"""
Storage configuration loader.

Reads from /etc/fester/storage.json by default, or from
FESTER_STORAGE_CONFIG env var. Falls back to sensible defaults
if the file doesn't exist or isn't readable.
"""

import json
import os
from pathlib import Path


DEFAULT_CONFIG_PATH = Path(
    os.environ.get("FESTER_STORAGE_CONFIG", "/etc/fester/storage.json")
)


DEFAULT_CONFIG = {
    "tmpfs": True,
    "btrfs": False,
    "qcow2_freeze": False,
    "btrfs_path": "/var/lib/fester/cas",
    "tmpfs_path": "/dev/shm/fester-build",
    "qcow2_path": "/var/lib/fester/snapshots",
}


def _writable_path(p: Path) -> bool:
    """Check if a path is writable (or can be created)."""
    try:
        p.mkdir(parents=True, exist_ok=True)
        # touch a test file
        test = p / ".fester_write_test"
        test.write_text("")
        test.unlink()
        return True
    except (OSError, PermissionError):
        return False


def _resolve_paths(cfg: dict) -> dict:
    """If a configured path isn't writable, fall back to user/tmp paths."""
    fallbacks = {
        "btrfs_path": [
            Path.home() / ".fester" / "cas",
            Path("/tmp/fester/cas"),
        ],
        "tmpfs_path": [
            Path.home() / ".fester" / "tmpfs",
            Path("/tmp/fester/tmpfs"),
        ],
        "qcow2_path": [
            Path.home() / ".fester" / "snapshots",
            Path("/tmp/fester/snapshots"),
        ],
    }
    for key, alts in fallbacks.items():
        p = Path(cfg[key])
        if not _writable_path(p):
            for alt in alts:
                if _writable_path(alt):
                    cfg[key] = str(alt)
                    break
    return cfg


def load_storage_config() -> dict:
    """Load storage config with graceful fallbacks."""
    cfg = DEFAULT_CONFIG.copy()

    if DEFAULT_CONFIG_PATH.exists():
        try:
            with open(DEFAULT_CONFIG_PATH) as f:
                user_cfg = json.load(f)
            cfg.update(user_cfg)
        except (json.JSONDecodeError, OSError):
            pass

    cfg = _resolve_paths(cfg)
    return cfg


def save_storage_config(cfg: dict) -> bool:
    """Persist config to disk. Returns True on success."""
    try:
        DEFAULT_CONFIG_PATH.parent.mkdir(parents=True, exist_ok=True)
        with open(DEFAULT_CONFIG_PATH, "w") as f:
            json.dump(cfg, f, indent=2)
        return True
    except (OSError, PermissionError):
        return False