const _ = require('lodash')
const { Set } = require('immutable')
const fillPath = (path, data) =>
  path.replace(/:(\w+)/g, (text, key) => data[key] || text)

const diffBy = (before, after, selector) => {
  // Collect new, collect old, collect same
  const beforeDict = _.fromPairs(before.map(x => [selector(x), x]))
  const afterDict = _.fromPairs(before.map(x => [selector(x), x]))
  const beforeKeys = new Set(before.map(selector))
  const afterKeys = new Set(after.map(selector))

  const newKeys = afterKeys.subtract(beforeKeys)
  const oldKeys = beforeKeys.subtract(afterKeys)
  const commonKeys = beforeKeys.intersect(afterKeys)

  return {
    'new': newKeys.map(key => afterDict[key]),
    old: oldKeys.map(key => beforeDict[key]),
    common: commonKeys.map(key => [beforeDict[key], afterDict[key]])
  }
}

module.exports = {
  fillPath,
  diffBy
}