Migrate data from points to record

Merge !60 (merged) first.

This migration adds transforms the existing data from points to match record. It runs this in a Django migration, meaning the data migration will automatically run as part of the CI/CD process. It also includes a way to rollback this migration if we ever need to. I tested both by running it on my local copy of the database.

I copied some of the code rather than import it because I don't want the result of this migration to change in the future if someone changes the estimation function.

championship/migrations/0019_eventplayerresult_migrate_from_points_to_record.py

+from django.db import migrations, models
+import math
+
+
+def estimate_rounds(match_point_list: list[int]) -> int:
+    """Estimates the number of rounds based on a list of the match point.
+
+    Copied from general parser functions so that future edits to this file
+    don't change the results of this migration.
+    """
+    num_players = len(match_point_list)
+
+    # The number of rounds needs to be at least the amount wins + draws of an individual player
+    min_num_rounds = max([mp // 3 + mp % 3 for mp in match_point_list])
+
+    # We add +1 because the actual rounds is likely to be 1 higher
+    byes = min_num_rounds + 1 if num_players % 2 == 1 else 0
+
+    total_wins = sum([mp // 3 for mp in match_point_list]) - byes
+    total_losses = total_wins
+    total_draws = sum([mp % 3 for mp in match_point_list])
+
+    # We can estimate the number of rounds played based on the total number of wins, losses, draws and byes
+    number_of_matches_per_player = (
+        total_wins + total_draws + total_losses + byes
+    ) / num_players
+
+    # We round it up, since some players might drop out
+    rounds_estimate = math.ceil(number_of_matches_per_player)
+
+    return max(rounds_estimate, min_num_rounds)
+
+
+def migrate_to_points(apps, schema_editor):
+    EventPlayerResult = apps.get_model("championship", "EventPlayerResult")
+    Event = apps.get_model("championship", "Event")
+    db_alias = schema_editor.connection.alias
+
+    for event in (
+        Event.objects.using(db_alias)
+        .annotate(num_results=models.Count("eventplayerresult"))
+        .filter(num_results__gt=0)
+    ):
+        points = [
+            e.points
+            for e in EventPlayerResult.objects.using(db_alias).filter(event=event)
+        ]
+        rounds = estimate_rounds(points)
+
+        for epr in EventPlayerResult.objects.using(db_alias).filter(event=event):
+            if epr.win_count + epr.loss_count + epr.draw_count > 0:
+                continue
+            epr.win_count = epr.points // 3
+            epr.draw_count = epr.points % 3
+            epr.loss_count = rounds - epr.win_count - epr.draw_count
+            epr.migrated_from_points_to_record = True
+            epr.save()
+
+
+def revert_migration(apps, schema_editor):
+    EventPlayerResult = apps.get_model("championship", "EventPlayerResult")
+    db_alias = schema_editor.connection.alias
+    for epr in EventPlayerResult.objects.using(db_alias).filter(
+        migrated_from_points_to_record=True
+    ):
+        epr.win_count = 0
+        epr.loss_count = 0
+        epr.draw_count = 0
+        epr.save()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("championship", "0018_eventplayerresult_points_to_record"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="eventplayerresult",
+            name="migrated_from_points_to_record",
+            field=models.BooleanField(
+                default=False,
+                help_text="Indicates whether this result was automatically migrated from points to records. Used for diagnostics.",
+            ),
+        ),
+        migrations.RunPython(migrate_to_points, revert_migration),
+    ]