From a643d2e58260d4cfac589deae5faafb60cd11f14 Mon Sep 17 00:00:00 2001
From: George Payne <georgepayne@hotmail.com>
Date: Mon, 13 May 2024 10:51:42 +0200
Subject: [PATCH] add getOrInsert method to ListStore

---
 .changeset/beige-pans-try.md                  | 12 ++++++++++++
 packages/stores/src/stores/createListStore.ts |  8 ++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 .changeset/beige-pans-try.md

diff --git a/.changeset/beige-pans-try.md b/.changeset/beige-pans-try.md
new file mode 100644
index 00000000..0fcc1647
--- /dev/null
+++ b/.changeset/beige-pans-try.md
@@ -0,0 +1,12 @@
+---
+'@eventstore-ui/stores': minor
+---
+
+Get's a single item from the list store, or inserts a default and returns it.
+
+```ts
+const item = store.getOrInsert('my-id', () => ({
+    id: 'my-id',
+    value: Math.random(),
+}));
+```
diff --git a/packages/stores/src/stores/createListStore.ts b/packages/stores/src/stores/createListStore.ts
index b0ca8e7d..8456796a 100644
--- a/packages/stores/src/stores/createListStore.ts
+++ b/packages/stores/src/stores/createListStore.ts
@@ -21,6 +21,8 @@ export interface ListStore<T> {
     ) => Array<R>;
     /** Get a single item from the list. */
     get: (id: string) => T | undefined;
+    /** Get a single item from the list, or insert a default and return it */
+    getOrInsert: (id: string, defaultValue: () => T) => T;
     /** Check if an item is available in the list. */
     has: (id: string) => boolean;
     /** Returns an array of all the keys in the store. */
@@ -99,6 +101,12 @@ export const createListStore = <T>(
                 return acc;
             }, []),
         get: (id) => state[id],
+        getOrInsert: (id, defaultValue) => {
+            if (!(id in state)) {
+                state[id] = defaultValue();
+            }
+            return state[id];
+        },
         has: (id) => id in state,
         keys: () => Object.keys(state),
         onChange: (...args: any[]) => {