(sessions): Add study_time_since function.

New `study_time_since` database function from session history.
Add `Lion.timezone`.
Add `Lion.day_start`.
Add `Lion.studied_today`.
Made `Table.queries` an instance variable.
Renamed the session channel types.

bot/modules/study/tracking/data.py

@@ -1,7 +1,21 @@
 from data import Table, RowTable, tables
+from utils.lib import FieldEnum
+
 
 untracked_channels = Table('untracked_channels')
 
+
+class SessionChannelType(FieldEnum):
+    """
+    The possible session channel types.
+    """
+    # NOTE: "None" stands for Unknown, and the STANDARD description should be replaced with the channel name
+    STANDARD = 'STANDARD', "Standard"
+    ACCOUNTABILITY = 'ACCOUNTABILITY', "Accountability Room"
+    RENTED = 'RENTED', "Private Room"
+    EXTERNAL = 'EXTERNAL', "Unknown"
+
+
 session_history = Table('session_history')
 current_sessions = RowTable(
     'current_sessions',
@@ -30,3 +44,16 @@ def close_study_session(guildid, userid):
     current_sessions.row_cache.pop((guildid, userid), None)
     # Use the function output to update the member cache
     tables.lions._make_rows(*rows)
+
+
+@session_history.save_query
+def study_time_since(guildid, userid, timestamp):
+    """
+    Retrieve the total member study time (in seconds) since the given timestamp.
+    Includes the current session, if it exists.
+    """
+    with session_history.conn as conn:
+        cursor = conn.cursor()
+        cursor.callproc('study_time_since', (guildid, userid, timestamp))
+        rows = cursor.fetchall()
+    return (rows[0][0] if rows else None) or 0