scanner.go

package markers

import (
	"fmt"
)

const Whitespace = 1<<'\t' | 1<<'\r' | 1<<' '

const (
	EOF = -(iota + 1)
	Identifier
	IntegerValue
	StringValue
)

type Scanner struct {
	source             []byte
	tokenStartPosition int
	tokenEndPosition   int
	searchIndex        int
	character          rune

	errorCount    int
	ErrorCallback func(scanner *Scanner, message string)
}

func NewScanner(source string) *Scanner {
	return &Scanner{
		source:             []byte(source),
		character:          Identifier,
		tokenStartPosition: -1,
		tokenEndPosition:   0,
		searchIndex:        -1,
		errorCount:         0,
	}
}

func (scanner *Scanner) SearchIndex() int {
	return scanner.searchIndex
}

func (scanner *Scanner) SourceLength() int {
	return len(scanner.source)
}

func (scanner *Scanner) ErrorCount() int {
	return scanner.errorCount
}

func (scanner *Scanner) AddError(message string) {
	scanner.errorCount++

	if scanner.ErrorCallback != nil {
		scanner.ErrorCallback(scanner, message)
	}
}

func (scanner *Scanner) Peek() rune {
	if scanner.character == Identifier {
		scanner.character = scanner.Next()
	}

	return scanner.character
}

func (scanner *Scanner) Expect(expected rune, description string) bool {
	token := scanner.Scan()

	if token != expected {
		//scanner.AddError(fmt.Sprintf("got %q; want %s", scanner.Token(), description))
		return false
	}

	return true
}

func (scanner *Scanner) Reset() {
	scanner.searchIndex = 0
	scanner.character = rune(scanner.source[0])
	scanner.tokenStartPosition = 0
	scanner.tokenEndPosition = 0
}

func (scanner *Scanner) SetSearchIndex(searchIndex int) {
	if searchIndex >= scanner.SourceLength() {
		scanner.searchIndex = scanner.SourceLength()
		return
	}

	scanner.searchIndex = searchIndex
	scanner.character = rune(scanner.source[searchIndex])
}

func (scanner *Scanner) Next() rune {
	scanner.searchIndex++

	if scanner.searchIndex >= scanner.SourceLength() {
		return EOF
	}

	return rune(scanner.source[scanner.searchIndex])
}

func (scanner *Scanner) SkipWhitespaces() rune {
	character := scanner.Peek()

	for Whitespace&(1<<uint(character)) != 0 {
		character = scanner.Next()
	}

	scanner.character = character
	return character
}

func (scanner *Scanner) Scan() rune {
	character := scanner.SkipWhitespaces()

	token := character
	if IsIdentifier(character, 0) {
		token = Identifier
		character = scanner.ScanIdentifier()
	} else if IsDecimal(character) {
		token = IntegerValue
		character = scanner.ScanNumber()
	} else if character == EOF {
		return EOF
	} else if character == '"' {
		token = StringValue
		scanner.ScanString('"')
		character = scanner.Peek()
	} else if character == '`' {
		token = StringValue
		scanner.ScanString('`')
		character = scanner.Peek()
	} else {
		scanner.tokenStartPosition = scanner.searchIndex
		character = scanner.Next()
		scanner.tokenEndPosition = scanner.searchIndex
	}

	scanner.character = character
	return token
}

func (scanner *Scanner) ScanNumber() rune {
	if IsDecimal(scanner.SkipWhitespaces()) {
		scanner.tokenStartPosition = scanner.searchIndex
	}

	character := scanner.SkipWhitespaces()

	for IsDecimal(character) {
		character = scanner.Next()
	}

	scanner.tokenEndPosition = scanner.searchIndex
	scanner.character = character
	return character
}

func (scanner *Scanner) ScanIdentifier() rune {
	if IsIdentifier(scanner.SkipWhitespaces(), 1) {
		scanner.tokenStartPosition = scanner.searchIndex
	}

	character := scanner.SkipWhitespaces()

	for index := 1; IsIdentifier(character, index); index++ {
		character = scanner.Next()
	}

	scanner.tokenEndPosition = scanner.searchIndex
	scanner.character = character
	return character
}

func (scanner *Scanner) ScanString(quote rune) (len int) {
	scanner.tokenStartPosition = scanner.searchIndex
	character := scanner.Next()

	for character != quote {
		if character == '\n' || character < 0 {
			scanner.AddError(fmt.Sprintf("'%c' is missing", quote))
			return
		}

		character = scanner.Next()
		len++
	}

	character = scanner.Next()
	scanner.tokenEndPosition = scanner.searchIndex
	scanner.character = character
	return
}

func (scanner *Scanner) Token() string {
	if scanner.tokenStartPosition < 0 {
		return ""
	}

	return string(scanner.source[scanner.tokenStartPosition:scanner.tokenEndPosition])
}