package generate

import "io"
import "bufio"
import "unicode"
import "unicode/utf8"
import "git.tebibyte.media/sashakoshka/goparse"

const (
	TokenMethod parse.TokenKind = iota
	TokenKey
	TokenIdent
	TokenComma
	TokenLBrace
	TokenRBrace
	TokenLBracket
	TokenRBracket
)

var tokenNames = map[parse.TokenKind] string {
	TokenMethod:   "Method",
	TokenKey:      "Key",
	TokenIdent:    "Ident",
	TokenComma:    "Comma",
	TokenLBrace:   "LBrace",
	TokenRBrace:   "RBrace",
	TokenLBracket: "LBracket",
	TokenRBracket: "RBracket",
}

func Lex(fileName string, reader io.Reader) (parse.Lexer, error) {
	lex := &lexer {
		fileName: fileName,
		lineScanner: bufio.NewScanner(reader),
	}
	lex.nextRune()
	return lex, nil
}

type lexer struct {
	fileName    string
	lineScanner *bufio.Scanner
	rune        rune
	line        string
	lineFood    string
	
	offset   int
	row      int
	column   int

	eof bool

}

func (this *lexer) Next() (parse.Token, error) {
	token, err := this.nextInternal()
	if err == io.EOF { err = this.errUnexpectedEOF() }
	return token, err
}

func (this *lexer) nextInternal() (token parse.Token, err error) {
	err = this.skipWhitespace()
	token.Position = this.pos()
	if this.eof {
		token.Kind = parse.EOF
		err = nil
		return
	}
	if err != nil { return }

	appendRune := func () {
		token.Value += string(this.rune)
		err = this.nextRune()
	}

	doNumber := func () {
		for isDigit(this.rune) {
			appendRune()
			if this.eof { err = nil; return }
			if err != nil { return }
		}
	}

	defer func () {
		newPos := this.pos()
		newPos.End -- // TODO figure out why tf we have to do this
		token.Position = token.Position.Union(newPos)
	} ()

	switch {
	// Method
	case this.rune == 'M':
		token.Kind = TokenMethod
		err = this.nextRune()
		if err != nil { return }
		doNumber()
		if this.eof { err = nil; return }
	// Key
	case isDigit(this.rune):
		token.Kind = TokenKey
		doNumber()
		if this.eof { err = nil; return }
	// Ident
	case unicode.IsUpper(this.rune):
		token.Kind = TokenIdent
		for unicode.IsLetter(this.rune) || isDigit(this.rune) {
			appendRune()
			if this.eof { err = nil; return }
			if err != nil { return }
		}
	// Comma
	case this.rune == ',':
		token.Kind = TokenComma
		appendRune()
		if this.eof { err = nil; return }
	// LBrace
	case this.rune == '{':
		token.Kind = TokenLBrace
		appendRune()
		if this.eof { err = nil; return }
	// RBrace
	case this.rune == '}':
		token.Kind = TokenRBrace
		appendRune()
		if this.eof { err = nil; return }
	// LBracket
	case this.rune == '[':
		token.Kind = TokenLBracket
		appendRune()
		if this.eof { err = nil; return }
	// RBracket
	case this.rune == ']':
		token.Kind = TokenRBracket
		appendRune()
		if this.eof { err = nil; return }
	case unicode.IsPrint(this.rune):
		err = parse.Errorf (
			this.pos(), "unexpected rune '%c'",
			this.rune)
	default:
		err = parse.Errorf (
			this.pos(), "unexpected rune %U",
			this.rune)
	}

	return
}

func (this *lexer) nextRune() error {
	if this.lineFood == "" {
		ok := this.lineScanner.Scan()
		if ok {
			this.line     = this.lineScanner.Text()
			this.lineFood = this.line
			this.rune     = '\n'
			this.column   = 0
			this.row      ++
		} else {
			err := this.lineScanner.Err()
			if err == nil {
				this.eof = true
				return io.EOF
			} else {
				return err
			}
		}
	} else {
		var ch   rune
		var size int
		for ch == 0 && this.lineFood != "" {
			ch, size = utf8.DecodeRuneInString(this.lineFood)
			this.lineFood = this.lineFood[size:]
		}
		this.rune = ch
		this.column ++
	}

	return nil
}

func (this *lexer) skipWhitespace() error {
	err := this.skipComment()
	if err != nil { return err }
	for isWhitespace(this.rune) {
		err := this.nextRune()
		if err != nil { return err }
		err = this.skipComment()
		if err != nil { return err }
	}
	return nil
}

func (this *lexer) skipComment() error {
	if this.rune == ';' {
		for this.rune != '\n' {
			err := this.nextRune()
			if err != nil { return err }
		}
	}
	return nil
}

func (this *lexer) pos() parse.Position {
	return parse.Position {
		File:   this.fileName,
		Line:   this.lineScanner.Text(),
		Row:    this.row    - 1,
		Start:  this.column - 1,
		End:    this.column,
	}
}

func (this *lexer) errUnexpectedEOF() error {
	return parse.Errorf(this.pos(), "unexpected EOF")
}

func isWhitespace(char rune) bool {
	switch char {
	case ' ', '\t', '\r', '\n': return true
	default: return false
	}
}

func isDigit(char rune) bool {
	return char >= '0' && char <= '9'
}

func isHexDigit(char rune) bool {
	return isDigit(char) || char >= 'a' && char <= 'f' || char >= 'A' && char <= 'F'
}