实现报销材料合并预览与差旅概要（07-27-yang-jun-reimbursement-readiness）

server/src/services/reimbursementMaterialPdf.js

@@ -0,0 +1,100 @@
+const crypto = require("node:crypto");
+const { PDFDocument } = require("pdf-lib");
+const sharp = require("sharp");
+
+const FIXED_PDF_DATE = new Date("2000-01-01T00:00:00.000Z");
+const PDF_CREATOR = "hyb-oa";
+const PDF_PRODUCER = "hyb-oa reimbursement material merger";
+
+function materialCollectionHash(materials, mergerVersion) {
+  const hash = crypto.createHash("sha256");
+  hash.update(String(mergerVersion));
+  for (const material of materials) {
+    hash.update("\0");
+    hash.update([
+      material.materialType,
+      material.id,
+      material.fileSha256 ?? "",
+      material.mimeType,
+      String(material.fileSize),
+    ].join("\u001f"));
+  }
+  return hash.digest("hex");
+}
+
+async function normalizeImageForPdf(source, limits) {
+  const image = sharp(source, { failOn: "error", limitInputPixels: limits.maxImagePixels }).rotate();
+  const metadata = await image.metadata();
+  if (!metadata.width || !metadata.height || metadata.width * metadata.height > limits.maxImagePixels) {
+    throw new Error("material_preview_image_invalid");
+  }
+  const normalized = await image
+    .flatten({ background: "#ffffff" })
+    .jpeg({ quality: 90, chromaSubsampling: "4:4:4", mozjpeg: false })
+    .toBuffer();
+  return { buffer: normalized, width: metadata.width, height: metadata.height };
+}
+
+function fitPage(width, height) {
+  const maxSide = 842;
+  const scale = Math.min(1, maxSide / Math.max(width, height));
+  return { width: Math.max(1, width * scale), height: Math.max(1, height * scale) };
+}
+
+async function mergeMaterialsToPdf(materials, limits) {
+  const output = await PDFDocument.create();
+  output.setCreationDate(FIXED_PDF_DATE);
+  output.setModificationDate(FIXED_PDF_DATE);
+  output.setCreator(PDF_CREATOR);
+  output.setProducer(PDF_PRODUCER);
+  output.setTitle("Reimbursement Material Preview");
+  output.setSubject("Derived preview; originals retained separately");
+
+  let pageCount = 0;
+  for (const material of materials) {
+    const source = Buffer.from(material.source);
+    if (material.mimeType === "application/pdf") {
+      let input;
+      try {
+        input = await PDFDocument.load(source, { updateMetadata: false });
+      } catch {
+        throw new Error("material_preview_pdf_invalid");
+      }
+      const indices = input.getPageIndices();
+      if (!indices.length || pageCount + indices.length > limits.maxPages) {
+        throw new Error(indices.length ? "material_preview_page_limit" : "material_preview_pdf_empty");
+      }
+      const pages = await output.copyPages(input, indices);
+      pages.forEach((page) => output.addPage(page));
+      pageCount += pages.length;
+      continue;
+    }
+
+    if (pageCount + 1 > limits.maxPages) throw new Error("material_preview_page_limit");
+    let normalized;
+    try {
+      normalized = await normalizeImageForPdf(source, limits);
+    } catch (error) {
+      if (error?.message === "material_preview_image_invalid") throw error;
+      throw new Error("material_preview_image_invalid");
+    }
+    const embedded = await output.embedJpg(normalized.buffer);
+    const size = fitPage(normalized.width, normalized.height);
+    const page = output.addPage([size.width, size.height]);
+    page.drawImage(embedded, { x: 0, y: 0, width: size.width, height: size.height });
+    pageCount += 1;
+  }
+
+  if (!pageCount) throw new Error("material_preview_empty");
+  const bytes = await output.save({
+    useObjectStreams: true,
+    addDefaultPage: false,
+    objectsPerTick: 50,
+    updateFieldAppearances: false,
+  });
+  const buffer = Buffer.from(bytes);
+  if (buffer.length > limits.maxOutputBytes) throw new Error("material_preview_output_size_limit");
+  return { buffer, pageCount };
+}
+
+module.exports = { materialCollectionHash, mergeMaterialsToPdf };