use crate::*;

pub struct When<T>(pub bool, pub T);

impl<S: Screen, T: Draw<S>> Draw<S> for When<T> {
    fn draw (&self, to: &mut S) -> Drawn<S::Unit> {
        #[cfg(feature = "prof")] profiling::scope!("when");
        if self.0 {
            self.1.draw(to)
        } else {
            Ok(Default::default())
        }
    }
}

impl<T> When<T> {

    fn_kw_layout!(interpret |state, output, expr| {
        #[cfg(feature = "prof")] profiling::scope!("kw_when");
        let thunk = draw(move|screen|ok_flat(expr.nth(2)?.map(|x|state.interpret(screen, x))));
        ok_flat(matches!(expr.head()?, Some("when")).then(||{
            when(state.namespace(&expr.nth(1)?)?.unwrap(), thunk).draw(output)
        }))
    });
}

/// Only render when condition is true.
///
/// ```
/// # use ::tengri::*; fn test <'a> () -> impl Draw<Tui> {
///     when(true, "Yes")
/// # }
/// ```
pub const fn when <'a, T: Screen> (condition: bool, item: impl Draw<T>) -> impl Draw<T> {
    When(condition, item)
}

fn_kw_layout!(kw_either |state, output, expr| {
    #[cfg(feature = "prof")] profiling::scope!("kw_layout");
    let thunk_a = draw(move|screen|ok_flat(expr.nth(2)?.map(|x|state.interpret(screen, x))));
    let thunk_b = draw(move|screen|ok_flat(expr.nth(3)?.map(|x|state.interpret(screen, x))));
    ok_flat(matches!(expr.head()?, Some("either")).then(||{
        either(state.namespace(&expr.nth(1)?)?.unwrap(), thunk_a, thunk_b).draw(output)
    }))
});

/// Render one thing if a condition is true and another false.
///
/// ```
/// # use ::tengri::*; fn test <'a> () -> impl Draw<Tui> {
///     either(true, "Yes", "No")
/// # }
/// ```
pub const fn either <'a, T: Screen> (
    condition: bool, a: impl Draw<T>, b: impl Draw<T>
) -> impl Draw<T> {
    draw(move|to: &mut T|{
        #[cfg(feature = "prof")] profiling::scope!("either");
        if condition { a.draw(to) } else { b.draw(to) }
    })
}