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use crate::lua_generator::{LuaGenerator, ToLua};
use crate::nodes::Expression;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum UnaryOperator {
    Length,
    Minus,
    Not,
}

fn break_minus(last_string: &str) -> bool {
    if let Some(last_char) = last_string.chars().last() {
        last_char == '-'
    } else {
        false
    }
}

impl ToLua for UnaryOperator {
    fn to_lua(&self, generator: &mut LuaGenerator) {
        match self {
            Self::Length => generator.push_char('#'),
            Self::Minus => generator.push_char_and_break_if('-', break_minus),
            Self::Not => generator.push_str("not"),
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct UnaryExpression {
    operator: UnaryOperator,
    expression: Expression,
}

impl UnaryExpression {
    pub fn new(operator: UnaryOperator, expression: Expression) -> Self {
        Self {
            operator,
            expression,
        }
    }

    pub fn get_expression(&self) -> &Expression {
        &self.expression
    }

    pub fn mutate_expression(&mut self) -> &mut Expression {
        &mut self.expression
    }

    pub fn operator(&self) -> UnaryOperator {
        self.operator
    }
}

impl ToLua for UnaryExpression {
    fn to_lua(&self, generator: &mut LuaGenerator) {
        self.operator.to_lua(generator);

        match &self.expression {
            Expression::Binary(binary) if !binary.operator().precedes_unary_expression() => {
                generator.push_char('(');
                self.expression.to_lua(generator);
                generator.push_char(')');
            },
            _ => self.expression.to_lua(generator),
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::nodes::{BinaryExpression, BinaryOperator, DecimalNumber};

    #[test]
    fn generate_unary_expression() {
        let output = UnaryExpression::new(
            UnaryOperator::Not,
            Expression::True,
        ).to_lua_string();

        assert_eq!(output, "not true");
    }

    #[test]
    fn generate_two_unary_minus_breaks_between_them() {
        let output = UnaryExpression::new(
            UnaryOperator::Minus,
            UnaryExpression::new(
                UnaryOperator::Minus,
                Expression::Identifier("a".to_owned()),
            ).into(),
        ).to_lua_string();

        assert_eq!(output, "- -a");
    }

    #[test]
    fn wraps_in_parens_if_an_inner_binary_has_lower_precedence() {
        let output = UnaryExpression::new(
            UnaryOperator::Not,
            BinaryExpression::new(
                BinaryOperator::Or,
                Expression::False,
                Expression::True,
            ).into(),
        ).to_lua_string();

        assert_eq!(output, "not(false or true)");
    }

    #[test]
    fn does_not_wrap_in_parens_if_an_inner_binary_has_higher_precedence() {
        let output = UnaryExpression::new(
            UnaryOperator::Minus,
            BinaryExpression::new(
                BinaryOperator::Caret,
                DecimalNumber::new(2.0).into(),
                DecimalNumber::new(2.0).into(),
            ).into(),
        ).to_lua_string();

        assert_eq!(output, "-2^2");
    }
}