Add some sort of work on decode

encoding/gsm7.go

@@ -3,6 +3,7 @@ package encoding
 import (
 	"bytes"
 	"fmt"
+	"log"
 )
 
 type GSM7Coder struct{}
@@ -10,9 +11,11 @@ type GSM7Coder struct{}
 func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
 	// utf8 := *(*[]byte)(unsafe.Pointer(&s))
 	utf8 := []byte(s)
-	var offset int = 1
-	var bitshift byte = 0
-	var leap, shift bool
+	var (
+		offset      int  = 1
+		bitshift    byte = 0
+		leap, shift bool
+	)
 
 	for index, septet := range utf8 {
 		if septet > 0b01111111 {
@@ -60,5 +63,62 @@ func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
 }
 
 func (c *GSM7Coder) Decode(buf *bytes.Buffer) (string, error) {
-	return buf.String(), nil
+	gsm7 := buf.Bytes()
+	var (
+		output      []byte = make([]byte, len(gsm7)*8/7)
+		offset      int    = (len(gsm7) / 8) + 1
+		bitshift    byte   = 0
+		leap, shift bool
+	)
+	log.Println(len(output))
+
+	for index := len(gsm7) - 2; index >= 0; index-- {
+		octet := gsm7[index]
+		bitshift = byte((index + 1) % 8)
+		if bitshift == 7 {
+			leap = true
+		}
+		log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) Output(%-3d):%08b (%-3d) Leap:%5v", index, offset, bitshift, gsm7[index], gsm7[index], index+offset, output[index+offset], output[index+offset], leap)
+
+		mask := byte(255 << (8 - bitshift))
+		masked := (mask & octet) >> (8 - bitshift)
+		log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d Mask:%08b Masked:%08b", index, offset, bitshift, mask, masked)
+		output[index+offset] |= masked
+
+		continue
+		gsm7[index+offset] |= masked
+		gsm7[index] <<= bitshift
+
+		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
+		}
+	}
+	return "", nil
+}
+
+// Allocation free
+// Which means data MUST have space for value
+func InsertAt(data *[]byte, index int, value byte) {
+    copy((*data)[index+1:], (*data)[index:])
+    (*data)[index] = value
 }