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package byteutil
import (
"fmt"
"sort"
)
var (
// ErrInvalideLetter means invalid letter
ErrInvalideLetter = fmt.Errorf("ByteCoder: invalid letter")
// ErrInvalideCode means invalid code
ErrInvalideCode = fmt.Errorf("ByteCoder: invalid code")
)
// ByteCoder is used to convert betweeen byte and int
type ByteCoder struct {
Alphabet []byte
alphabetQuerySlice []byte
bytes2int []int
int2bytes []byte
}
// NewByteCoder Create a ByteCoder type
func NewByteCoder(alphabet []byte) (*ByteCoder, error) {
if len(alphabet) == 0 {
return nil, fmt.Errorf("ByteCoder: alphabet should not be empty")
}
m := make(map[byte]struct{}, len(alphabet))
for _, a := range alphabet {
m[a] = struct{}{}
}
max := -1
var b int
for a := range m {
b = int(a)
if max < b {
max = b
}
}
alphabet2 := make([]byte, len(m))
slice := make([]byte, max+1)
i := 0
for a := range m {
slice[a-'\x00'] = a
alphabet2[i] = a
i++
}
sort.Sort(ByteSlice(alphabet2))
bytes2int := make([]int, max+1)
int2bytes := make([]byte, len(m))
for i, a := range alphabet2 {
bytes2int[a-'\x00'] = i
int2bytes[i] = a
}
return &ByteCoder{Alphabet: alphabet2, alphabetQuerySlice: slice,
bytes2int: bytes2int, int2bytes: int2bytes}, nil
}
func (coder *ByteCoder) String() string {
return fmt.Sprintf(`ByteCoder: alphabet:"%s" num:%d`, coder.Alphabet, len(coder.Alphabet))
}
// Encode converts []byte to []int
func (coder *ByteCoder) Encode(s []byte) ([]int, error) {
code := make([]int, len(s))
for i, b := range s {
if int(b) > len(coder.alphabetQuerySlice) {
return nil, ErrInvalideLetter
}
v := coder.alphabetQuerySlice[b-'\x00']
if v == 0 {
return nil, ErrInvalideLetter
}
code[i] = coder.bytes2int[v]
}
return code, nil
}
// Decode convert []int to []byte
func (coder *ByteCoder) Decode(code []int) ([]byte, error) {
bytes := make([]byte, len(code))
for i, b := range code {
if b >= len(coder.int2bytes) {
return nil, ErrInvalideCode
}
v := coder.int2bytes[b]
if v == 0 {
return nil, ErrInvalideCode
}
bytes[i] = v
}
return bytes, nil
}
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