From 8acffb49af72a0a3bcf1f9bc969350bf4fdaf6f1 Mon Sep 17 00:00:00 2001
From: Steve Boyd <emteknetnz@gmail.com>
Date: Fri, 13 Sep 2024 11:33:26 +1200
Subject: [PATCH] NEW Allow database read-only replicas

---
 src/Core/CoreKernel.php | 81 ++++++++++++++++++++++++++++++++++-------
 src/ORM/DB.php          | 10 ++++-
 2 files changed, 77 insertions(+), 14 deletions(-)

diff --git a/src/Core/CoreKernel.php b/src/Core/CoreKernel.php
index 7f968c8a3f4..4389797c94b 100644
--- a/src/Core/CoreKernel.php
+++ b/src/Core/CoreKernel.php
@@ -98,20 +98,58 @@ protected function bootDatabaseEnvVars()
         $databaseConfig = $this->getDatabaseConfig();
         $databaseConfig['database'] = $this->getDatabaseName();
         DB::setConfig($databaseConfig);
+
+        // Set database replicas config
+        for ($i = 1; $i <= 99; $i++) {
+            $replicaKey = $this->getReplicaKey('SS_DATABASE_SERVER', $i);
+            if (!Environment::hasEnv($replicaKey)) {
+                break;
+            }
+            $replicaDatabaseConfig = $this->getDatabaseReplicaConfig($i);
+            $name = 'replica_' . str_pad($i, 2, '0', STR_PAD_LEFT);
+            DB::setConfig($replicaDatabaseConfig, $name);
+        }
     }
 
     /**
-     * Load database config from environment
-     *
-     * @return array
+     * Convert a database key to a replica key
+     * e.g. SS_DATABASE_SERVER -> SS_DATABASE_SERVER_REPLICA_01
      */
-    protected function getDatabaseConfig()
+    private function getReplicaKey(string $key, int $replica): string
+    {
+        // Left pad replica number with a zero if it's less than 10
+        return $key . '_REPLICA_' . str_pad($replica, 2, '0', STR_PAD_LEFT);
+    }
+
+    /**
+     * Reads a single database configuration variable from the environment
+     * For replica databases, it will first attempt to find replica-specific configuration
+     * before falling back to the default configuration.
+     * 
+     * Replicate specific configuration has `_REPLICA_01` appended to the key
+     * where 01 is the replica number.
+     */
+    private function getDatabaseConfigVariable(string $key, int $replica): string
+    {
+        if ($replica > 0) {
+            $replicaKey = $this->getReplicaKey($key, $replica);
+            if (Environment::hasEnv($replicaKey)) {
+                return Environment::getEnv($replicaKey);
+            }
+        }
+        if (Environment::hasEnv($key)) {
+            return Environment::getEnv($key);
+        }
+        return '';
+    }
+
+    private function getSingleDataBaseConfig(int $replica): array
     {
         $databaseConfig = [
-            "type" => Environment::getEnv('SS_DATABASE_CLASS') ?: 'MySQLDatabase',
-            "server" => Environment::getEnv('SS_DATABASE_SERVER') ?: 'localhost',
-            "username" => Environment::getEnv('SS_DATABASE_USERNAME') ?: null,
-            "password" => Environment::getEnv('SS_DATABASE_PASSWORD') ?: null,
+            "type" => $this->getDatabaseConfigVariable('SS_DATABASE_CLASS', $replica) ?: 'MySQLDatabase',
+            "server" => $this->getDatabaseConfigVariable('SS_DATABASE_SERVER', $replica) ?: 'localhost',
+            "username" => $this->getDatabaseConfigVariable('SS_DATABASE_USERNAME', $replica) ?: null,
+            "password" => $this->getDatabaseConfigVariable('SS_DATABASE_PASSWORD', $replica) ?: null,
         ];
 
         // Only add SSL keys in the array if there is an actual value associated with them
@@ -122,7 +160,7 @@ protected function getDatabaseConfig()
             'ssl_cipher' => 'SS_DATABASE_SSL_CIPHER',
         ];
         foreach ($sslConf as $key => $envVar) {
-            $envValue = Environment::getEnv($envVar);
+            $envValue = $this->getDatabaseConfigVariable($envVar, $replica);
             if ($envValue) {
                 $databaseConfig[$key] = $envValue;
             }
@@ -138,25 +176,25 @@ protected function getDatabaseConfig()
         }
 
         // Set the port if called for
-        $dbPort = Environment::getEnv('SS_DATABASE_PORT');
+        $dbPort = $this->getDatabaseConfigVariable('SS_DATABASE_PORT', $replica);
         if ($dbPort) {
             $databaseConfig['port'] = $dbPort;
         }
 
         // Set the timezone if called for
-        $dbTZ = Environment::getEnv('SS_DATABASE_TIMEZONE');
+        $dbTZ = $this->getDatabaseConfigVariable('SS_DATABASE_TIMEZONE', $replica);
         if ($dbTZ) {
             $databaseConfig['timezone'] = $dbTZ;
         }
 
         // For schema enabled drivers:
-        $dbSchema = Environment::getEnv('SS_DATABASE_SCHEMA');
+        $dbSchema = $this->getDatabaseConfigVariable('SS_DATABASE_SCHEMA', $replica);
         if ($dbSchema) {
             $databaseConfig["schema"] = $dbSchema;
         }
 
         // For SQlite3 memory databases (mainly for testing purposes)
-        $dbMemory = Environment::getEnv('SS_DATABASE_MEMORY');
+        $dbMemory = $this->getDatabaseConfigVariable('SS_DATABASE_MEMORY', $replica);
         if ($dbMemory) {
             $databaseConfig["memory"] = $dbMemory;
         }
@@ -166,6 +204,22 @@ protected function getDatabaseConfig()
         return $databaseConfig;
     }
 
+    /**
+     * Load database config from environment
+     *
+     * @return array
+     */
+    protected function getDatabaseConfig()
+    {
+        return $this->getSingleDataBaseConfig(0);
+    }
+
+    protected function getDatabaseReplicaConfig(int $replica)
+    {
+        $replica = 1;
+        return $this->getSingleDataBaseConfig($replica);
+    }
+
     /**
      * @return string
      */
@@ -184,6 +238,7 @@ protected function getDatabaseSuffix()
 
     /**
      * Get name of database
+     * Note that any replicas must have the same database name
      *
      * @return string
      */
diff --git a/src/ORM/DB.php b/src/ORM/DB.php
index 054b858d02f..a036b2fd463 100644
--- a/src/ORM/DB.php
+++ b/src/ORM/DB.php
@@ -311,11 +311,19 @@ public static function setConfig($databaseConfig, $name = 'default')
      */
     public static function getConfig($name = 'default')
     {
-        if (isset(static::$configs[$name])) {
+        if (static::hasConfig($name)) {
             return static::$configs[$name];
         }
     }
 
+    /**
+     * Check if a named connection config exists
+     */
+    public static function hasConfig($name = 'default'): bool
+    {
+        return isset(static::$configs[$name]);
+    }
+
     /**
      * Returns true if a database connection has been attempted.
      * In particular, it lets the caller know if we're still so early in the execution pipeline that