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#![allow(dead_code)]
use crate::lexer::Token;
use std::fmt;
use std::iter::Iterator;

#[derive(PartialEq, Debug)]
pub enum Expression {
    Identifier(String),
    Number(String),
    ProcudureCall(Box<Expression>, Vec<Box<Expression>>),
}

#[derive(Debug, PartialEq)]
pub struct SyntaxError {
    error: String,
}

impl fmt::Display for SyntaxError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Syntax error: {}", self.error)
    }
}

macro_rules! syntax_error {
    ($($arg:tt)*) => (
        return Err(SyntaxError { error: format!($($arg)*) });
    )
}

pub struct Parser<TokenIter: Iterator<Item = Token> + Clone> {
    current: Option<Token>,
    lexer: TokenIter,
}

impl<TokenIter: Iterator<Item = Token> + Clone> Parser<TokenIter> {
    pub fn new(mut lexer: TokenIter) -> Parser<TokenIter> {
        Self {
            current: lexer.next(),
            lexer: lexer,
        }
    }

    pub fn parse(&mut self) -> Result<Option<Box<Expression>>, SyntaxError> {
        match self.current.clone() {
            Some(token) => match token {
                Token::Number(a) => self.generate(Box::new(Expression::Number(a))),
                Token::Identifier(a) => self.generate(Box::new(Expression::Identifier(a))),
                Token::LeftParen => self.procedure_call(),
                _ => Ok(None),
            },
            None => Ok(None),
        }
    }

    fn procedure_call(&mut self) -> Result<Option<Box<Expression>>, SyntaxError> {
        self.advance();
        let operator = self.parse()?.unwrap();
        let mut params: Vec<Box<Expression>> = vec![];
        loop {
            match &self.current {
                Some(Token::RightParen) => {
                    return self.generate(Box::new(Expression::ProcudureCall(operator, params)));
                }
                None => syntax_error!("Unmatched Parentheses!"),
                _ => params.push(self.parse()?.unwrap()),
            }
        }
    }

    fn advance(&mut self) {
        self.current = self.lexer.next();
    }

    fn generate(&mut self, ast: Box<Expression>) -> Result<Option<Box<Expression>>, SyntaxError> {
        self.advance();
        Ok(Some(ast))
    }
}

#[test]
fn empty() {
    let tokens = Vec::new();
    let mut parser = Parser::new(tokens.into_iter());
    let ast = parser.parse().unwrap();
    assert_eq!(ast, None);
}

#[test]
fn number() {
    let tokens = vec![Token::Number("1".to_string())];
    let mut parser = Parser::new(tokens.into_iter());
    let ast = parser.parse().unwrap().unwrap();
    assert_eq!(*ast, Expression::Number("1".to_string()));
}

#[test]
fn identifier() {
    let tokens = vec![Token::Identifier("test".to_string())];
    let mut parser = Parser::new(tokens.into_iter());
    let ast = parser.parse().unwrap().unwrap();
    assert_eq!(*ast, Expression::Identifier("test".to_string()));
}

#[test]
fn procedure_call() {
    let tokens = vec![
        Token::LeftParen,
        Token::Identifier("+".to_string()),
        Token::Number("1".to_string()),
        Token::Number("2".to_string()),
        Token::Number("3".to_string()),
        Token::RightParen,
    ];
    let mut parser = Parser::new(tokens.into_iter());
    let ast = parser.parse().unwrap().unwrap();
    assert_eq!(
        *ast,
        Expression::ProcudureCall(
            Box::new(Expression::Identifier("+".to_string())),
            vec![
                Box::new(Expression::Number("1".to_string())),
                Box::new(Expression::Number("2".to_string())),
                Box::new(Expression::Number("3".to_string())),
            ]
        )
    );
}

#[test]
fn unmatched_parantheses() {
    let tokens = vec![
        Token::LeftParen,
        Token::Identifier("+".to_string()),
        Token::Number("1".to_string()),
        Token::Number("2".to_string()),
        Token::Number("3".to_string()),
    ];
    let mut parser = Parser::new(tokens.into_iter());
    assert_eq!(
        parser.parse(),
        Err(SyntaxError {
            error: "Unmatched Parentheses!".to_string()
        })
    );
}

#[test]
fn nested_procedure_call() {
    let tokens = vec![
        Token::LeftParen,
        Token::Identifier("+".to_string()),
        Token::Number("1".to_string()),
        Token::LeftParen,
        Token::Identifier("-".to_string()),
        Token::Number("2".to_string()),
        Token::Number("3".to_string()),
        Token::RightParen,
        Token::RightParen,
    ];
    let mut parser = Parser::new(tokens.into_iter());
    let ast = parser.parse().unwrap().unwrap();
    assert_eq!(
        *ast,
        Expression::ProcudureCall(
            Box::new(Expression::Identifier("+".to_string())),
            vec![
                Box::new(Expression::Number("1".to_string())),
                Box::new(Expression::ProcudureCall(
                    Box::new(Expression::Identifier("-".to_string())),
                    vec![
                        Box::new(Expression::Number("2".to_string())),
                        Box::new(Expression::Number("3".to_string()))
                    ]
                )),
            ]
        )
    );
}