Change map pool selection (#952)

* Select opposing players based on displayed rating

instead of mean

* Select map pool based on average rating of the players

* Make map pool selection configurable

* Refactor if-chain to static mapping in config.py

---------

Co-authored-by: Askaholic <[email protected]>

server/config.py

@@ -5,6 +5,7 @@
 import asyncio
 import logging
 import os
+import statistics
 from typing import Callable
 
 import trueskill
@@ -26,6 +27,11 @@
 # see: http://forums.faforever.com/viewtopic.php?f=45&t=11698#p119599
 # Optimum values for ladder here, using them for global as well.
 trueskill.setup(mu=1500, sigma=500, beta=240, tau=10, draw_probability=0.10)
+MAP_POOL_RATING_SELECTION_FUNCTIONS = {
+    "mean": statistics.mean,
+    "min": min,
+    "max": max,
+}
 
 
 @with_logger
@@ -131,7 +137,10 @@ def __init__(self):
         self.LADDER_SEARCH_EXPANSION_STEP = 0.05
         self.LADDER_TOP_PLAYER_SEARCH_EXPANSION_MAX = 0.3
         self.LADDER_TOP_PLAYER_SEARCH_EXPANSION_STEP = 0.15
-        # The maximum amount of time in seconds) to wait between pops.
+        # The method for choosing map pool rating
+        # Can be "mean", "min", or "max"
+        self.MAP_POOL_RATING_SELECTION = "mean"
+        # The maximum amount of time in seconds to wait between pops
         self.QUEUE_POP_TIME_MAX = 90
         # The number of possible matches we would like to have when the queue
         # pops. The queue pop time will be adjusted based on the current rate of

server/ladder_service/ladder_service.py

@@ -14,7 +14,7 @@
 from sqlalchemy import and_, func, select, text, true
 
 from server import metrics
-from server.config import config
+from server.config import MAP_POOL_RATING_SELECTION_FUNCTIONS, config
 from server.core import Service
 from server.db import FAFDatabase
 from server.db.models import (
@@ -499,10 +499,17 @@ async def _start_game(
                 queue.id,
                 limit=config.LADDER_ANTI_REPETITION_LIMIT
             )
-            rating = min(
-                player.ratings[queue.rating_type].displayed()
-                for player in all_players
+
+            def get_displayed_rating(player: Player) -> float:
+                return player.ratings[queue.rating_type].displayed()
+
+            ratings = (get_displayed_rating(player) for player in all_players)
+            func = MAP_POOL_RATING_SELECTION_FUNCTIONS.get(
+                config.MAP_POOL_RATING_SELECTION,
+                statistics.mean
             )
+            rating = func(ratings)
+
             pool = queue.get_map_pool_for_rating(rating)
             if not pool:
                 raise RuntimeError(f"No map pool available for rating {rating}!")
@@ -521,11 +528,8 @@ async def _start_game(
             game.map_file_path = map_path
             game.set_name_unchecked(game_name(team1, team2))
 
-            def get_player_mean(player: Player) -> float:
-                return player.ratings[queue.rating_type].mean
-
-            team1 = sorted(team1, key=get_player_mean)
-            team2 = sorted(team2, key=get_player_mean)
+            team1 = sorted(team1, key=get_displayed_rating)
+            team2 = sorted(team2, key=get_displayed_rating)
 
             # Shuffle the teams such that direct opponents remain the same
             zipped_teams = list(zip(team1, team2))