diff --git a/vendor/github.com/looplab/fsm/.gitignore b/vendor/github.com/looplab/fsm/.gitignore
new file mode 100644
index 0000000..969bdaa
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/.gitignore
@@ -0,0 +1,28 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+
+*.sublime-project
+*.sublime-workspace
+
+.DS_Store
+.wercker
diff --git a/vendor/github.com/looplab/fsm/.travis.yml b/vendor/github.com/looplab/fsm/.travis.yml
new file mode 100644
index 0000000..b9b0eda
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/.travis.yml
@@ -0,0 +1,26 @@
+language: go
+
+go:
+  - "1.11"
+
+services:
+  - docker
+
+cache:
+  directories:
+    - ${GOPATH}/pkg/mod
+
+jobs:
+  include:
+    - stage: test
+      if: type == pull_request
+      script: make test
+      env:
+        - GO111MODULE=on
+
+    - stage: test_and_cover
+      name: "Test (with coverage)"
+      if: type != pull_request
+      script: make cover publish_cover
+      env:
+        - GO111MODULE=on
diff --git a/vendor/github.com/looplab/fsm/LICENSE b/vendor/github.com/looplab/fsm/LICENSE
new file mode 100644
index 0000000..37ec93a
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/LICENSE
@@ -0,0 +1,191 @@
+Apache License
+Version 2.0, January 2004
+http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+"License" shall mean the terms and conditions for use, reproduction, and
+distribution as defined by Sections 1 through 9 of this document.
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+"Licensor" shall mean the copyright owner or entity authorized by the copyright
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+"Contributor" shall mean Licensor and any individual or Legal Entity on behalf
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+
+5. Submission of Contributions.
+
+Unless You explicitly state otherwise, any Contribution intentionally submitted
+for inclusion in the Work by You to the Licensor shall be under the terms and
+conditions of this License, without any additional terms or conditions.
+Notwithstanding the above, nothing herein shall supersede or modify the terms of
+any separate license agreement you may have executed with Licensor regarding
+such Contributions.
+
+6. Trademarks.
+
+This License does not grant permission to use the trade names, trademarks,
+service marks, or product names of the Licensor, except as required for
+reasonable and customary use in describing the origin of the Work and
+reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty.
+
+Unless required by applicable law or agreed to in writing, Licensor provides the
+Work (and each Contributor provides its Contributions) on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied,
+including, without limitation, any warranties or conditions of TITLE,
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+solely responsible for determining the appropriateness of using or
+redistributing the Work and assume any risks associated with Your exercise of
+permissions under this License.
+
+8. Limitation of Liability.
+
+In no event and under no legal theory, whether in tort (including negligence),
+contract, or otherwise, unless required by applicable law (such as deliberate
+and grossly negligent acts) or agreed to in writing, shall any Contributor be
+liable to You for damages, including any direct, indirect, special, incidental,
+or consequential damages of any character arising as a result of this License or
+out of the use or inability to use the Work (including but not limited to
+damages for loss of goodwill, work stoppage, computer failure or malfunction, or
+any and all other commercial damages or losses), even if such Contributor has
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+offer, and charge a fee for, acceptance of support, warranty, indemnity, or
+other liability obligations and/or rights consistent with this License. However,
+in accepting such obligations, You may act only on Your own behalf and on Your
+sole responsibility, not on behalf of any other Contributor, and only if You
+agree to indemnify, defend, and hold each Contributor harmless for any liability
+incurred by, or claims asserted against, such Contributor by reason of your
+accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work
+
+To apply the Apache License to your work, attach the following boilerplate
+notice, with the fields enclosed by brackets "[]" replaced with your own
+identifying information. (Don't include the brackets!) The text should be
+enclosed in the appropriate comment syntax for the file format. We also
+recommend that a file or class name and description of purpose be included on
+the same "printed page" as the copyright notice for easier identification within
+third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/vendor/github.com/looplab/fsm/Makefile b/vendor/github.com/looplab/fsm/Makefile
new file mode 100644
index 0000000..6cad29f
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/Makefile
@@ -0,0 +1,22 @@
+default: services test
+
+.PHONY: test
+test:
+	go test ./...
