Add cache implementation

This avoids frequent MQTT messages containing the same state.

1 files changed, 44 insertions, 0 deletions

diff --git a/cache.go b/cache.go
new file mode 100644
index 0000000..081621d
--- /dev/null
+++ b/cache.go
@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+	"log"
+
+	mqtt "github.com/eclipse/paho.mqtt.golang"
+)
+
+type States map[string]bool
+
+type Cache struct {
+	Client mqtt.Client
+	States map[string]bool
+}
+
+func NewCache(client mqtt.Client) Cache {
+	var cache Cache
+
+	cache.Client = client
+	cache.States = make(States)
+
+	return cache
+}
+
+func (c *Cache) Update(states States) {
+	if c.States == nil {
+		log.Fatal("Cache states is nil.")
+	}
+
+	if states == nil {
+		log.Fatal("Given states is nil.")
+	}
+
+	for id, state := range states {
+		cached, known := c.States[id]
+		if !known || cached != state {
+			topic := fmt.Sprintf("%s/contact/%s/state", TOPIC_PREFIX, id)
+			payload := []byte(fmt.Sprintf("%t", state))
+			_ = c.Client.Publish(topic, QOS, RETAINED, payload)
+		}
+		c.States[id] = state
+	}
+}