use crate::syn::{ast::*, error::*, lexer::Lexer, op::*, span::*, token::*};
use std::{convert::TryFrom, mem};

const BASE_EXPR_START: &[TokenKind] = &[
    TokenKind::Ident,
    TokenKind::Num,
    TokenKind::Str,
    TokenKind::Sym,
    TokenKind::LParen,
    TokenKind::LBracket,
    TokenKind::LBrace,
    TokenKind::ObjBrace,
];

const UN_EXPR_START: &[TokenKind] = &[TokenKind::Plus, TokenKind::Minus, TokenKind::Bang];

pub struct Parser<'t> {
    lexer: Lexer<'t>,
    curr_token: Option<Token>,
    skip_newlines: bool,
}

impl<'t> Parser<'t> {
    pub fn new(lexer: Lexer<'t>) -> Result<Self> {
        let mut parser = Parser {
            lexer,
            curr_token: None,
            skip_newlines: false,
        };
        parser.adv_token()?;
        Ok(parser)
    }

    pub fn is_eof(&self) -> bool {
        self.lexer.is_eof()
    }

    pub fn pos(&self) -> Pos {
        self.span().start
    }

    pub fn set_skip_newlines(&mut self, skip: bool) -> Result<bool> {
        let prev = mem::replace(&mut self.skip_newlines, skip);
        match self.skip_newlines() {
            Ok(()) => Ok(prev),
            Err(e) => {
                self.skip_newlines = prev;
                Err(e)
            }
        }
    }

    pub fn is_skip_newlines(&self) -> bool {
        self.skip_newlines
    }

    fn skip_newlines(&mut self) -> Result<()> {
        if self.is_skip_newlines() && self.is_token_kind(TokenKind::Newline) {
            self.adv_token()?;
        }
        Ok(())
    }
}

////////////////////////////////////////////////////////////////////////////////
// Statement parsing
////////////////////////////////////////////////////////////////////////////////
impl<'t> Parser<'t> {
    pub fn next_stmt(&mut self) -> Result<Stmt> {
        todo!()
    }
}

////////////////////////////////////////////////////////////////////////////////
// Expression parsing
////////////////////////////////////////////////////////////////////////////////

macro_rules! bin_expr {
    ($name:ident, $op_tokens:expr, $next:ident) => {
        fn $name(&mut self) -> Result<Expr> {
            let lhs = self.$next()?;
            if let Some(token) = self.match_token_where(|t| $op_tokens.contains(&t.kind()))? {
                let op = BinOp::from(token);
                let rhs = self.$name()?;
                let span = lhs.span().union(rhs.span());
                Ok(BinExpr { lhs, op, rhs, span }.into())
            } else {
                Ok(lhs)
            }
        }
    };
}

impl<'t> Parser<'t> {
    pub fn next_expr(&mut self) -> Result<Expr> {
        self.next_bin_cmp_expr()
    }

    // == < > <= >=
    bin_expr!(
        next_bin_cmp_expr,
        &[
            TokenKind::EqEq,
            TokenKind::Lt,
            TokenKind::Gt,
            TokenKind::LtEq,
            TokenKind::GtEq
        ],
        next_bin_add_expr
    );
    // + -
    bin_expr!(
        next_bin_add_expr,
        &[TokenKind::Plus, TokenKind::Minus],
        next_bin_mul_expr
    );
    // * /
    bin_expr!(
        next_bin_mul_expr,
        &[TokenKind::FSlash, TokenKind::Splat],
        next_un_expr
    );

    fn next_un_expr(&mut self) -> Result<Expr> {
        if let Some(un_op) = self.match_token_where(|t| UN_EXPR_START.contains(&t.kind()))? {
            let start = un_op.span();
            let expr = self.next_un_expr()?;
            let end = expr.span();

