use crate::lisp::{
    error::{ParseError, ParseErrorKind},
    lex::{Lexer, Span, Token},
    number::LispNumber,
    LispExpr,
};

pub struct Parser<'lex> {
    lexer: Lexer<'lex>,
    cur_token: Option<(Span, Token<'lex>)>,
}

enum Group {
    Backticks(i32),
    CommaAt,
    Quotes(u32),
    Parens(Vec<LispExpr>),
}

impl<'lex> Parser<'lex> {
    pub fn new(lexer: Lexer<'lex>) -> Self {
        Self {
            lexer,
            cur_token: None,
        }
    }

    pub fn parse_expr(&mut self) -> Result<LispExpr, ParseError> {
        let mut stack = Vec::new();
        let mut total_backticks = 0;
        loop {
            let (span, token) = self.next()?;
            let r: Result<LispExpr, ParseError> =
                match token {
                    Token::LeftParen => {
                        stack.push(Group::Parens(Vec::new()));
                        continue;
                    }
                    Token::RightParen => {
                        let group = stack
                            .pop()
                            .ok_or_else(|| ParseError::new(span, ParseErrorKind::UnmatchedParen))?;
                        match group {
                            Group::Parens(v) => {
                                if v.is_empty() {
                                    Ok(LispExpr::Unit)
                                } else {
                                    Ok(LispExpr::List(v))
                                }
                            }
                            _ => Err(ParseError::new(
                                span,
                                ParseErrorKind::UnexpectedToken {
                                    expected: "expression",
                                    found: "(",
                                },
                            )),
                        }
                    }
                    Token::Float(f) => f
                        .parse::<f64>()
                        .map(|n| LispExpr::Number(LispNumber::Float(n)))
                        .map_err(|_| ParseError::new(span, ParseErrorKind::LiteralParseError)),
                    Token::Integer(i) => i
                        .parse::<i64>()
                        .map(|n| LispExpr::Number(LispNumber::Integer(n)))
                        .map_err(|_| ParseError::new(span, ParseErrorKind::LiteralParseError)),
                    Token::String(s) => Ok(LispExpr::StringLit(s[1..s.len() - 1].into())),
                    Token::Char(s) => Ok(LispExpr::Char(s.chars().nth(2).ok_or_else(|| {
                        ParseError::new(span, ParseErrorKind::LiteralParseError)
                    })?)),
                    Token::Name(n) => Ok(name_expr(n)),
                    Token::BackQuote => {
                        total_backticks += 1;
                        if let Some(&mut Group::Backticks(ref mut n)) = stack.last_mut() {
                            *n += 1;
                            continue;
                        }
                        stack.push(Group::Backticks(1));
                        continue;
                    }
                    Token::Comma => {
                        if total_backticks <= 0 {
                            return Err(ParseError::new(span, ParseErrorKind::UnbalancedComma));
                        }
                        total_backticks -= 1;
                        if let Some(&mut Group::Backticks(ref mut n)) = stack.last_mut() {
                            *n -= 1;
                            continue;
                        }
                        stack.push(Group::Backticks(-1));
                        continue;
                    }
                    Token::CommaAt => {
                        if total_backticks <= 0 {
                            return Err(ParseError::new(span, ParseErrorKind::UnbalancedComma));
                        }
                        total_backticks -= 1;
                        stack.push(Group::CommaAt);
                        continue;
                    }
                    Token::Quote => {
                        if let Some(&mut Group::Quotes(ref mut n)) = stack.last_mut() {
                            *n += 1;
                            continue;
                        }
                        stack.push(Group::Quotes(1));
                        continue;
                    }
                    Token::End => {
                        if stack.iter().any(|group| matches!(*group, Group::Parens(_))) {
                            Err(ParseError::new(span, ParseErrorKind::MissingCloseParen))
                        } else {
                            Err(ParseError::new(span, ParseErrorKind::UnexpectedEof))
                        }
                    }
                };
            let mut v = r?;
            loop {
                match stack.last_mut() {
                    None => return Ok(v),
                    Some(&mut Group::Parens(ref mut values)) => {
                        values.push(v);
                        break;
                    }
                    _ => (),
                }

                let group = stack.pop().unwrap();

                match group {
                    Group::Backticks(n) if n > 0 => {
                        total_backticks -= n;
                        v = v.quasiquote(n as u32);
                    }
                    Group::Backticks(n) if n < 0 => {
                        total_backticks -= n;
                        v = v.comma((-n) as u32);
                    }
                    Group::CommaAt => {
                        total_backticks += 1;
                        v = v.comma_at(1);
                    }
                    Group::Quotes(n) => v = v.quote(n),
                    _ => (),
                }
            }
        }
    }

    fn next(&mut self) -> Result<(Span, Token<'lex>), ParseError> {
        let r = self.peek()?;
        self.cur_token = None;
        Ok(r)
    }

    fn peek(&mut self) -> Result<(Span, Token<'lex>), ParseError> {
        if let Some(tok) = self.cur_token {
            Ok(tok)
        } else {
            let tok = self.lexer.next_token()?;
            self.cur_token = Some(tok);
            Ok(tok)
        }
    }

    pub fn parse_single_expr(&mut self) -> Result<LispExpr, ParseError> {
        let expr = self.parse_expr()?;

        match self.next()? {
            (_, Token::End) => Ok(expr),
            (span, token) => Err(ParseError::new(
                span,
                ParseErrorKind::UnexpectedToken {
                    expected: "EOF",
                    found: token.name(),
                },
            )),
        }
    }

    pub fn parse_exprs(&mut self) -> Result<Vec<LispExpr>, ParseError> {
        let mut res = Vec::new();
        loop {
            match self.peek()? {
                (_, Token::End) => break,
                _ => res.push(self.parse_expr()?),
            }
        }
        Ok(res)
    }
}

fn name_expr(input: &str) -> LispExpr {
    match input {
        "#t" => LispExpr::BoolLit(true),
        "#f" => LispExpr::BoolLit(false),
        _ => LispExpr::Ident(input.into()),
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    fn parse(input: &str) -> Result<LispExpr, ParseError> {
        let mut parser = Parser::new(Lexer::new(input));

        parser.parse_single_expr()
    }

    #[test]
    fn parse_lisp_expr() {
        assert_eq!(
            parse("1.5").unwrap(),
            LispExpr::Number(LispNumber::Float(1.5))
        );

        assert_eq!(
            parse(r#""hello""#).unwrap(),
            LispExpr::StringLit("hello".into())
        );

        assert_eq!(parse("foo").unwrap(), LispExpr::Ident("foo".into()));

        let items = (1..=5)
            .map(LispNumber::Integer)
            .map(LispExpr::Number)
            .collect::<Vec<_>>();
        assert_eq!(parse("(1 2 3 4 5)").unwrap(), LispExpr::List(items));

        let foo = LispExpr::Ident("foo".into());
        let bar = LispExpr::Comma(Box::new(LispExpr::Ident("bar".into())), 1);
        assert_eq!(
            parse("`(foo ,bar)").unwrap(),
            LispExpr::Quasiquote(Box::new(LispExpr::List(vec![foo, bar])), 1)
        )
    }

    #[should_panic]
    #[test]
    fn unbalanced_comma() {
        parse("`(foo ,,bar)").unwrap();
    }

    #[should_panic]
    #[test]
    fn unbalanced_paren() {
        parse("(foo").unwrap();
    }
}