isbn3/lib/get_group.js

ISBN utils: parse, validate, format, audit

const groups = require('./groups')

module.exports = isbn13 => {
  const prefix = isbn13.substring(0, 3)
  const restAfterPrefix = isbn13.substring(3)
  const foundGroup = findGroup(prefix, restAfterPrefix, 5)
  if (!foundGroup) return null
  return {
    group: foundGroup.groupId,
    groupPrefix: foundGroup.groupPrefix,
    ranges: foundGroup.groupData.ranges,
    restAfterGroup: restAfterPrefix.slice(foundGroup.groupId.length)
  }
}

function findGroup (prefix, restAfterPrefix, maxGroupIdLength) {
  let length = 0
  while (length <= maxGroupIdLength) {
    const groupId = restAfterPrefix.slice(0, length)
    const groupPrefix = `${prefix}-${groupId}`
    const groupData = groups[groupPrefix]
    if (groupData) return { groupId, groupPrefix, groupData }
    else length++
  }
}