use crate::{
    ast::{nothing, Function, ItemInterface},
    lexer::{Ident, Span, Spanned, Token},
};

use super::{Parser, ParserError};

impl<'a> Parser<'a> {
    pub fn ask_interface(&mut self) -> Result<Spanned<ItemInterface>, ParserError> {
        // Interface
        let Spanned(_, mut span) = self.get_real(
            |token| matches!(token, Token::Ident(Ident::Interface)),
            "the `Interface` keyword",
        )?;
        // InterfaceName
        let Spanned(name, _) = self.ask_ident()?;

        // {
        self.get_real(
            |token| matches!(token, Token::LeftCurly),
            "opening curly brackets",
        )?;

        let mut functions = vec![];

        loop {
            match self.tokens.peek()? {
                Spanned(Token::RightCurly, end) => {
                    self.eat();
                    span += end;
                    break;
                }
                Spanned(Token::Ident(Ident::Function), _) => functions.push(self.ask_function()?.0),
                _ => return Err(self.expected("A function or closing curly braces")),
            }
        }

        Ok(Spanned(ItemInterface { name, functions }, span))
    }

    pub fn ask_function(&mut self) -> Result<Spanned<Function>, ParserError> {
        let Spanned(_, bsp) = self.get_real(
            |token| matches!(token, Token::Ident(Ident::Function)),
            "the `Function` keyword",
        )?;

        let Spanned(name, _) = self.ask_ident()?;

        let Spanned(next, esp) = self.tokens.next()?;
        match next {
            Token::Ident(Ident::Takes) => {
                self.get_real(
                    |token| matches!(token, Token::LeftParen),
                    "Opening parentheses",
                )?;

                let mut takes = vec![];
                let mut returns = nothing();
                loop {
                    let Spanned(peeked, _) = self.tokens.peek()?;
                    match peeked {
                        Token::Ident(_) => {
                            takes.push(self.ask_type()?.0);
                            match self.tokens.peek()?.0 {
                                Token::Comma => {
                                    self.eat();
                                }
                                Token::RightParen => {}
                                _ => return Err(self.expected("a comma or closing parentheses")),
                            };
                        }
                        Token::RightParen => {
                            self.eat();
                            break;
                        }
                        _ => return Err(self.expected("closing parentheses or a type name")),
                    }
                }

                match self.tokens.next()?.0 {
                    Token::Semicolon => {}
                    Token::Ident(Ident::Returns) => {
                        self.get_real(
                            |token| matches!(token, Token::LeftParen),
                            "opening parentheses",
                        )?;

                        let Spanned(returns_, _) = self.ask_type()?;

                        returns = returns_;

                        self.get_real(
                            |token| matches!(token, Token::RightParen),
                            "closing parentheses",
                        )?;

                        self.semi()?;
                    }
                    _ => return Err(self.expected("a semicolon or a Returns clause")),
                }

                Ok(Spanned(
                    Function {
                        name,
                        takes,
                        returns,
                    },
                    bsp + Span(self.tokens.lexer.span()),
                ))
            }
            Token::Ident(Ident::Returns) => {
                self.get_real(
                    |token| matches!(token, Token::LeftParen),
                    "Opening parentheses",
                )?;

                let Spanned(returns, _) = self.ask_type()?;

                self.get_real(
                    |token| matches!(token, Token::RightParen),
                    "Closing parentheses",
                )?;

                Ok(Spanned(
                    Function {
                        name,
                        takes: Vec::new(),
                        returns,
                    },
                    bsp + self.semi()?,
                ))
            }
            Token::Semicolon => Ok(Spanned(
                Function {
                    name,
                    takes: Vec::new(),
                    returns: nothing(),
                },
                bsp + esp,
            )),
            _ => Err(self.expected("a Takes clause, a Returns clause or a semicolon")),
        }
    }
}