docs/lib/get-applicable-versions.js

const allVersions = require('./all-versions')
const versionSatisfiesRange = require('./version-satisfies-range')
const checkIfNextVersionOnly = require('./check-if-next-version-only')

// return an array of versions that an article's product versions encompasses
function getApplicableVersions (frontmatterVersions, filepath) {
  if (typeof frontmatterVersions === 'undefined') {
    throw new Error(`No \`versions\` frontmatter found in ${filepath}`)
  }

  // all versions are applicable!
  if (frontmatterVersions === '*') {
    return Object.keys(allVersions)
  }

  // get an array like: [ 'free-pro-team@latest', 'enterprise-server@2.21', 'enterprise-cloud@latest' ]
  const applicableVersions = []

  let isNextVersionOnly = false

  // where frontmatter is something like:
  //   fpt: '*'
  //   ghes: '>=2.19'
  //   ghae: '*'
  // ^ where each key corresponds to a plan's short name (defined in lib/all-versions.js)
  Object.entries(frontmatterVersions)
    .forEach(([plan, planValue]) => {
      // Special handling for frontmatter that evalues to the next GHES release number or a hardcoded `next`.
      isNextVersionOnly = checkIfNextVersionOnly(planValue)

      // For each plan (e.g., enterprise-server), get matching versions from allVersions object
      Object.values(allVersions)
        .filter(relevantVersion => relevantVersion.plan === plan || relevantVersion.shortName === plan)
        .forEach(relevantVersion => {
          // Use a dummy value of '1.0' for non-numbered versions like free-pro-team and github-ae
          // This will evaluate to true against '*' but false against 'next', which is what we want.
          const versionToCompare = relevantVersion.hasNumberedReleases ? relevantVersion.currentRelease : '1.0'

          if (versionSatisfiesRange(versionToCompare, planValue)) {
            applicableVersions.push(relevantVersion.version)
          }
        })
    })

  if (!applicableVersions.length && !isNextVersionOnly) {
    throw new Error(`No applicable versions found for ${filepath}. Please double-check the page's \`versions\` frontmatter.`)
  }

  return applicableVersions
}

module.exports = getApplicableVersions