text: const path = require(`path`);
  const { createFilePath } = require(`gatsby-source-filesystem`);
  
  exports.createPages = ({ graphql, actions }) => {
    const { createPage } = actions;
  
    const blogPost = path.resolve(`./src/templates/blog-post.jsx`);
    return graphql(
      `
        {
          allMarkdownRemark(
            sort: { fields: [frontmatter___date], order: DESC }
            limit: 1000
          ) {
            edges {
              node {
                fields {
                  slug
                }
                frontmatter {
                  title
                }
              }
            }
          }
        }
      `
    ).then(result => {
      if (result.errors) {
        throw result.errors;
      }
  
      // Create blog posts pages.
      const posts = result.data.allMarkdownRemark.edges;
  
      posts.forEach((post, index) => {
        const previous =
          index === posts.length - 1 ? null : posts[index + 1].node;
        const next = index === 0 ? null : posts[index - 1].node;
  
        createPage({
          path: post.node.fields.slug,
          component: blogPost,
          context: {
            slug: post.node.fields.slug,
            previous,
            next,
          },
        });
      });
  
      return null;
    });
  };
  
  exports.onCreateNode = ({ node, actions, getNode }) => {
    const { createNodeField } = actions;
  
    if (node.internal.type === `MarkdownRemark`) {
      const value = createFilePath({ node, getNode });
      createNodeField({
        name: `slug`,
        node,
        value,
      });
    }
  };
  