Added ArticleFooter and SequenceNav

src/lib/site/navigation.ts

@@ -1,5 +1,30 @@
 import type { Article } from './types'
 
+export type Sequence = {
+  parent: Article
+  siblings: Article[]
+  position: number
+  previous: Article | null
+  next: Article | null
+}
+
+export function sequenceOf(article: Article): Sequence | null {
+  const parent = article.parent
+  if (!parent?.route.sequence) return null
+
+  const siblings = parent.children
+  const position = siblings.indexOf(article)
+  if (position === -1 || siblings.length < 2) return null
+
+  return {
+    parent,
+    siblings,
+    position,
+    previous: siblings[position - 1] ?? null,
+    next: siblings[position + 1] ?? null,
+  }
+}
+
 export function trailOf(article: Article): Article[] {
   const trail: Article[] = []
   for (let node: Article | null = article; node; node = node.parent) trail.unshift(node)