module.exports = (config) => {

  // add collection for pages
  config.addCollection('pages', (collection) => {
    let sorted = []
    let unsorted = []
    const pages = collection.getFilteredByGlob('**/*.md')

    for (let page of pages) {
      if (page.data.sort) {
        if (sorted[page.data.sort]) {
          sorted.splice(page.data.sort, 0, page)
        } else {
          sorted[page.data.sort] = page
        }
      } else {
        unsorted.push(page)
      }
    }

    return sorted.concat(unsorted)
  })

  // custom filters
  config.addFilter("makeLowercase", (value) => {
    if (typeof value === 'string' || value instanceof String) {
      return value.toLowerCase()
    }
  })

  // added passthrough for global assets
  config.addPassthroughCopy("assets")
  // added passthrough for images in their respective folders
  config.addPassthroughCopy("_content/**/images/**")

  // reutrn updated config
  return {
    dir: {
      input: "_content", // content
      includes: "../_includes", // templates
      output: "_site", // rendered site
      data: "../_data" // global data files
    }
  }
}