initial commit

hameter/cost_state.py

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+"""Persistent cost state management.
+
+Cost state is stored at /data/cost_state.json, separate from config.json.
+This file is updated each time a cost calculation occurs, enabling
+persistence across restarts without bloating the config file.
+"""
+
+import json
+import logging
+import os
+import tempfile
+from typing import Optional
+
+logger = logging.getLogger(__name__)
+
+COST_STATE_PATH = "/data/cost_state.json"
+
+
+def load_cost_state(path: Optional[str] = None) -> dict:
+    """Load persisted cost state from disk.
+
+    Returns:
+        Dict keyed by meter_id (str) with cost state values.
+    """
+    path = path or COST_STATE_PATH
+    if not os.path.isfile(path):
+        return {}
+    try:
+        with open(path) as f:
+            return json.load(f)
+    except Exception as e:
+        logger.warning("Failed to load cost state: %s", e)
+        return {}
+
+
+def save_cost_state(states: dict, path: Optional[str] = None):
+    """Atomically save cost state to disk."""
+    path = path or COST_STATE_PATH
+    dir_path = os.path.dirname(path)
+    if dir_path:
+        os.makedirs(dir_path, exist_ok=True)
+
+    fd, tmp_path = tempfile.mkstemp(dir=dir_path or ".", suffix=".tmp")
+    try:
+        with os.fdopen(fd, "w") as f:
+            json.dump(states, f, indent=2)
+            f.write("\n")
+            f.flush()
+            os.fsync(f.fileno())
+        os.replace(tmp_path, path)
+    except Exception:
+        try:
+            os.unlink(tmp_path)
+        except OSError:
+            pass
+        raise