+
+.PHONY: cover
+cover:
+	go list -f '{{if len .TestGoFiles}}"go test -coverprofile={{.Dir}}/.coverprofile {{.ImportPath}}"{{end}}' ./... | xargs -L 1 sh -c
+
+.PHONY: publish_cover
+publish_cover: cover
+	go get -d golang.org/x/tools/cmd/cover
+	go get github.com/modocache/gover
+	go get github.com/mattn/goveralls
+	gover
+	@goveralls -coverprofile=gover.coverprofile -service=travis-ci -repotoken=$(COVERALLS_TOKEN)
+
+.PHONY: clean
+clean:
+	@find . -name \.coverprofile -type f -delete
+	@rm -f gover.coverprofile
diff --git a/vendor/github.com/looplab/fsm/README.md b/vendor/github.com/looplab/fsm/README.md
new file mode 100644
index 0000000..f07e5eb
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/README.md
@@ -0,0 +1,117 @@
+[![Build Status](https://travis-ci.com/looplab/fsm.svg?branch=master)](https://travis-ci.com/looplab/fsm)
+[![Coverage Status](https://img.shields.io/coveralls/looplab/fsm.svg)](https://coveralls.io/r/looplab/fsm)
+[![GoDoc](https://godoc.org/github.com/looplab/fsm?status.svg)](https://godoc.org/github.com/looplab/fsm)
+[![Go Report Card](https://goreportcard.com/badge/looplab/fsm)](https://goreportcard.com/report/looplab/fsm)
+
+# FSM for Go
+
+FSM is a finite state machine for Go.
+
+It is heavily based on two FSM implementations:
+
+- Javascript Finite State Machine, https://github.com/jakesgordon/javascript-state-machine
+
+- Fysom for Python, https://github.com/oxplot/fysom (forked at https://github.com/mriehl/fysom)
+
+For API docs and examples see http://godoc.org/github.com/looplab/fsm
+
+# Basic Example
+
+From examples/simple.go:
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/looplab/fsm"
+)
+
+func main() {
+    fsm := fsm.NewFSM(
+        "closed",
+        fsm.Events{
+            {Name: "open", Src: []string{"closed"}, Dst: "open"},
+            {Name: "close", Src: []string{"open"}, Dst: "closed"},
+        },
+        fsm.Callbacks{},
+    )
+
+    fmt.Println(fsm.Current())
+
+    err := fsm.Event("open")
+    if err != nil {
+        fmt.Println(err)
+    }
+
+    fmt.Println(fsm.Current())
+
+    err = fsm.Event("close")
+    if err != nil {
+        fmt.Println(err)
+    }
+
+    fmt.Println(fsm.Current())
+}
+```
+
+# Usage as a struct field
+
+From examples/struct.go:
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/looplab/fsm"
+)
+
+type Door struct {
+    To  string
+    FSM *fsm.FSM
+}
+
+func NewDoor(to string) *Door {
+    d := &Door{
+        To: to,
+    }
+
+    d.FSM = fsm.NewFSM(
+        "closed",
+        fsm.Events{
+            {Name: "open", Src: []string{"closed"}, Dst: "open"},
+            {Name: "close", Src: []string{"open"}, Dst: "closed"},
+        },
+        fsm.Callbacks{
+            "enter_state": func(e *fsm.Event) { d.enterState(e) },
+        },
+    )
+
+    return d
+}
+
+func (d *Door) enterState(e *fsm.Event) {
+    fmt.Printf("The door to %s is %s\n", d.To, e.Dst)
+}
+
+func main() {
+    door := NewDoor("heaven")
+
+    err := door.FSM.Event("open")
+    if err != nil {
+        fmt.Println(err)
+    }
+
+    err = door.FSM.Event("close")
+    if err != nil {
+        fmt.Println(err)
+    }
+}
+```
+
+# License
+
+FSM is licensed under Apache License 2.0
+
+http://www.apache.org/licenses/LICENSE-2.0
diff --git a/vendor/github.com/looplab/fsm/errors.go b/vendor/github.com/looplab/fsm/errors.go
new file mode 100644
index 0000000..9c32a49
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/errors.go
@@ -0,0 +1,100 @@
+// Copyright (c) 2013 - Max Persson <max@looplab.se>
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fsm
+
+// InvalidEventError is returned by FSM.Event() when the event cannot be called
+// in the current state.
