use std::str::FromStr;
use crate::ast;
use crate::types;

grammar;


pub LiteralInt: ast::LiteralInt = {
    <literal:r"[0-9]+"> => ast::LiteralInt{value: i64::from_str(literal).unwrap()}
};

pub Identifier: ast::Identifier = {
    <i:r"[A-Za-z][A-Za-z0-9_]*"> => ast::Identifier{name: i.to_string()}
};

pub FunctionCall: ast::FunctionCall = {
    <i:Spanned<Identifier>> "(" <args:Comma<Spanned<Expression>>> ")" => ast::FunctionCall{name:i, arguments: args}
}

pub Expression: Box<ast::Expression> = {
    <l:Spanned<Expression>> "+" <r:Spanned<Factor>> => Box::new(ast::Expression::Op(ast::Operation{left: l, op: ast::Operator::Plus, right: r})),
    <l:Spanned<Expression>> "-" <r:Spanned<Factor>> => Box::new(ast::Expression::Op(ast::Operation{left: l, op: ast::Operator::Minus, right: r})),
    Factor,
}

pub Factor: Box<ast::Expression> = {
    <l:Spanned<Factor>> "*" <r:Spanned<Term>> => Box::new(ast::Expression::Op(ast::Operation{left: l, op: ast::Operator::Mul, right: r})),
    <l:Spanned<Factor>> "/" <r:Spanned<Term>> => Box::new(ast::Expression::Op(ast::Operation{left: l, op: ast::Operator::Div, right: r})),
    Term,
}

pub Term: Box<ast::Expression> = {
    Spanned<LiteralInt> => Box::new(ast::Expression::LiteralInt(<>)),
    Spanned<Identifier> => Box::new(ast::Expression::Identifier(<>)),
    Spanned<FunctionCall> => Box::new(ast::Expression::FunctionCall(<>)),
    "(" <e:Expression> ")" => e
}

pub LetStatement: ast::Assignment = {
    //TODO: support destructuring with tuples, when they exist.
    //TODO: add mut, weak
    "let" <n:Spanned<Identifier>> "=" <e:Spanned<Expression>> => ast::Assignment{name: n, type_usage: None, expression: e},
    "let" <n:Spanned<Identifier>> ":" <t:Spanned<TypeUsage>> "=" <e:Spanned<Expression>> => ast::Assignment{name: n, type_usage: Some(t), expression: e},
}

pub Statement: ast::Statement = {
    <l:Spanned<LetStatement>> => ast::Statement::Assignment(l),
    <e:Spanned<Expression>> => ast::Statement::Expression(e),
}

pub Block: ast::Block = {
    "{" <s:LineDelimiter<Spanned<Statement>>> "}" => ast::Block{statements: s}
}

pub TypeUsage: ast::TypeUsage = {
    <n:Spanned<Identifier>> => ast::TypeUsage{name: n, ty: types::SpecifiedType::Unknown}
}

pub VariableDeclaration: ast::VariableDeclaration = {
    <i:Spanned<Identifier>> ":" <t:Spanned<TypeUsage>> => ast::VariableDeclaration{name: i, type_usage: t},
}

pub Function: ast::Function = {
    "fn" <n:Spanned<Identifier>> "(" <args:Comma<VariableDeclaration>> ")" <rt:Spanned<TypeUsage>> <b:Block> => ast::Function{name: n, arguments: args, block: b, return_type: rt}
}


pub Module: ast::Module = {
    <fs:Function*> => ast::Module{functions: fs}
}


// From https://lalrpop.github.io/lalrpop/tutorial/006_macros.html
// Comma seperated list of T with optional trailing comma
Comma<T>: Vec<T> = {
    <v:(<T> ",")*> <e:T?> => match e {
        None => v,
        Some(e) => {
            let mut v = v;
            v.push(e);
            v
        }
    }
};


LineDelimiter<T>: Vec<T> = {
    <v:(<T> r"\n|;")*> <e:T> => {
        let mut v = v;
        v.push(e);
        v
    }
};


Spanned<Rule>: ast::Spanned<Rule> = {
  <l: @L> <rule: Rule> <r: @R> => ast::Spanned{span: ast::Span{left: l, right: r}, value: rule}
};