From ad8eaff93091fb4c30f27b3e4af35895b63a9f97 Mon Sep 17 00:00:00 2001
From: PhatPhuckDave <david.majdandzic@hotmail.com>
Date: Wed, 31 Jul 2024 12:45:31 +0200
Subject: [PATCH] Fully implement GSM7 decode

---
 encoding/gsm7.go      | 44 +++++-------------------
 encoding/gsm7_test.go | 80 +++++++++++++++++++++----------------------
 2 files changed, 49 insertions(+), 75 deletions(-)

diff --git a/encoding/gsm7.go b/encoding/gsm7.go
index dd750c7..429443b 100644
--- a/encoding/gsm7.go
+++ b/encoding/gsm7.go
@@ -22,7 +22,7 @@ func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
 	encodedSize := GSM7EncodesInto(&s)
 	cap := buf.Cap()
 	if cap < encodedSize {
-		buf.Grow(encodedSize-cap)
+		buf.Grow(encodedSize - cap)
 	}
 
 	for index, septet := range utf8 {
@@ -73,23 +73,26 @@ func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
 func (c *GSM7Coder) Decode(buf *bytes.Buffer) (string, error) {
 	gsm7 := buf.Bytes()
 	var (
-		offset      int  = (len(gsm7) / 8) + 1
-		bitshift    byte = 0
-		leap, shift bool
+		offset   int
+		bitshift byte = 0
+		leap     bool
 	)
 	outLength := GSM7DecodesInto(buf)
 	lengthDiff := outLength - len(gsm7)
 	gsm7 = append(gsm7, make([]byte, lengthDiff)...)
+	start := len(gsm7) - 2
 
 	// We don't care about the last byte
 	// Unless it's the %8.......
 	// We'll deal with that later
-	for index := len(gsm7) - 2; index >= 0; index-- {
+	for index := start; index >= 0; index-- {
 		octet := gsm7[index]
-		bitshift = byte((index + 1) % 8)
+		bitshift = byte((index % 7) + 1)
 		if bitshift == 7 {
 			leap = true
 		}
+		offset = 1
+		// log.Println(offset, index, index+offset)
 		// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) OffsetByte(%-3d):%08b (%-3d) Leap:%5v", index, offset, bitshift, gsm7[index], gsm7[index], index+offset, gsm7[index+offset], gsm7[index+offset], leap)
 
 		mask := byte(255 << (8 - bitshift))
@@ -107,36 +110,7 @@ func (c *GSM7Coder) Decode(buf *bytes.Buffer) (string, error) {
 
 		// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) OffsetByte(%-3d):%08b (%-3d) Leap:%5v", index, offset, bitshift, gsm7[index], gsm7[index], index+offset, gsm7[index+offset], gsm7[index+offset], leap)
 		leap = false
-		continue
-
-		if !leap {
-			buf.WriteByte(gsm7[index+offset])
-		}
-		if index == len(gsm7)-1 && gsm7[index] > 0 {
-			buf.WriteByte(gsm7[index])
-		}
-		// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) OffsetByte:%08b (%-3d) Leap:%5v", index, offset, bitshift, gsm7[index], gsm7[index], gsm7[index-offset], gsm7[index-offset], leap)
-		if bitshift >= 7 {
-			if leap {
-				// log.Printf("Shift at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
-				leap = false
-				bitshift = 0
-				offset++
-				shift = true
-				continue
-			}
-			// log.Printf("Leap at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
-			leap = true
-			bitshift = 6
-		}
-		if shift {
-			offset = 1
-		}
 	}
-	// log.Printf("Result: %+v", gsm7)
-	// for _, v := range gsm7 {
-	// log.Printf("%08b", v)
-	// }
 	return string(gsm7), nil
 }
 
diff --git a/encoding/gsm7_test.go b/encoding/gsm7_test.go
index be7c2e4..e2818c2 100644
--- a/encoding/gsm7_test.go
+++ b/encoding/gsm7_test.go
@@ -141,57 +141,57 @@ func TestGSM7DecodeSimpleASCIIString(t *testing.T) {
 	}
 }
 
-// func TestGSM7DecodeComplexASCIIString(t *testing.T) {
-// 	coder := &GSM7Coder{}
-// 	var buf bytes.Buffer
-// 	input := longNot8nStringEncodedBytes
+func TestGSM7DecodeComplexASCIIString(t *testing.T) {
+	coder := &GSM7Coder{}
+	var buf bytes.Buffer
+	input := longNot8nStringEncodedBytes
 
-// 	expected := longNot8nString
-// 	buf.Write(input)
-// 	actual, err := coder.Decode(&buf)
+	expected := longNot8nString
+	buf.Write(input)
+	actual, err := coder.Decode(&buf)
 
-// 	if err != nil {
-// 		t.Errorf("Expected no error, but got %v", err)
-// 	}
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
-// 	if actual != expected {
-// 		t.Errorf("Expected '%v', but got '%v'", expected, actual)
-// 	}
-// }
+	if actual != expected {
+		t.Errorf("Expected '%v', but got '%v'", expected, actual)
+	}
+}
 
-// func TestGSM7DecodeComplex8nASCIIString(t *testing.T) {
-// 	coder := &GSM7Coder{}
-// 	var buf bytes.Buffer
-// 	input := long8nStringEncodedBytes
+func TestGSM7DecodeComplex8nASCIIString(t *testing.T) {
+	coder := &GSM7Coder{}
+	var buf bytes.Buffer
+	input := long8nStringEncodedBytes
 
-// 	expected := long8nString
-// 	buf.Write(input)
-// 	actual, err := coder.Decode(&buf)
+	expected := long8nString
+	buf.Write(input)
+	actual, err := coder.Decode(&buf)
 
-// 	if err != nil {
-// 		t.Errorf("Expected no error, but got %v", err)
-// 	}
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
-// 	if actual != expected {
-// 		t.Errorf("Expected '%v', but got '%v'", expected, actual)
-// 	}
-// }
+	if actual != expected {
+		t.Errorf("Expected '%v', but got '%v'", expected, actual)
+	}
+}
 
-// func TestGSM7DecodeEmptyString(t *testing.T) {
-// 	coder := &GSM7Coder{}
-// 	buf := bytes.NewBuffer([]byte{})
+func TestGSM7DecodeEmptyString(t *testing.T) {
+	coder := &GSM7Coder{}
+	buf := bytes.NewBuffer([]byte{})
 
-// 	expected := ""
-// 	actual, err := coder.Decode(buf)
+	expected := ""
+	actual, err := coder.Decode(buf)
 
-// 	if err != nil {
-// 		t.Errorf("Expected no error, but got %v", err)
-// 	}
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
-// 	if actual != expected {
-// 		t.Errorf("Expected '%v', but got '%v'", expected, actual)
-// 	}
-// }
+	if actual != expected {
+		t.Errorf("Expected '%v', but got '%v'", expected, actual)
+	}
+}
 
 // region insertat
 func TestInsertAtBeginning(t *testing.T) {