macltok

use std::cell::RefCell;

type Handler = Box<dyn Fn(&str)>;

thread_local! {

    static HANDLER: RefCell<Option<Handler>> = const { RefCell::new(None) };

}

/// a panic on wasm32 traps the task that raised it and nothing unwinds, so the engine

/// catches nothing. the rest of it keeps running in an undefined state and goes silent,

/// no `Failed` and no `Stopped`. `handler` runs from the panic hook with the message,

/// after whatever hook was there before, and is the host's one chance to react, say by

/// terminating the worker and starting a fresh one. a second call replaces the handler

pub fn on_panic(handler: impl Fn(&str) + 'static) {

    let installed = HANDLER.with(|slot| slot.replace(Some(Box::new(handler))).is_some());

    if installed {

        return;

    }

    let previous = std::panic::take_hook();

    std::panic::set_hook(Box::new(move |info| {

        previous(info);

        let message = info.to_string();

        HANDLER.with(|slot| {

            if let Some(handler) = &*slot.borrow() {

                handler(&message);

            }

        });

    }));

}