feat(ux): dark mode & accessibility contrast improvements

packages/backend/app/services/accessibility.py

@@ -0,0 +1,54 @@
+"""Dark mode & accessibility settings (issue #104)."""
+import json, logging
+from ..extensions import redis_client
+
+logger = logging.getLogger("finmind.a11y")
+PREFS_KEY = "a11y:prefs:{user_id}"
+TTL = 60 * 60 * 24 * 365
+
+THEMES = {
+    "dark":  {"bg": "#0f0f0f", "surface": "#1a1a2e", "primary": "#7c3aed",
+               "text": "#f8fafc", "muted": "#94a3b8", "border": "#334155"},
+    "light": {"bg": "#ffffff", "surface": "#f8fafc", "primary": "#7c3aed",
+               "text": "#0f172a", "muted": "#64748b", "border": "#e2e8f0"},
+    "high_contrast": {"bg": "#000000", "surface": "#0a0a0a", "primary": "#ffffff",
+                       "text": "#ffffff", "muted": "#cccccc", "border": "#ffffff"},
+    "solarized": {"bg": "#002b36", "surface": "#073642", "primary": "#268bd2",
+                   "text": "#839496", "muted": "#586e75", "border": "#657b83"},
+}
+
+FONT_SIZES = {"small": 13, "medium": 16, "large": 19, "xlarge": 22}
+
+
+def get_preferences(user_id: int) -> dict:
+    raw = redis_client.get(PREFS_KEY.format(user_id=user_id))
+    if raw: return json.loads(raw)
+    return {"theme": "dark", "font_size": "medium", "reduce_motion": False,
+            "high_contrast": False, "focus_indicators": True, "dense_mode": False}
+
+
+def set_preferences(user_id: int, prefs: dict) -> dict:
+    current = get_preferences(user_id)
+    current.update({k: v for k, v in prefs.items() if k in current})
+    redis_client.setex(PREFS_KEY.format(user_id=user_id), TTL, json.dumps(current))
+    return current
+
+
+def get_theme_tokens(user_id: int) -> dict:
+    prefs = get_preferences(user_id)
+    theme_name = "high_contrast" if prefs.get("high_contrast") else prefs.get("theme", "dark")
+    theme = THEMES.get(theme_name, THEMES["dark"])
+    return {"theme": theme_name, "tokens": theme,
+            "font_size_px": FONT_SIZES.get(prefs.get("font_size","medium"), 16),
+            "reduce_motion": prefs.get("reduce_motion", False)}
+
+
+def get_wcag_contrast_ratio(color1: str, color2: str) -> float:
+    def luminance(hex_color):
+        hex_color = hex_color.lstrip("#")
+        r, g, b = (int(hex_color[i:i+2], 16) / 255.0 for i in (0, 2, 4))
+        def adj(c): return c/12.92 if c <= 0.04045 else ((c+0.055)/1.055)**2.4
+        return 0.2126*adj(r) + 0.7152*adj(g) + 0.0722*adj(b)
+    l1, l2 = luminance(color1), luminance(color2)
+    if l1 < l2: l1, l2 = l2, l1
+    return round((l1 + 0.05) / (l2 + 0.05), 2)

packages/backend/tests/test_accessibility.py

@@ -0,0 +1,34 @@
+from unittest.mock import MagicMock, patch
+
+def _mock_redis():
+    store = {}
+    r = MagicMock()
+    def setex(k,t,v): store[k]=v
+    def get(k): v=store.get(k); return v.encode() if isinstance(v,str) else v
+    r.setex.side_effect=setex; r.get.side_effect=get
+    return r
+
+def test_default_prefs():
+    with patch("app.services.accessibility.redis_client", _mock_redis()):
+        from app.services.accessibility import get_preferences
+        p = get_preferences(999)
+        assert p["theme"] == "dark" and "font_size" in p
+
+def test_set_preferences():
+    r = _mock_redis()
+    with patch("app.services.accessibility.redis_client", r):
+        from app.services.accessibility import set_preferences, get_preferences
+        set_preferences(1, {"theme": "light", "font_size": "large"})
+        p = get_preferences(1)
+        assert p["theme"] == "light" and p["font_size"] == "large"
+
+def test_theme_tokens():
+    with patch("app.services.accessibility.redis_client", _mock_redis()):
+        from app.services.accessibility import get_theme_tokens
+        t = get_theme_tokens(999)
+        assert "tokens" in t and "font_size_px" in t
+
+def test_wcag_contrast():
+    from app.services.accessibility import get_wcag_contrast_ratio
+    ratio = get_wcag_contrast_ratio("#ffffff", "#000000")
+    assert ratio == 21.0  # max contrast