            Ok(UnExpr {
                op: un_op.kind().into(),
                expr,
                span: start.union(end),
            }
            .into())
        } else {
            self.next_base_expr()
        }
    }

    fn next_base_expr(&mut self) -> Result<Expr> {
        let token =
            self.expect_token_where(|t| BASE_EXPR_START.contains(&t.kind()), "base expression")?;
        let expr: Expr = match token.kind() {
            TokenKind::Ident => BaseExpr {
                kind: BaseExprKind::Ident,
                span: token.span(),
            }
            .into(),
            TokenKind::Num => BaseExpr {
                kind: BaseExprKind::Num,
                span: token.span(),
            }
            .into(),
            TokenKind::Str => BaseExpr {
                kind: BaseExprKind::Str,
                span: token.span(),
            }
            .into(),
            TokenKind::Sym => BaseExpr {
                kind: BaseExprKind::Sym,
                span: token.span(),
            }
            .into(),
            TokenKind::LBracket => {
                let prev_skip = self.set_skip_newlines(true)?;
                let expr_list = self.next_expr_list(TokenKind::RBracket)?;
                self.set_skip_newlines(prev_skip)?;
                let end_token =
                    self.expect_token_kind(TokenKind::RBracket, "end of list (right bracket)")?;
                let span = token.span().union(end_token.span());
                BaseExpr {
                    kind: BaseExprKind::List(expr_list),
                    span,
                }
                .into()
            }
            TokenKind::LBrace => todo!("TODO body expressions"),
            TokenKind::ObjBrace => {
                let prev_skip = self.set_skip_newlines(true)?;
                let object = self.next_obj_list()?;
                let end_token = self.expect_token_kind(TokenKind::RBrace, "end of object (right curly brace)")?;
                let span = token.span().union(end_token.span());
                Expr::Base(BaseExpr {
                    kind: BaseExprKind::Object(object),
                    span,
                })
            }
            TokenKind::LParen => {
                let prev_skip = self.set_skip_newlines(true)?;
                let first = self.next_expr()?;
                if let Some(_) = self.match_token_kind(TokenKind::Comma)? {
                    let mut list = self.next_expr_list(TokenKind::RParen)?;

                    self.set_skip_newlines(prev_skip)?;
                    let end_token = self.expect_token_kind(TokenKind::RParen, "end of tuple")?;

                    let span = token.span().union(end_token.span());
                    list.insert(0, first);
                    Expr::Base(
                        BaseExpr {
                            kind: BaseExprKind::Tuple(list),
                            span,
                        }
                        .into(),
                    )
                } else {
                    self.set_skip_newlines(prev_skip)?;
                    self.expect_token_kind(TokenKind::RParen, "end of expression")?;
                    first
                }
            }
            _ => unreachable!(),
        };

        Ok(expr)
    }

    /// Gets a list of expressions separated by commas, stopping when EOF or specified end token is
    /// reached.
    fn next_expr_list(&mut self, stop_before: TokenKind) -> Result<Vec<Expr>> {
        let mut list_items = Vec::new();

        while !self.is_token_kind(stop_before) {
            list_items.push(self.next_expr()?);

            // match a comma, otherwise exit the loop
            if self.match_token_kind(TokenKind::Comma)?.is_none() {
                break;
            }
        }
        Ok(list_items)
    }

    /// Parses the tail of a `BaseExprKind::Object` expression.
    ///
    /// This function expects that the initial object brace `%{` has already been eaten.
    fn next_obj_list(&mut self) -> Result<Vec<(Expr, Expr)>> {
        let mut object = Vec::new();

        // Parses this pattern:
        // ( key EQ value ( COMMA key = value )* COMMA? )?
        while !self.is_token_kind(TokenKind::RBrace) {
            let key = self.next_expr()?;
            self.expect_token_kind(TokenKind::Eq, "equals sign for object item")?;
            let value = self.next_expr()?;
            object.push((key, value));

            // match a comma, otherwise exit the loop
            if self.match_token_kind(TokenKind::Comma)?.is_none() {
                break;
            }
        }
        Ok(object)
    }

    ////////////////////////////////////////////////////////////////////////////////
    // Token matching functions
    ////////////////////////////////////////////////////////////////////////////////

    fn adv_token(&mut self) -> Result<Option<Token>> {
        let mut next_token = self.lexer.next_token()?;

        if self.is_skip_newlines() {
            while next_token
                .map(|t| t.kind() == TokenKind::Newline)
                .unwrap_or(false)
            {
                next_token = self.lexer.next_token()?;
            }

            if self.is_token_kind(TokenKind::Newline) {
                self.curr_token = next_token;
                while next_token
                    .map(|t| t.kind() == TokenKind::Newline)
                    .unwrap_or(false)
                {
                    next_token = self.lexer.next_token()?;
                }
            }
        }