+type InvalidEventError struct {
+	Event string
+	State string
+}
+
+func (e InvalidEventError) Error() string {
+	return "event " + e.Event + " inappropriate in current state " + e.State
+}
+
+// UnknownEventError is returned by FSM.Event() when the event is not defined.
+type UnknownEventError struct {
+	Event string
+}
+
+func (e UnknownEventError) Error() string {
+	return "event " + e.Event + " does not exist"
+}
+
+// InTransitionError is returned by FSM.Event() when an asynchronous transition
+// is already in progress.
+type InTransitionError struct {
+	Event string
+}
+
+func (e InTransitionError) Error() string {
+	return "event " + e.Event + " inappropriate because previous transition did not complete"
+}
+
+// NotInTransitionError is returned by FSM.Transition() when an asynchronous
+// transition is not in progress.
+type NotInTransitionError struct{}
+
+func (e NotInTransitionError) Error() string {
+	return "transition inappropriate because no state change in progress"
+}
+
+// NoTransitionError is returned by FSM.Event() when no transition have happened,
+// for example if the source and destination states are the same.
+type NoTransitionError struct {
+	Err error
+}
+
+func (e NoTransitionError) Error() string {
+	if e.Err != nil {
+		return "no transition with error: " + e.Err.Error()
+	}
+	return "no transition"
+}
+
+// CanceledError is returned by FSM.Event() when a callback have canceled a
+// transition.
+type CanceledError struct {
+	Err error
+}
+
+func (e CanceledError) Error() string {
+	if e.Err != nil {
+		return "transition canceled with error: " + e.Err.Error()
+	}
+	return "transition canceled"
+}
+
+// AsyncError is returned by FSM.Event() when a callback have initiated an
+// asynchronous state transition.
+type AsyncError struct {
+	Err error
+}
+
+func (e AsyncError) Error() string {
+	if e.Err != nil {
+		return "async started with error: " + e.Err.Error()
+	}
+	return "async started"
+}
+
+// InternalError is returned by FSM.Event() and should never occur. It is a
+// probably because of a bug.
+type InternalError struct{}
+
+func (e InternalError) Error() string {
+	return "internal error on state transition"
+}
diff --git a/vendor/github.com/looplab/fsm/event.go b/vendor/github.com/looplab/fsm/event.go
new file mode 100644
index 0000000..fdca2d0
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/event.go
@@ -0,0 +1,62 @@
+// Copyright (c) 2013 - Max Persson <max@looplab.se>
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fsm
+
+// Event is the info that get passed as a reference in the callbacks.
+type Event struct {
+	// FSM is a reference to the current FSM.
+	FSM *FSM
+
+	// Event is the event name.
+	Event string
+
+	// Src is the state before the transition.
+	Src string
+
+	// Dst is the state after the transition.
+	Dst string
+
+	// Err is an optional error that can be returned from a callback.
+	Err error
+
+	// Args is a optinal list of arguments passed to the callback.
+	Args []interface{}
+
+	// canceled is an internal flag set if the transition is canceled.
+	canceled bool
+
+	// async is an internal flag set if the transition should be asynchronous
+	async bool
+}
+
+// Cancel can be called in before_<EVENT> or leave_<STATE> to cancel the
+// current transition before it happens. It takes an opitonal error, which will
+// overwrite e.Err if set before.
