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.tsx`)
    return graphql(
      `
        {
          allMdx(sort: {fields: [frontmatter___date], order: DESC}, limit: 1000) {
            edges {
              node {
                slug
                frontmatter {
                  title
                }
                id
              }
            }
          }
        }
      `
    ).then(result => {
      if (result.errors) {
        throw result.errors
      }
  
      // Create blog posts pages.
      const posts = result.data.allMdx.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.slug,
          component: blogPost,
          context: {
            slug: post.node.slug,
            id: post.node.id.
            previous,
            next,
          },
        })
      })
    })
  }
  
  exports.onCreateNode = ({ node, actions, getNode }) => {
    const { createNodeField } = actions
    if (node.internal.type === 'Mdx') {
      const value = createFilePath({ node, getNode })
      createNodeField({
        name: `slug`,
        node,
        value,
      })
    }
  }
  