fsm: improve and convert to interface

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

fsm/default.go

@@ -0,0 +1,126 @@
+package fsm
+
+import (
+	"context"
+	"fmt"
+	"sync"
+)
+
+type state struct {
+	body interface{}
+	name string
+}
+
+var _ State = &state{}
+
+func (s *state) Name() string {
+	return s.name
+}
+
+func (s *state) Body() interface{} {
+	return s.body
+}
+
+// fsm is a finite state machine
+type fsm struct {
+	statesMap   map[string]StateFunc
+	current     string
+	statesOrder []string
+	opts        Options
+	mu          sync.Mutex
+}
+
+// NewFSM creates a new finite state machine having the specified initial state
+// with specified options
+func NewFSM(opts ...Option) *fsm {
+	return &fsm{
+		statesMap: map[string]StateFunc{},
+		opts:      NewOptions(opts...),
+	}
+}
+
+// Current returns the current state
+func (f *fsm) Current() string {
+	f.mu.Lock()
+	s := f.current
+	f.mu.Unlock()
+	return s
+}
+
+// Current returns the current state
+func (f *fsm) Reset() {
+	f.mu.Lock()
+	f.current = f.opts.Initial
+	f.mu.Unlock()
+}
+
+// State adds state to fsm
+func (f *fsm) State(state string, fn StateFunc) {
+	f.mu.Lock()
+	f.statesMap[state] = fn
+	f.statesOrder = append(f.statesOrder, state)
+	f.mu.Unlock()
+}
+
+// Start runs state machine with provided data
+func (f *fsm) Start(ctx context.Context, args interface{}, opts ...Option) (interface{}, error) {
+	var err error
+
+	f.mu.Lock()
+	options := f.opts
+
+	for _, opt := range opts {
+		opt(&options)
+	}
+
+	sopts := []StateOption{StateDryRun(options.DryRun)}
+
+	cstate := options.Initial
+	states := make(map[string]StateFunc, len(f.statesMap))
+	for k, v := range f.statesMap {
+		states[k] = v
+	}
+	f.current = cstate
+	f.mu.Unlock()
+
+	var s State
+	s = &state{name: cstate, body: args}
+	nstate := s.Name()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		default:
+			fn, ok := states[nstate]
+			if !ok {
+				return nil, fmt.Errorf(`state "%s" %w`, nstate, ErrInvalidState)
+			}
+			f.mu.Lock()
+			f.current = nstate
+			f.mu.Unlock()
+
+			// wrap the handler func
+			for i := len(options.Wrappers); i > 0; i-- {
+				fn = options.Wrappers[i-1](fn)
+			}
+
+			s, err = fn(ctx, s, sopts...)
+
+			switch {
+			case err != nil:
+				return s.Body(), err
+			case s.Name() == StateEnd:
+				return s.Body(), nil
+			case s.Name() == "":
+				for idx := range f.statesOrder {
+					if f.statesOrder[idx] == nstate && len(f.statesOrder) > idx+1 {
+						nstate = f.statesOrder[idx+1]
+					}
+				}
+			default:
+				nstate = s.Name()
+			}
+		}
+	}
+}