// Remove removes the exported value with handle id from the table, if present.
// If present, a check is performed that importer is the same one, registered
// with the table. If not, an error is returned.
func (exp *expTabl) Remove(id circuit.HandleID, importer n.Addr) {
	if importer == nil {
		panic("cannot remove perm handles from exp")
	}
	exp.lk.Lock()
	defer exp.lk.Unlock()

	exph, present := exp.id[id]
	if !present {
		return
	}
	if importer.WorkerID() != exph.Importer.WorkerID() {
		panic("releasing importer different than original")
	}
	delete(exp.id, id)

	impTabl, present := exp.nonperm[exph.Importer.WorkerID()]
	if !present {
		panic("missing importer map")
	}
	delete(impTabl, exph.Value.Interface())

	if len(impTabl) == 0 {
		delete(exp.nonperm, exph.Importer.WorkerID())
	}
}

func (exp *expTabl) RemoveImporter(importer n.Addr) {
	if importer == nil {
		panic("nil importer")
	}
	exp.lk.Lock()
	defer exp.lk.Unlock()

	impTabl, present := exp.nonperm[importer.WorkerID()]
	if !present {
		return
	}
	delete(exp.nonperm, importer.WorkerID())

	for _, exph := range impTabl {
		delete(exp.id, exph.ID)
	}
	runtime.GC()
}

func (d *Dialer) Dial(addr n.Addr) (conn n.Conn, err error) {
	d.Lock()
	defer d.Unlock()
	//
	workerID := addr.WorkerID()
	s, present := d.open[workerID]
	if !present {
		// Make new session to worker if one not present
		s = d.sub.DialSession(addr.(*Addr).TCP, func() {
			d.scrub(addr.WorkerID())
		})
		if err = d.auth(addr, s.Dial()); err != nil {
			s.Close()
			return nil, err
		}
		d.open[workerID] = s
		go d.watch(workerID, s) // Watch for idleness and close
	}
	return NewConn(s.Dial(), addr.(*Addr)), nil
}

// exportPtr returns *permPtrMsg if importer is nil, and *ptrMsg otherwise.
func (r *Runtime) exportPtr(v interface{}, importer n.Addr) interface{} {
	// Add exported value to export table
	exph := r.exp.Add(v, importer)
	// log.Printf("exporting %T with handle %s for importer %v", v, exph.ID.String(), importer)

	if importer == nil {
		return &permPtrMsg{ID: exph.ID, TypeID: exph.Type.ID}
	}

	// Monitor the importer for liveness.
	// DropPtr the handles upon importer death.
	r.lk.Lock()
	defer r.lk.Unlock()
	_, ok := r.live[importer.WorkerID()]
	if !ok {
		r.live[importer.WorkerID()] = struct{}{}

		// The anonymous function creates a "lifeline" connection to the worker importing v.
		// When this conncetion is broken, v is released.
		go func() {

			// Defer removal of v's handle from the export table to the end of this function
			defer func() {
				r.lk.Lock()
				delete(r.live, importer.WorkerID())
				r.lk.Unlock()
				// DropPtr/forget all exported handles
				r.exp.RemoveImporter(importer)
			}()

			conn, err := r.t.Dial(importer)
			if err != nil {
				// log.Println("problem dialing lifeline to", importer.String(), err.Error())
				return
			}
			defer conn.Close()

			if conn.Write(&dontReplyMsg{}) != nil {
				log.Println("problem writing on lifeline to", importer.String(), err.Error())
				return
			}
			// Read returns when the remote dies and
			// runs the conn into an error
			conn.Read()
		}()
	}
	return &ptrMsg{ID: exph.ID, TypeID: exph.Type.ID}
}

func (exp *expTabl) Add(receiver interface{}, importer n.Addr) *expHandle {
	if receiver == nil {
		panic("bug: nil receiver in export")
	}

	exp.lk.Lock()
	defer exp.lk.Unlock()

	// Is receiver already exported in the respective perm/nonperm fashion?
	var impHere bool
	var impTabl map[interface{}]*expHandle
	if importer != nil {
		// Non-permanent case
		impTabl, impHere = exp.nonperm[importer.WorkerID()]
		if impHere {
			exph, present := impTabl[receiver]
			if present {
				return exph
			}
		}
	} else {
		// Permanent case
		if exph, present := exp.perm[receiver]; present {
			return exph
		}
	}

	// Build exported handle object
	//fmt.Printf("recv (%#T): %#v\n", receiver, receiver)
	typ := exp.tt.TypeOf(receiver)
	if typ.Type != reflect.TypeOf(receiver) {
		panic("bug: wrong type")
	}
	exph := &expHandle{
		ID:       circuit.ChooseHandleID(),
		Importer: importer,
		Value:    reflect.ValueOf(receiver),
		Type:     typ,
	}

	// Insert in handle map
	if _, present := exp.id[exph.ID]; present {
		panic("handle id collision")
	}
	exp.id[exph.ID] = exph

	// Insert in value map
	if importer != nil {
		// Non-permanent case
		if !impHere {
			impTabl = make(map[interface{}]*expHandle)
			exp.nonperm[importer.WorkerID()] = impTabl
		}
		impTabl[receiver] = exph
	} else {
		// Permanent case
		exp.perm[receiver] = exph
	}

	return exph
}