js-assign-givers

const siblings = {
  Anthony: ['Kristin'],
  Tony: ['Sarah'],
  Joshua: ['Leah'],
  Kristin: ['Anthony'],
  Jonathon: [],
  Leah: ['Joshua'],
  Donald: ['Rebekah'],
  Sarah: ['Tony'],
  Rebekah: ['Donald'],
  Daniel: ['Rachel'],
  Rachel: ['Daniel'],
  Ruth: ['Benjamin'],
  Benjamin: ['Ruth'],
  Alyssa: ['Tyler'],
  Tyler: ['Alyssa'],
  Josiah: [],
  Kayla: ['Noah'],
  Noah: ['Kayla']
}

const cousins = {
  Bennett: ['Ella', 'Livi'],
  Ella: ['Bennett', 'Livi'],
  Livi: ['Bennett', 'Ella'],
  Kayla: ['Emily', 'Mariah', 'Olivia', 'Anthony', 'Julie'],
  Emily: ['Kayla', 'Mariah', 'Olivia', 'Anthony', 'Julie'],
  Mariah: ['Kayla', 'Emily', 'Olivia', 'Anthony', 'Julie'],
  Olivia: ['Kayla', 'Emily', 'Mariah', 'Anthony', 'Julie'],
  Anthony: ['Kayla', 'Emily', 'Mariah', 'Olivia', 'Julie'],
  Julie: ['Kayla', 'Emily', 'Mariah', 'Olivia', 'Anthony'],
  Michael: ['Sophia', 'Jonathan'],
  Sophia: ['Michael', 'Jonathan'],
  Jonathan: ['Michael', 'Sophia'],
  Riley: ['Jack', 'Grey', 'Beck'],
  Jack: ['Riley', 'Grey', 'Beck'],
  Grey: ['Riley', 'Jack', 'Beck'],
  Beck: ['Riley', 'Jack', 'Grey'],
  Madeline: [],
  Evelyn: ['Jackie'],
  Jackie: ['Evelyn']
}

const getValidReceivers = (receivers, givers, giver) => {
  receivers = [...receivers]

  const exclusions = [...givers[giver], giver]

  exclusions.forEach((exclusion, index) => {
    const exclusionIndex = receivers.indexOf(exclusion)
    const exclusionExistsInReceivers = exclusionIndex >= 0

    if (exclusionExistsInReceivers) {
      receivers.splice(exclusionIndex, 1)
    }
  })

  return receivers
}

const assignGivers = (givers) => {
  const giverList = Object.keys(givers)
  const receivers = [...giverList]
  let matches = []

  giverList.forEach((giver, index) => {
    const validReceivers = getValidReceivers(receivers, givers, giver)
    const receiver = validReceivers[Math.floor(Math.random() * validReceivers.length)];

    matches.push({
      'giver': giver,
      'receiver': receiver
    })

    // remove matched receiver from list
    receivers.splice(receivers.indexOf(receiver), 1)
  })
  
  let rerun = false;
  matches.forEach(({ receiver }, index) => {
    if (typeof receiver === 'undefined') {
      rerun = true;
    }
  })
  
  if (rerun) {
    // A little hackey, but it's possible to get down to the last giver without a valid
    // receiver, so rerun the assignments until all assignments are successful
    // TODO: figure out a better way to retrieve valid receivers that includes a check 
    // for future givers
    assignGivers(givers);
  }
  else {
    console.log(matches.map((match) => {
      let encouragment = ''

      if (match.receiver === 'Jonathon') {
        encouragment = ' They’d better not mess it up.'
      }

      return match.giver + ' is giving a gift to ' + match.receiver + '.' + encouragment
    }).join('\n'))
  }
}

console.log('Siblings:')
assignGivers(siblings)

console.log('Cousins:')
assignGivers(cousins)