use crate::lexer::Token;
use crate::lexer::Tokens;

#[derive(Debug, Clone)]
pub enum Datum {
    Boolean(bool),
    Number(i64),
    Symbol(String),
    List(Vec<Datum>),
    Procedure(fn(Vec<Datum>) -> Datum),
    Unspecified,
}

pub fn make_symbol(s: &str) -> Datum {
    Datum::Symbol(s.to_string())
}

impl Default for Datum {
    fn default() -> Self {
        Datum::Unspecified
    }
}

pub fn parse(tokens: Tokens) -> Datum {
    let (datum, _) = parse_datum(&tokens, 0);
    datum
}

fn parse_datum(tokens: &Tokens, ix: usize) -> (Datum, usize) {
    match &tokens[ix] {
        Token::Identifier(s) => (Datum::Symbol(s.to_string()), ix + 1),
        Token::Boolean(b) => (Datum::Boolean(*b), ix + 1),
        Token::Number(n) => (Datum::Number(*n), ix + 1),
        Token::LeftRoundBracket => parse_list(tokens, ix + 1),
        _ => panic!("Unexpected token {:?}", tokens[ix]),
    }
}

pub fn parse_list(tokens: &Tokens, mut ix: usize) -> (Datum, usize) {
    let mut datums = vec![];

    while ix < tokens.len() && tokens[ix] != Token::RightRoundBracket {
        let (datum, new_ix) = parse_datum(tokens, ix);
        datums.push(datum);
        ix = new_ix;
    }
    if ix == tokens.len() {
        panic!("PARSE_LIST -- missing closing bracket {:?}", tokens)
    }

    (Datum::List(datums), ix + 1)
}