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//! Mocking utility actor
//! This actor wraps any actor, and replaces instances of that actor with mocker actor, which is
//! able to accept all messages which the actor can receive.
//!
//! Mocking is intended to be achieved by using a pattern similar to
//! ```rust,ignore
//! #[cfg(not(test))]
//! type DBClientAct = DBClientActor;
//! #[cfg(test)]
//! type DBClientAct = Mocker<DBClientActor>;
//! ```
//! Then, the actor should be used as a System Service (or Arbiter Service, but take care that all
//! the places which will use the mocked actor is on the same arbiter). Thus, in a test, it will
//! retrieve the mocker from the registry instead of the actual actor.
//!
//! To set the mock function in the actor, the init_actor function is used, which allows the state
//! of an actor to be set when it is started as a arbiter or system service. A closure which takes
//! Box<Any> is evaluated for every message, and must return Box<Any>, specifically the return type
//! for the message type send.
//!
//! See the mock example to see how it can be used.

use std::marker::PhantomData;
use std::any::Any;
use std::mem;

use prelude::*;
use handler::MessageResponse;

/// This actor is able to wrap another actor and accept all the messages the wrapped actor can,
/// passing it to a closure which can mock the response of the actors
pub struct Mocker<T: Sized + 'static>{
    phantom: PhantomData<T>,
    mock: Box<FnMut(Box<Any>, &mut Context<Mocker<T>>) -> Box<Any>>
}

impl<T> Mocker<T> {
    pub fn mock(mock: Box<FnMut(Box<Any>, &mut Context<Mocker<T>>) -> Box<Any>>) -> Mocker<T> {
        Mocker::<T> {
            phantom: PhantomData,
            mock
        }
    }
}

impl<T: SystemService> actix::SystemService for Mocker<T> {}
impl<T: ArbiterService> actix::ArbiterService for Mocker<T> {}
impl<T> Supervised for Mocker<T> {}

impl<T> Default for Mocker<T> {
    fn default() -> Self {
        panic!("Mocker actor used before set")
    }
}

impl<T: Sized + 'static> Actor for Mocker<T> {
    type Context = Context<Self>;
}

impl<M: 'static, T: Sized + 'static> Handler<M> for Mocker<T> where M: Message, <M as actix::Message>::Result: MessageResponse<Mocker<T>, M> {
    type Result = M::Result;
    fn handle(&mut self, msg: M, ctx: &mut Self::Context) -> M::Result {
        let mut ret = (self.mock)(Box::new(msg), ctx);
        let out = mem::replace(ret.downcast_mut::<Option<M::Result>>().expect("wrong return type for message"), None);
        match out {
            Some(a) => return a,
            _ => panic!()
        }
    }
}