From 81fde2ebd3d5389328b5de87a863136fb7241bb4 Mon Sep 17 00:00:00 2001
From: Joakim Carlstein <joakim@aboviq.com>
Date: Wed, 15 Nov 2023 16:00:21 +0100
Subject: [PATCH] feat(plugin-tools): add types for "loader" plugins

---
 .changeset/spicy-seahorses-listen.md |  5 +++++
 packages/plugin-tools/src/types.ts   | 28 ++++++++++++++++++++++++++--
 2 files changed, 31 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/spicy-seahorses-listen.md

diff --git a/.changeset/spicy-seahorses-listen.md b/.changeset/spicy-seahorses-listen.md
new file mode 100644
index 0000000..4979c11
--- /dev/null
+++ b/.changeset/spicy-seahorses-listen.md
@@ -0,0 +1,5 @@
+---
+'@emigrate/plugin-tools': minor
+---
+
+Prepare for supporting "loader" plugins. A loader plugin is used to transform a migration file of a given type (file extension) to a function that will execute the actual migration.
diff --git a/packages/plugin-tools/src/types.ts b/packages/plugin-tools/src/types.ts
index a35e013..90bb5f7 100644
--- a/packages/plugin-tools/src/types.ts
+++ b/packages/plugin-tools/src/types.ts
@@ -87,12 +87,36 @@ export type GeneratorPlugin = {
 
 export type GenerateMigrationFunction = GeneratorPlugin['generateMigration'];
 
+export type MigrationFunction = () => Promise<void>;
+
+export type MigrationMetadata = {
+  name: string;
+  filename: string;
+  extension: string;
+};
+
+export type LoaderPlugin = {
+  /**
+   * The file extensions that this plugin can load.
+   */
+  loadableExtensions: string[];
+  /**
+   * Used to load a migration file, i.e. transform it into a function that can be executed.
+   *
+   * @param migration Some metadata about the migration file that should be loaded.
+   * @returns A function that will execute the migration.
+   */
+  loadMigration(migration: MigrationMetadata): Promise<MigrationFunction>;
+};
+
 export type Plugin = StoragePlugin | GeneratorPlugin;
 
-export type PluginType = 'storage' | 'generator';
+export type PluginType = 'storage' | 'generator' | 'loader';
 
 export type PluginFromType<T extends PluginType> = T extends 'storage'
   ? StoragePlugin
   : T extends 'generator'
     ? GeneratorPlugin
-    : never;
+    : T extends 'loader'
+      ? LoaderPlugin
+      : never;