feat(v2): implement blog (#1062)

* feat(v2): implement blog

* expect flat blog structure

* \n

* blogpage can import many posts

v2/lib/load/blog.js

@@ -0,0 +1,73 @@
+const globby = require('globby');
+const path = require('path');
+const fs = require('fs-extra');
+const {parse, idx} = require('./utils');
+
+function fileToUrl(fileName) {
+  return fileName
+    .replace('-', '/')
+    .replace('-', '/')
+    .replace('-', '/')
+    .replace(/\.md$/, '');
+}
+
+async function loadBlog({blogDir, env, siteConfig}) {
+  const blogFiles = await globby(['*.md'], {
+    cwd: blogDir,
+  });
+
+  const {baseUrl} = siteConfig;
+
+  /* Prepare metadata container */
+  const blogMetadatas = [];
+
+  /* the language for each blog page */
+  const defaultLangTag = idx(env, ['translation', 'defaultLanguage', 'tag']);
+
+  await Promise.all(
+    blogFiles.map(async relativeSource => {
+      const source = path.join(blogDir, relativeSource);
+
+      const blogFileName = path.basename(relativeSource);
+      // Extract, YYYY, MM, DD from the file name
+      const filePathDateArr = blogFileName.split('-');
+      const date = new Date(
+        `${filePathDateArr[0]}-${filePathDateArr[1]}-${
+          filePathDateArr[2]
+        }T06:00:00.000Z`,
+      );
+
+      const fileString = await fs.readFile(source, 'utf-8');
+      const {metadata: rawMetadata} = parse(fileString);
+      const metadata = {
+        permalink: path.join(baseUrl, `blog`, fileToUrl(blogFileName)),
+        source,
+        ...rawMetadata,
+        date,
+        language: defaultLangTag,
+      };
+      blogMetadatas.push(metadata);
+    }),
+  );
+  blogMetadatas.sort((a, b) => a.date - b.date);
+
+  // blogpage handling. Example: `/blog`, `/blog/page1`, `/blog/page2`
+  const perPage = 10;
+  const numOfBlog = blogMetadatas.length;
+  const numberOfPage = Math.ceil(numOfBlog / perPage);
+  const basePageUrl = path.join(baseUrl, 'blog');
+
+  /* eslint-disable */
+  for (let page = 0; page < numberOfPage; page++) {
+    blogMetadatas.push({
+      permalink: path.join(basePageUrl, `${page > 0 ? `page${page + 1}` : ''}`),
+      language: defaultLangTag,
+      isBlogPage: true,
+      posts: blogMetadatas.slice(page * perPage, (page + 1) * perPage),
+    });
+  }
+
+  return blogMetadatas;
+}
+
+module.exports = loadBlog;