+func (e *Event) Cancel(err ...error) {
+	e.canceled = true
+
+	if len(err) > 0 {
+		e.Err = err[0]
+	}
+}
+
+// Async can be called in leave_<STATE> to do an asynchronous state transition.
+//
+// The current state transition will be on hold in the old state until a final
+// call to Transition is made. This will comlete the transition and possibly
+// call the other callbacks.
+func (e *Event) Async() {
+	e.async = true
+}
diff --git a/vendor/github.com/looplab/fsm/fsm.go b/vendor/github.com/looplab/fsm/fsm.go
new file mode 100644
index 0000000..9da9db3
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/fsm.go
@@ -0,0 +1,447 @@
+// Copyright (c) 2013 - Max Persson <max@looplab.se>
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package fsm implements a finite state machine.
+//
+// It is heavily based on two FSM implementations:
+//
+// Javascript Finite State Machine
+// https://github.com/jakesgordon/javascript-state-machine
+//
+// Fysom for Python
+// https://github.com/oxplot/fysom (forked at https://github.com/mriehl/fysom)
+//
+package fsm
+
+import (
+	"strings"
+	"sync"
+)
+
+// transitioner is an interface for the FSM's transition function.
+type transitioner interface {
+	transition(*FSM) error
+}
+
+// FSM is the state machine that holds the current state.
+//
+// It has to be created with NewFSM to function properly.
+type FSM struct {
+	// current is the state that the FSM is currently in.
+	current string
+
+	// transitions maps events and source states to destination states.
+	transitions map[eKey]string
+
+	// callbacks maps events and targers to callback functions.
+	callbacks map[cKey]Callback
+
+	// transition is the internal transition functions used either directly
+	// or when Transition is called in an asynchronous state transition.
+	transition func()
+	// transitionerObj calls the FSM's transition() function.
+	transitionerObj transitioner
+
+	// stateMu guards access to the current state.
+	stateMu sync.RWMutex
+	// eventMu guards access to Event() and Transition().
+	eventMu sync.Mutex
+}
+
+// EventDesc represents an event when initializing the FSM.
+//
+// The event can have one or more source states that is valid for performing
+// the transition. If the FSM is in one of the source states it will end up in
+// the specified destination state, calling all defined callbacks as it goes.
+type EventDesc struct {
+	// Name is the event name used when calling for a transition.
+	Name string
+
+	// Src is a slice of source states that the FSM must be in to perform a
+	// state transition.
+	Src []string
+
+	// Dst is the destination state that the FSM will be in if the transition
+	// succeds.
+	Dst string
+}
+
+// Callback is a function type that callbacks should use. Event is the current
+// event info as the callback happens.
+type Callback func(*Event)
+
+// Events is a shorthand for defining the transition map in NewFSM.
+type Events []EventDesc
+
+// Callbacks is a shorthand for defining the callbacks in NewFSM.a
+type Callbacks map[string]Callback
+
+// NewFSM constructs a FSM from events and callbacks.
+//
+// The events and transitions are specified as a slice of Event structs
+// specified as Events. Each Event is mapped to one or more internal
+// transitions from Event.Src to Event.Dst.
+//
+// Callbacks are added as a map specified as Callbacks where the key is parsed
+// as the callback event as follows, and called in the same order:
+//
+// 1. before_<EVENT> - called before event named <EVENT>
+//
+// 2. before_event - called before all events
+//
+// 3. leave_<OLD_STATE> - called before leaving <OLD_STATE>
+//
+// 4. leave_state - called before leaving all states
+//
+// 5. enter_<NEW_STATE> - called after entering <NEW_STATE>
+//
+// 6. enter_state - called after entering all states
+//
+// 7. after_<EVENT> - called after event named <EVENT>
+//
+// 8. after_event - called after all events
+//
+// There are also two short form versions for the most commonly used callbacks.
