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worker/partial.ts

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+import { PartialMessageMime } from './types';
+import { stat, readFile, unlink } from 'fs/promises';
+import { simpleParser } from 'mailparser';
+
+export const checkAndCombinePartial = async (partial: PartialMessageMime['params']) => {
+  const allStats = await Promise.allSettled(
+    [...
+      Array(partial.total)
+      .fill(null)
+      .map((_, i) => stat(`./partials/${partial.id}-part_${i + 1}-attachment`)),
+      ...Array(partial.total)
+        .fill(null)
+        .map((_, i) => stat(`./partials/${partial.id}-part_${i + 1}-article.json`)),
+      ]
+  );
+  const allExists = allStats.every((result) => result.status === 'fulfilled' && result.value.isFile());
+
+  if (!allExists) {
+    return null;
+  }
+
+  //combine all partials
+  const filesReadPromises = Array(partial.total)
+    .fill(null)
+    .map((_, index) => {
+      console.log(`Reading file ./partials/${partial.id}-part_${index + 1}-attachment`)
+      return readFile(`./partials/${partial.id}-part_${index + 1}-attachment`)
+    })
+
+  const files = await Promise.all(filesReadPromises);
+
+  const file = Buffer.concat(files);
+
+  const parsed = await simpleParser(file);
+  const xrefs = new Set<string>();
+  let articleId = '';
+  const articlesReadPromises = Array(partial.total)
+    .fill(null)
+    .map(async (_, index) => {
+      console.log(`Reading file ./partials/${partial.id}-part_${index + 1}-article.json`)
+      const articleJson = await readFile(`./partials/${partial.id}-part_${index + 1}-article.json`)
+      const article = JSON.parse(articleJson.toString());
+      if (index === 0) {
+        articleId = article.articleId;
+      }
+      if (article && article.headers && article.headers.xref) {
+        return article.headers.xref as string;
+      }
+    })
+
+  const articlesXrefs = await Promise.all(articlesReadPromises);
+
+  articlesXrefs.forEach((xref) => {
+    if (xref) {
+      xref.split(' ').forEach(xre => xrefs.add(xre))
+    }
+  })
+
+  parsed.headers.set('xref', Array.from(xrefs).join(' '));
+
+  if (!articleId) {
+    throw new Error(`articleId not found for ${partial.id}`);
+  }
+
+  const deletePromises = Array(partial.total)
+    .fill(null)
+    .map(async (_, index) => {
+      console.log(`Deleting file ./partials/${partial.id}-part_${index + 1}-article.json`)
+      await unlink(`./partials/${partial.id}-part_${index + 1}-article.json`)
+      console.log(`Deleting file ./partials/${partial.id}-part_${index + 1}-attachment`)
+      await unlink(`./partials/${partial.id}-part_${index + 1}-attachment`)
+    })
+
+  await Promise.all(deletePromises);
+  parsed.headers.set('messageId', articleId);
+  parsed.messageId = articleId;
+
+  return parsed;
+}