Move VersionedAttributes code into appropriotely named module.

[plomtask] / plomtask / versioned_attributes.py

diff --git a/plomtask/versioned_attributes.py b/plomtask/versioned_attributes.py
new file mode 100644 (file)
index 0000000..ab39df0
--- /dev/null
+++ b/plomtask/versioned_attributes.py
@@ -0,0 +1,68 @@
+"""Attributes whose values are recorded as a timestamped history."""
+from datetime import datetime
+from typing import Any
+from sqlite3 import Row
+from time import sleep
+from plomtask.db import DatabaseConnection
+
+TIMESTAMP_FMT = '%Y-%m-%d %H:%M:%S.%f'
+
+
+class VersionedAttribute:
+    """Attributes whose values are recorded as a timestamped history."""
+
+    def __init__(self,
+                 parent: Any, table_name: str, default: str | float) -> None:
+        self.parent = parent
+        self.table_name = table_name
+        self.default = default
+        self.history: dict[str, str | float] = {}
+
+    @property
+    def _newest_timestamp(self) -> str:
+        """Return most recent timestamp."""
+        return sorted(self.history.keys())[-1]
+
+    @property
+    def newest(self) -> str | float:
+        """Return most recent value, or self.default if self.history empty."""
+        if 0 == len(self.history):
+            return self.default
+        return self.history[self._newest_timestamp]
+
+    def set(self, value: str | float) -> None:
+        """Add to self.history if and only if not same value as newest one.
+
+        Note that we wait one micro-second, as timestamp comparison to check
+        most recent elements only goes up to that precision.
+
+        Also note that we don't check against .newest because that may make us
+        compare value against .default even if not set. We want to be able to
+        explicitly set .default as the first element.
+        """
+        sleep(0.00001)
+        if 0 == len(self.history) \
+                or value != self.history[self._newest_timestamp]:
+            self.history[datetime.now().strftime(TIMESTAMP_FMT)] = value
+
+    def history_from_row(self, row: Row) -> None:
+        """Extend self.history from expected table row format."""
+        self.history[row[1]] = row[2]
+
+    def at(self, queried_time: str) -> str | float:
+        """Retrieve value of timestamp nearest queried_time from the past."""
+        sorted_timestamps = sorted(self.history.keys())
+        if 0 == len(sorted_timestamps):
+            return self.default
+        selected_timestamp = sorted_timestamps[0]
+        for timestamp in sorted_timestamps[1:]:
+            if timestamp > queried_time:
+                break
+            selected_timestamp = timestamp
+        return self.history[selected_timestamp]
+
+    def save(self, db_conn: DatabaseConnection) -> None:
+        """Save as self.history entries, but first wipe old ones."""
+        db_conn.rewrite_relations(self.table_name, 'parent', self.parent.id_,
+                                  [[item[0], item[1]]
+                                   for item in self.history.items()])