[REF] refactor on nasty Dedupe function

I found with other pieces of refactoring static functions that creating a class to support the refactor
made it much easier as that way I could leverage the fact thatt classes have properties and
get away from the crazy param passing that characterizes a nest of static functions.

This adds a class for that purpose and moves a small chunk of code handling into the class.

The goal is to move the handling is done purely for the form back onto the form....

CRM/Dedupe/MergeHandler.php

@@ -0,0 +1,113 @@
+<?php
+/*
+ +--------------------------------------------------------------------+
+ | CiviCRM version 5                                                  |
+ +--------------------------------------------------------------------+
+ | Copyright CiviCRM LLC (c) 2004-2020                                |
+ +--------------------------------------------------------------------+
+ | This file is a part of CiviCRM.                                    |
+ |                                                                    |
+ | CiviCRM is free software; you can copy, modify, and distribute it  |
+ | under the terms of the GNU Affero General Public License           |
+ | Version 3, 19 November 2007 and the CiviCRM Licensing Exception.   |
+ |                                                                    |
+ | CiviCRM is distributed in the hope that it will be useful, but     |
+ | WITHOUT ANY WARRANTY; without even the implied warranty of         |
+ | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.               |
+ | See the GNU Affero General Public License for more details.        |
+ |                                                                    |
+ | You should have received a copy of the GNU Affero General Public   |
+ | License and the CiviCRM Licensing Exception along                  |
+ | with this program; if not, contact CiviCRM LLC                     |
+ | at info[AT]civicrm[DOT]org. If you have questions about the        |
+ | GNU Affero General Public License or the licensing of CiviCRM,     |
+ | see the CiviCRM license FAQ at http://civicrm.org/licensing        |
+ +--------------------------------------------------------------------+
+ */
+
+/**
+ *
+ * @package CRM
+ * @copyright CiviCRM LLC (c) 2004-2020
+ *
+ * This class exists primarily for the purposes of supporting code clean up in the Merger class.
+ *
+ * It is expected to be fast-moving and calling it outside the refactoring work is not advised.
+ */
+class CRM_Dedupe_MergeHandler {
+
+  /**
+   * ID of contact to be kept.
+   *
+   * @var int
+   */
+  protected $toKeepID;
+
+  /**
+   * ID of contact to be merged and deleted.
+   *
+   * @var int
+   */
+  protected $toRemoveID;
+
+  /**
+   * @return mixed
+   */
+  public function getToKeepID() {
+    return $this->toKeepID;
+  }
+
+  /**
+   * @param mixed $toKeepID
+   */
+  public function setToKeepID($toKeepID) {
+    $this->toKeepID = $toKeepID;
+  }
+
+  /**
+   * @return mixed
+   */
+  public function getToRemoveID() {
+    return $this->toRemoveID;
+  }
+
+  /**
+   * @param mixed $toRemoveID
+   */
+  public function setToRemoveID($toRemoveID) {
+    $this->toRemoveID = $toRemoveID;
+  }
+
+  /**
+   * CRM_Dedupe_MergeHandler constructor.
+   *
+   * @param int $toKeepID
+   *   ID of contact to be kept.
+   * @param int $toRemoveID
+   *   ID of contact to be removed.
+   */
+  public function __construct(int $toKeepID, int $toRemoveID) {
+    $this->setToKeepID($toKeepID);
+    $this->setToRemoveID($toRemoveID);
+  }
+
+  /**
+   * Get an array of tables that relate to the contact entity and will need consideration in a merge.
+   *
+   * The list of potential tables is filtered by tables which have data for the relevant contacts.
+   */
+  public function getTablesRelatedToTheMergePair() {
+    $relTables = CRM_Dedupe_Merger::relTables();
+    $activeRelTables = CRM_Dedupe_Merger::getActiveRelTables($this->toRemoveID);
+    $activeMainRelTables = CRM_Dedupe_Merger::getActiveRelTables($this->toKeepID);
+    foreach ($relTables as $name => $null) {
+      if (!in_array($name, $activeRelTables, TRUE) &&
+        !(($name === 'rel_table_users') && in_array($name, $activeMainRelTables, TRUE))
+      ) {
+        unset($relTables[$name]);
+      }
+    }
+    return $relTables;
+  }
+
+}

CRM/Dedupe/Merger.php

@@ -1315,17 +1315,9 @@ public static function getRowsElementsAndInfo($mainId, $otherId, $checkPermissio
       }
     }
 
-    $relTables = CRM_Dedupe_Merger::relTables();
-    $activeRelTables = CRM_Dedupe_Merger::getActiveRelTables($otherId);
-    $activeMainRelTables = CRM_Dedupe_Merger::getActiveRelTables($mainId);
+    $mergeHandler = new CRM_Dedupe_MergeHandler((int) $mainId, (int) $otherId);
+    $relTables = $mergeHandler->getTablesRelatedToTheMergePair();
     foreach ($relTables as $name => $null) {
-      if (!in_array($name, $activeRelTables) &&
-        !(($name == 'rel_table_users') && in_array($name, $activeMainRelTables))
-      ) {
-        unset($relTables[$name]);
-        continue;
-      }
-
       $relTableElements[] = ['checkbox', "move_$name"];
       $migrationInfo["move_$name"] = 1;