"""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