refactor: using react hooks

src/hooks/index.js

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+// @flow
+export { default as useSiteMetadata } from './use-site-metadata';
+export { default as useCategoriesList } from './use-categories-list';
+export { default as useTagsList } from './use-tags-list';

src/hooks/use-categories-list.js

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+// @flow
+import { useStaticQuery, graphql } from 'gatsby';
+
+const useCategoriesList = () => {
+  const { allMarkdownRemark } = useStaticQuery(
+    graphql`
+      query CategoriesListQuery {
+        allMarkdownRemark(
+          filter: { frontmatter: { template: { eq: "post" }, draft: { ne: true } } }
+        ) {
+          group(field: frontmatter___category) {
+            fieldValue
+            totalCount
+          }
+        }
+      }
+    `
+  );
+
+  return allMarkdownRemark.group;
+};
+
+export default useCategoriesList;

src/hooks/use-site-metadata.js

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+// @flow
+import { useStaticQuery, graphql } from 'gatsby';
+
+const useSiteMetadata = () => {
+  const { site } = useStaticQuery(
+    graphql`
+      query SiteMetaData {
+        site {
+          siteMetadata {
+            author {
+              name
+              bio
+              photo
+              contacts {
+                email
+                telegram
+                twitter
+                github
+                rss
+                vkontakte
+              }
+            }
+            menu {
+              label
+              path
+            }
+            url
+            title
+            subtitle
+            copyright
+            disqusShortname
+          }
+        }
+      }
+    `
+  );
+
+  return site.siteMetadata;
+};
+
+export default useSiteMetadata;

src/hooks/use-tags-list.js

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+// @flow
+import { useStaticQuery, graphql } from 'gatsby';
+
+const useTagsList = () => {
+  const { allMarkdownRemark } = useStaticQuery(
+    graphql`
+      query TagsListQuery {
+        allMarkdownRemark(
+          filter: { frontmatter: { template: { eq: "post" }, draft: { ne: true } } }
+        ) {
+          group(field: frontmatter___tags) {
+            fieldValue
+            totalCount
+          }
+        }
+      }
+    `
+  );
+
+  return allMarkdownRemark.group;
+};
+
+export default useTagsList;