Persist accessible colour and motion preferences (issue #80)

Implement Amber/Nord/High Contrast theme presets with XDG user-scoped persistence and reduced motion toggle. Covers TPH-10 and preference integration with TPH-2. - preferences.py: safe load/save with XDG_CONFIG_HOME/fenris/preferences.json - themes.py: three Textual Theme objects with graph colour roles - TUI: t cycles presets, m toggles reduced motion, both persist across restart - Status composition receives reduced_motion from preferences - 56 new tests covering persistence, themes, TUI integration, CLI isolation - All 590 existing tests continue to pass
2026-09-14 16:31:36 +05:30
parent 30122c5e6d
commit 79478653fa
7 changed files with 1276 additions and 7 deletions
@@ -0,0 +1,98 @@
+"""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 = {"amber", "nord", "high_contrast"}
+DEFAULT_THEME = "amber"
+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 (Amber 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}