Some code cleaning up and refactoring.

app/Support/Models/TagSupport.php

@@ -0,0 +1,78 @@
+<?php
+declare(strict_types = 1);
+
+namespace FireflyIII\Support\Models;
+
+use FireflyIII\Models\Tag;
+use Illuminate\Database\Eloquent\Model;
+
+class TagSupport extends Model
+{
+    /**
+     * Can a tag become an advance payment?
+     *
+     * @param Tag $tag
+     *
+     * @return bool
+     */
+    public static function tagAllowAdvance(Tag $tag): bool
+    {
+        /*
+                * If this tag is a balancing act, and it contains transfers, it cannot be
+                * changes to an advancePayment.
+                */
+
+        if ($tag->tagMode == 'balancingAct' || $tag->tagMode == 'nothing') {
+            foreach ($tag->transactionjournals as $journal) {
+                if ($journal->isTransfer()) {
+                    return false;
+                }
+            }
+        }
+
+        /*
+         * If this tag contains more than one expenses, it cannot become an advance payment.
+         */
+        $count = 0;
+        foreach ($tag->transactionjournals as $journal) {
+            if ($journal->isWithdrawal()) {
+                $count++;
+            }
+        }
+        if ($count > 1) {
+            return false;
+        }
+
+        return true;
+    }
+
+    /**
+     * Can a tag become a balancing act?
+     *
+     * @param Tag $tag
+     *
+     * @return bool
+     */
+    public static function tagAllowBalancing(Tag $tag): bool
+    {
+        /*
+         * If has more than two transactions already, cannot become a balancing act:
+         */
+        if ($tag->transactionjournals->count() > 2) {
+            return false;
+        }
+
+        /*
+         * If any transaction is a deposit, cannot become a balancing act.
+         */
+        foreach ($tag->transactionjournals as $journal) {
+            if ($journal->isDeposit()) {
+                return false;
+            }
+        }
+
+        return true;
+
+    }
+
+}