Add whisper backend method to get closest sample from timestamp.

src/biomon/whisper_backend.py

@@ -28,6 +28,7 @@ import whisper
 
 from django.conf import settings
 
+from . import time_utils
 
 class WhisperBackend():
 
@@ -114,3 +115,30 @@ class WhisperBackend():
         if values:
             return min(values)
         return None
+
+    def get_closest(self, timestamp, lookup_range=None):
+        if not timestamp:
+            return None
+        before = None
+        after = None
+        data = self.get_timestamped_data(lookup_range, timestamp - 1)
+        if data:
+            before = data[-1]
+        if before and timestamp == time_utils.unix_time(before[0]):
+            return before
+        data = self.get_timestamped_data(lookup_range,
+            timestamp + lookup_range - 1)
+        if data:
+            after = data[0]
+        if not before and not after:
+            return None
+        if before and not after:
+            return before
+        if after and not before:
+            return after
+        diff_before = timestamp - time_utils.unix_time(before[0])
+        diff_after = time_utils.unix_time(after[0]) - timestamp
+        if diff_before <= diff_after:
+            return before
+        else:
+            return after