        Ok(mem::replace(&mut self.curr_token, next_token))
    }

    fn match_token_where<P>(&mut self, pred: P) -> Result<Option<Token>>
    where
        P: Fn(Token) -> bool,
    {
        if self.is_token_match(pred) {
            self.adv_token()
        } else {
            Ok(None)
        }
    }

    fn match_token_kind(&mut self, kind: TokenKind) -> Result<Option<Token>> {
        if self.is_token_kind(kind) {
            self.adv_token()
        } else {
            Ok(None)
        }
    }

    fn is_token_match<P>(&self, pred: P) -> bool
    where
        P: Fn(Token) -> bool,
    {
        match self.curr_token {
            Some(token) => (pred)(token),
            None => false,
        }
    }

    fn is_token_kind(&self, kind: TokenKind) -> bool {
        self.is_token_match(|t| t.kind() == kind)
    }

    fn expect_token_where<P>(&mut self, pred: P, expected: impl ToString) -> Result<Token>
    where
        P: Fn(Token) -> bool,
    {
        self.match_token_where(pred)?
            .ok_or_else(|| Error::ExpectedGot {
                expected: expected.to_string(),
                got: self
                    .curr_token
                    .map(|token| token.kind().to_string())
                    .unwrap_or_else(|| "EOF".to_string()),
                pos: self.pos(),
            })
    }

    fn expect_token_kind(&mut self, kind: TokenKind, expected: impl ToString) -> Result<Token> {
        self.expect_token_where(|t| t.kind() == kind, expected)
    }
}

impl<'t> Spanned for Parser<'t> {
    fn span(&self) -> Span {
        self.curr_token
            .as_ref()
            .map(Spanned::span)
            .unwrap_or(Span::default())
    }
}

impl<'t> TryFrom<Lexer<'t>> for Parser<'t> {
    type Error = Error;

    fn try_from(lexer: Lexer<'t>) -> Result<Self> {
        Parser::new(lexer)
    }
}

impl<'t> TryFrom<&'t str> for Parser<'t> {
    type Error = Error;

    fn try_from(text: &'t str) -> Result<Self> {
        Parser::new(Lexer::new(text))
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_adv_token() {
        const EXPECTED: &'static [TokenKind] = &[
            TokenKind::Num,
            TokenKind::Ident,
            TokenKind::Sym,
            TokenKind::Str,
        ];
        let mut parser = Parser::try_from("1 ident :sym 'string'").unwrap();

        for expected in EXPECTED.iter().copied() {
            let token = parser.adv_token().unwrap();
            let kind = token.unwrap().kind();
            assert_eq!(kind, expected);
        }
        assert!(parser.is_eof());
    }

    #[test]
    fn test_match_token_where() {
        let mut parser = Parser::try_from("1 ident :sym 'string'").unwrap();

        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Num),
            Ok(Some(_))
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Num),
            Ok(None)
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Ident),
            Ok(Some(_))
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Ident),
            Ok(None)
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Sym),
            Ok(Some(_))
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Sym),
            Ok(None)
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Str),
            Ok(Some(_))
        ));
        assert!(matches!(
            parser.match_token_where(|token| token.kind() == TokenKind::Str),
            Ok(None)
        ));
        assert!(parser.is_eof());
    }

    macro_rules! test_parser {
        ($parser:expr, $($tail:tt)+) => {{
            let mut parser = $parser;
            test_parser!(@TAIL, &mut parser, $($tail)+);
        }};

        (@TAIL, $parser:expr, $method:ident, $expected:expr) => {{
            assert_eq!($parser.$method().unwrap(), $expected);
        }};

        (@TAIL, $parser:expr, $method:ident, $expected:expr, $($tail:tt)+) => {{
            test_parser!(@TAIL, $parser, $method, $expected);
            test_parser!(@TAIL, $parser, $($tail)*);
        }};

