From 2a24bf156480479843a7f17d36eb54320127ee93 Mon Sep 17 00:00:00 2001
From: William Banfield <wbanfield@gmail.com>
Date: Fri, 18 Feb 2022 17:36:18 -0500
Subject: [PATCH] stepper: initial passing test

---
 internal/consensus/stepper/stepper.go | 45 +++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 internal/consensus/stepper/stepper.go

diff --git a/internal/consensus/stepper/stepper.go b/internal/consensus/stepper/stepper.go
new file mode 100644
index 000000000..dd5219a4c
--- /dev/null
+++ b/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
+}