analytics: Move time_range from views.py to lib/time_utils.py

analytics/lib/time_utils.py

@@ -0,0 +1,29 @@
+from zerver.lib.timestamp import ceiling_to_hour, ceiling_to_day, timestamp_to_datetime
+from analytics.lib.counts import CountStat
+
+from datetime import datetime, timedelta
+from typing import List, Optional
+
+# If min_length is None, returns end_times from ceiling(start) to ceiling(end), inclusive.
+# If min_length is greater than 0, pads the list to the left.
+# So informally, time_range(Sep 20, Sep 22, day, None) returns [Sep 20, Sep 21, Sep 22],
+# and time_range(Sep 20, Sep 22, day, 5) returns [Sep 18, Sep 19, Sep 20, Sep 21, Sep 22]
+def time_range(start, end, interval, min_length):
+    # type: (datetime, datetime, str, Optional[int]) -> List[datetime]
+    if interval == CountStat.HOUR:
+        end = ceiling_to_hour(end)
+        step = timedelta(hours=1)
+    elif interval == CountStat.DAY:
+        end = ceiling_to_day(end)
+        step = timedelta(days=1)
+    else:
+        raise ValueError(_("Unknown interval."))
+
+    times = []
+    if min_length is not None:
+        start = min(start, end - (min_length-1)*step)
+    current = end
+    while current >= start:
+        times.append(current)
+        current -= step
+    return list(reversed(times))