export interface JsonHalLinkList {
  self: string
  [link: string]: string
}

export interface JsonHalPagination {
  first: boolean
  last: boolean
  size: number
  totalElements: number
  totalPages: number
  number: number
}

export interface JsonHalObject {
  ID: string
  links: JsonHalLinkList
}

export interface JsonHalCollection {
  links: JsonHalLinkList
  page: JsonHalPagination
}

const emptyPagination = (size: number = 0): JsonHalPagination => ({
  first: true,
  last: true,
  number: 0,
  size,
  totalElements: size,
  totalPages: 0,
})

const convertLinks = (links: any): JsonHalLinkList => !links ? { self: '' } :
  Object.keys(links).reduce((list: JsonHalLinkList, link: string) => {
    list[link] = links[link].href
    return list
  }, {}) as JsonHalLinkList

const extractId = (link: string) => {
  const idMatch = link.match(/([^\/\{]+)(\{[^\}]+\})?$/)
  return idMatch && idMatch[1]
}

const extractPagination = (size: number, page: JsonHalPagination = emptyPagination(size)) => ({
  ...page,
  first: page.number <= 0,
  last: page.number >= page.totalPages - 1,
})

/**
 * Expects a valid jsonHal json and returns the meta data for an object response
 */
export const object = (response: any): JsonHalObject => {
  const links = convertLinks(response._links)
  return {
    ID: (links.self && extractId(links.self)) || null,
    links,
  }
}

/**
 * Expects a valid jsonHal json and returns the meta data for a collection response
 * @type {[type]}
 */
export const collection = (response: any, size: number = 0): JsonHalCollection => ({
  links: convertLinks(response._links),
  page: extractPagination(size, response.page),
})