+// They are simply the name of the event or state:
+//
+// 1. <NEW_STATE> - called after entering <NEW_STATE>
+//
+// 2. <EVENT> - called after event named <EVENT>
+//
+// If both a shorthand version and a full version is specified it is undefined
+// which version of the callback will end up in the internal map. This is due
+// to the psuedo random nature of Go maps. No checking for multiple keys is
+// currently performed.
+func NewFSM(initial string, events []EventDesc, callbacks map[string]Callback) *FSM {
+	f := &FSM{
+		transitionerObj: &transitionerStruct{},
+		current:         initial,
+		transitions:     make(map[eKey]string),
+		callbacks:       make(map[cKey]Callback),
+	}
+
+	// Build transition map and store sets of all events and states.
+	allEvents := make(map[string]bool)
+	allStates := make(map[string]bool)
+	for _, e := range events {
+		for _, src := range e.Src {
+			f.transitions[eKey{e.Name, src}] = e.Dst
+			allStates[src] = true
+			allStates[e.Dst] = true
+		}
+		allEvents[e.Name] = true
+	}
+
+	// Map all callbacks to events/states.
+	for name, fn := range callbacks {
+		var target string
+		var callbackType int
+
+		switch {
+		case strings.HasPrefix(name, "before_"):
+			target = strings.TrimPrefix(name, "before_")
+			if target == "event" {
+				target = ""
+				callbackType = callbackBeforeEvent
+			} else if _, ok := allEvents[target]; ok {
+				callbackType = callbackBeforeEvent
+			}
+		case strings.HasPrefix(name, "leave_"):
+			target = strings.TrimPrefix(name, "leave_")
+			if target == "state" {
+				target = ""
+				callbackType = callbackLeaveState
+			} else if _, ok := allStates[target]; ok {
+				callbackType = callbackLeaveState
+			}
+		case strings.HasPrefix(name, "enter_"):
+			target = strings.TrimPrefix(name, "enter_")
+			if target == "state" {
+				target = ""
+				callbackType = callbackEnterState
+			} else if _, ok := allStates[target]; ok {
+				callbackType = callbackEnterState
+			}
+		case strings.HasPrefix(name, "after_"):
+			target = strings.TrimPrefix(name, "after_")
+			if target == "event" {
+				target = ""
+				callbackType = callbackAfterEvent
+			} else if _, ok := allEvents[target]; ok {
+				callbackType = callbackAfterEvent
+			}
+		default:
+			target = name
+			if _, ok := allStates[target]; ok {
+				callbackType = callbackEnterState
+			} else if _, ok := allEvents[target]; ok {
+				callbackType = callbackAfterEvent
+			}
+		}
+
+		if callbackType != callbackNone {
+			f.callbacks[cKey{target, callbackType}] = fn
+		}
+	}
+
+	return f
+}
+
+// Current returns the current state of the FSM.
+func (f *FSM) Current() string {
+	f.stateMu.RLock()
+	defer f.stateMu.RUnlock()
+	return f.current
+}
+
+// Is returns true if state is the current state.
+func (f *FSM) Is(state string) bool {
+	f.stateMu.RLock()
+	defer f.stateMu.RUnlock()
+	return state == f.current
+}
+
+// SetState allows the user to move to the given state from current state.
+// The call does not trigger any callbacks, if defined.
+func (f *FSM) SetState(state string) {
+	f.stateMu.Lock()
+	defer f.stateMu.Unlock()
+	f.current = state
+	return
+}
+
+// Can returns true if event can occur in the current state.
+func (f *FSM) Can(event string) bool {
+	f.stateMu.RLock()
+	defer f.stateMu.RUnlock()
+	_, ok := f.transitions[eKey{event, f.current}]
+	return ok && (f.transition == nil)
+}
+
+// AvailableTransitions returns a list of transitions avilable in the
+// current state.
+func (f *FSM) AvailableTransitions() []string {
+	f.stateMu.RLock()
+	defer f.stateMu.RUnlock()
+	var transitions []string
+	for key := range f.transitions {
+		if key.src == f.current {
+			transitions = append(transitions, key.event)
+		}
+	}
+	return transitions
+}
+
+// Cannot returns true if event can not occure in the current state.
