✨(backend) attribute a color to each participant

Color is stored in participant's metadata.
Using a hash of some participant's info allow to persist the color
for logged-in participant without storing the color in db.

Please feel free to tune the saturation and lightness range.
Code is inspired by a tutorial found online.

src/backend/core/utils.py

@@ -2,6 +2,10 @@
 Utils functions used in the core app
 """
 
+# ruff: noqa:S311
+
+import json
+import random
 from typing import Optional
 from uuid import uuid4
 
@@ -10,6 +14,24 @@ from django.conf import settings
 from livekit.api import AccessToken, VideoGrants
 
 
+def generate_color(identity: str) -> str:
+    """Generates a consistent HSL color based on a given identity string.
+
+    The function seeds the random generator with the identity's hash,
+    ensuring consistent color output. The HSL format allows fine-tuned control
+    over saturation and lightness, empirically adjusted to produce visually
+    appealing and distinct colors. HSL is preferred over hex to constrain the color
+    range and ensure predictability.
+    """
+
+    random.seed(hash(identity))
+    hue = random.randint(0, 360)
+    saturation = random.randint(50, 75)
+    lightness = random.randint(25, 60)
+
+    return f"hsl({hue}, {saturation}%, {lightness}%)"
+
+
 def generate_token(room: str, user, username: Optional[str] = None) -> str:
     """Generate a LiveKit access token for a user in a specific room.
 
@@ -49,6 +71,7 @@ def generate_token(room: str, user, username: Optional[str] = None) -> str:
         .with_grants(video_grants)
         .with_identity(identity)
         .with_name(username or default_username)
+        .with_metadata(json.dumps({"color": generate_color(identity)}))
     )
 
     return token.to_jwt()