package lexer

import java.util.LinkedList

class Lexer(private val source: String) {
    private var tokens: List<Token> = LinkedList()
    private val position: LexerPosition = LexerPosition(0, 0, 0)
    private var offset: Int = 0

    fun scan(): List<Token> {
        while (hasNext()) {
            val token = scanToken()
            tokens += token
        }

        tokens += Token(TokenType.EOF, position)

        return tokens
    }

    private fun scanToken(): Token {
        val c = peek()
        val token = when (c) {
            '.' -> Token(TokenType.DOT, position)
            else -> throw Error("Unknown symbol: $c", position)
        }

        offset++
        position.column++
        return token
    }

    private fun hasNext(): Boolean {
        return offset < source.length
    }

    private fun peek(): Char {
        if (!hasNext()) {
            throw Error("Unexpected end of input", position)
        }

        return source[offset]
    }
}