
+	t.Setenv("FRB_COMPATIBILITY_MODE", "")
+}

reader.go

@@ -421,10 +421,13 @@ func (r *Reader) parseCheckDetailAddendumA() error {
 		msg := fmt.Sprint(msgFileBundleOutside)
 		return r.error(&FileError{FieldName: "CheckDetailAddendumA", Msg: msg})
 	}
-	lineOut, err := r.decodeLine(r.line)
+	inputBytes := []byte(r.line)
+	adjustedBytes := handleIBM1047Compatibility(inputBytes)
+	lineOut, err := r.decodeLine(string(adjustedBytes))
 	if err != nil {
 		return err
 	}
+
 	cdAddendumA := NewCheckDetailAddendumA()
 	cdAddendumA.Parse(lineOut)
 	if err := cdAddendumA.Validate(); err != nil {
@@ -436,6 +439,29 @@ func (r *Reader) parseCheckDetailAddendumA() error {
 	return nil
 }
 
+func handleIBM1047Compatibility(input []byte) []byte {
+	if !IsFRBCompatibilityModeEnabled() {
+		return input
+	}
+
+	output := make([]byte, len(input))
+	copy(output, input)
+
+	// Replace bytes that map differently between IBM037 and IBM1047
+	// but only for the ascii subset see https://en.wikibooks.org/wiki/Character_Encodings/Code_Tables/EBCDIC/EBCDIC_1047
+	for i, b := range output {
+		switch b {
+		case 0xAD: // Ý -> [
+			output[i] = 0xBA
+		case 0xBD: // ¨ -> ]
+			output[i] = 0xBB
+		case 0x5F: // ¬ -> ^
+			output[i] = 0xB0
+		}
+	}
+	return output
+}
+
 // parseCheckDetailAddendumB takes the input record string and parses the CheckDetailAddendumB values
 func (r *Reader) parseCheckDetailAddendumB() error {
 	r.recordName = "CheckDetailAddendumB"