Introduce an image sizes cache to improve feed layouts (close #213) (#335)

* Introduce an image sizes cache to improve feed layouts (close #213)

* Clear out resolved promises from the image cache

1 files changed, 44 insertions, 0 deletions

diff --git a/src/state/models/cache/link-metas.ts b/src/state/models/cache/link-metas.ts
new file mode 100644
index 000000000..607968c80
--- /dev/null
+++ b/src/state/models/cache/link-metas.ts
@@ -0,0 +1,44 @@
+import {makeAutoObservable} from 'mobx'
+import {LRUMap} from 'lru_map'
+import {RootStoreModel} from '../root-store'
+import {LinkMeta, getLinkMeta} from 'lib/link-meta/link-meta'
+
+type CacheValue = Promise<LinkMeta> | LinkMeta
+export class LinkMetasCache {
+  cache: LRUMap<string, CacheValue> = new LRUMap(100)
+
+  constructor(public rootStore: RootStoreModel) {
+    makeAutoObservable(
+      this,
+      {
+        rootStore: false,
+        cache: false,
+      },
+      {autoBind: true},
+    )
+  }
+
+  // public api
+  // =
+
+  async getLinkMeta(url: string) {
+    const cached = this.cache.get(url)
+    if (cached) {
+      try {
+        return await cached
+      } catch (e) {
+        // ignore, we'll try again
+      }
+    }
+    try {
+      const promise = getLinkMeta(this.rootStore, url)
+      this.cache.set(url, promise)
+      const res = await promise
+      this.cache.set(url, res)
+      return res
+    } catch (e) {
+      this.cache.delete(url)
+      throw e
+    }
+  }
+}