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use std::ptr;
use libc::c_void;
use chakracore_sys::*;
use context::ContextGuard;
use super::{Value, Object};

/// A JavaScript external object.
pub struct External(JsValueRef);

// TODO: Make the entire implementation generic
impl External {
    /// Creates a new object with external data.
    ///
    /// The object takes ownership of the resource. It is undetermined when, and
    /// even if, the destructor is called. It relies on the engine's finalize
    /// callback.
    ///
    /// As long as the object is referenced on the stack or in any script
    /// context, the `external` data will be kept alive (i.e it is not tied to
    /// the handle).
    pub fn new<T>(_guard: &ContextGuard, external: Box<T>) -> Self {
        let mut value = JsValueRef::new();
        unsafe {
            jsassert!(JsCreateExternalObject(Box::into_raw(external) as *mut _,
                                            Some(Self::finalize::<T>),
                                            &mut value));
            Self::from_raw(value)
        }
    }

    /// Creates a new object with external data.
    ///
    /// This is unsafe because the object does not take ownership of the
    /// resource. Therefore the data may become a dangling pointer. The caller
    /// is responsible for keeping the reference alive.
    pub unsafe fn from_ptr<T>(_guard: &ContextGuard, external: *mut T) -> Self {
        let mut value = JsValueRef::new();
        jsassert!(JsCreateExternalObject(external as *mut _,
                                         None,
                                         &mut value));
        Self::from_raw(value)
    }

    /// Returns the external object's data.
    pub unsafe fn value<T>(&self) -> &mut T {
        let mut data = ptr::null_mut();
        jsassert!(JsGetExternalData(self.as_raw(), &mut data));
        (data as *mut T).as_mut().expect("retrieving external data")
    }

    /// Returns true if the value is an `External`.
    pub fn is_same(value: &Value) -> bool {
        value.get_type() == JsValueType::Object && Self::has_external_data(value)
    }

    /// Returns whether the value has external data or not.
    fn has_external_data(value: &Value) -> bool {
        let mut result = false;
        jsassert!(unsafe { JsHasExternalData(value.as_raw(), &mut result) });
        result
    }

    /// A finalizer callback, triggered before an external is removed.
    unsafe extern "system" fn finalize<T>(data: *mut c_void) {
        Box::from_raw(data as *mut T);
    }
}

reference!(External);
inherit!(External, Object);
subtype!(External, Value);

#[cfg(test)]
mod tests {
    use {test, value};

    #[test]
    fn destructor() {
        static mut CALLED: bool = false;
        {
            struct Foo(i32);
            impl Drop for Foo {
                fn drop(&mut self) {
                    assert_eq!(self.0, 10);
                    unsafe { CALLED = true };
                }
            }

            test::run_with_context(|guard| {
                let _ = value::External::new(guard, Box::new(Foo(10)));
            });
        }
        assert!(unsafe { CALLED });
    }
}