use egg::{RecExpr, Id};
use crate::language::EquationLanguage;

// there is already a Display implementation generated by define_langauge!
// but we want an alternative string conversion
pub fn print_term(expr: &RecExpr<EquationLanguage>) -> String {
	let root_id = Id::from(expr.as_ref().len()-1);
	print_term_inner(expr, root_id).0
}

// the second result is the precedence of the top level op: 1 = '+-', 2 = '*/', 3 = '^', 4 = primitive
fn print_term_inner(expr: &RecExpr<EquationLanguage>, id: Id) -> (String, usize) {
	match &expr[id] {
		EquationLanguage::Num(c) => {
			(format!("{}", c), if c.denom == 1 { 4 } else { 2 })
		},
		EquationLanguage::Neg([a]) => {
			(print_unary(expr, *a, "-", 1), 1)
		},
		EquationLanguage::Add([a,b]) => {
			(print_binary(expr, *a, *b, "+", 1), 1)
		},
		EquationLanguage::Sub([a,b]) => {
			(print_binary(expr, *a, *b, "-", 1), 1)
		},
		EquationLanguage::Mul([a,b]) => {
			(print_binary(expr, *a, *b, "*", 2), 2)
		},
		EquationLanguage::Div([a,b]) => {
			(print_binary(expr, *a, *b, "/", 2), 2)
		},
		EquationLanguage::Power([a,b]) => {
			(print_binary(expr, *a, *b, "^", 3), 3)
		},
		_ => unimplemented!()
	}
}

fn print_unary(expr: &RecExpr<EquationLanguage>, a: Id, op: &str, precedence: usize) -> String {
	let (astr, aprec) = print_term_inner(expr, a);

	if aprec > precedence {
		format!("{}{}", op, astr)
	} else {
		format!("{}({})", op, astr)
	}
}

fn print_binary(expr: &RecExpr<EquationLanguage>, a: Id, b: Id, op: &str, precedence: usize) -> String {
	let (astr, aprec) = print_term_inner(expr, a);
	let (bstr, bprec) = print_term_inner(expr, b);

	if aprec > precedence {
		if bprec > precedence {
			format!("{} {} {}", astr, op, bstr)
		} else {
			format!("{} {} ({})", astr, op, bstr)
		}
	} else {
		if bprec > precedence {
			format!("({}) {} {}", astr, op, bstr)
		} else {
			format!("({}) {} ({})", astr, op, bstr)
		}
	}
}