module Quandl
  module Operation
    class Collapse
      class Guess
        class << self
          def frequency(data)
            return :annual unless data && data[0] && data[0][0]
            # find the smallest point of difference between dates
            gap = find_average_gap(data)
            # ensure gap is not negative
            gap = ensure_positive_gap(gap)
            # determine the freq from the size of the smallest gap
            frequency_from_gap(gap)
          end

          def find_smallest_gap(data)
            # init
            gap = 100_000
            pdate = nil
            # find the smallest gap
            data.each do |row|
              # if the gap is 1, we're done
              break if gap <= 1
              # this row's date
              date = row[0]
              # only if pdate is present
              if pdate
                # calculate the gap
                diff = (pdate - date).to_i
                # replace the previous gap if it is smaller
                gap = diff if diff < gap
              end
              # previous row's date
              pdate = date
            end
            gap
          end

          def find_average_gap(data)
            # init
            pdate = nil
            row_count = data.count
            majority_count = (row_count * 0.55).to_i
            gaps = {}
            # find the smallest gap
            data.each do |row|
              # this row's date
              date = row[0]
              # only if pdate is present
              if pdate
                # calculate the gap
                diff = (pdate - date).to_i
                # increment the gap counter
                gaps[diff] ||= 0
                gaps[diff] += 1
                # if the diff count is greater than majority_count, we have a consensus
                return diff if gaps[diff] > majority_count
              end
              # previous row's date
              pdate = date
            end
            gaps.to_a.sort_by { |r| r[1] }.try(:last).try(:first)
          end

          def frequency_from_gap(gap)
            case
            when gap <= 1 then :daily
            when gap <= 10 then :weekly
            when gap <= 31 then :monthly
            when gap <= 93 then :quarterly
            else :annual
            end
          end

          def ensure_positive_gap(gap)
            gap = gap.to_i
            gap *= -1 if gap < 0
            gap
          end
        end
      end
    end
  end
end