First code for the piggy bank API.

app/Rules/IsAssetAccountId.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace FireflyIII\Rules;
+
+use FireflyIII\Models\Account;
+use FireflyIII\Models\AccountType;
+use Illuminate\Contracts\Validation\Rule;
+
+/**
+ *
+ * Class IsAssetAccountId
+ */
+class IsAssetAccountId implements Rule
+{
+    /**
+     * Get the validation error message. This is not translated because only the API uses it.
+     *
+     * @return string
+     */
+    public function message(): string
+    {
+        return 'This is not an asset account.';
+    }
+
+    /**
+     * Determine if the validation rule passes.
+     *
+     * @param  string $attribute
+     * @param  mixed  $value
+     *
+     * @return bool
+     */
+    public function passes($attribute, $value): bool
+    {
+        $accountId = (int)$value;
+        $account   = Account::with('accountType')->find($accountId);
+        if (null === $account) {
+            return false;
+        }
+        if ($account->accountType->type !== AccountType::ASSET && $account->accountType->type !== AccountType::DEFAULT) {
+            return false;
+        }
+
+        return true;
+    }
+}