From d786b7d683f84e062241d3f3fbdfa2f0b42b21ac Mon Sep 17 00:00:00 2001
From: Noel De Martin <noel@moodle.com>
Date: Mon, 19 Dec 2022 12:35:10 +0100
Subject: [PATCH] MOBILE-4081 core: Use inmemory database singletons

---
 .../classes/database/eager-database-table.ts  |  4 +-
 .../database/inmemory-database-table.ts       | 73 +++++++++++++++++++
 .../classes/database/lazy-database-table.ts   |  4 +-
 3 files changed, 77 insertions(+), 4 deletions(-)
 create mode 100644 src/core/classes/database/inmemory-database-table.ts

diff --git a/src/core/classes/database/eager-database-table.ts b/src/core/classes/database/eager-database-table.ts
index 1a03e0fda96..5db50316286 100644
--- a/src/core/classes/database/eager-database-table.ts
+++ b/src/core/classes/database/eager-database-table.ts
@@ -14,8 +14,8 @@
 
 import { CoreError } from '@classes/errors/error';
 import { SQLiteDBRecordValues } from '@classes/sqlitedb';
+import { CoreInMemoryDatabaseTable } from './inmemory-database-table';
 import {
-    CoreDatabaseTable,
     CoreDatabaseConditions,
     GetDBRecordPrimaryKey,
     CoreDatabaseReducer,
@@ -32,7 +32,7 @@ export class CoreEagerDatabaseTable<
     DBRecord extends SQLiteDBRecordValues = SQLiteDBRecordValues,
     PrimaryKeyColumn extends keyof DBRecord = 'id',
     PrimaryKey extends GetDBRecordPrimaryKey<DBRecord, PrimaryKeyColumn> = GetDBRecordPrimaryKey<DBRecord, PrimaryKeyColumn>
-> extends CoreDatabaseTable<DBRecord, PrimaryKeyColumn, PrimaryKey> {
+> extends CoreInMemoryDatabaseTable<DBRecord, PrimaryKeyColumn, PrimaryKey> {
 
     protected records: Record<string, DBRecord> = {};
 
diff --git a/src/core/classes/database/inmemory-database-table.ts b/src/core/classes/database/inmemory-database-table.ts
new file mode 100644
index 00000000000..6637f1f5416
--- /dev/null
+++ b/src/core/classes/database/inmemory-database-table.ts
@@ -0,0 +1,73 @@
+// (C) Copyright 2015 Moodle Pty Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import { CoreConstants } from '@/core/constants';
+import { SQLiteDB, SQLiteDBRecordValues } from '@classes/sqlitedb';
+import { CoreLogger } from '@singletons/logger';
+import { CoreDatabaseTable, GetDBRecordPrimaryKey } from './database-table';
+
+/**
+ * Database wrapper that caches database records in memory to speed up read operations.
+ *
+ * Extensions of this class should only be used as singletons, or the data integrity of the inmemory cache
+ * could be compromised.
+ */
+export abstract class CoreInMemoryDatabaseTable<
+    DBRecord extends SQLiteDBRecordValues = SQLiteDBRecordValues,
+    PrimaryKeyColumn extends keyof DBRecord = 'id',
+    PrimaryKey extends GetDBRecordPrimaryKey<DBRecord, PrimaryKeyColumn> = GetDBRecordPrimaryKey<DBRecord, PrimaryKeyColumn>
+> extends CoreDatabaseTable<DBRecord, PrimaryKeyColumn, PrimaryKey> {
+
+    private static readonly ACTIVE_TABLES: WeakMap<SQLiteDB, Set<string>> = new WeakMap();
+    private static readonly LOGGER: CoreLogger = CoreLogger.getInstance('CoreInMemoryDatabaseTable');
+
+    /**
+     * @inheritdoc
+     */
+    async initialize(): Promise<void> {
+        await super.initialize();
+
+        const activeTables = CoreInMemoryDatabaseTable.ACTIVE_TABLES.get(this.database) ?? new Set();
+
+        if (activeTables.has(this.tableName)) {
+            const message = `Trying to create multiple instances of an in-memory table for '${this.tableName}', ` +
+                'use singletons instead.';
+
+            if (!CoreConstants.BUILD.isProduction) {
+                throw new Error(message);
+            }
+
+            CoreInMemoryDatabaseTable.LOGGER.warn(message);
+        }
+
+        activeTables.add(this.tableName);
+        CoreInMemoryDatabaseTable.ACTIVE_TABLES.set(this.database, activeTables);
+    }
+
+    /**
+     * @inheritdoc
+     */
+    async destroy(): Promise<void> {
+        await super.destroy();
+
+        const activeTables = CoreInMemoryDatabaseTable.ACTIVE_TABLES.get(this.database);
+
+        activeTables?.delete(this.tableName);
+
+        if (activeTables?.size === 0) {
+            CoreInMemoryDatabaseTable.ACTIVE_TABLES.delete(this.database);
+        }
+    }
+
+}
diff --git a/src/core/classes/database/lazy-database-table.ts b/src/core/classes/database/lazy-database-table.ts
index 2e1aabcc5ff..faee315d0c5 100644
--- a/src/core/classes/database/lazy-database-table.ts
+++ b/src/core/classes/database/lazy-database-table.ts
@@ -14,9 +14,9 @@
 
 import { CoreError } from '@classes/errors/error';
 import { SQLiteDBRecordValues } from '@classes/sqlitedb';
+import { CoreInMemoryDatabaseTable } from './inmemory-database-table';
 import {
     CoreDatabaseConfiguration,
-    CoreDatabaseTable,
     CoreDatabaseConditions,
     GetDBRecordPrimaryKey,
     CoreDatabaseQueryOptions,
@@ -32,7 +32,7 @@ export class CoreLazyDatabaseTable<
     DBRecord extends SQLiteDBRecordValues = SQLiteDBRecordValues,
     PrimaryKeyColumn extends keyof DBRecord = 'id',
     PrimaryKey extends GetDBRecordPrimaryKey<DBRecord, PrimaryKeyColumn> = GetDBRecordPrimaryKey<DBRecord, PrimaryKeyColumn>
-> extends CoreDatabaseTable<DBRecord, PrimaryKeyColumn, PrimaryKey> {
+> extends CoreInMemoryDatabaseTable<DBRecord, PrimaryKeyColumn, PrimaryKey> {
 
     protected readonly DEFAULT_CACHE_LIFETIME = 60000;