Content pages: various improvements

CONTRIBUTING.md

@@ -128,6 +128,8 @@ When contributing new data (categories, functors, properties, implications), ple
 
 - **Simplify Implications**: When adding a new implication, check if it simplifies existing implications and if it deduces some previously non-deduced properties for categories.
 
+- **Long-form content**: If a proof for a property becomes very long, move it into a markdown-generated content page and link to that page. These files are located in the `/content` folder. For example, `/content/cocongruences_of_groups.md` is rendered at [`/content/cocongruences_of_groups`](https://catdat.app/content/cocongruences_of_groups). Content pages are also used for reusable lemmas that apply to multiple property assignments.
+
 - **New Combinations**: Add new categories that satisfy combinations of satisfied properties and unsatisfied properties and not yet in the database. For example, you may add a category that is abelian but neither cocomplete nor essentially small (if it is not already present). The [page with missing data](https://catdat.app/missing) lists consistent combinations of the form $p \land \neg q$ that are not yet witnessed by a category in the database. The same remarks apply to functors.
 
 ### Redundancy Script

src/routes/content/[id]/+page.server.ts

@@ -1,6 +1,9 @@
 import { content_ids, get_rendered_content } from '$lib/server/markdown'
 import { error } from '@sveltejs/kit'
 import type { EntryGenerator } from './$types'
+import { batch } from '$lib/server/db.catdat'
+import sql from 'sql-template-tag'
+import type { CategoryShort, PropertyShort } from '$lib/commons/types'
 
 export const entries: EntryGenerator = () => {
 	return content_ids.map((id) => ({ id }))
@@ -10,5 +13,33 @@ export const load = async (event) => {
 	const id = event.params.id
 	const content = get_rendered_content(id)
 	if (!content) error(404, 'Not Found')
-	return content
+
+	const { results, err: err_categories } = batch<
+		[CategoryShort, PropertyShort, { id: string }]
+	>([
+		sql`
+			SELECT c.id, c.name FROM categories c
+			WHERE EXISTS (
+				SELECT 1
+				FROM category_property_assignments cp
+				WHERE
+					cp.category_id = c.id
+					AND cp.reason LIKE '%/content/' || ${id} || '%'
+			)
+		`,
+		sql`
+			SELECT id, relation FROM category_properties
+			WHERE description LIKE '%/content/' || ${id} || '%'
+		`,
+		sql`
+			SELECT id FROM category_implications
+			WHERE reason LIKE '%/content/' || ${id} || '%'
+		`,
+	])
+
+	if (err_categories) error(500, 'Could not load context')
+
+	const [categories, category_properties, category_implications] = results
+
+	return { ...content, categories, category_properties, category_implications }
 }

src/routes/content/[id]/+page.svelte

@@ -1,5 +1,8 @@
 <script lang="ts">
+	import CategoryList from '$components/CategoryList.svelte'
 	import MetaData from '$components/MetaData.svelte'
+	import PropertyList from '$components/PropertyList.svelte'
+	import SuggestionForm from '$components/SuggestionForm.svelte'
 
 	let { data } = $props()
 </script>
@@ -14,6 +17,36 @@
 	<p class="hint">Author: {data.meta_data.author}</p>
 {/if}
 
+{#if data.categories.length > 0 || data.category_properties.length > 0 || data.category_implications.length > 0}
+	<h3>Context</h3>
+
+	{#if data.categories.length > 0}
+		<p class="hint">This page is referenced by the following categories.</p>
+
+		<CategoryList categories={data.categories} />
+	{/if}
+
+	{#if data.category_properties.length > 0}
+		<p class="hint">This page is referenced by the following properties.</p>
+
+		<PropertyList properties={data.category_properties} />
+	{/if}
+
+	{#if data.category_implications.length > 0}
+		<p class="hint">This page is referenced by the following implications.</p>
+
+		<ul>
+			{#each data.category_implications as { id }}
+				<li>
+					<a href="/category-implication/{id}">{id}</a>
+				</li>
+			{/each}
+		</ul>
+	{/if}
+{/if}
+
+<SuggestionForm />
+
 <style>
 	.content {
 		line-height: 1.6;