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preprocess.go
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preprocess.go
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package import_file
import "fmt"
const space byte = ' '
const dblQuote byte = '"'
const pipe byte = '|'
const escape byte = '\\'
const null byte = 0
func Preprocess(value []byte) []byte {
p := &preprocessor{}
return p.preprocess(value)
}
type preprocessor struct {
sourceIndex int
value []byte
destIndex int
isQuoted bool
isEscaped bool
extraSpaceLen int
lastCharIsPipe bool
}
func (p *preprocessor) preprocess(value []byte) []byte {
p.resetFor(value)
for p.processByte() {
}
return value[:p.destIndex]
}
func (p *preprocessor) resetFor(value []byte) {
p.sourceIndex = 0
p.value = value
p.destIndex = 0
p.isQuoted = false
p.isEscaped = false
p.extraSpaceLen = 0
p.lastCharIsPipe = false
}
func (p *preprocessor) processByte() bool {
if p.sourceIndex >= len(p.value) {
return false
}
currentByte := p.value[p.sourceIndex]
p.sourceIndex++
if currentByte == pipe {
return p.processPipe()
}
if currentByte == escape {
return p.processEscape()
}
if p.isEscaped {
return p.processCharAfterEscape(currentByte)
}
if currentByte == dblQuote {
return p.processDoubleQuote()
}
if currentByte == space {
return p.processSpace()
}
if p.whiteSpaceIsSignificant(currentByte) {
p.catchUpSignificantWhitespace()
}
return p.processNormalChar(currentByte)
}
func (p *preprocessor) processPipe() bool {
if p.isQuoted {
return p.processNormalChar('|')
}
p.lastCharIsPipe = true
p.value[p.destIndex] = null
p.destIndex++
return true
}
func (p *preprocessor) processEscape() bool {
if p.isEscaped {
p.value[p.destIndex] = escape
p.destIndex++
p.isEscaped = false
} else {
p.extraSpaceLen = 0
p.lastCharIsPipe = false
p.isEscaped = true
}
return true
}
func (p *preprocessor) processCharAfterEscape(currentByte byte) bool {
switch currentByte {
case 'r':
p.value[p.destIndex] = '\r'
case 'n':
p.value[p.destIndex] = '\n'
case dblQuote:
p.value[p.destIndex] = dblQuote
default:
panic(fmt.Sprintf(`invalid escape sequence \%v at position %v`, string(currentByte), p.sourceIndex))
}
p.destIndex++
p.isEscaped = false
return true
}
func (p *preprocessor) processDoubleQuote() bool {
p.isQuoted = !p.isQuoted
p.extraSpaceLen = 0
p.lastCharIsPipe = false
p.value[p.destIndex] = '"'
p.destIndex++
return true
}
func (p *preprocessor) processSpace() bool {
if p.isQuoted {
p.value[p.destIndex] = space
p.destIndex++
} else {
p.extraSpaceLen++
}
return true
}
func (p *preprocessor) processNormalChar(currentByte byte) bool {
p.extraSpaceLen = 0
p.lastCharIsPipe = false
p.value[p.destIndex] = currentByte
p.destIndex++
return true
}
func (p *preprocessor) whiteSpaceIsSignificant(currentByte byte) bool {
return p.extraSpaceLen > 0 && currentByte != pipe && !p.lastCharIsPipe
}
func (p *preprocessor) catchUpSignificantWhitespace() {
for index := 0; index < p.extraSpaceLen; index++ {
p.value[p.destIndex] = space
p.destIndex++
}
}