use nom::{
    IResult,
    Parser,
    branch::alt,
    multi::many0,
    bytes::complete::{tag, take_while1},
    character::complete::multispace1,
};

use crate::sexp::{SExp, SExp::*, SLeaf::*, util::*};


#[derive(Debug,PartialEq)]
pub enum Token {
    ParOpen,
    ParClose,
    Num(i32),
    Sym(String),
    Whitespace(String),
}

use Token::*;
use crate::parse::util::*;

fn parse_token(s: &str) -> IResult<&str, Token> {
    alt((
            tag("(").map(|_| ParOpen),
            tag(")").map(|_| ParClose),
            multispace1.map(whitespace),
            nom::character::complete::i32.map(Num),
            take_while1(|c| !(" \n\t()".contains(c))).map(sym),
    )).parse(s)
}

fn tokenize(s: &str) -> Result<Vec<Token>, String> {
    match many0(parse_token).parse(s) {
        Ok(("", res)) => Ok(res),
        Ok((rest, _)) => Err(format!("all data should be tokenizable, '{rest}' was not")),
        Err(e) => Err(e.to_string()),
    }
}


fn tokens_to_ast(tokens: Vec<Token>) -> Result<SExp, String> {
    todo!()
}


#[cfg(test)]
mod private_parsing_tests {
    use super::{*, parse_token};

    #[test]
    fn test_parse_token() {
        assert_eq!(parse_token("()"), Ok((")", ParOpen)));
        assert_eq!(parse_token(")"), Ok(("", ParClose)));

        assert_eq!(parse_token(" \t\n"), Ok(("", whitespace(" \t\n"))));

        assert_eq!(parse_token("1 23"), Ok((" 23", Num(1))));
        assert_eq!(parse_token("23"), Ok(("", Num(23))));

        assert_eq!(parse_token("Nil a"), Ok((" a", sym("Nil"))));
        assert_eq!(parse_token("a"), Ok(("", sym("a"))));

        assert!(parse_token("").is_err())
    }

    #[test]
    fn test_tokenize() {
        assert_eq!(
            tokenize("(+ 1 2 (\t\n a)").unwrap(),
            vec![
                ParOpen,
                sym("+"), whitespace(" "),
                Num(1), whitespace(" "),
                Num(2), whitespace(" "),
                ParOpen, whitespace("\t\n "),
                sym("a"),
                ParClose
            ]
        );
    }

    #[test]
    fn test_tokens_to_ast() {
	// Syms are parsed to vars,
	// and everything is wrapped in an extra layer of scons
	// so that multi-expression programs can be returned
	// as one single SExp.
	assert_eq!(
	    tokens_to_ast(vec![sym("a")]),
	    Ok(scons(var("a"), Nil))
	);

	// Lists are pased to scons linked lists
        assert_eq!(
            tokens_to_ast(vec![
		ParOpen,
		sym("a"), whitespace(" "),
		sym("b"), whitespace(" "),
		sym("c"), whitespace(" "),
		ParClose,
	    ]),
	    Ok(scons(scons(var("a"), scons(var("b"), scons(var("c"), Nil))), Nil))
        );

	// Nesting should work.
	assert_eq!(
	    tokens_to_ast(vec![
		ParOpen,
		sym("a"), whitespace(" "),
		ParOpen,
		sym("b"), whitespace(" "),
		sym("c"), whitespace(" "),
		ParClose, whitespace(" "),
		sym("d"),
		ParClose
	    ]),
	    Ok(
		scons(scons(var("a"), scons(
		    scons(var("b"), scons(var("c"), Nil))
		, scons(var("d"), Nil))), Nil)
	    )
	);

	// Multiple expressions should be parseable
	assert_eq!(
	    tokens_to_ast(vec![
		ParOpen,
		sym("a"),
		ParClose,
		sym("b"),
		ParOpen,
		sym("c"),
		ParClose,
	    ]),
	    Ok(scons(
		scons(var("a"), Nil),
		scons(var("b"),
		scons(scons(var("c"), Nil), Nil))))
	);

	// Operators are parsed correctly
	assert_eq!(
	    tokens_to_ast(vec![
		ParOpen,
		sym("+"), whitespace(" "),
		sym("-"), whitespace(" "),
		sym("*"), whitespace(" "),
		sym("/"),
		ParClose
	    ]),
	    Ok(scons(
		scons(Add,
		      scons(Sub,
			    scons(Mul,
				  scons(Div,
					Nil)))), Nil))
	);

	// Integers are parsed correctly
	assert_eq!(
	    tokens_to_ast(vec![Num(5)]),
	    Ok(scons(Int(5), Nil))
	);

	// Nil can be parsed
	assert_eq!(
	    tokens_to_ast(vec![ParOpen,ParClose]),
	    Ok(scons(Nil, Nil))
	);

	// Quote can be parsed
	assert_eq!(
	    tokens_to_ast(vec![
		ParOpen,
		sym("quote"), whitespace(" "),
		sym("a"), whitespace(" "),
		sym("b"), whitespace(" ")
	    ]),
	    Ok(scons(Quote, scons(var("a"), scons(var("b"), Nil))))
	);
    }

    #[test]
    fn test_tokens_to_ast_failing() {
	assert!(
	    tokens_to_ast(vec![ParClose]).is_err(),
	    "Invalid parentheses should fail"
	);
	assert!(
	    tokens_to_ast(vec![ParOpen]).is_err(),
	    "Invalid parentheses should fail"
	);
	assert!(
	    tokens_to_ast(vec![ParClose, ParOpen]).is_err(),
	    "Invalid parentheses should fail"
	);
	assert!(
	    tokens_to_ast(vec![ParOpen, ParOpen, ParClose]).is_err(),
	    "Invalid parentheses should fail"
	);

	assert!(
	    tokens_to_ast(vec![Num(1), sym("a")]).is_err(),
	    "Having a symbol starting with a number should fail."
	);

	assert!(
	    tokens_to_ast(vec![sym("quote"), sym("a")]).is_err(),
	    "There should be whitespace between quote and other symbols"
	);
    }

}