generate changes from git diff Gemfile.lock

diff-gemfile.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

def read_changes
  gem_changes = {}

  ARGF.each_line do |line|
    next unless /(?<op>[-+])    (?<name>\S+) \((?<ver>\S+)\)/ =~ line.strip

    gem_changes[name] ||= {}
    gem_changes[name][op] = ver
  end

  gem_changes
end

def format_changes(changes)
  case changes.keys.sort
  when %w[-]
    "#{changes['-']} => (removed)"
  when %w[+]
    "(new) => #{changes['+']}"
  when %w[+ -]
    "#{changes['-']} => #{changes['+']}"
  else
    raise "unknown changes: #{changes}"
  end
end

lines = read_changes
        .map { |name, changes| [name, format_changes(changes)] }
        .sort_by { |name, _msg| name }
        .map { |name, msg| "- #{name}: #{msg}" }

puts lines.join("\n")