1 files changed, 62 insertions, 0 deletions
diff --git a/frontend/src/lib/Reader.ts b/frontend/src/lib/Reader.ts
new file mode 100644
index 0000000..8777b9b
--- /dev/null
+++ b/frontend/src/lib/Reader.ts
@@ -0,0 +1,62 @@
+import { Layout, type PageFragment } from '$gql/graphql';
+import { getContext, setContext } from 'svelte';
+import { writable, type Writable } from 'svelte/store';
+
+export interface Chunk {
+	main: PageFragment;
+	secondary?: PageFragment;
+	index: number;
+}
+
+class ReaderContext {
+	visible = false;
+	sidebar = false;
+	pages: PageFragment[] = [];
+	page = 0;
+
+	open(page: number) {
+		this.page = page;
+		this.visible = true;
+
+		return this;
+	}
+}
+
+export function initReaderContext() {
+	return setContext<Writable<ReaderContext>>('reader', writable(new ReaderContext()));
+}
+
+export function getReaderContext() {
+	return getContext<Writable<ReaderContext>>('reader');
+}
+
+export function partition(pages: PageFragment[], layout: Layout): [Chunk[], number[]] {
+	const single = layout === Layout.Single;
+	const offset = layout === Layout.DoubleOffset;
+
+	const chunks: Chunk[] = [];
+	const lookup: number[] = Array<number>(pages.length);
+
+	for (let chunkIndex = 0, pageIndex = 0; pageIndex < pages.length; chunkIndex++) {
+		const wide = () => pages[pageIndex].image.aspectRatio > 1;
+
+		const nextPage = () => {
+			lookup[pageIndex] = chunkIndex;
+			return pages[pageIndex++];
+		};
+
+		const offsetFirst = pageIndex === 0 && offset;
+		const full = single || wide() || offsetFirst;
+
+		const chunk: Chunk = { index: pageIndex, main: nextPage() };
+
+		if (!full && pageIndex < pages.length) {
+			if (!wide()) {
+				chunk.secondary = nextPage();
+			}
+		}
+
+		chunks.push(chunk);
+	}
+	return [chunks, lookup];
+}