feat: implement Redis queue helper functions for Matching Service

Author: SherwynNg

services/matching-service/app/services/queue.py

@@ -0,0 +1,40 @@
+import redis
+import json
+import time
+
+r = redis.Redis(host="localhost", port=6379, db=0, decode_responses=True)
+
+def _queue_key(difficulty: str, topic: str, language: str) -> str:
+    return f"match_queue:{difficulty}:{topic}:{language}"
+
+def enqueue_user(difficulty: str, topic: str, language: str, user_id: str):
+    key = _queue_key(difficulty, topic, language)
+    # add to the end of the queue
+    r.rpush(key, user_id)
+    r.hset("match_timestamps", user_id, int(time.time()))
+
+def dequeue_user(difficulty: str, topic: str, language: str):
+    key = _queue_key(difficulty, topic, language)
+    # pop from the front (FIFO)
+    user_id = r.lpop(key)
+    if user_id:
+        r.hdel("match_timestamps", user_id)
+    return user_id
+
+def get_queue_position(difficulty: str, topic: str, language: str, user_id: str):
+    key = _queue_key(difficulty, topic, language)
+    queue = r.lrange(key, 0, -1)
+    try:
+        return queue.index(user_id) + 1
+    except ValueError:
+        return None
+    
+def remove_user(difficulty: str, topic: str, language: str, user_id: str):
+    key = _queue_key(difficulty, topic, language)
+    removed = r.lrem(key, 0, user_id)
+    r.hdel("match_timestamps", user_id)
+    return removed > 0
+
+def get_user_join_time(user_id: str):
+    ts = r.hget("match_timestamps", user_id)
+    return int(ts) if ts else None