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    //! Wayland objects map

    use {Interface, MessageGroup, NoMessage};

    /// Limit separating server-created from client-created objects IDs in the namespace
    pub const SERVER_ID_LIMIT: u32 = 0xFF000000;

    /// A trait representing the metadata a wayland implementation
    /// may attach to an object.
    pub trait ObjectMetadata: Clone {
        /// Create the metadata for a child object
        ///
        /// Mostly needed for client side, to propagate the event queues
        fn child(&self) -> Self;
    }

    impl ObjectMetadata for () {
        fn child(&self) -> () {
            ()
        }
    }

    /// The representation of a protocol object
    #[derive(Clone)]
    pub struct Object<Meta: ObjectMetadata> {
        /// Interface name of this object
        pub interface: &'static str,
        /// Version of this object
        pub version: u32,
        /// Description of the requests of this object
        pub requests: &'static [::wire::MessageDesc],
        /// Description of the events of this object
        pub events: &'static [::wire::MessageDesc],
        /// Metadata associated to this object (ex: its event queue client side)
        pub meta: Meta,
        /// A function which, from an opcode, a version, and the Meta, creates a child
        /// object associated with this event if any
        pub childs_from_events: fn(u16, u32, &Meta) -> Option<Object<Meta>>,
        /// A function which, from an opcode, a version, and the Meta, creates a child
        /// object associated with this request if any
        pub childs_from_requests: fn(u16, u32, &Meta) -> Option<Object<Meta>>,
    }

    impl<Meta: ObjectMetadata> Object<Meta> {
        /// Create an Object corresponding to given interface and version
        pub fn from_interface<I: Interface>(version: u32, meta: Meta) -> Object<Meta> {
            Object {
                interface: I::NAME,
                version: version,
                requests: I::Request::MESSAGES,
                events: I::Event::MESSAGES,
                meta: meta,
                childs_from_events: childs_from::<I::Event, Meta>,
                childs_from_requests: childs_from::<I::Request, Meta>,
            }
        }

        /// Create an optional `Object` corresponding to the possible `new_id` associated
        /// with given event opcode
        pub fn event_child(&self, opcode: u16) -> Option<Object<Meta>> {
            (self.childs_from_events)(opcode, self.version, &self.meta)
        }

        /// Create an optional `Object` corresponding to the possible `new_id` associated
        /// with given request opcode
        pub fn request_child(&self, opcode: u16) -> Option<Object<Meta>> {
            (self.childs_from_requests)(opcode, self.version, &self.meta)
        }

        /// Check whether this object is of given interface
        pub fn is_interface<I: Interface>(&self) -> bool {
            // TODO: we might want to be more robust than that
            self.interface == I::NAME
        }

        /// Create a placeholder object that will be filled-in by the message logic
        pub fn placeholder(meta: Meta) -> Object<Meta> {
            Object {
                interface: "",
                version: 0,
                requests: &[],
                events: &[],
                meta: meta,
                childs_from_events: childs_from::<NoMessage, Meta>,
                childs_from_requests: childs_from::<NoMessage, Meta>,
            }
        }
    }

    fn childs_from<M: MessageGroup, Meta: ObjectMetadata>(
        opcode: u16,
        version: u32,
        meta: &Meta,
    ) -> Option<Object<Meta>> {
        M::child(opcode, version, meta)
    }

    /// A holder for the object store of a connection
    ///
    /// Keeps track of which object id is associated to which
    /// interface object, and which is currently unused.
    pub struct ObjectMap<Meta: ObjectMetadata> {
        client_objects: Vec<Option<Object<Meta>>>,
        server_objects: Vec<Option<Object<Meta>>>,
    }

    impl<Meta: ObjectMetadata> ObjectMap<Meta> {
        /// Create a new empty object map
        pub fn new() -> ObjectMap<Meta> {
            ObjectMap {
                client_objects: Vec::new(),
                server_objects: Vec::new(),
            }
        }

