#!/usr/bin/ruby

require 'rubygems/package'

module RubyGemsReq
  module Helpers
    # Expands '~>' and '!=' gem requirements.
    def self.expand_requirement(requirements)
      requirements.inject([]) do |output, r|
        output.concat case r.first
        when '~>'
          expand_pessimistic_requirement(r)
        when '!='
          expand_not_equal_requirement(r)
        else
          [r]
        end
      end
    end

    # Expands the pessimistic version operator '~>' into equivalent '>=' and
    # '<' pair.
    def self.expand_pessimistic_requirement(requirement)
      next_version = Gem::Version.create(requirement.last).bump
      return ['>=', requirement.last], ['<', next_version]
    end

    # Expands the not equal version operator '!=' into equivalent '<' and
    # '>' pair.
    def self.expand_not_equal_requirement(requirement)
      return ['<', requirement.last], ['>', requirement.last]
    end

    # Converts Gem::Requirement into array of requirements strings compatible
    # with RPM .spec file.
    def self.requirement_versions_to_rpm(requirement)
      self.expand_requirement(requirement.requirements).map do |op, version|
        version == Gem::Version.new(0) ? "" : "#{op} #{version}"
      end
    end
  end

  # Report RubyGems dependency, versioned if required.
  def self.rubygems_dependency(specification)
    Helpers::requirement_versions_to_rpm(specification.required_rubygems_version).each do |requirement|
      dependency_string = "ruby(rubygems)"
      dependency_string += " #{specification.required_rubygems_version}" if requirement && requirement.length > 0
      puts dependency_string
    end
  end

  # Report all gem dependencies including their version.
  def self.gem_depenencies(specification)
    specification.runtime_dependencies.each do |dependency|
      Helpers::requirement_versions_to_rpm(dependency.requirement).each do |requirement|
        dependency_string = "rubygem(#{dependency.name})"
        dependency_string += " #{requirement}" if requirement && requirement.length > 0
        puts dependency_string
      end
    end
  end

  # Reports all requirements specified by all provided .gemspec files.
  def self.requires
    while filename = gets
      filename.strip!
      begin
        specification = Gem::Specification.load filename

        rubygems_dependency(specification)
        gem_depenencies(specification)
      rescue => e
        # Ignore all errors.
      end
    end
  end
end

if __FILE__ == $0
  RubyGemsReq::requires
end