feat: implement post existence check and detail page

apps/backend/src/lib/pixiv.ts

@@ -1,3 +1,5 @@
+import { MediaUpload } from "@/models/media";
+
 function fetchPixivData(url: string): Promise<any> {
     // https://www.pixiv.net/artworks/143552616
     const match = url.match(/\/artworks\/(\d+)/);
@@ -30,4 +32,27 @@ function fetchPixivData(url: string): Promise<any> {
         });
 }
 
-export { fetchPixivData };
+async function checkPixivData(url: string, selected: Array<boolean>) {
+    const match = url.match(/\/artworks\/(\d+)/);
+    if (!match) {
+        throw new Error("Invalid Pixiv URL");
+    }
+
+    const artworkId = match[1];
+    const selectedIndices = selected
+        .map((isSelected, index) => (isSelected ? index : -1))
+        .filter((index) => index >= 0);
+
+    if (selectedIndices.length === 0) {
+        return false;
+    }
+
+    const existing = await MediaUpload.findOne({
+        "tweet.id": artworkId,
+        mediaIndex: { $in: selectedIndices },
+    });
+
+    return existing !== null;
+}
+
+export { checkPixivData, fetchPixivData };