merge files inital commit

src/pdf/pdfMergeService.test.ts

@@ -0,0 +1,57 @@
+import { PDFDocument } from 'pdf-lib';
+import { describe, expect, it } from 'vitest';
+import type { PdfFile } from './pdfTypes';
+import { mergePdfFilesAtPosition } from './pdfService';
+
+async function makePdf(name: string, pageCount: number): Promise<PdfFile> {
+  const doc = await PDFDocument.create();
+  for (let i = 0; i < pageCount; i += 1) {
+    doc.addPage([100, 100]);
+  }
+
+  const bytes = await doc.save();
+  const arrayBuffer = new ArrayBuffer(bytes.byteLength);
+  new Uint8Array(arrayBuffer).set(bytes);
+
+  return {
+    id: name,
+    name,
+    doc,
+    pageCount,
+    arrayBuffer,
+  };
+}
+
+describe('mergePdfFilesAtPosition', () => {
+  it('merges a queue without a current base PDF', async () => {
+    const first = await makePdf('first.pdf', 1);
+    const second = await makePdf('second.pdf', 2);
+
+    const merged = await mergePdfFilesAtPosition({
+      basePdf: null,
+      incomingPdfs: [first, second],
+      insertAt: 0,
+      name: 'merged.pdf',
+    });
+
+    expect(merged.name).toBe('merged.pdf');
+    expect(merged.pageCount).toBe(3);
+    expect(merged.doc.getPageCount()).toBe(3);
+  });
+
+  it('inserts queued PDFs into a current base PDF at the requested slot', async () => {
+    const base = await makePdf('base.pdf', 3);
+    const incoming = await makePdf('incoming.pdf', 2);
+
+    const merged = await mergePdfFilesAtPosition({
+      basePdf: base,
+      incomingPdfs: [incoming],
+      insertAt: 1,
+      name: 'base_plus_incoming.pdf',
+    });
+
+    expect(merged.name).toBe('base_plus_incoming.pdf');
+    expect(merged.pageCount).toBe(5);
+    expect(merged.doc.getPageCount()).toBe(5);
+  });
+});

src/pdf/pdfService.ts

@@ -77,6 +77,76 @@ export async function mergePdfFiles(
   };
 }
 
+interface MergePdfFilesAtPositionOptions {
+  basePdf: PdfFile | null;
+  incomingPdfs: PdfFile[];
+  insertAt: number;
+  name: string;
+}
+
+export async function mergePdfFilesAtPosition({
+  basePdf,
+  incomingPdfs,
+  insertAt,
+  name,
+}: MergePdfFilesAtPositionOptions): Promise<PdfFile> {
+  if (!basePdf && incomingPdfs.length === 0) {
+    throw new Error('At least one PDF is required for merging');
+  }
+
+  const mergedDoc = await PDFDocument.create();
+
+  const addAllPages = async (sourcePdf: PdfFile) => {
+    const sourceDoc =
+      sourcePdf.doc ?? (await PDFDocument.load(sourcePdf.arrayBuffer));
+    const pageCount = sourceDoc.getPageCount();
+    const pages = await mergedDoc.copyPages(
+      sourceDoc,
+      Array.from({ length: pageCount }, (_, i) => i)
+    );
+    pages.forEach((page) => mergedDoc.addPage(page));
+  };
+
+  if (!basePdf) {
+    for (const incomingPdf of incomingPdfs) {
+      await addAllPages(incomingPdf);
+    }
+  } else {
+    const baseDoc =
+      basePdf.doc ?? (await PDFDocument.load(basePdf.arrayBuffer));
+    const basePageCount = baseDoc.getPageCount();
+    const clampedInsertAt = Math.min(Math.max(insertAt, 0), basePageCount);
+
+    const basePages = await mergedDoc.copyPages(
+      baseDoc,
+      Array.from({ length: basePageCount }, (_, i) => i)
+    );
+
+    for (let i = 0; i < clampedInsertAt; i += 1) {
+      mergedDoc.addPage(basePages[i]);
+    }
+
+    for (const incomingPdf of incomingPdfs) {
+      await addAllPages(incomingPdf);
+    }
+
+    for (let i = clampedInsertAt; i < basePages.length; i += 1) {
+      mergedDoc.addPage(basePages[i]);
+    }
+  }
+
+  const bytes = await mergedDoc.save();
+  const buffer = pdfBytesToArrayBuffer(bytes);
+
+  return {
+    id: createId(),
+    name,
+    arrayBuffer: buffer,
+    pageCount: mergedDoc.getPageCount(),
+    doc: mergedDoc,
+  };
+}
+
 export async function splitIntoSinglePages(
   pdf: PdfFile
 ): Promise<SplitResult[]> {