mod enumeration;
mod expr;
mod interface;
mod structure;
mod types;

use logos::{Lexer, Logos};

use crate::{
    ast::{IDLModule, Item, ItemAlias, ItemConstant, UseDecl},
    lexer::{Ident, Span, Spanned, Token},
};
use std::iter::Iterator;

pub struct TokenIterator<'a> {
    lexer: Lexer<'a, Token>,
    peeked: Option<Option<Token>>,
}

fn token_is_not_comment(a: &Result<Token, ()>) -> bool {
    !matches!(a, Err(_) | Ok(Token::Comment(..)))
}

impl<'a> TokenIterator<'a> {
    pub fn new(src: &'a str) -> Self {
        let lexer = Token::lexer(src);

        Self {
            lexer,
            peeked: None,
        }
    }
    pub fn next(&mut self) -> Result<Spanned<Token>, ParserError> {
        let n = match self.peeked.take() {
            Some(thing) => thing,
            None => self.lexer.find(token_is_not_comment).and_then(Result::ok),
        };
        let nxt = n.map(|token| Spanned(token, Span(self.lexer.span())));
        // println!("[NEXT] {:#?}", nxt);
        nxt.ok_or(ParserError::UnexpectedEOF)
    }

    fn _peek(&mut self) -> Option<&Token> {
        self.peeked
            .get_or_insert_with(|| self.lexer.find(token_is_not_comment).and_then(Result::ok))
            .as_ref()
    }

    pub fn peek(&mut self) -> Result<Spanned<&Token>, ParserError> {
        let span = Span(self.lexer.span());
        let peek = self._peek().map(|token| Spanned(token, span));
        // println!("[PEEK] {:#?}", peek);
        peek.ok_or(ParserError::UnexpectedEOF)
    }

    pub fn current(&self) -> Spanned<String> {
        Spanned(self.lexer.slice().to_owned(), self.span())
    }

    pub fn span(&self) -> Span {
        Span(self.lexer.span())
    }
}

pub(crate) struct Parser<'a> {
    tokens: TokenIterator<'a>,
}

impl<'a> Parser<'a> {
    pub fn new(src: &'a str) -> Self {
        Self {
            tokens: TokenIterator::new(src),
        }
    }

    fn eat(&mut self) {
        let _ = self.tokens.next();
    }

    fn get_real(
        &mut self,
        matcher: impl Fn(&Token) -> bool,
        expected: &'static str,
    ) -> Result<Spanned<Token>, ParserError> {
        if matcher(self.tokens.peek()?.0) {
            self.tokens.next()
        } else {
            Err(self.expected(expected))
        }
    }

    fn expected(&self, expected: &'static str) -> ParserError {
        ParserError::Unexpected(expected.to_owned(), self.tokens.current())
    }

    fn semi(&mut self) -> Result<Span, ParserError> {
        Ok(self
            .get_real(|token| matches!(token, Token::Semicolon), "a semicolon")?
            .1)
    }

    fn ask_ident(&mut self) -> Result<Spanned<String>, ParserError> {
        Ok(
            match self.get_real(
                |token| {
                    matches!(
                        token,
                        Token::Ident(Ident::Other(_) | Ident::Underscore) | Token::NumberSuffix(_)
                    )
                },
                "an identifier",
            )? {
                Spanned(Token::Ident(Ident::Other(ident)), span) => Spanned(ident, span),
                Spanned(Token::Ident(Ident::Underscore), span) => Spanned("_".to_owned(), span),
                Spanned(Token::NumberSuffix(suffix), span) => Spanned(suffix.to_string(), span),
                _ => unreachable!(),
            },
        )
    }

    fn ask_alias(&mut self) -> Result<Spanned<ItemAlias>, ParserError> {
        let Spanned(_, kSp) = self.get_real(
            |token| matches!(token, Token::Ident(Ident::Alias)),
            "`Alias`",
        )?;
        let Spanned(name, nSp) = self.ask_ident()?;

        let Spanned(_, eqSp) = self.get_real(|token| matches!(token, Token::Equals), "`=`")?;
        let Spanned(referree, rSp) = self.ask_type()?;

