Add ability to document FSM visually.

README.md

@@ -22,6 +22,31 @@ f.Transition(
 )
 ```
 
+_Visual simple event_:
+```mermaid
+flowchart LR
+	id0(StateBar)
+	id1(StateFoo)
+	id1--> |EventFoo| id0
+```
+
+Transitions can be triggered the second time an event occurs:
+
+```go
+f.Transition(
+    fsm.On(EventFoo), fsm.Src(StateFoo), fsm.Times(2),
+    fsm.Dst(StateBar),
+)
+```
+
+_Visual repeated event_:
+```mermaid
+flowchart LR
+	id0(StateBar)
+	id1(StateFoo)
+	id1--> |2 x EventFoo| id0
+```
+
 You can have custom checks or actions:
 
 ```go
@@ -35,15 +60,6 @@ f.Transition(
 )
 ```
 
-Transitions can be triggered the second time an event occurs:
-
-```go
-f.Transition(
-    fsm.On(EventFoo), fsm.Src(StateFoo), fsm.Times(2),
-    fsm.Dst(StateBar),
-)
-```
-
 Functions can be called when entering or leaving a state:
 
 ```go

cmd/doc.go

@@ -0,0 +1,68 @@
+//go:generate stringer -type=State,Event --output=doc_fsm_string.go
+//go:generate go run -tags doc doc.go doc_fsm_string.go ../README.md
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/cocoonspace/fsm"
+)
+
+type State fsm.State
+type Event fsm.Event
+
+func (s State) State() fsm.State {
+	return fsm.State(s)
+}
+
+func (e Event) Event() fsm.Event {
+	return fsm.Event(e)
+}
+
+var _ fsm.NamedState = (*State)(nil)
+var _ fsm.NamedEvent = (*Event)(nil)
+
+const (
+	StateFoo State = iota
+	StateBar
+)
+
+const (
+	EventFoo Event = iota
+)
+
+func example1() *fsm.FSM {
+	f := fsm.New(StateFoo.State())
+
+	f.Transition(
+		fsm.On(EventFoo),
+		fsm.Src(StateFoo),
+		fsm.Dst(StateBar),
+	)
+
+	return f
+}
+
+func example2() *fsm.FSM {
+	f := fsm.New(StateFoo.State())
+
+	f.Transition(
+		fsm.On(EventFoo),
+		fsm.Times(2),
+		fsm.Src(StateFoo),
+		fsm.Dst(StateBar),
+	)
+
+	return f
+}
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Println("use go generate")
+		return
+	}
+	example1().GenerateDoc("Visual simple event", os.Args[1])
+	example2().GenerateDoc("Visual repeated event", os.Args[1])
+}