implement mcache

mcache.go

@@ -5,25 +5,57 @@ import (
 )
 
 func NewMessageCache(gossip, history int) *MessageCache {
-	return &MessageCache{}
+	return &MessageCache{
+		msgs:    make(map[string]*pb.Message),
+		history: make([][]CacheEntry, history),
+		gossip:  gossip,
+	}
 }
 
 type MessageCache struct {
+	msgs    map[string]*pb.Message
+	history [][]CacheEntry
+	gossip  int
+}
+
+type CacheEntry struct {
+	mid    string
+	topics []string
 }
 
 func (mc *MessageCache) Put(msg *pb.Message) {
-	// TODO
+	mid := msgID(msg)
+	mc.msgs[mid] = msg
+	mc.history[0] = append(mc.history[0], CacheEntry{mid: mid, topics: msg.GetTopicIDs()})
 }
 
 func (mc *MessageCache) Get(mid string) (*pb.Message, bool) {
-	// TODO
-	return nil, false
+	m, ok := mc.msgs[mid]
+	return m, ok
 }
 
 func (mc *MessageCache) GetGossipIDs(topic string) []string {
-	return nil
+	var mids []string
+	for _, entries := range mc.history[:mc.gossip] {
+		for _, entry := range entries {
+			for _, t := range entry.topics {
+				if t == topic {
+					mids = append(mids, entry.mid)
+					break
+				}
+			}
+		}
+	}
+	return mids
 }
 
 func (mc *MessageCache) Shift() {
-	// TODO
+	last := mc.history[len(mc.history)-1]
+	for _, entry := range last {
+		delete(mc.msgs, entry.mid)
+	}
+	for i := len(mc.history) - 2; i >= 0; i-- {
+		mc.history[i+1] = mc.history[i]
+	}
+	mc.history[0] = nil
 }