Filling in missing dates

date_structs.rb

#!/usr/bin/env ruby

require 'date'


def to_date(string)
  Date.strptime(string, '%Y-%m-%d')
end


# Transform the input to a hash whose keys are date objects
# and whose values are the original input records
def transform_input_to_hash(input_records)
  input_records.each_with_object({}) do |record, hsh|
    key = to_date(record[:date])
    hsh[key] = record
  end
end


def fill_in_missing_dates(input_records)
  input_record_hash = transform_input_to_hash(input_records)

  start_date = input_record_hash.keys.first
  output_dates = ((start_date - 6)..start_date).to_a.reverse

  output_dates.each_with_object([]) do |date, array|
    array << if input_record_hash.keys.include?(date)
      input_record_hash[date]
    else
      { date: date, amount: 0 }
    end
  end
end



INPUT_RECORDS = [
  {
    date: "2016-05-14",
    amount: 6000
  },
  {
    date: "2016-05-12",
    amount: 12000
  }
]



output_array = fill_in_missing_dates(INPUT_RECORDS)
puts output_array