        (@TAIL, $parser:expr) => {
            assert!($parser.is_eof());
        };
        (@TAIL, $parser:expr,) => {
            assert!($parser.is_eof());
        };
    }

    fn bin_expr(lhs: Expr, op: BinOp, rhs: Expr) -> Expr {
        Expr::Bin(
            BinExpr {
                lhs,
                op,
                rhs,
                span: Default::default(),
            }
            .into(),
        )
    }

    fn un_expr(op: UnOp, expr: Expr) -> Expr {
        Expr::Un(
            UnExpr {
                op,
                expr,
                span: Default::default(),
            }
            .into(),
        )
    }

    fn base_expr(kind: BaseExprKind) -> Expr {
        Expr::Base(BaseExpr {
            kind,
            span: Default::default(),
        })
    }

    #[test]
    fn test_base_expr() {
        test_parser!(
            Parser::try_from("1 x 'value' :sym").unwrap(),
            // 1
            next_expr,
            base_expr(BaseExprKind::Num),
            // x
            next_expr,
            base_expr(BaseExprKind::Ident),
            // 'value'
            next_expr,
            base_expr(BaseExprKind::Str),
            // :sym
            next_expr,
            base_expr(BaseExprKind::Sym)
        );
    }

    #[test]
    fn test_list_expr() {
        test_parser!(
            Parser::try_from("[1, x, 'value', :sym]").unwrap(),
            next_expr,
            base_expr(BaseExprKind::List(vec![
                base_expr(BaseExprKind::Num),
                base_expr(BaseExprKind::Ident),
                base_expr(BaseExprKind::Str),
                base_expr(BaseExprKind::Sym),
            ]))
        );

        test_parser!(
            Parser::try_from("[1, x, 'value', :sym,]").unwrap(),
            next_expr,
            base_expr(BaseExprKind::List(vec![
                base_expr(BaseExprKind::Num),
                base_expr(BaseExprKind::Ident),
                base_expr(BaseExprKind::Str),
                base_expr(BaseExprKind::Sym),
            ]))
        );
    }

    #[test]
    fn test_tuple_expr() {
        test_parser!(
            Parser::try_from("(1, :sym)").unwrap(),
            next_expr,
            base_expr(BaseExprKind::Tuple(vec![
                base_expr(BaseExprKind::Num),
                base_expr(BaseExprKind::Sym),
            ]))
        );

        test_parser!(
            Parser::try_from("(:sym,)").unwrap(),
            next_expr,
            base_expr(BaseExprKind::Tuple(vec![base_expr(BaseExprKind::Sym),]))
        );

        test_parser!(
            Parser::try_from("(:sym)").unwrap(),
            next_expr,
            base_expr(BaseExprKind::Sym)
        );
    }

    #[test]
    fn test_object_expr() {
        test_parser!(
            Parser::try_from(
                r#"%{
                    :sym = value,
                    key = "value",
                    "lit" = 1,
                }"#
            )
            .unwrap(),
            next_expr,
            base_expr(BaseExprKind::Object(vec![
                    (base_expr(BaseExprKind::Sym), base_expr(BaseExprKind::Ident)),
                    (base_expr(BaseExprKind::Ident), base_expr(BaseExprKind::Str)),
                    (base_expr(BaseExprKind::Str), base_expr(BaseExprKind::Num)),
            ]))
        );
    }

    #[test]
    fn test_bin_expr() {
        test_parser!(
            Parser::try_from("x + 2").unwrap(),
            next_expr,
            bin_expr(
                base_expr(BaseExprKind::Ident),
                BinOp::Plus,
                base_expr(BaseExprKind::Num)
            )
        );

        test_parser!(
            Parser::try_from("1 + 2 * 3 - 4 / 5").unwrap(),
            next_expr,
            bin_expr(
                base_expr(BaseExprKind::Num),
                BinOp::Plus,
                bin_expr(
                    bin_expr(
                        base_expr(BaseExprKind::Num),
                        BinOp::Times,
                        base_expr(BaseExprKind::Num)
                    ),
                    BinOp::Minus,
                    bin_expr(
                        base_expr(BaseExprKind::Num),
                        BinOp::Div,
                        base_expr(BaseExprKind::Num)
                    )
                )
            )
        );

