Add cache implementation

This avoids frequent MQTT messages containing the same state.

3 files changed, 56 insertions, 8 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
+	}
+}
diff --git a/main.go b/main.go
index 6ef4c63..051deef 100644
--- a/main.go
+++ b/main.go
@@ -35,14 +35,18 @@ func main() {
 			log.Fatalf("Failed startup process: %v", err)
 		}
 
+		cache := NewCache(client)
+
 		for {
 			start := time.Now()
 
-			err = Poll(req, inventory, client)
+			states, err := Poll(req, inventory)
 			if err != nil {
 				log.Fatalf("Failed to poll states: %v", err)
 			}
 
+			cache.Update(states)
+
 			WaitUntil(start.Add(POLLING_PERIOD))
 		}
 	}()
@@ -102,21 +106,20 @@ func Stop(c mqtt.Client) {
 	log.Println("Disconnected from MQTT broker.")
 }
 
-func Poll(req homematic.Requester, inventory homematic.Devices, client mqtt.Client) error {
+func Poll(req homematic.Requester, inventory homematic.Devices) (States, error) {
+	states := make(States)
+
 	for _, device := range inventory {
 		if device.Type == `SHUTTER_CONTACT` {
 			state, err := req.GetValue(device.Address)
 			if err != nil {
-				return fmt.Errorf("Failed to get value: %w", err)
+				return states, fmt.Errorf("Failed to get value: %w", err)
 			}
-
-			topic := fmt.Sprintf("%s/contact/%s/state", TOPIC_PREFIX, device.Address)
-			payload := []byte(fmt.Sprintf("%t", state))
-			_ = client.Publish(topic, QOS, RETAINED, payload)
+			states[device.Address] = state
 		}
 	}
 
-	return nil
+	return states, nil
 }
 
 func Await(signals ...syscall.Signal) {
diff --git a/meson.build b/meson.build
index d264c35..e2ce711 100644
--- a/meson.build
+++ b/meson.build
@@ -5,6 +5,7 @@ go = find_program('go', required : true)
 sia_server = custom_target(
   input : [
     meson.current_source_dir() / 'main.go',
+    meson.current_source_dir() / 'cache.go',
   ],
   output : 'sia-server',
   command : [