SpreadEvenly.coffee

buckets = [
  {
    capacity: 17,
    bookings: [2,2,2,2,2,2] 
  },
  {
    capacity: 17,
    bookings: [0] 
  },

  {
    capacity: 2,
    bookings: [0] 
  }  
]

bookings = buckets.map (bucket) ->
  bucket.bookings.reduce (sum, booking) -> sum + booking
total = bookings.reduce (sum, booking) -> 
  sum + booking  
average = total / buckets.length



spread_evenly = (buckets,average) ->
  
  pre_process = (buckets) ->

    buckets_pre_processed = buckets.map (bucket) ->
      bucket.sum_bookings = bucket.bookings.reduce (sum, booking) -> sum + booking
      bucket.bookings = bucket.bookings.sort (a,b) -> a-b
      bucket.difference = bucket.sum_bookings - average
      bucket

    buckets_pre_processed.sort (a,b) ->
      b.difference - a.difference
  
  sorted_buckets = pre_process(buckets)
  
  try_swap = (over, under)->
    
    i = 0
    
    end_absolute_difference = 1
    start_absolute_difference = 0
    did_swap = false
 
    while !did_swap && end_absolute_difference > start_absolute_difference && i < over.bookings.length
      
      over_to_move = over.bookings[i]
      
      start_absolute_difference = Math.abs(over.difference) + Math.abs(under.difference)
      end_absolute_difference = Math.abs(over.difference - over_to_move) + Math.abs(under.difference)

      if end_absolute_difference > start_absolute_difference || (under.sum_bookings + over_to_move > under.capacity)
        
      else
        under.bookings.push(over_to_move)
        over.bookings.splice(i,1)
        did_swap = true
       
      i++
    
    did_swap
    
   
   found_swap = false
   i = 0
   largest_over =  sorted_buckets[i]
   largest_under = sorted_buckets[sorted_buckets.length-1]   
   while !found_swap && largest_over.difference > 0
     found_swap = try_swap(largest_over, largest_under)
     largest_over =  sorted_buckets[++i]
   
   if found_swap 
      spread_evenly(sorted_buckets, average)
    else
      sorted_buckets

final_result = spread_evenly(buckets,average)

console.log "All Done"
console.log final_result