2 files changed, 60 insertions(+), 49 deletions(-)

M cmd/tallyard/main.go
M election/map.go

@@ 72,7 72,7 @@ func main() {
 	}()
 	client.Store = store
 
-	elections, err := election.GetElections()
+	elections, err := election.GetElectionsMap()
 	if err != nil {
 		panic(err)
 	}

@@ 17,69 17,51 @@ import (
 
 type ElectionsMap struct {
 	sync.RWMutex
-	M map[id.EventID]*Election
 
-	// by room, sorted list of elections by CreationTimestamp (newest to oldest)
-	L     map[id.RoomID][]*Election
-	Ltime time.Time // last time list was update
-
-	Joins map[id.EventID]*Voter
-	Save  func()
+	// The version of the elections map.  If the version in the file doesn't
+	// match the current version then we can give a clear error message
+	// telling the user to update their file to the current version.  The
+	// version in the file should only be different if there has been a
+	// breaking change to the elections map format.
+	Version int `json:"version"`
+
+	// Maps election create event IDs to the corresponding election.
+	M map[id.EventID]*Election `json:"elections"`
+
+	// Maps room to a list of the room's elections, reverse sorted by
+	// CreationTimestamp (i.e. newest to oldest).  Here for convenience.
+	L map[id.RoomID][]*Election `json:"-"`
+	// The latest time L was updated
+	Ltime time.Time `json:"-"`
+
+	// maps join event ID to voter. This is a convenience in scenarios when
+	// we don't know the exact election
+	Joins map[id.EventID]*Voter `json:"-"`
 }
 
+const electionsMapVersion = 1
+
 var electionsFname = xdg.DataHome() + "/tallyard/elections.json"
 
-func GetElections() (elections *ElectionsMap, err error) {
-	elections = NewElectionsMap()
+func GetElectionsMap() (em *ElectionsMap, err error) {
+	em = &ElectionsMap{}
 	if _, err = os.Stat(electionsFname); os.IsNotExist(err) {
-		return elections, nil
+		return newElectionsMap(), nil
 	}
 	jsonBytes, err := ioutil.ReadFile(electionsFname)
 	if err != nil {
 		return nil, fmt.Errorf("error reading data file %s: %s", electionsFname, err)
 	}
-	err = json.Unmarshal(jsonBytes, elections)
+	err = json.Unmarshal(jsonBytes, em)
 	if err != nil {
 		return nil, fmt.Errorf("error unmarshalling data file: %s", err)
 	}
-	return
-}
-
-func NewElectionsMap() *ElectionsMap {
-	em := &ElectionsMap{
-		M:     make(map[id.EventID]*Election),
-		L:     make(map[id.RoomID][]*Election, 0),
-		Ltime: time.Now(),
-		Joins: make(map[id.EventID]*Voter),
-	}
-	em.Save = func() {
-		em.RLock()
-		defer em.RUnlock()
-		for _, el := range em.M {
-			el.RLock()
-			defer el.RUnlock()
-		}
-		jsonBytes, err := json.Marshal(em)
-		if err != nil {
-			log.Errorf("couldn't marshal elections: %s", err)
-		}
-		err = ioutil.WriteFile(electionsFname, jsonBytes, 0600)
-		if err != nil {
-			log.Errorf("couldn't save elections: %s", err)
-		}
-	}
-	return em
-}
-
-func (em *ElectionsMap) MarshalJSON() ([]byte, error) {
-	return json.Marshal(em.M)
-}
-
-func (em *ElectionsMap) UnmarshalJSON(b []byte) error {
-	if err := json.Unmarshal(b, &em.M); err != nil {
-		return err
+	if em.Version != electionsMapVersion {
+		return nil, fmt.Errorf("Your stored elections schema version (%d) is incompitable with the latest schema version (%d).",
+			em.Version, electionsMapVersion)
 	}
 	em.L = make(map[id.RoomID][]*Election, 0)
+	em.Ltime = time.Now()
 	for createEventId, el := range em.M {
 		em.insort(createEventId, el)
 	}


@@ 90,7 72,36 @@ func (em *ElectionsMap) UnmarshalJSON(b []byte) error {
 			em.Joins[joinEventId] = voter
 		}
 	}
-	return nil
+	return
+}
+
+func newElectionsMap() *ElectionsMap {
+	return &ElectionsMap{
+		Version: electionsMapVersion,
+		M:       make(map[id.EventID]*Election),
+		L:       make(map[id.RoomID][]*Election),
+		Ltime:   time.Now(),
+		Joins:   make(map[id.EventID]*Voter),
+	}
+}
+
+func (em *ElectionsMap) Save() {
+	em.RLock()
+	defer em.RUnlock()
+	for _, el := range em.M {
+		el.RLock()
+		defer el.RUnlock()
+	}
+	jsonBytes, err := json.Marshal(em)
+	if err != nil {
+		log.Errorf("couldn't marshal elections: %s", err)
+		return
+	}
+	err = ioutil.WriteFile(electionsFname, jsonBytes, 0600)
+	if err != nil {
+		log.Errorf("couldn't save elections: %s", err)
+		return
+	}
 }
 
 func (em *ElectionsMap) Get(createEventID id.EventID) *Election {