+// It is a convenience method to help code read nicely.
+func (f *FSM) Cannot(event string) bool {
+	return !f.Can(event)
+}
+
+// Event initiates a state transition with the named event.
+//
+// The call takes a variable number of arguments that will be passed to the
+// callback, if defined.
+//
+// It will return nil if the state change is ok or one of these errors:
+//
+// - event X inappropriate because previous transition did not complete
+//
+// - event X inappropriate in current state Y
+//
+// - event X does not exist
+//
+// - internal error on state transition
+//
+// The last error should never occur in this situation and is a sign of an
+// internal bug.
+func (f *FSM) Event(event string, args ...interface{}) error {
+	f.eventMu.Lock()
+	defer f.eventMu.Unlock()
+
+	f.stateMu.RLock()
+	defer f.stateMu.RUnlock()
+
+	if f.transition != nil {
+		return InTransitionError{event}
+	}
+
+	dst, ok := f.transitions[eKey{event, f.current}]
+	if !ok {
+		for ekey := range f.transitions {
+			if ekey.event == event {
+				return InvalidEventError{event, f.current}
+			}
+		}
+		return UnknownEventError{event}
+	}
+
+	e := &Event{f, event, f.current, dst, nil, args, false, false}
+
+	err := f.beforeEventCallbacks(e)
+	if err != nil {
+		return err
+	}
+
+	if f.current == dst {
+		f.afterEventCallbacks(e)
+		return NoTransitionError{e.Err}
+	}
+
+	// Setup the transition, call it later.
+	f.transition = func() {
+		f.stateMu.Lock()
+		f.current = dst
+		f.stateMu.Unlock()
+
+		f.enterStateCallbacks(e)
+		f.afterEventCallbacks(e)
+	}
+
+	if err = f.leaveStateCallbacks(e); err != nil {
+		if _, ok := err.(CanceledError); ok {
+			f.transition = nil
+		}
+		return err
+	}
+
+	// Perform the rest of the transition, if not asynchronous.
+	f.stateMu.RUnlock()
+	err = f.doTransition()
+	f.stateMu.RLock()
+	if err != nil {
+		return InternalError{}
+	}
+
+	return e.Err
+}
+
+// Transition wraps transitioner.transition.
+func (f *FSM) Transition() error {
+	f.eventMu.Lock()
+	defer f.eventMu.Unlock()
+	return f.doTransition()
+}
+
+// doTransition wraps transitioner.transition.
+func (f *FSM) doTransition() error {
+	return f.transitionerObj.transition(f)
+}
+
+// transitionerStruct is the default implementation of the transitioner
+// interface. Other implementations can be swapped in for testing.
+type transitionerStruct struct{}
+
+// Transition completes an asynchrounous state change.
+//
+// The callback for leave_<STATE> must prviously have called Async on its
+// event to have initiated an asynchronous state transition.
+func (t transitionerStruct) transition(f *FSM) error {
+	if f.transition == nil {
+		return NotInTransitionError{}
+	}
+	f.transition()
+	f.transition = nil
+	return nil
+}
+
+// beforeEventCallbacks calls the before_ callbacks, first the named then the
+// general version.
+func (f *FSM) beforeEventCallbacks(e *Event) error {
+	if fn, ok := f.callbacks[cKey{e.Event, callbackBeforeEvent}]; ok {
+		fn(e)
+		if e.canceled {
+			return CanceledError{e.Err}
+		}
+	}
+	if fn, ok := f.callbacks[cKey{"", callbackBeforeEvent}]; ok {
+		fn(e)
+		if e.canceled {
+			return CanceledError{e.Err}
+		}
+	}
+	return nil
+}
+
+// leaveStateCallbacks calls the leave_ callbacks, first the named then the
+// general version.
