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// vim: shiftwidth=4 tabstop=4 noexpandtab
package main
import (
"log"
"time"
)
// This struct represents the statemachine.
type Machine struct {
name string
initial string
current string
states StateMap
api chan string
state_listeners []*(chan string)
}
type StateMap map[string]MachineState
type MachineState struct {
on TransitionMap
}
type TransitionMap map[string]MachineTransition
type MachineTransition struct {
to string
}
// This will run the statemachine (blocking).
func (m *Machine) Run() {
var event string
for {
event = <-m.api // read api (blocking)
m.processEvent(event)
}
}
// A simple Getter to retrieve the current state.
func (m Machine) GetState() string {
if m.current == "" {
return m.initial
}
return m.current
}
// This function blocks until the current state differs
// from the 'known' state. It then returns the current
// state.
func (m *Machine) GetStateOnChange(known string) string {
listener := make(chan string)
var current string
m.registerListener(&listener)
defer m.deregisterListener(&listener)
for {
if m.GetState() != known {
current = m.GetState()
break
}
current = <-listener
if current != known {
break
}
}
return current
}
// Use this function to send an event to the statemachine.
func (m *Machine) SendEvent(event string) {
m.api <- event // blocks until m.run() goroutine handles this event
}
func (m *Machine) registerListener(listener *(chan string)) {
m.state_listeners = append(m.state_listeners, listener)
}
func (m *Machine) deregisterListener(listener *(chan string)) {
wasRemoved := false
if len(m.state_listeners) == 0 {
log.Println("Not able to unregister listener from empty state_listener slice")
}
for index,item := range(m.state_listeners) {
if item == listener {
if index == len(m.state_listeners) - 1 {
m.state_listeners = m.state_listeners[: len(m.state_listeners) - 1]
} else {
m.state_listeners[index] = m.state_listeners[len(m.state_listeners) - 1]
m.state_listeners = m.state_listeners[: len(m.state_listeners) - 1]
}
wasRemoved = true
}
}
if !wasRemoved {
log.Println("Could not find listener in slice state_listeners")
}
}
func (m *Machine) processEvent(event string) string {
current := m.GetState()
next := m.states[current].on[event].to
if next != "" {
log.Printf("State machine '%s' changes from '%s' to '%s'\n", m.name, current, next)
m.current = next
m.runHooks(current, next)
return next
}
return current
}
// In this function one can implement callback functions
// which will be triggered on certain transitions.
func (m *Machine) runHooks(last string, next string) {
for _,listener := range(m.state_listeners) {
*listener <- next
}
if last == "idle" && next == "single_picture" {
// TODO implement launch of python subprocess here
go func() {
time.Sleep(1 * time.Second)
m.SendEvent("single_picture_taken")
}()
}
}
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