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 { data: normalized, info } = await image
    .flatten({ background: "#ffffff" })
    .jpeg({ quality: 90, chromaSubsampling: "4:4:4", mozjpeg: false })
    .toBuffer({ resolveWithObject: true });
  if (!info.width || !info.height || info.width * info.height > limits.maxImagePixels) {
    throw new Error("material_preview_image_invalid");
  }
  return { buffer: normalized, width: info.width, height: info.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 };