+func (f *FSM) leaveStateCallbacks(e *Event) error {
+	if fn, ok := f.callbacks[cKey{f.current, callbackLeaveState}]; ok {
+		fn(e)
+		if e.canceled {
+			return CanceledError{e.Err}
+		} else if e.async {
+			return AsyncError{e.Err}
+		}
+	}
+	if fn, ok := f.callbacks[cKey{"", callbackLeaveState}]; ok {
+		fn(e)
+		if e.canceled {
+			return CanceledError{e.Err}
+		} else if e.async {
+			return AsyncError{e.Err}
+		}
+	}
+	return nil
+}
+
+// enterStateCallbacks calls the enter_ callbacks, first the named then the
+// general version.
+func (f *FSM) enterStateCallbacks(e *Event) {
+	if fn, ok := f.callbacks[cKey{f.current, callbackEnterState}]; ok {
+		fn(e)
+	}
+	if fn, ok := f.callbacks[cKey{"", callbackEnterState}]; ok {
+		fn(e)
+	}
+}
+
+// afterEventCallbacks calls the after_ callbacks, first the named then the
+// general version.
+func (f *FSM) afterEventCallbacks(e *Event) {
+	if fn, ok := f.callbacks[cKey{e.Event, callbackAfterEvent}]; ok {
+		fn(e)
+	}
+	if fn, ok := f.callbacks[cKey{"", callbackAfterEvent}]; ok {
+		fn(e)
+	}
+}
+
+const (
+	callbackNone int = iota
+	callbackBeforeEvent
+	callbackLeaveState
+	callbackEnterState
+	callbackAfterEvent
+)
+
+// cKey is a struct key used for keeping the callbacks mapped to a target.
+type cKey struct {
+	// target is either the name of a state or an event depending on which
+	// callback type the key refers to. It can also be "" for a non-targeted
+	// callback like before_event.
+	target string
+
+	// callbackType is the situation when the callback will be run.
+	callbackType int
+}
+
+// eKey is a struct key used for storing the transition map.
+type eKey struct {
+	// event is the name of the event that the keys refers to.
+	event string
+
+	// src is the source from where the event can transition.
+	src string
+}
diff --git a/vendor/github.com/looplab/fsm/go.mod b/vendor/github.com/looplab/fsm/go.mod
new file mode 100644
index 0000000..4ae0575
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/go.mod
@@ -0,0 +1 @@
+module github.com/looplab/fsm
diff --git a/vendor/github.com/looplab/fsm/utils.go b/vendor/github.com/looplab/fsm/utils.go
new file mode 100644
index 0000000..e49892e
--- /dev/null
+++ b/vendor/github.com/looplab/fsm/utils.go
@@ -0,0 +1,45 @@
+package fsm
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// Visualize outputs a visualization of a FSM in Graphviz format.
+func Visualize(fsm *FSM) string {
+	var buf bytes.Buffer
+
+	states := make(map[string]int)
+
+	buf.WriteString(fmt.Sprintf(`digraph fsm {`))
+	buf.WriteString("\n")
+
+	// make sure the initial state is at top
+	for k, v := range fsm.transitions {
+		if k.src == fsm.current {
+			states[k.src]++
+			states[v]++
+			buf.WriteString(fmt.Sprintf(`    "%s" -> "%s" [ label = "%s" ];`, k.src, v, k.event))
+			buf.WriteString("\n")
+		}
+	}
+
+	for k, v := range fsm.transitions {
+		if k.src != fsm.current {
+			states[k.src]++
+			states[v]++
+			buf.WriteString(fmt.Sprintf(`    "%s" -> "%s" [ label = "%s" ];`, k.src, v, k.event))
+			buf.WriteString("\n")
+		}
+	}
+
+	buf.WriteString("\n")
+
+	for k := range states {
+		buf.WriteString(fmt.Sprintf(`    "%s";`, k))
+		buf.WriteString("\n")
+	}
+	buf.WriteString(fmt.Sprintln("}"))
+
+	return buf.String()
+}