gatsby-node.js

const path = require(`path`)
const { createFilePath } = require(`gatsby-source-filesystem`)

function createBlogPosts(blogPosts, createPage) {
  const blogPost = path.resolve(`./src/templates/blog-post.js`)
  const blogPostAmp = path.resolve(`./src/templates/blog-post.amp.js`)
  const tagTemplate = path.resolve('./src/templates/tag.js')
  blogPosts.forEach((post, index) => {
    const previous =
      index === blogPosts.length - 1 ? null : blogPosts[index + 1].node
    const next = index === 0 ? null : blogPosts[index - 1].node

    createPage({
      path: post.node.fields.slug,
      component: blogPost,
      context: {
        slug: post.node.fields.slug,
        previous,
        next,
      },
    })

    createPage({
      path: `/amp/${post.node.fields.slug}`,
      component: blogPostAmp,
      context: {
        slug: post.node.fields.slug,
        previous,
        next,
      },
    })
  })
  // Create tag pages
  let tags = []
  // Iterate through each post, putting all found tags into `tags`
  blogPosts.forEach(edge => {
    if (edge.node.frontmatter.tags) {
      tags = tags.concat(edge.node.frontmatter.tags)
    }
  })
  // Eliminate duplicate tags
  tags = Array.from(new Set(tags))

  // Make tag pages
  tags.forEach(tag => {
    createPage({
      // Creating kebab case for tag link
      path: `/tags/${tag
        .replace(/([a-z])([A-Z])/g, '$1-$2')
        .replace(/\s+/g, '-')
        .toLowerCase()}/`,
      component: tagTemplate,
      context: {
        tag,
      },
    })
  })
}

function createSinglePages(pages, createPage) {
  const aboutPage = path.resolve(`./src/templates/about.js`)
  pages.forEach(page => {
    createPage({
      path: page.node.fields.slug,
      component: aboutPage,
      context: {
        slug: page.node.fields.slug,
      },
    })
  })
}

exports.createPages = ({ graphql, actions }) => {
  const { createPage, createRedirect } = actions

  // Migrate from wordpress
  createRedirect({
    fromPath: '/2017/03/19/cach-gap-fork-mot-repository-tren-github/',
    toPath: '/cach-gap-fork-mot-repository-tren-github/',
    isPermanent: true,
    redirectInBrowser: true,
  })

  return new Promise((resolve, reject) => {
    resolve(
      graphql(
        `
          {
            allMarkdownRemark(
              sort: { fields: [frontmatter___date], order: DESC }
              limit: 1000
            ) {
              edges {
                node {
                  fields {
                    slug
                  }
                  frontmatter {
                    title
                    tags
                    type
                  }
                }
              }
            }
          }
        `
      ).then(result => {
        if (result.errors) {
          console.log(result.errors)
          reject(result.errors)
        }

        const blogPosts = result.data.allMarkdownRemark.edges.filter(
          ({ node }) => node.frontmatter.type === 'blog'
        )
        const pages = result.data.allMarkdownRemark.edges.filter(
          ({ node }) => node.frontmatter.type === 'page'
        )

        createBlogPosts(blogPosts, createPage)
        createSinglePages(pages, createPage)
      })
    )
  })
}

exports.onCreateNode = ({ node, actions, getNode }) => {
  const { createNodeField } = actions

  if (node.internal.type === `MarkdownRemark`) {
    const value = createFilePath({ node, getNode })
    createNodeField({
      name: `slug`,
      node,
      value,
    })
  }
}