fsm: initial import

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

fsm/fsm.go

@@ -0,0 +1,151 @@
+package fsm // import "go.unistack.org/micro/v3/fsm"
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sync"
+)
+
+var (
+	ErrInvalidState = errors.New("does not exists")
+	StateEnd        = "end"
+)
+
+// Options struct holding fsm options
+type Options struct {
+	// Initial state
+	Initial string
+	// HooksBefore func slice runs in order before state
+	HooksBefore []HookBeforeFunc
+	// HooksAfter func slice runs in order after state
+	HooksAfter []HookAfterFunc
+}
+
+// HookBeforeFunc func signature
+type HookBeforeFunc func(ctx context.Context, state string, args map[string]interface{})
+
+// HookAfterFunc func signature
+type HookAfterFunc func(ctx context.Context, state string, args map[string]interface{})
+
+// Option func signature
+type Option func(*Options)
+
+// StateInitial sets init state for state machine
+func StateInitial(initial string) Option {
+	return func(o *Options) {
+		o.Initial = initial
+	}
+}
+
+// StateHookBefore provides hook func slice
+func StateHookBefore(fns ...HookBeforeFunc) Option {
+	return func(o *Options) {
+		o.HooksBefore = fns
+	}
+}
+
+// StateHookAfter provides hook func slice
+func StateHookAfter(fns ...HookAfterFunc) Option {
+	return func(o *Options) {
+		o.HooksAfter = fns
+	}
+}
+
+// StateFunc called on state transition and return next step and error
+type StateFunc func(ctx context.Context, args map[string]interface{}) (string, map[string]interface{}, error)
+
+// FSM is a finite state machine
+type FSM struct {
+	mu      sync.Mutex
+	states  map[string]StateFunc
+	opts    *Options
+	current string
+}
+
+// New creates a new finite state machine having the specified initial state
+// with specified options
+func New(opts ...Option) *FSM {
+	options := &Options{}
+
+	for _, opt := range opts {
+		opt(options)
+	}
+
+	return &FSM{
+		states: map[string]StateFunc{},
+		opts:   options,
+	}
+}
+
+// Current returns the current state
+func (f *FSM) Current() string {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.current
+}
+
+// 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.states[state] = fn
+	f.mu.Unlock()
+}
+
+// Start runs state machine with provided data
+func (f *FSM) Start(ctx context.Context, args map[string]interface{}, opts ...Option) (map[string]interface{}, error) {
+	var err error
+	var ok bool
+	var fn StateFunc
+	var nstate string
+
+	f.mu.Lock()
+	options := f.opts
+
+	for _, opt := range opts {
+		opt(options)
+	}
+
+	cstate := options.Initial
+	states := make(map[string]StateFunc, len(f.states))
+	for k, v := range f.states {
+		states[k] = v
+	}
+	f.current = cstate
+	f.mu.Unlock()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		default:
+			fn, ok = states[cstate]
+			if !ok {
+				return nil, fmt.Errorf(`state "%s" %w`, cstate, ErrInvalidState)
+			}
+			f.mu.Lock()
+			f.current = cstate
+			f.mu.Unlock()
+			for _, fn := range options.HooksBefore {
+				fn(ctx, cstate, args)
+			}
+			nstate, args, err = fn(ctx, args)
+			for _, fn := range options.HooksAfter {
+				fn(ctx, cstate, args)
+			}
+			if err != nil {
+				return args, err
+			} else if nstate == "" || nstate == StateEnd {
+				return args, nil
+			}
+			cstate = nstate
+		}
+	}
+}