calculat0r 0.1.0

mod cursor;
pub mod span;

use cursor::Cursor;
use span::FilePosition;
pub use span::Span;

pub mod token;
use token::{Token, TokenKind};

use crate::Result;

pub fn tokenize(src: &str) -> Result<Vec<Token>> {
    Lexer {
        c: Cursor::new(src)
    }.tokenize()
}

struct Lexer<'a> {
    c: Cursor<'a>,
}

impl Lexer<'_> {
    fn tokenize(&mut self) -> Result<Vec<Token>> {
        let mut tokens: Vec<Token> = Vec::new();
        while !self.c.is_finished() {
            self.c.step();
            if let Some(t) = self.next_token()? {
                tokens.push(t);
            }
        }
        Ok(tokens)
    }
    #[allow(clippy::unnecessary_wraps)]
    fn add_token(&self, token_type: TokenKind) -> Result<Option<Token>> {
        Ok(Some(Token::new(token_type, self.c.get_span())))
    }
    fn next_token(&mut self) -> Result<Option<Token>> {
        let c = self.c.advance();
        match c {
            '*' => self.add_token(TokenKind::Mul),
            '-' => self.add_token(TokenKind::Minus),
            '+' => self.add_token(TokenKind::Plus),
            '/' => self.add_token(TokenKind::Slash),
            '%' => self.add_token(TokenKind::Mod),
            '(' => self.add_token(TokenKind::LParen),
            ')' => self.add_token(TokenKind::RParen),
            ' ' | '\n' | '\r' | '\t' => Ok(None), // Ignore whitespace.
            c => {
                if c.is_numeric() {
                    self.number()
                } else {
                    self.error(&format!("Unexpected character '{c}'"))?;
                    Ok(None)
                }
            }
        }
    }
    fn number(&mut self) -> Result<Option<Token>> {
        self.c.advance_while(|c| c.is_numeric());
        if self.c.peek() == '.' && self.c.peek_next().is_numeric() {
            self.c.advance();
            self.c.advance_while(|c| c.is_numeric());
        }
        self.add_token(TokenKind::Number)
    }
    fn error(&mut self, msg: &str) -> Result<Option<Token>> {
        let FilePosition {
            start_line,
            start_col,
            ..
        } = self.c.file_pos();
        let msg = format!("[{start_line}:{start_col}] {msg}");
        Err(msg.into())
    }
}