use crate::*;

fn_kw_layout!(kw_when |state, output, expr| {
    let thunk = draw(move|screen|ok_flat(expr.nth(2)?.map(|x: &'a str|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<'a, Tui> {
///     when(true, "Yes")
/// # }
/// ```
pub const fn when <'a, T: Screen> (condition: bool, item: impl Draw<'a, T>) -> impl Draw<'a, T> {
    draw(move|to: &mut T|if condition { item.draw(to) } else { Ok(Default::default()) })
}

fn_kw_layout!(kw_either |state, output, expr| {
    let thunk_a = draw(move|screen|ok_flat(expr.nth(2)?.map(|x: &'a str|state.interpret(screen, x))));
    let thunk_b = draw(move|screen|ok_flat(expr.nth(3)?.map(|x: &'a str|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<'a, Tui> {
///     either(true, "Yes", "No")
/// # }
/// ```
pub const fn either <'a, T: Screen> (
    condition: bool, a: impl Draw<'a, T>, b: impl Draw<'a, T>
) -> impl Draw<'a, T> {
    draw(move|to: &mut T|if condition { a.draw(to) } else { b.draw(to) })
}