Metadata (looplab#63)

* added data feature

* added commit for NoDataError

* added NoDataError

* added data.go to demonstrate usage of data feature

* renamed data to metadata

* removed key level locks from metadata

* removed NoDataError

Co-authored-by: Aman Sai Ankam <aman.sai@PP-C02CP5SYMD6M.local>

examples/data.go

@@ -0,0 +1,49 @@
+// +build ignore
+
+package main
+
+import (
+	"fmt"
+
+	"github.com/looplab/fsm"
+)
+
+func main() {
+	fsm := fsm.NewFSM(
+		"idle",
+		fsm.Events{
+			{Name: "produce", Src: []string{"idle"}, Dst: "idle"},
+			{Name: "consume", Src: []string{"idle"}, Dst: "idle"},
+		},
+		fsm.Callbacks{
+			"produce": func(e *fsm.Event) {
+				e.FSM.SetMetadata("message", "hii")
+				fmt.Println("produced data")
+			},
+			"consume": func(e *fsm.Event) {
+				message, ok := e.FSM.Metadata("message")
+				if ok {
+					fmt.Println("message = " + message.(string))
+				}
+
+			},
+		},
+	)
+
+	fmt.Println(fsm.Current())
+
+	err := fsm.Event("produce")
+	if err != nil {
+		fmt.Println(err)
+	}
+
+	fmt.Println(fsm.Current())
+
+	err = fsm.Event("consume")
+	if err != nil {
+		fmt.Println(err)
+	}
+
+	fmt.Println(fsm.Current())
+
+}

fsm.go

@@ -44,10 +44,8 @@ type FSM struct {
 	// transitions maps events and source states to destination states.
 	transitions map[EventKey]string
 
-	// callbacks maps events and targers to callback functions.
-	callbacks map[CallbackKey]Callback
-
-	message map[EventKey]string
+	// callbacks maps events and targets 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.
@@ -61,6 +59,11 @@ type FSM struct {
 	stateMu sync.RWMutex
 	// eventMu guards access to Event() and Transition().
 	eventMu sync.Mutex
+	// metadata can be used to store and load data that maybe used across events
+	// use methods SetMetadata() and Metadata() to store and load data
+	metadata map[string]interface{}
+
+	metadataMu sync.RWMutex
 }
 
 // EventDesc represents an event when initializing the FSM.
@@ -133,9 +136,9 @@ func NewFSM(initial string, events []*EventDesc, callbacks map[string]Callback)
 	f := &FSM{
 		transitionerObj: &transitionerStruct{},
 		current:         initial,
-		transitions:     make(map[EventKey]string),
-		callbacks:       make(map[CallbackKey]Callback),
-		message:         make(map[EventKey]string),
+		transitions:     make(map[eKey]string),
+		callbacks:       make(map[cKey]Callback),
+		metadata:        make(map[string]interface{}),
 	}
 
 	// Build transition map and store sets of all events and states.
@@ -253,7 +256,7 @@ func (f *FSM) Can(event string) bool {
 	return ok && (f.transition == nil)
 }
 
-// AvailableTransitions returns a list of transitions avilable in the
+// AvailableTransitions returns a list of transitions available in the
 // current state.
 func (f *FSM) AvailableTransitions() []string {
 	f.stateMu.RLock()
@@ -273,6 +276,21 @@ func (f *FSM) Cannot(event string) bool {
 	return !f.Can(event)
 }
 
+// Metadata returns the value stored in metadata
+func (f *FSM) Metadata(key string) (interface{}, bool) {
+	f.metadataMu.RLock()
+	defer f.metadataMu.RUnlock()
+	dataElement, ok := f.metadata[key]
+	return dataElement, ok
+}
+
+// SetMetadata stores the dataValue in metadata indexing it with key
+func (f *FSM) SetMetadata(key string, dataValue interface{}) {
+	f.metadataMu.Lock()
+	defer f.metadataMu.Unlock()
+	f.metadata[key] = dataValue
+}
+
 // Event initiates a state transition with the named event.
 //
 // The call takes a variable number of arguments that will be passed to the

visualizer.go

@@ -13,9 +13,9 @@ const (
 	GRAPHVIZ VisualizeType = "graphviz"
 	// MERMAID the type for mermaid output (https://mermaid-js.github.io/mermaid/#/stateDiagram) in the stateDiagram form
 	MERMAID VisualizeType = "mermaid"
-	// MERMAID the type for mermaid output (https://mermaid-js.github.io/mermaid/#/stateDiagram) in the stateDiagram form
+	// MermaidStateDiagram the type for mermaid output (https://mermaid-js.github.io/mermaid/#/stateDiagram) in the stateDiagram form
 	MermaidStateDiagram VisualizeType = "mermaid-state-diagram"
-	// MERMAID the type for mermaid output (https://mermaid-js.github.io/mermaid/#/flowchart) in the flow chart form
+	// MermaidFlowChart the type for mermaid output (https://mermaid-js.github.io/mermaid/#/flowchart) in the flow chart form
 	MermaidFlowChart VisualizeType = "mermaid-flow-chart"
 )