1 files changed, 105 insertions, 0 deletions
diff --git a/workflow.go b/workflow.go
new file mode 100644
index 0000000..8911cec
--- /dev/null
+++ b/workflow.go
@@ -0,0 +1,105 @@
+package workflow
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrCantApply          = errors.New("cant apply transition")
+	ErrTransitionNotFound = errors.New("transition not found")
+)
+
+// Workflow state machine
+type Workflow struct {
+	transitions  map[string]transition
+	initialPlace Place
+}
+
+// NewWorkflow returns new Workflow instance
+func NewWorkflow(initialPlace Place) *Workflow {
+	return &Workflow{initialPlace: initialPlace, transitions: map[string]transition{}}
+}
+
+// Can returns nil if transition applicable to object and error if not
+func (w *Workflow) Can(obj Placeer, transition string) error {
+	currentPlace := obj.GetPlace()
+	if currentPlace == "" {
+		currentPlace = w.initialPlace
+	}
+	tr, ok := w.transitions[transition]
+	if !ok {
+		return ErrTransitionNotFound
+	}
+	for _, f := range tr.From {
+		if f == currentPlace {
+			return nil
+		}
+	}
+	return ErrCantApply
+}
+
+// GetEnabledTransitions return all applicable transitions for object
+func (w *Workflow) GetEnabledTransitions(obj Placeer) []string {
+	currentPlace := obj.GetPlace()
+	if currentPlace == "" {
+		currentPlace = w.initialPlace
+	}
+	result := make([]string, 0)
+	for name, t := range w.transitions {
+		for _, f := range t.From {
+			if f == currentPlace {
+				result = append(result, name)
+				break
+			}
+		}
+	}
+	return result
+}
+
+// Apply next state from transition to object
+func (w *Workflow) Apply(obj Placeer, transition string) error {
+	currentPlace := obj.GetPlace()
+	if currentPlace == "" {
+		currentPlace = w.initialPlace
+	}
+	tr, ok := w.transitions[transition]
+	if !ok {
+		return ErrTransitionNotFound
+	}
+	for _, f := range tr.From {
+		if f == currentPlace {
+			return obj.SetPlace(tr.To)
+		}
+	}
+	return ErrCantApply
+}
+
+// AddTransition to workflow
+func (w *Workflow) AddTransition(name string, from []Place, to Place) {
+	w.transitions[name] = transition{
+		From: from,
+		To:   to,
+	}
+}
+
+// DumpToDot dumps transitions to Graphviz Dot format
+func (w *Workflow) DumpToDot() []byte {
+	buf := bytes.NewBufferString(fmt.Sprintf("digraph {\n%s[color=\"blue\"]\n", w.initialPlace))
+	for name, t := range w.transitions {
+		for _, f := range t.From {
+			_, _ = buf.WriteString(fmt.Sprintf("%s -> %s[label=\"%s\"];\n", f, t.To, name))
+		}
+	}
+	buf.WriteString("}")
+	return buf.Bytes()
+}
+
+// Place is one of state
+type Place string
+
+type transition struct {
+	From []Place
+	To   Place
+}