text: const path = require(`path`)
  const { createFilePath } = require(`gatsby-source-filesystem`)
  
  exports.createPages = async ({ graphql, actions, reporter }) => {
    const { createPage } = actions
  
    // Define a template for blog post
    const blogPost = path.resolve(`./src/templates/blog-post.js`)
  
    // Get all markdown blog posts sorted by date
    const result = await graphql(
      `
        {
          allMarkdownRemark(
            sort: { fields: [frontmatter___date], order: ASC }
            limit: 1000
          ) {
            nodes {
              id
              fields {
                slug
              }
            }
          }
        }
      `
    )
  
    if (result.errors) {
      reporter.panicOnBuild(
        `There was an error loading your blog posts`,
        result.errors
      )
      return
    }
  
    const posts = result.data.allMarkdownRemark.nodes
  
    // Create blog posts pages
    // But only if there's at least one markdown file found at "content/blog" (defined in gatsby-config.js)
    // `context` is available in the template as a prop and as a variable in GraphQL
  
    if (posts.length > 0) {
      posts.forEach((post, index) => {
        const previousPostId = index === 0 ? null : posts[index - 1].id
        const nextPostId = index === posts.length - 1 ? null : posts[index + 1].id
  
        createPage({
          path: `/blog${post.fields.slug}`,
          component: blogPost,
          context: {
            id: post.id,
            previousPostId,
            nextPostId,
          },
        })
      })
    }
  }
  
  exports.onCreateNode = ({ node, actions, getNode }) => {
    const { createNodeField } = actions
  
    if (node.internal.type === `MarkdownRemark`) {
      const value = createFilePath({ node, getNode })
  
      createNodeField({
        name: `slug`,
        node,
        value,
      })
    }
  }
  
  exports.createSchemaCustomization = ({ actions }) => {
    const { createTypes } = actions
  
    // Explicitly define the siteMetadata {} object
    // This way those will always be defined even if removed from gatsby-config.js
  
    // Also explicitly define the Markdown frontmatter
    // This way the "MarkdownRemark" queries will return `null` even when no
    // blog posts are stored inside "content/blog" instead of returning an error
    createTypes(`
      type SiteSiteMetadata {
        author: Author
        siteUrl: String
        social: Social
      }
  
      type Author {
        name: String
        summary: String
      }
  
      type Social {
        twitter: String
      }
  
      type MarkdownRemark implements Node {
        frontmatter: Frontmatter
        fields: Fields
      }
  
      type Frontmatter {
        title: String
        description: String
        date: Date @dateformat
      }
  
      type Fields {
        slug: String
      }
    `)
  }
  