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lexer.go
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lexer.go
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package filter
const (
EOF = 0
COLON = ':'
COMMA = ','
AND = COMMA
OR = '|'
EQ = '='
LIKE = '~'
NOT = '!'
LT = '<'
GT = '>'
QUOTE = '"'
SQUOTE = '\''
ESCAPE = '\\'
SPACE = ' '
LPAREN = '('
RPAREN = ')'
)
const (
LITERAL = 0x01
STRING = 0x02
OPERATOR = 0x03
)
//
// Lexer token reader.
type Lexer struct {
tokens []Token
index int
}
//
// With builds with the specified filter.
func (r *Lexer) With(filter string) (err error) {
reader := Reader{input: filter}
var bfr []byte
push := func(kind byte) {
if len(bfr) == 0 {
return
}
r.tokens = append(
r.tokens,
Token{
Kind: kind,
Value: string(bfr),
})
bfr = nil
}
for {
ch := reader.next()
if ch == EOF {
break
}
switch ch {
case QUOTE,
SQUOTE:
reader.put()
push(LITERAL)
q := Quoted{Reader: &reader}
token, nErr := q.Read()
if nErr != nil {
err = nErr
return
}
r.tokens = append(r.tokens, token)
case SPACE:
push(LITERAL)
case LPAREN:
bfr = append(bfr, ch)
push(LPAREN)
case RPAREN:
push(LITERAL)
bfr = append(bfr, ch)
push(RPAREN)
case COLON,
COMMA,
OR,
EQ,
LIKE,
NOT,
LT,
GT:
reader.put()
push(LITERAL)
q := Operator{Reader: &reader}
token, nErr := q.Read()
if nErr != nil {
err = nErr
return
}
r.tokens = append(r.tokens, token)
default:
bfr = append(bfr, ch)
}
}
push(LITERAL)
return
}
//
// next returns the next token.
func (r *Lexer) next() (token Token, next bool) {
if r.index < len(r.tokens) {
token = r.tokens[r.index]
next = true
r.index++
}
return
}
//
// Put rewinds the lexer by 1 token.
func (r *Lexer) put() {
if r.index > 0 {
r.index--
}
}
//
// Token scanned token.
type Token struct {
Kind byte
Value string
}
//
// Reader scan the input.
type Reader struct {
input string
index int
}
//
// Next character.
// Returns 0 at EOF.
func (r *Reader) next() (ch byte) {
if r.index < len(r.input) {
ch = r.input[r.index]
r.index++
}
return
}
//
// Put rewinds one character.
func (r *Reader) put() {
if r.index > 0 {
r.index--
}
}
//
// Quoted string token reader.
type Quoted struct {
*Reader
}
//
// Read token.
func (q *Quoted) Read() (token Token, err error) {
lastCh := byte(0)
var bfr []byte
quote := q.next()
for {
ch := q.next()
if ch == EOF {
break
}
switch ch {
case quote:
if lastCh != ESCAPE {
token.Kind = STRING
token.Value = string(bfr)
return
}
default:
bfr = append(bfr, ch)
}
lastCh = ch
}
err = Errorf("End (%c) not found.", quote)
return
}
//
// Operator token reader.
type Operator struct {
*Reader
}
//
// Read token.
func (q *Operator) Read() (token Token, err error) {
var bfr []byte
for {
ch := q.next()
if ch == EOF {
break
}
switch ch {
case COLON,
COMMA,
OR,
EQ,
LIKE,
NOT,
LT,
GT:
bfr = append(bfr, ch)
default:
q.put()
token.Kind = OPERATOR
token.Value = string(bfr)
return
}
}
err = Errorf("End of operator not found.")
return
}