Add redirects migration

web/modules/custom/custom/migrations/migrate_plus.migration.redirect.yml

@@ -0,0 +1,51 @@
+id: redirect
+
+source:
+  plugin: url
+  data_fetcher_plugin: http
+  data_parser_plugin: json
+
+  urls: https://deploy-preview-213--opdavies.netlify.app/redirects.json
+
+  ids:
+    id:
+      type: integer
+
+  item_selector: redirects/
+
+  fields:
+    - name: id
+      selector: id
+      label: Redirect ID
+
+    - name: from
+      selector: from
+      label: From
+
+    - name: to
+      selector: to
+      label: To
+
+process:
+  redirect_source/path: from
+  redirect_redirect/uri:
+    plugin: opd_redirect
+    source: to
+
+  language:
+    plugin: default_value
+    default_value: und
+
+  status_code:
+    plugin: default_value
+    default_value: 301
+
+  uid:
+    plugin: default_value
+    default_value: 1
+
+destination:
+  plugin: 'entity:redirect'
+
+migration_dependencies:
+  required: { }

web/modules/custom/custom/src/Plugin/migrate/process/OpdRedirect.php

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+<?php
+
+namespace Drupal\custom\Plugin\migrate\process;
+
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Illuminate\Support\Str;
+
+/**
+ * Perform custom value transformations.
+ *
+ * @MigrateProcessPlugin(
+ *   id = "opd_redirect"
+ * )
+ */
+class OpdRedirect extends ProcessPluginBase {
+
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    if (Str::startsWith($value, '/')) {
+      return "internal:{$value}";
+    }
+
+    return $value;
+  }
+
+}