From 2ab7cafdf572fa17234e44fbde01ec86edd6411e Mon Sep 17 00:00:00 2001
From: DjeAvd <djelal.avdil@master.hes-so.ch>
Date: Wed, 27 May 2026 08:47:48 +0200
Subject: [PATCH] feat(gateway): add deduplication and continuous BLE scan
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- Add 10-second deduplication window per MAC address to avoid
  duplicate entries in the database (each Thingy advertises 3-4
  times per frame on BLE channels 37, 38 and 39)
- Configure BleakScanner with continuous scan (interval = window = 10ms)
  to ensure no advertising packets are missed during the 500ms
  Thingy advertising window

Assisted-by: Claude:claude-sonnet-4-6 — BleakScanner scan interval and window configuration
---
 gateway/gateway.py | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/gateway/gateway.py b/gateway/gateway.py
index 4280de2..ec34879 100644
--- a/gateway/gateway.py
+++ b/gateway/gateway.py
@@ -32,6 +32,11 @@ class Gateway:
     # 5 keys (1B each) + window(1B) + humidity(1B) + temp(2B) + co2(4B) + battery(1B) = 14 bytes
     EXPECTED_PAYLOAD_SIZE = 14
 
+    # Deduplication window in seconds — ignore packets from the same node
+    # within this period to avoid duplicate entries in the database.
+    # Each node advertises 3-4 times per frame on BLE channels 37, 38 and 39.
+    DEDUP_WINDOW_SECONDS = 10
+
     def __init__(self, config: dict):
         self.gateway_id  = config["gateway_id"]
         self.mqtt_broker = config["mqtt"]["broker"]
@@ -40,6 +45,11 @@ class Gateway:
         # BLE service UUID used to identify Thingy:52 advertising packets
         self.service_uuid = config["ble"]["service_uuid"]
 
+        # Deduplication cache — stores the last time a packet was published
+        # for each MAC address. Packets received within DEDUP_WINDOW_SECONDS
+        # from the same node are ignored.
+        self._last_published = {}
+
         log.info(f"Gateway ID : {self.gateway_id}")
         log.info(f"MQTT broker: {self.mqtt_broker}:{self.mqtt_port}")
 
@@ -128,6 +138,23 @@ class Gateway:
                 break
         return result
 
+    def is_duplicate(self, mac: str) -> bool:
+        """Check if a packet from this MAC was already published recently.
+
+        Each Thingy:52 advertises 3-4 times per broadcast frame on BLE
+        advertising channels 37, 38 and 39. Without deduplication, the same
+        measurement would be published multiple times to the broker.
+        This method ignores packets from the same node received within
+        DEDUP_WINDOW_SECONDS of the last published packet.
+        """
+        now = datetime.now(timezone.utc)
+        last = self._last_published.get(mac)
+        if last and (now - last).total_seconds() < self.DEDUP_WINDOW_SECONDS:
+            log.debug(f"{mac} | duplicate ignored — last published {(now - last).total_seconds():.1f}s ago")
+            return True
+        self._last_published[mac] = now
+        return False
+
     def publish(self, mac: str, data: dict):
         """Publish decoded sensor data to MQTT broker.
         Topic: {gateway_id}/{thingy_mac}/update
@@ -163,6 +190,10 @@ class Gateway:
             log.debug(f"{device.address} | ignored — unexpected payload size: {len(raw)}")
             return
 
+        # Deduplication — ignore packets from the same node within 10 seconds
+        if self.is_duplicate(device.address):
+            return
+
         log.debug(f"{device.address} | Thingy detected, raw: {list(raw)}")
 
         data = self.decode_payload(raw)
@@ -174,9 +205,20 @@ class Gateway:
         self.publish(device.address, data)
 
     async def run(self):
-        """Start passive BLE scan and run indefinitely."""
+        """Start passive BLE scan and run indefinitely.
+
+        Scanner is configured with a continuous scan (interval = window = 10ms)
+        to ensure no advertising packets are missed. By default, BlueZ uses
+        an interval of 1280ms and a window of 11.25ms — less than 1% duty cycle.
+        With the Thingy:52 advertising window of only 500ms, packets could be
+        missed. Setting interval = window guarantees continuous listening on
+        all three BLE advertising channels (37, 38 and 39).
+        """
         log.info("BLE scan started, listening for Thingy:52 advertising packets...")
-        scanner = BleakScanner(detection_callback=self.on_device_found)
+        scanner = BleakScanner(
+            detection_callback=self.on_device_found,
+            bluez={"interval": 0x0010, "window": 0x0010}
+        )
         await scanner.start()
         while True:
             await asyncio.sleep(1)