        Ok(Spanned::new(
            ItemAlias { name, referree },
            [kSp, nSp, eqSp, rSp, self.semi()?],
        ))
    }

    fn ask_constant(&mut self) -> Result<Spanned<ItemConstant>, ParserError> {
        let Spanned(_, kSp) = self.get_real(
            |token| matches!(token, Token::Ident(Ident::Constant)),
            "`Constant`",
        )?;
        let Spanned(name, nSp) = self.ask_ident()?;
        let Spanned(_, eqSp) = self.get_real(|token| matches!(token, Token::Equals), "`=`")?;
        let Spanned(expr, exprSp) = self.ask_expr()?;

        Ok(Spanned::new(
            ItemConstant { name, expr },
            [kSp, nSp, eqSp, exprSp, self.semi()?],
        ))
    }

    fn ask_item(&mut self) -> Result<Spanned<Item>, ParserError> {
        Ok(match self.tokens.peek()?.0 {
            Token::Ident(Ident::Other(_)) => {
                Err(self.expected("a keyword, not just an identifier"))?
            }
            Token::Ident(keyword) => match keyword {
                Ident::Interface => self.ask_interface()?.map(Item::Interface),
                Ident::Structure => self.ask_structure()?.map(Item::Structure),
                Ident::Alias => self.ask_alias()?.map(Item::Alias),
                Ident::Constant => self.ask_constant()?.map(Item::Constant),
                Ident::Function => self.ask_function()?.map(Item::Function),
                Ident::Enumeration => self.ask_enumeration()?.map(Item::Enumeration),
                _ => Err(self.expected("an item denoting keyword (Interface, Structure, Alias, Constant, Function, Enumeration)"))?,
            },
            _ => Err(self.expected("a keyword"))?,
        })
    }

    fn ask_use(&mut self) -> Result<Spanned<UseDecl>, ParserError> {
        let Spanned(_, span) = {
            match self.tokens.peek()? {
                Spanned(Token::Ident(Ident::Use), _) => Ok(self.tokens.next()?),
                _ => Err(ParserError::PleaseStopParsingUse),
            }
        }?;
        let mut path = (self.ask_ident()?.0, None);

        if let Token::Dot = self.tokens.peek()?.0 {
            self.eat();
            path.1 = Some(self.ask_ident()?.0);
        }

        Ok(Spanned::new(UseDecl { path }, [span, self.semi()?]))
    }

    pub fn parse(mut self) -> Result<IDLModule, ParserError> {
        Ok(IDLModule {
            name: {
                self.get_real(
                    |token| matches!(token, Token::Ident(Ident::Module)),
                    "the `Module` keyword",
                )?;
                let name = self.ask_ident()?.0;
                self.semi()?;
                name
            },
            uses: {
                let mut real = vec![];
                loop {
                    let r = self.ask_use();
                    match r {
                        Ok(Spanned(a, _)) => real.push(a),
                        Err(ParserError::UnexpectedEOF) => return Err(ParserError::UnexpectedEOF),
                        Err(ParserError::PleaseStopParsingUse) => break,
                        Err(unexpected @ ParserError::Unexpected(..)) => return Err(unexpected),
                    }
                }
                Ok(real)
            }?,
            items: fill_while(|| self.ask_item())?,
        })
    }
}

fn fill_while<T>(
    mut f: impl FnMut() -> Result<Spanned<T>, ParserError>,
) -> Result<Vec<T>, ParserError> {
    let mut real = vec![];
    loop {
        match f() {
            Ok(Spanned(next, _)) => real.push(next),
            Err(unexpected @ ParserError::Unexpected(..)) => return Err(unexpected),
            Err(ParserError::UnexpectedEOF) => break,
            Err(ParserError::PleaseStopParsingUse) => unreachable!(),
        }
    }
    Ok(real)
}

pub fn parse(source: &str) -> Result<IDLModule, ParserError> {
    Parser::new(source).parse()
}

#[derive(thiserror::Error, Debug)]
pub enum ParserError {
    // expected, got
    #[error("Unexpected `{_1}`, expected {_0}")]
    Unexpected(String, Spanned<String>),
    #[error("Unexpected end of file")]
    UnexpectedEOF,
    #[error("please stop.")]
    PleaseStopParsingUse,
}