        /// Find an object in the store
        pub fn find(&self, id: u32) -> Option<Object<Meta>> {
            if id >= SERVER_ID_LIMIT {
                self.server_objects
                    .get((id - SERVER_ID_LIMIT) as usize)
                    .and_then(|x| x.clone())
            } else {
                self.client_objects.get((id - 1) as usize).and_then(|x| x.clone())
            }
        }

        /// Remove an object from the store
        ///
        /// Does nothing if the object didn't previously exists
        pub fn remove(&mut self, id: u32) {
            if id >= SERVER_ID_LIMIT {
                if let Some(place) = self.server_objects.get_mut((id - SERVER_ID_LIMIT) as usize) {
                    *place = None;
                }
            } else {
                if let Some(place) = self.client_objects.get_mut((id - 1) as usize) {
                    *place = None;
                }
            }
        }

        /// Insert given object for given id
        ///
        /// Can fail if the requested id is not the next free id of this store.
        /// (In which case this is a protocol error)
        pub fn insert_at(&mut self, id: u32, object: Object<Meta>) -> Result<(), ()> {
            if id >= SERVER_ID_LIMIT {
                insert_in_at(&mut self.server_objects, (id - SERVER_ID_LIMIT) as usize, object)
            } else {
                insert_in_at(&mut self.client_objects, (id - 1) as usize, object)
            }
        }

        /// Allocate a new id for an object in the client namespace
        pub fn client_insert_new(&mut self, object: Object<Meta>) -> u32 {
            insert_in(&mut self.client_objects, object) + 1
        }

        /// Allocate a new id for an object in the server namespace
        pub fn server_insert_new(&mut self, object: Object<Meta>) -> u32 {
            insert_in(&mut self.server_objects, object) + SERVER_ID_LIMIT
        }

        /// Mutably access an object of the map
        pub fn with<T, F: FnOnce(&mut Object<Meta>) -> T>(&mut self, id: u32, f: F) -> Result<T, ()> {
            if id >= SERVER_ID_LIMIT {
                if let Some(&mut Some(ref mut obj)) = self.server_objects.get_mut((id - SERVER_ID_LIMIT) as usize)
                {
                    Ok(f(obj))
                } else {
                    Err(())
                }
            } else {
                if let Some(&mut Some(ref mut obj)) = self.client_objects.get_mut((id - 1) as usize) {
                    Ok(f(obj))
                } else {
                    Err(())
                }
            }
        }

        /// Mutably access all objects of the map in sequence
        pub fn with_all<F: FnMut(u32, &mut Object<Meta>)>(&mut self, mut f: F) {
            for (id, place) in self.client_objects.iter_mut().enumerate() {
                if let Some(ref mut obj) = *place {
                    f(id as u32 + 1, obj);
                }
            }
            for (id, place) in self.server_objects.iter_mut().enumerate() {
                if let Some(ref mut obj) = *place {
                    f(id as u32 + SERVER_ID_LIMIT, obj);
                }
            }
        }
    }

    // insert a new object in a store at the first free place
    fn insert_in<Meta: ObjectMetadata>(store: &mut Vec<Option<Object<Meta>>>, object: Object<Meta>) -> u32 {
        match store.iter().position(|o| o.is_none()) {
            Some(id) => {
                store[id] = Some(object);
                id as u32
            }
            None => {
                store.push(Some(object));
                (store.len() - 1) as u32
            }
        }
    }

    // insert an object at a given place in a store
    fn insert_in_at<Meta: ObjectMetadata>(
        store: &mut Vec<Option<Object<Meta>>>,
        id: usize,
        object: Object<Meta>,
    ) -> Result<(), ()> {
        if id > store.len() {
            Err(())
        } else if id == store.len() {
            store.push(Some(object));
            Ok(())
        } else {
            let previous = &mut store[id];
            if !previous.is_none() {
                return Err(());
            }
            *previous = Some(object);
            Ok(())
        }
    }

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