gatsby-node.js

const path = require(`path`)
const { postsPerPage } = require(`./src/utils/siteConfig`)
const { paginate } = require(`gatsby-awesome-pagination`)

/**
 * Here is the place where Gatsby creates the URLs for all the
 * posts, tags, pages and authors that we fetched from the Ghost site.
 */
exports.createPages = async ({ graphql, actions }) => {
    const { createPage } = actions

    const result = await graphql(`
        {
            allGhostPost(sort: { order: ASC, fields: published_at }) {
                edges {
                    node {
                        slug
                    }
                }
            }
            allGhostTag(sort: { order: ASC, fields: name }) {
                edges {
                    node {
                        slug
                        url
                        postCount
                    }
                }
            }
            allGhostAuthor(sort: { order: ASC, fields: name }) {
                edges {
                    node {
                        slug
                        url
                        postCount
                    }
                }
            }
            allGhostPage(sort: { order: ASC, fields: published_at }) {
                edges {
                    node {
                        slug
                        url
                    }
                }
            }
        }
    `)

    // Check for any errors
    if (result.errors) {
        throw new Error(result.errors)
    }

    // Extract query results
    const tags = result.data.allGhostTag.edges
    const pages = result.data.allGhostPage.edges
    const posts = result.data.allGhostPost.edges

    // Load templates
    const indexTemplate = path.resolve(`./src/templates/index.js`)
    const tagsTemplate = path.resolve(`./src/templates/tag.js`)
    const pageTemplate = path.resolve(`./src/templates/page.js`)
    const postTemplate = path.resolve(`./src/templates/post.js`)

    // Create tag pages
    tags.forEach(({ node }) => {
        const totalPosts = node.postCount !== null ? node.postCount : 0
        const numberOfPages = Math.ceil(totalPosts / postsPerPage)

        // This part here defines, that our tag pages will use
        // a `/tag/:slug/` permalink.
        node.url = `/tag/${node.slug}/`

        Array.from({ length: numberOfPages }).forEach((_, i) => {
            const currentPage = i + 1
            const prevPageNumber = currentPage <= 1 ? null : currentPage - 1
            const nextPageNumber =
                currentPage + 1 > numberOfPages ? null : currentPage + 1
            const previousPagePath = prevPageNumber
                ? prevPageNumber === 1
                    ? node.url
                    : `${node.url}page/${prevPageNumber}/`
                : null
            const nextPagePath = nextPageNumber
                ? `${node.url}page/${nextPageNumber}/`
                : null

            createPage({
                path: i === 0 ? node.url : `${node.url}page/${i + 1}/`,
                component: tagsTemplate,
                context: {
                    // Data passed to context is available
                    // in page queries as GraphQL variables.
                    slug: node.slug,
                    limit: postsPerPage,
                    skip: i * postsPerPage,
                    numberOfPages: numberOfPages,
                    humanPageNumber: currentPage,
                    prevPageNumber: prevPageNumber,
                    nextPageNumber: nextPageNumber,
                    previousPagePath: previousPagePath,
                    nextPagePath: nextPagePath,
                },
            })
        })
    })

    // Create pages
    pages.forEach(({ node }) => {
        // This part here defines, that our pages will use
        // a `/:slug/` permalink.
        node.url = `/${node.slug}/`

        createPage({
            path: node.url,
            component: pageTemplate,
            context: {
                // Data passed to context is available
                // in page queries as GraphQL variables.
                slug: node.slug,
            },
        })
    })

    // Create post pages
    posts.forEach(({ node }) => {
        // This part here defines, that our posts will use
        // a `/:slug/` permalink.
        node.url = `/${node.slug}/`

        createPage({
            path: node.url,
            component: postTemplate,
            context: {
                // Data passed to context is available
                // in page queries as GraphQL variables.
                slug: node.slug,
            },
        })
    })

    // Create pagination
    paginate({
        createPage,
        items: posts,
        itemsPerPage: postsPerPage,
        component: indexTemplate,
        pathPrefix: ({ pageNumber }) => {
            if (pageNumber === 0) {
                return `/`
            } else {
                return `/page`
            }
        },
    })
}