Begin to implement import on visibility for publication content

src/lib/components/Publication.svelte

@@ -9,25 +9,64 @@
     TextPlaceholder,
     Tooltip,
   } from "flowbite-svelte";
-  import { onMount } from "svelte";
+  import { getContext, onMount } from "svelte";
   import { BookOutline } from "flowbite-svelte-icons";
-  import Preview from "./Preview.svelte";
-  import { pharosInstance } from "$lib/parser";
   import { page } from "$app/state";
-  import { ndkInstance } from "$lib/ndk";
   import type { NDKEvent } from "@nostr-dev-kit/ndk";
   import PublicationSection from "./PublicationSection.svelte";
+  import type { PublicationTree } from "$lib/data_structures/publication_tree";
 
-  let { rootId, publicationType, indexEvent } = $props<{ 
-    rootId: string, 
+  let { rootAddress, publicationType, indexEvent } = $props<{ 
+    rootAddress: string, 
     publicationType: string,
     indexEvent: NDKEvent
   }>();
 
-  if (rootId !== $pharosInstance.getRootIndexId()) {
-    console.error("Root ID does not match parser root index ID");
+  const publicationTree = getContext('publicationTree') as PublicationTree;
+
+  // #region Loading
+
+  // TODO: Test load handling.
+
+  let leaves = $state<NDKEvent[]>([]);
+  let isLoading = $state<boolean>(false);
+  let lastElementRef = $state<HTMLElement | null>(null);
+
+  let observer: IntersectionObserver;
+
+  async function loadMore(count: number) {
+    isLoading = true;
+
+    for (let i = 0; i < count; i++) {
+      const nextItem = await publicationTree.next();
+      if (nextItem.done) {
+        break;
+      }
+      leaves.push(nextItem.value);
+    }
+
+    isLoading = false;
+  }
+
+  function setLastElementRef(el: HTMLElement, i: number) {
+    if (i === leaves.length - 1) {
+      lastElementRef = el;
+    }
   }
 
+  $effect(() => {
+    if (!lastElementRef) {
+      return;
+    }
+
+    observer.observe(lastElementRef!);
+    return () => observer.unobserve(lastElementRef!);
+  });
+
+  // #endregion
+
+  // #region ToC
+
   const tocBreakpoint = 1140;
 
   let activeHash = $state(page.url.hash);
@@ -82,21 +121,33 @@
     }
   }
 
+  // #endregion
+
   onMount(() => {
     // Always check whether the TOC sidebar should be visible.
     setTocVisibilityOnResize();
-
     window.addEventListener("hashchange", scrollToElementWithOffset);
     // Also handle the case where the user lands on the page with a hash in the URL
     scrollToElementWithOffset();
-
     window.addEventListener("resize", setTocVisibilityOnResize);
     window.addEventListener("click", hideTocOnClick);
 
+    // Set up the intersection observer.
+    observer = new IntersectionObserver((entries) => {
+      entries.forEach((entry) => {
+        if (entry.isIntersecting && !isLoading) {
+          loadMore(8);
+        }
+      });
+    }, { threshold: 0.5 });
+    loadMore(16);
+
     return () => {
       window.removeEventListener("hashchange", scrollToElementWithOffset);
       window.removeEventListener("resize", setTocVisibilityOnResize);
       window.removeEventListener("click", hideTocOnClick);
+
+      observer.disconnect();
     };
   });
 </script>
@@ -115,7 +166,7 @@
   </Button>
   <Tooltip>Show Table of Contents</Tooltip>
 {/if}
-<!-- TODO: Get TOC from parser. -->
+<!-- TODO: Use loader to build ToC. -->
 <!-- {#if showToc}
   <Sidebar class='sidebar-leather fixed top-20 left-0 px-4 w-60' {activeHash}>
     <SidebarWrapper>
@@ -132,8 +183,13 @@
   </Sidebar>
 {/if} -->
 <div class="flex flex-col space-y-4 max-w-2xl">
-  <!-- TODO: Pass in the correct address for each section. -->
-  <PublicationSection rootAddress={rootId} address={''} />
+  {#each leaves as leaf, i}
+    <PublicationSection
+      rootAddress={rootAddress}
+      address={leaf.tagAddress()}
+      ref={(el) => setLastElementRef(el, i)}
+    />
+  {/each}
 </div>
 
 <style>

src/lib/components/PublicationSection.svelte

@@ -4,7 +4,15 @@
   import { TextPlaceholder } from "flowbite-svelte";
   import { getContext } from "svelte";
 
-  let { address, rootAddress }: { address: string, rootAddress: string } = $props();
+  let {
+    address,
+    rootAddress,
+    ref,
+  }: {
+    address: string,
+    rootAddress: string,
+    ref: (ref: HTMLElement) => void,
+  } = $props();
 
   const publicationTree = getContext<PublicationTree>('publicationTree');
 
@@ -14,10 +22,20 @@
     (await rootEvent)?.getMatchingTags('type')[0]?.[1]);
   let hierarchy = $derived.by(async () => await publicationTree.getHierarchy(address));
   let depth = $derived.by(async () => (await hierarchy).length);
+
+  let sectionRef: HTMLElement;
+
+  $effect(() => {
+    if (!sectionRef) {
+      return;
+    }
+
+    ref(sectionRef);
+  })
 </script>
 
 <!-- TODO: Correctly handle events that are the start of a content section. -->
-<section>
+<section bind:this={sectionRef}>
   {#await Promise.all([sectionEvent, publicationType])}
     <TextPlaceholder size='xxl' />
   {:then [sectionEvent, publicationType]}

src/routes/publication/+page.svelte

@@ -18,7 +18,7 @@
   // Get image and summary from the event tags if available
   // If image unavailable, use the Alexandria default pic.
   let image = $derived(data.indexEvent?.getMatchingTags('image')[0]?.[1] || '/screenshots/old_books.jpg');
-  let summary = $derived(data.indexEvent?.getMatchingTags('summary')[0]?.[1] || 'Alexandria is a digital library, utilizing Nostr events for curated publications and wiki pages.');
+  let summary = $derived(data.indexEvent?.getMatchingTags('summary')[0]?.[1] || 'Alexandria is a digital library, utilizing Nostr events for curated publications and wiki pages.');  
 
   onDestroy(() => data.parser.reset());
 </script>
@@ -48,9 +48,9 @@
     <TextPlaceholder divClass='skeleton-leather w-full' size="xxl" />
   {:then}
     <Publication 
-      rootId={data.parser.getRootIndexId()} 
+      rootAddress={data.indexEvent.tagAddress()} 
       publicationType={data.publicationType} 
-      indexEvent={data.indexEvent} 
+      indexEvent={data.indexEvent}
     />
   {/await}
 </main>