monitoring/commands: Add `CommandTransport' factory

Instead of auto-detecting which transport class to use, the instances configuration
now supports a new setting named `transport' with the possible values 'local' and 'remote'.

refs #6593

modules/monitoring/library/Monitoring/Command/Transport/CommandTransport.php

@@ -0,0 +1,101 @@
+<?php
+// {{{ICINGA_LICENSE_HEADER}}}
+// {{{ICINGA_LICENSE_HEADER}}}
+
+namespace Icinga\Module\Monitoring\Command\Transport;
+
+use Zend_Config;
+use Icinga\Application\Config;
+use Icinga\Exception\ConfigurationError;
+
+/**
+ * Command transport factory
+ *
+ * This class is subject to change as we do not have environments yet (#4471).
+ */
+abstract class CommandTransport
+{
+    /**
+     * Transport configuration
+     *
+     * @var Config
+     */
+    protected static $config;
+
+    /**
+     * Get transport configuration
+     *
+     * @return Config
+     * @throws ConfigurationError
+     */
+    public static function getConfig()
+    {
+        if (! isset(self::$config)) {
+            self::$config = Config::module('monitoring', 'instances');
+            if (self::$config->count() === 0) {
+                throw new ConfigurationError;
+            }
+        }
+        return self::$config;
+    }
+
+    /**
+     * Create a transport from config
+     *
+     * @param   Zend_Config $config
+     *
+     * @return  LocalCommandFile|RemoteCommandFile
+     * @throws  ConfigurationError
+     */
+    public static function fromConfig(Zend_Config $config)
+    {
+        switch (strtolower($config->transport)) {
+            case 'remote':
+                $transport = new RemoteCommandFile();
+                break;
+            case 'local':
+            case '':  // Casting null to string is the empty string
+                $transport = new LocalCommandFile();
+                break;
+            default:
+                throw new ConfigurationError;
+        }
+        unset($config->transport);
+        foreach ($config as $key => $value) {
+            $method = 'set' . ucfirst($key);
+            if (! method_exists($transport, $method)) {
+                throw new ConfigurationError;
+            }
+            $transport->$method($value);
+        }
+        return $transport;
+    }
+
+    /**
+     * Create a transport by name
+     *
+     * @param   string $name
+     *
+     * @return  LocalCommandFile|RemoteCommandFile
+     * @throws  ConfigurationError
+     */
+    public static function create($name)
+    {
+        $config = self::getConfig()->get($name);
+        if ($config === null) {
+            throw new ConfigurationError;
+        }
+        return self::fromConfig($config);
+    }
+
+    /**
+     * Create a transport by the first section of the configuration
+     *
+     * @return LocalCommandFile|RemoteCommandFile
+     */
+    public static function first()
+    {
+        $config = self::getConfig()->current();
+        return self::fromConfig($config);
+    }
+}