stepper: initial passing test

internal/consensus/stepper/stepper.go

@@ -0,0 +1,45 @@
+package stepper
+
+import (
+	"errors"
+
+	"github.com/tendermint/tendermint/internal/consensus/types"
+)
+
+var (
+	ErrNoValidTransition = errors.New("no valid transition")
+)
+
+type (
+	Transition func(types.RoundState) types.RoundState
+	Predicate  func(types.RoundState) bool
+)
+
+var emptyTransition = func(types.RoundState) types.RoundState { return types.RoundState{} }
+
+type Operation struct {
+	P Predicate
+	T Transition
+}
+
+type stepper struct {
+	ops []Operation
+}
+
+func New(ops []Operation) stepper {
+	return stepper{ops: ops}
+}
+
+func (s *stepper) Next(state types.RoundState) (types.RoundState, error) {
+	if t, ok := s.pickTransition(state); ok {
+		return t(state), nil
+	}
+	return types.RoundState{}, ErrNoValidTransition
+}
+
+func (s *stepper) pickTransition(state types.RoundState) (Transition, bool) {
+	for _, op := range s.ops {
+		return op.T, true
+	}
+	return emptyTransition, false
+}