refactor(core): add reusable rxSwr operator

packages/sanity/src/core/util/index.ts

@@ -9,6 +9,7 @@ export * from './isString'
 export * from './isTruthy'
 export * from './PartialExcept'
 export * from './resizeObserver'
+export * from './rxSwr'
 export * from './schemaUtils'
 export * from './searchUtils'
 export * from './supportsTouch'

packages/sanity/src/core/util/rxSwr.ts

@@ -0,0 +1,55 @@
+import QuickLRU from 'quick-lru'
+import {concat, defer, EMPTY, map, type Observable, of, type OperatorFunction} from 'rxjs'
+import {tap} from 'rxjs/operators'
+
+interface SWRCache<T> {
+  /**
+   * Note: This will throw if key does not exist. Always check for existence with `has` before calling
+   */
+  get(key: string): T
+  has(key: string): boolean
+  set(key: string, value: T): void
+  delete(key: string): void
+}
+
+const createSWRCache = createLRUCache
+
+export function createSWR<T>(options: {maxSize: number}) {
+  const cache = createSWRCache<T>(options)
+  return function rxSwr(key: string): OperatorFunction<T, {fromCache: boolean; value: T}> {
+    return (input$: Observable<T>) => {
+      return concat(
+        defer(() => (cache.has(key) ? of({fromCache: true, value: cache.get(key)}) : EMPTY)),
+        input$.pipe(
+          tap((result) => cache.set(key, result)),
+          map((value) => ({
+            fromCache: false,
+            value: value,
+          })),
+        ),
+      )
+    }
+  }
+}
+
+function createLRUCache<T>(options: {maxSize: number}): SWRCache<T> {
+  const lru = new QuickLRU<string, {value: T}>(options)
+  return {
+    get(key: string) {
+      const entry = lru.get(key)
+      if (!entry) {
+        throw new Error(`Key not found in LRU cache: ${key}`)
+      }
+      return entry.value
+    },
+    set(key: string, value: T) {
+      lru.set(key, {value})
+    },
+    delete(key: string) {
+      lru.delete(key)
+    },
+    has(key: string) {
+      return lru.has(key)
+    },
+  }
+}