add is_winner winner marker

2 files changed, 74 insertions, 28 deletions

diff --git a/internal/quorum/quorum.go b/internal/quorum/quorum.go
index 04e41ce..b29b428 100644
--- a/internal/quorum/quorum.go
+++ b/internal/quorum/quorum.go
@@ -29,6 +29,20 @@ type Score struct {
 	Value int
 }
 
+func (s Score) Is(other Score) bool {
+	return s.ID == other.ID && s.Value == other.Value
+}
+
+type Scores []Score
+
+func (s Scores) Winner() (Score, error) {
+	if len(s) == 0 {
+		return Score{}, fmt.Errorf("emtpy score, no winner")
+	}
+
+	return s[0], nil
+}
+
 func New(conf config.Config) Quorum {
 	return Quorum{
 		conf:   conf,
@@ -70,16 +84,9 @@ func (quo Quorum) Start(ctx context.Context) <-chan vote.Vote {
 				return
 			}
 
-			scoresStr, err := quo.persist()
-			if err != nil {
+			if err := quo.persist(changed); err != nil {
 				log.Println("quorum:", err)
 				notifyError(quo.conf, err)
-				continue
-			}
-			if changed {
-				if err := notify(quo.conf, "GORUM: Quorum changed", scoresStr); err != nil {
-					log.Println("quorum:", err)
-				}
 			}
 		}
 	}()
@@ -97,7 +104,7 @@ func (quo Quorum) vote(v vote.Vote) {
 	quo.votes[v.FromID] = v
 }
 
-func (quo Quorum) scores() (scores []Score) {
+func (quo Quorum) scores() (scores Scores) {
 	scoreMap := make(map[string]int)
 
 	for _, vote := range quo.votes {
@@ -122,17 +129,26 @@ func (quo Quorum) scores() (scores []Score) {
 	return
 }
 
-func (quo *Quorum) str() string {
+func (quo *Quorum) strs() (string, string) {
 	scores := quo.scores()
 	log.Println("quorum scores:", scores)
+	winner, err := scores.Winner()
+	if err != nil {
+		log.Println("the winner is", winner.ID)
+	}
 
 	var sb strings.Builder
+	winnerStr := ""
+
 	for i, score := range scores {
 		sb.WriteString("At position ")
 		sb.WriteString(strconv.Itoa(i + 1))
 
 		if score.ID == quo.conf.MyID {
 			sb.WriteString(" is current node ")
+			if score.Is(winner) {
+				winnerStr = fmt.Sprintf("Yeah, I, %s, am the winner!", winner.ID)
+			}
 		} else {
 			sb.WriteString(" is partner node ")
 		}
@@ -147,36 +163,40 @@ func (quo *Quorum) str() string {
 		sb.WriteString("\n")
 	}
 
-	return sb.String()
+	return winnerStr, sb.String()
 }
 
-func (quo *Quorum) persist() (string, error) {
-	scoresStr := quo.str()
+func (quo *Quorum) persist(changed bool) error {
+	winnerStr, scoresStr := quo.strs()
+
+	if changed {
+		if err := notify(quo.conf, "GORUM: Quorum changed", scoresStr); err != nil {
+			return err
+		}
+	}
 
 	if _, err := os.Stat(quo.conf.StateDir); os.IsNotExist(err) {
 		if err := os.MkdirAll(quo.conf.StateDir, 0755); err != nil {
-			return scoresStr, err
+			return err
 		}
 	}
 
-	stateFile := fmt.Sprintf("%s/scores", quo.conf.StateDir)
-	stateTmpFile := fmt.Sprintf("%s.tmp", stateFile)
-
-	// TODO: Also create a "is_leader" marker file in the fs!
-	fd, err := os.Create(stateTmpFile)
-	if err != nil {
-		return scoresStr, err
+	if err := quo.persistWinner(winnerStr); err != nil {
+		return err
 	}
-	defer fd.Close()
 
-	if _, err := fd.WriteString(scoresStr); err != nil {
-		return scoresStr, err
-	}
+	return writeFileViaTmp(fmt.Sprintf("%s/scores", quo.conf.StateDir), scoresStr)
+}
 
-	if err := fd.Sync(); err != nil {
-		return scoresStr, err
+func (quo *Quorum) persistWinner(winnerStr string) error {
+	winnerFile := fmt.Sprintf("%s/is_winner", quo.conf.StateDir)
+	if winnerStr == "" {
+		if _, err := os.Stat(winnerFile); err != nil {
+			return os.Remove(winnerFile)
+		}
+		return nil
 	}
-	return scoresStr, os.Rename(stateTmpFile, stateFile)
+	return writeFileViaTmp(winnerFile, winnerStr)
 }
 
 func (quo *Quorum) makeMyVote() (vote.Vote, bool) {
@@ -213,3 +233,24 @@ func (quo Quorum) expireOldVotes() (vote.Vote, error) {
 
 	return vote.New(quo.conf, live...)
 }
+
+// Create tmp file first, and then, once written, rename it.
+func writeFileViaTmp(filePath, content string) error {
+	tmpFilePath := fmt.Sprintf("%s.tmp", filePath)
+
+	fd, err := os.Create(tmpFilePath)
+	if err != nil {
+		return err
+	}
+	defer fd.Close()
+
+	if _, err := fd.WriteString(content); err != nil {
+		return err
+	}
+
+	if err := fd.Sync(); err != nil {
+		return err
+	}
+
+	return os.Rename(tmpFilePath, filePath)
+}
diff --git a/internal/quorum/quorum_test.go b/internal/quorum/quorum_test.go
index 7ddcdb2..0a8a35c 100644
--- a/internal/quorum/quorum_test.go
+++ b/internal/quorum/quorum_test.go
@@ -45,6 +45,11 @@ func TestScore(t *testing.T) {
 	if scores[0].ID != "bar" || scores[0].Value != 306 {
 		t.Errorf("Expected score[0] to be {bar,306}: %v", scores[0])
 	}
+
+	winner, _ := scores.Winner()
+	if winner.ID != "bar" {
+		t.Errorf("expectted bar to be the winner, but the winner is %s", winner.ID)
+	}
 }
 
 func TestTieScore(t *testing.T) {