package tokenize

import "fmt"
import "strings"

type reader struct {
	data string
	pos  uint
}

func (self *reader) len() uint {
	return uint(len(self.data))
}

func (self *reader) checkPos() {
	if self.pos > uint(len(self.data)) {
		panic(fmt.Sprintf("invalid cursor state: pos=%d but len(data)=%d", self.pos, len(self.data)))
	}
}

func (self *reader) peekChar() (byte, bool) {
	self.checkPos()
	if self.done() {
		return 0, false
	}
	return self.data[self.pos], true
}

func (self *reader) takeChar() (string, bool) {
	self.checkPos()
	if self.pos == self.len() {
		return "", false
	}
	self.pos += 1
	return self.data[self.pos-1 : self.pos], true
}

func (self *reader) takeUntil(needle string) (string, bool) {
	self.checkPos()
	idx := strings.Index(self.data[self.pos:], needle)
	if idx == -1 {
		return "", false
	}
	end := self.pos + uint(idx)
	out := self.data[self.pos:end]
	self.pos = end
	return out, true
}

func (self *reader) tossUntilNeitherOf(needles string) bool {
	self.checkPos()
	tossed := uint(0)
	for {
		idx := self.pos + tossed
		if idx == self.len() {
			break
		}
		if hasByte(self.data[idx], needles) {
			tossed += 1
			continue
		}
		break
	}
	self.pos += tossed
	return tossed > 0
}

func hasByte(b byte, ns string) bool {
	for i := range len(ns) {
		if b == ns[i] {
			return true
		}
	}
	return false
}

func (self *reader) tossChar() {
	self.checkPos()
	self.pos += 1
}

func (self *reader) done() bool {
	self.checkPos()
	return self.pos == self.len()
}

type builder struct {
	tokens    []string
	buf_set   bool
	buf_chars string
}

func make_builder() builder {
	return builder{tokens: make([]string, 0), buf_set: false, buf_chars: ""}
}

func (self *builder) bufAppend(chars string) {
	if self.buf_set {
		self.buf_chars += chars
	} else {
		self.buf_chars = chars
		self.buf_set = true
	}
}

func (self *builder) bufAppendChar(char byte) {
	if !self.buf_set {
		self.buf_chars = ""
		self.buf_set = true
	}
	self.buf_chars += string(char)
}

func (self *builder) bufCommit() {
	if !self.buf_set {
		return
	}
	self.tokens = append(self.tokens, self.buf_chars)
	self.buf_chars = ""
	self.buf_set = false
}

type tokenizeResult struct {
	tokens  []string
	code    tokenizeResultCode
	err_loc uint
}

type tokenizeResultCode uint8

func (self tokenizeResultCode) String() string {
	switch self {
	case tokenizeResultCodeOk:
		return "tokenizeResultCodeOk"
	case tokenizeResultCodeMissingEndSingleQuote:
		return "tokenizeResultCodeMissingEndSingleQuote"
	case tokenizeResultCodeMissingEndDoubleQuote:
		return "tokenizeResultCodeMissingEndDoubleQuote"
	case tokenizeResultCodeMissingEscapedCharacter:
		return "tokenizeResultCodeMissingEscapedCharacter"
	default:
		return fmt.Sprintf("unknown!tokenizeResultCode(%d)", self)
	}
}

const (
	tokenizeResultCodeOk tokenizeResultCode = iota
	tokenizeResultCodeMissingEndSingleQuote
	tokenizeResultCodeMissingEndDoubleQuote
	tokenizeResultCodeMissingEscapedCharacter
)

func tokenize(str string) tokenizeResult {
	rdr := reader{data: str}
	b := make_builder()
	for {
		this_char, ok := rdr.peekChar()
		if !ok {
			break
		}
		switch this_char {
		case ' ':
			b.bufCommit()
			rdr.tossUntilNeitherOf(" \t\n")
		case '\t':
			b.bufCommit()
			rdr.tossUntilNeitherOf(" \t\n")
		case '\n':
			b.bufCommit()
			rdr.tossUntilNeitherOf(" \t\n")
		case '\'':
			rdr.tossChar() // first `'`
			new_chars, found := rdr.takeUntil("'")
			if !found {
				return tokenizeResult{code: tokenizeResultCodeMissingEndSingleQuote, err_loc: rdr.pos - 1}
			}
			b.bufAppend(new_chars)
			rdr.tossChar() // the second `'`
		case '"':
			rdr.tossChar() // first `"`
			new_chars, found := rdr.takeUntil("\"")
			if !found {
				return tokenizeResult{code: tokenizeResultCodeMissingEndDoubleQuote, err_loc: rdr.pos - 1}
			}
			b.bufAppend(new_chars)
			rdr.tossChar() // the second `"`
		case '\\':
			rdr.tossChar()
			if rdr.done() {
				return tokenizeResult{code: tokenizeResultCodeMissingEscapedCharacter, err_loc: rdr.pos - 1}
			}
			new_chars, _ := rdr.takeChar()
			b.bufAppend(new_chars)
		default:
			b.bufAppendChar(this_char)
			rdr.tossChar()
		}
	}
	b.bufCommit()
	return tokenizeResult{tokens: b.tokens}
}

func Tokenize(str string) ([]string, error) {
	res := tokenize(str)
	switch res.code {
	case tokenizeResultCodeOk:
		return res.tokens, nil
	case tokenizeResultCodeMissingEndSingleQuote:
		return nil, TokenizeError{code: TokenizeErrorCodeMissingEndSingleQuote, loc: res.err_loc}
	case tokenizeResultCodeMissingEndDoubleQuote:
		return nil, TokenizeError{code: TokenizeErrorCodeMissingEndDoubleQuote, loc: res.err_loc}
	case tokenizeResultCodeMissingEscapedCharacter:
		return nil, TokenizeError{code: TokenizeErrorCodeMissingEscapedCharacter, loc: res.err_loc}
	default:
		return nil, TokenizeError{code: TokenizeErrorCodeGeneral, loc: res.err_loc}
	}
}

type TokenizeError struct {
	code TokenizeErrorCode
	loc  uint
}
type TokenizeErrorCode uint8

const (
	TokenizeErrorCodeGeneral TokenizeErrorCode = iota
	TokenizeErrorCodeMissingEndSingleQuote
	TokenizeErrorCodeMissingEndDoubleQuote
	TokenizeErrorCodeMissingEscapedCharacter
)

func (e TokenizeError) Error() string {
	switch e.code {
	case TokenizeErrorCodeMissingEndSingleQuote:
		return fmt.Sprintf("unterminated single-quote: at %d", e.loc)
	case TokenizeErrorCodeMissingEndDoubleQuote:
		return fmt.Sprintf("unterminated double-quote: at %d", e.loc)
	case TokenizeErrorCodeMissingEscapedCharacter:
		return fmt.Sprintf("missing escaped character: at %d", e.loc)
	default:
		return fmt.Sprintf("unknown TokenizeError code: .code=%d .loc=%d", e.code, e.loc)
	}
}