Add basic loading of older posts

src/lib/server/db.ts

@@ -172,15 +172,19 @@ export function savePost(post: Post): void {
     });
 }
 
-export async function getPosts(since: string | null, limit: number) {
+export async function getPosts(since: string | null, before: string | null, limit: number) {
   let promise = await new Promise<Post[]>((resolve, reject) => {
     let filter_query;
     let params: any = { $limit: limit };
-    if (since === null) {
+    if (since === null && before === null) {
       filter_query = '';
-    } else {
+    } else if (since !== null) {
       filter_query = 'WHERE posts.created_at > $since';
       params.$since = since;
+    } else if (before !== null) {
+      // Setting both, before and since doesn't make sense, so this case is not explicitly handled
+      filter_query = 'WHERE posts.created_at < $before';
+      params.$before = before;
     }
     const sql = `SELECT posts.id, posts.content, posts.created_at, posts.url,
     accounts.id AS account_id, accounts.acct, accounts.username, accounts.display_name,