module Icmp

Interactively compares two sorted enumerables by key. Yields a block with event (:compare, :added, :removed), current and previous enumerable items.

Parameters¶ ↑

• current - Array with current values

• previous - Array to compare with, previous values

• key_proc - Proc for retrieve key value from item. Sets to item by default

Example¶ ↑

require 'icmp'

# id - key element
current = [{ id: 1, state: :accept },
           { id: 2, state: :new },
           { id: 4, state: :canceled }]

previous = [{ id: 1, state: :new },
            { id: 3, state: :in_progress },
            { id: 4, state: :canceled }]

# Sets proc for key retrieve
Icmp.compare(current, previous, proc { |i| i[:id] }) do |event, cur_item, prev_item|
  print "ID: #{cur_item[:id]}, "

  case event
  when :compare
    if cur_item[:state] != prev_item[:state]
      puts "new state = #{cur_item[:state]}, old state = #{prev_item[:state]}"
    else
      puts "item is not changed, state = #{cur_item[:state]}"
    end
  when :added
    puts "item added with state = #{cur_item[:state]}"
  when :removed
    puts "item removed with state = #{cur_item[:state]}"
  end
end

Output¶ ↑

ID: 1, new state = accept, old state = new
ID: 2, item added with state = new
ID: 3, item removed with state = in_progress
ID: 4, item is not changed, state = canceled

# File lib/icmp.rb, line 49
def self.compare(current, previous, key_proc = proc { |item| item })
  raise RuntimeError.new('Block should be specified') unless block_given?

  while current.size > 0 && previous.size > 0
    cur_item = current.first
    prev_item = previous.first

    cur_key = key_proc.call(cur_item)
    prev_key = key_proc.call(prev_item)

    if cur_key == prev_key
      yield :compare, cur_item, prev_item

      current = current.drop(1)
      previous = previous.drop(1)
    elsif cur_key < prev_key
      yield :added, cur_item

      current = current.drop(1)
    else
      yield :removed, prev_item

      previous = previous.drop(1)
    end
  end

  current.each do |item|
    yield :added, item
  end

  previous.each do |item|
    yield :removed, item
  end
end