emoji: Migrate realm emoji to be addressed by id rather than name.

This commit migrates realm emoji to be addressed by their `id` rather
than their name. This fixes a long standing issue which was causing
an error on uploading an emoji with same name as a deactivated realm
emoji.

Fixes: #6977.

zerver/migrations/0149_realm_emoji_drop_unique_constraint.py

@@ -0,0 +1,111 @@
+# -*- coding: utf-8 -*-
+import os
+import shutil
+import tempfile
+
+from boto.s3.connection import S3Connection
+from django.conf import settings
+from django.db import migrations, models
+from django.db.backends.postgresql_psycopg2.schema import DatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+
+class Uploader:
+    def __init__(self) -> None:
+        self.old_orig_image_path_template = "{realm_id}/emoji/{emoji_file_name}.original"
+        self.old_path_template = "{realm_id}/emoji/{emoji_file_name}"
+        self.new_orig_image_path_template = "{realm_id}/emoji/images/{emoji_file_name}.original"
+        self.new_path_template = "{realm_id}/emoji/images/{emoji_file_name}"
+
+    def copy_files(self, src_path: str, dst_path: str) -> None:
+        raise NotImplementedError()
+
+    def ensure_emoji_images(self, realm_id: int, old_filename: str, new_filename: str) -> None:
+        # Copy original image file.
+        old_file_path = self.old_orig_image_path_template.format(realm_id=realm_id,
+                                                                 emoji_file_name=old_filename)
+        new_file_path = self.new_orig_image_path_template.format(realm_id=realm_id,
+                                                                 emoji_file_name=new_filename)
+        self.copy_files(old_file_path, new_file_path)
+
+        # Copy resized image file.
+        old_file_path = self.old_path_template.format(realm_id=realm_id,
+                                                      emoji_file_name=old_filename)
+        new_file_path = self.new_path_template.format(realm_id=realm_id,
+                                                      emoji_file_name=new_filename)
+        self.copy_files(old_file_path, new_file_path)
+
+class LocalUploader(Uploader):
+    def __init__(self) -> None:
+        super().__init__()
+
+    @staticmethod
+    def mkdirs(path: str) -> None:
+        dirname = os.path.dirname(path)
+        if not os.path.isdir(dirname):
+            os.makedirs(dirname)
+
+    def copy_files(self, src_path: str, dst_path: str) -> None:
+        src_path = os.path.join(settings.LOCAL_UPLOADS_DIR, 'avatars', src_path)
+        self.mkdirs(src_path)
+        dst_path = os.path.join(settings.LOCAL_UPLOADS_DIR, 'avatars', dst_path)
+        self.mkdirs(dst_path)
+        shutil.copyfile(src_path, dst_path)
+
+class S3Uploader(Uploader):
+    def __init__(self) -> None:
+        super().__init__()
+        conn = S3Connection(settings.S3_KEY, settings.S3_SECRET_KEY)
+        bucket_name = settings.S3_AVATAR_BUCKET
+        self.bucket = conn.get_bucket(bucket_name, validate=False)
+
+    def copy_files(self, src_key: str, dst_key: str) -> None:
+        self.bucket.copy_key(src_key, self.bucket, dst_key)
+
+def get_uploader() -> Uploader:
+    if settings.LOCAL_UPLOADS_DIR is None:
+        return S3Uploader()
+    return LocalUploader()
+
+def get_emoji_file_name(emoji_file_name: str, new_name: str) -> str:
+    _, image_ext = os.path.splitext(emoji_file_name)
+    return ''.join((new_name, image_ext))
+
+def migrate_realm_emoji_image_files(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
+    RealmEmoji = apps.get_model('zerver', 'RealmEmoji')
+    uploader = get_uploader()
+    for realm_emoji in RealmEmoji.objects.all():
+        old_file_name = realm_emoji.file_name
+        new_file_name = get_emoji_file_name(old_file_name, str(realm_emoji.id))
+        uploader.ensure_emoji_images(realm_emoji.realm_id, old_file_name, new_file_name)
+        realm_emoji.file_name = new_file_name
+        realm_emoji.save(update_fields=['file_name'])
+
+def reversal(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
+    # Ensures that migration can be re-run in case of a failure.
+    RealmEmoji = apps.get_model('zerver', 'RealmEmoji')
+    for realm_emoji in RealmEmoji.objects.all():
+        corrupt_file_name = realm_emoji.file_name
+        correct_file_name = get_emoji_file_name(corrupt_file_name, realm_emoji.name)
+        realm_emoji.file_name = correct_file_name
+        realm_emoji.save(update_fields=['file_name'])
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zerver', '0148_max_invites_forget_default'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='realmemoji',
+            unique_together=set([]),
+        ),
+        migrations.AlterField(
+            model_name='realmemoji',
+            name='file_name',
+            field=models.TextField(db_index=True, null=True, blank=True),
+        ),
+        migrations.RunPython(
+            migrate_realm_emoji_image_files,
+            reverse_code=reversal),
+    ]