%start Body

%left '||'
%left '&&'
%left '<' '>' '<=' '>=' '==' '!='
%left '*' '/'
%left '+' '-'

%avoid_insert "NUM" "SYM" "STRING" "||" "&&" "<" ">" "<=" ">=" "!=" "==" "+" "-" "*" "/" "{"

%%

Body -> Result<Vec<Stmt>>:
        Body 'EOL' Stmt {
            flatten($1, $3)
        }
    |   Body 'EOL' { $1 }
    |   Stmt { Ok(vec![$1?]) }
    |   { Ok(Vec::new()) }
    ;

Stmt -> Result<Stmt>:
        Expr { Ok(Stmt::Expr($1?)) }
    |   Assign { Ok(Stmt::Assign($1?)) }
    |   Return { Ok(Stmt::Return($1?)) }
    ;

Assign -> Result<AssignStmt>:
        LhsExpr '=' Expr {
            Ok(AssignStmt { lhs: $1?, rhs: $3? })
        }
    ;

LhsExpr -> Result<LhsExpr>: 
        AccessExpr {
            let lhs = match $1? {
                Expr::Access(access) => LhsExpr::SetAttr(*access),
                Expr::Atom(Atom::Ident(local)) => LhsExpr::Name(local),
                _ => todo!("TODO : invalid syntax, raise error"),
            };
            Ok(lhs)
        }
    ;

Return -> Result<ReturnStmt>:
        'return' Expr { Ok(ReturnStmt { expr: Some($2?), }) }
    |   'return'      { Ok(ReturnStmt { expr: None, }) }
    ;

Expr -> Result<Expr>: BinExpr { $1 };

BinExpr -> Result<Expr>:
        UnExpr '||' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Or, $3?)) }
    |   UnExpr '&&' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::And, $3?)) }
    |   UnExpr '<' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Lt, $3?)) }
    |   UnExpr '>' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Gt, $3?)) }
    |   UnExpr '<=' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Le, $3?)) }
    |   UnExpr '>=' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Ge, $3?)) }
    |   UnExpr '==' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Eq, $3?)) }
    |   UnExpr '!=' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Neq, $3?)) }
    |   UnExpr '*' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Times, $3?)) }
    |   UnExpr '/' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Div, $3?)) }
    |   UnExpr '+' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Plus, $3?)) }
    |   UnExpr '-' BinExpr { Ok(BinExpr::new_expr($1?, BinOp::Plus, $3?)) }
    |   UnExpr { $1 }
    ;

UnExpr -> Result<Expr>:
        '+' UnExpr { Ok(UnExpr::new_expr(UnOp::Plus, $2?)) }
    |   '-' UnExpr { Ok(UnExpr::new_expr(UnOp::Minus, $2?)) }
    |   CallIndexExpr { $1 }
    ;

CallIndexExpr -> Result<Expr>:
        IndexExpr { $1 }
    |   CallExpr { $1 }
    |   AccessExpr { $1 }
    ;

CallExpr -> Result<Expr>:
        CallIndexExpr '(' FunArgs ')' {
            Ok(CallExpr::new_expr($1?, $3?))
        }
    ;

FunArgs -> Result<Vec<Expr>>:
        FunArgsTail { $1 }
    |   { Ok(Vec::new()) }
    ;

FunArgsTail -> Result<Vec<Expr>>:
        FunArgsTail ',' Expr { flatten($1, $3) }
    |   Expr { Ok(vec![$1?]) }
    ;

IndexExpr -> Result<Expr>:
        CallIndexExpr '[' Expr ']' {
            Ok(IndexExpr::new_expr($1?, $3?))
        }
    ;

AccessExpr -> Result<Expr>:
        FunExpr { $1 }
    |   CallIndexExpr '.' Ident { Ok(AccessExpr::new_expr($1?, $3?)) }
    ;

FunExpr -> Result<Expr>:
        AtomExpr { $1 }
    |   'fn' '(' FunParams ')' '{' Body '}' { Ok(FunExpr::new_expr($3?, $6?)) }
    ;

FunParams -> Result<Vec<String>>:
        FunParamsTail { $1 }
    |   { Ok(Vec::new()) }
    ;

FunParamsTail -> Result<Vec<String>>:
        FunParamsTail ',' Ident { flatten($1, $3) }
    |   Ident { Ok(vec![$1?]) }
    ;

AtomExpr -> Result<Expr>:
        Atom { $1.map(Expr::Atom) }
    |   '(' Expr ')' { $2 }
    ;

Atom -> Result<Atom>:
        Ident { Ok(Atom::Ident($1?)) }
    |   'SYM' {
            let v = $1.map_err(|_| ())?;
            let sym = &$lexer.span_str(v.span())[1..];
            Ok(Atom::Sym(sym.to_string()))
        }
    |   'NUM' {
            let v = $1.map_err(|_| ())?;
            let num_text = &$lexer.span_str(v.span());
            Ok(Atom::Num(num_text.parse().unwrap()))
        }
    |   'STRING' {
            let v = $1.map_err(|_| ())?;
            let string = &$lexer.span_str(v.span())[1..];
            Ok(Atom::String(parse_string(string)))
        }
    ;

Ident -> Result<String>:
        'IDENT' {
            let v = $1.map_err(|_| ())?;
            let ident = $lexer.span_str(v.span()).to_string();
            Ok(ident)
        }
    ;

%%

use crate::syn::ast::*;

type Result<T> = std::result::Result<T, ()>;

fn flatten<T>(head: Result<Vec<T>>, tail: Result<T>) -> Result<Vec<T>> {
    let mut head = head?;
    let tail = tail?;
    head.push(tail);
    Ok(head)
}

fn parse_string(input: &str) -> String {
    let mut s = String::new();
    let input = &input[..input.bytes().len() - 1];
    let mut chars = input.chars();
    while let Some(c) = chars.next() {
        if c == '\\' {
            let next = chars.next().unwrap();
            let c = match next {
                '\\' => '\\',
                '\'' => '\'',
                '"' => '"',
                'n' => '\n',
                't' => '\t',
                _ => unreachable!(),
            };
            s.push(c);
        } else {
            s.push(c);
        }
    }
    s
}