# frozen_string_literal: true

# CSVUtils::CSVCompare purpose is to determine which rows in the secondary_data_file need to be created, deleted or updated
# **requires both CSV files to be sorted on the same columns, CSVUtils::CSVSort can accomplish this
# In order to receive updates, update_comparison_columns must configured or use inheritance and change the update_row? method
class CSVUtils::CSVCompare
  # primary_data_file is the source of truth
  # compare_proc used to compare the id column(s)
  # update_comparison_columns column(s) to compare for equality, ex: updated_at, timestamp, hash
  #  caveat: update_comparison_columns need to be in both csv files
  attr_reader :primary_data_file,
              :update_comparison_columns,
              :compare_proc

  def initialize(primary_data_file, update_comparison_columns=nil, &block)
    @primary_data_file = primary_data_file
    @update_comparison_columns = update_comparison_columns
    @compare_proc = block
  end

  def compare(secondary_data_file)
    src = CSV.open(primary_data_file)
    src_headers = src.shift
    dest = CSV.open(secondary_data_file)
    dest_headers = dest.shift

    read_next_src = true
    read_next_dest = true

    while(!src.eof? || !dest.eof?)
      src_record = next_record_from_file(src_headers, src) if read_next_src
      dest_record = next_record_from_file(dest_headers, dest) if read_next_dest

      if ! src_record
        read_next_src = false
        read_next_dest = true

        yield :delete, dest_record
      elsif ! dest_record
        read_next_src = true
        read_next_dest = false

        yield :create, src_record
      elsif compare_proc.call(src_record, dest_record) == 0
        read_next_src = true
        read_next_dest = true

        yield(:update, src_record) if update_row?(src_record, dest_record)
      elsif compare_proc.call(src_record, dest_record) > 0
        read_next_src = false
        read_next_dest = true

        yield :delete, dest_record
      else
        read_next_src = true
        read_next_dest = false

        yield :create, src_record
      end
    end

    src.close
    dest.close
  end

  private

  def next_record_from_file(headers, file)
    return nil if file.eof?

    Hash[headers.zip(file.shift)]
  end

  def update_row?(src_record, dest_record)
    return false unless update_comparison_columns

    update_comparison_columns.each do |column_name|
      return true unless src_record[column_name] == dest_record[column_name]
    end

    false
  end
end