        test_parser!(
            Parser::try_from("1+2*3-4/5").unwrap(),
            next_expr,
            bin_expr(
                base_expr(BaseExprKind::Num),
                BinOp::Plus,
                bin_expr(
                    bin_expr(
                        base_expr(BaseExprKind::Num),
                        BinOp::Times,
                        base_expr(BaseExprKind::Num)
                    ),
                    BinOp::Minus,
                    bin_expr(
                        base_expr(BaseExprKind::Num),
                        BinOp::Div,
                        base_expr(BaseExprKind::Num)
                    )
                )
            )
        );

        test_parser!(
            Parser::try_from("1 - -1 * 8").unwrap(),
            next_expr,
            bin_expr(
                base_expr(BaseExprKind::Num),
                BinOp::Minus,
                bin_expr(
                    un_expr(UnOp::Minus, base_expr(BaseExprKind::Num)),
                    BinOp::Times,
                    base_expr(BaseExprKind::Num)
                )
            )
        );

        test_parser!(
            Parser::try_from("1--1*8").unwrap(),
            next_expr,
            bin_expr(
                base_expr(BaseExprKind::Num),
                BinOp::Minus,
                bin_expr(
                    un_expr(UnOp::Minus, base_expr(BaseExprKind::Num)),
                    BinOp::Times,
                    base_expr(BaseExprKind::Num)
                )
            )
        );

        test_parser!(
            Parser::try_from("1 + 1 == 2").unwrap(),
            next_expr,
            bin_expr(
                bin_expr(
                    base_expr(BaseExprKind::Num),
                    BinOp::Plus,
                    base_expr(BaseExprKind::Num)
                ),
                BinOp::EqEq,
                base_expr(BaseExprKind::Num)
            )
        );

        test_parser!(
            Parser::try_from("3 >= 1 + 2").unwrap(),
            next_expr,
            bin_expr(
                base_expr(BaseExprKind::Num),
                BinOp::GtEq,
                bin_expr(
                    base_expr(BaseExprKind::Num),
                    BinOp::Plus,
                    base_expr(BaseExprKind::Num)
                )
            )
        );
    }

    #[test]
    fn test_multiline_exprs() {
        test_parser!(
            Parser::try_from(
                r"[
                1,
                x,
                ['value', :value],
                :sym
            ]"
            )
            .unwrap(),
            next_expr,
            base_expr(BaseExprKind::List(vec![
                base_expr(BaseExprKind::Num),
                base_expr(BaseExprKind::Ident),
                base_expr(BaseExprKind::List(vec![
                    base_expr(BaseExprKind::Str),
                    base_expr(BaseExprKind::Sym),
                ])),
                base_expr(BaseExprKind::Sym),
            ]))
        );

        test_parser!(
            Parser::try_from(
                r"(
                1,
                x,
                [
                    :key,
                    'value',
                ],
                :sym
            )"
            )
            .unwrap(),
            next_expr,
            base_expr(BaseExprKind::Tuple(vec![
                base_expr(BaseExprKind::Num),
                base_expr(BaseExprKind::Ident),
                base_expr(BaseExprKind::List(vec![
                    base_expr(BaseExprKind::Sym),
                    base_expr(BaseExprKind::Str),
                ])),
                base_expr(BaseExprKind::Sym),
            ]))
        );

        test_parser!(
            Parser::try_from(
                r"(
                + 1
                + 2
                + 3
                + 4
            )"
            )
            .unwrap(),
            next_expr,
            bin_expr(
                un_expr(UnOp::Plus, base_expr(BaseExprKind::Num)),
                BinOp::Plus,
                bin_expr(
                    base_expr(BaseExprKind::Num),
                    BinOp::Plus,
                    bin_expr(
                        base_expr(BaseExprKind::Num),
                        BinOp::Plus,
                        base_expr(BaseExprKind::Num)
                    )
                )
            )
        );

        test_parser!(
            Parser::try_from(
                r"(
                + 1
                + 2
                + 3
                + 4
                ,
            )"
            )
            .unwrap(),
            next_expr,
            base_expr(BaseExprKind::Tuple(vec![bin_expr(
                un_expr(UnOp::Plus, base_expr(BaseExprKind::Num)),
                BinOp::Plus,
                bin_expr(
                    base_expr(BaseExprKind::Num),
                    BinOp::Plus,
                    bin_expr(
                        base_expr(BaseExprKind::Num),
                        BinOp::Plus,
                        base_expr(BaseExprKind::Num)
                    )
                )
            )]))
        );
    }
}