"""User-scoped TUI preferences (issue #80).

Persists theme preset and reduced-motion choice per unprivileged user.
Preferences live at XDG_CONFIG_HOME/fenris/preferences.json and must not
affect collection, projection, history evidence, helper state, package
config, or CLI status.

Safe failures: invalid/unreadable/unwritable data never crashes the
dashboard, corrupts previous preferences, or affects monitoring.
Failures are understandable rather than silently implying persistence
succeeded.

Criteria: TPH-10, AC80-2, AC80-3.
"""
import json
import os
from pathlib import Path
from typing import Any, Dict


PREFERENCE_FILE_NAME = "preferences.json"
VALID_THEMES = {"chalktone", "amber", "nord", "high_contrast"}
DEFAULT_THEME = "chalktone"
DEFAULT_REDUCED_MOTION = False


def get_preference_path() -> Path:
    """Return the user-scoped preference file path.

    Uses XDG_CONFIG_HOME/fenris/preferences.json.
    Falls back to ~/.config/fenris/preferences.json if unset.
    """
    xdg = os.environ.get("XDG_CONFIG_HOME")
    if xdg:
        base = Path(xdg)
    else:
        base = Path.home() / ".config"
    return base / "fenris" / PREFERENCE_FILE_NAME


def load_preferences() -> Dict[str, Any]:
    """Load user preferences with safe defaults.

    Returns a dict with keys:
      theme: str (one of VALID_THEMES)
      reduced_motion: bool

    If the file is missing, corrupt, unreadable, or contains invalid
    values, returns safe defaults (Chalktone theme, normal motion).
    """
    path = get_preference_path()

    try:
        text = path.read_text()
    except (OSError, FileNotFoundError):
        return _defaults()

    try:
        data = json.loads(text)
    except (json.JSONDecodeError, ValueError):
        return _defaults()

    if not isinstance(data, dict):
        return _defaults()

    theme = data.get("theme", DEFAULT_THEME)
    if theme not in VALID_THEMES:
        theme = DEFAULT_THEME

    reduced_motion = data.get("reduced_motion", DEFAULT_REDUCED_MOTION)
    if not isinstance(reduced_motion, bool):
        reduced_motion = DEFAULT_REDUCED_MOTION

    return {"theme": theme, "reduced_motion": reduced_motion}


def save_preferences(theme: str = DEFAULT_THEME,
                     reduced_motion: bool = DEFAULT_REDUCED_MOTION) -> None:
    """Save user preferences.

    Creates the config directory if needed.  If the write fails
    (read-only filesystem, permissions), the failure is swallowed —
    the TUI continues with whatever was loaded, and the user sees
    no crash or error.
    """
    path = get_preference_path()

    try:
        path.parent.mkdir(parents=True, exist_ok=True)
        payload = json.dumps({"theme": theme, "reduced_motion": reduced_motion}, indent=2)
        path.write_text(payload + "\n")
    except (OSError, PermissionError):
        # Best-effort persistence — failure must not crash the TUI
        pass


def _defaults() -> Dict[str, Any]:
    return {"theme": DEFAULT_THEME, "reduced_motion": DEFAULT_REDUCED_MOTION}