class Bundler::Resolver

def error_message
  errors.inject("") do |o, (conflict, (origin, requirement))|
    # origin is the SpecSet of specs from the Gemfile that is conflicted with
    if origin
      o << %{Bundler could not find compatible versions for gem "#{origin.name}":\n}
      o << "  In Gemfile:\n"
      required_by = requirement.required_by
      o << gem_message(requirement, required_by)
      # If the origin is "bundler", the conflict is us
      if origin.name == "bundler"
        o << "  Current Bundler version:\n"
        other_bundler_required = !requirement.requirement.satisfied_by?(origin.version)
      # If the origin is a LockfileParser, it does not respond_to :required_by
      elsif !origin.respond_to?(:required_by) || !(origin.required_by.first)
        o << "  In snapshot (Gemfile.lock):\n"
      end
      required_by = origin.required_by[0..-2]
      o << gem_message(origin, required_by)
      # If the bundle wants a newer bundler than the running bundler, explain
      if origin.name == "bundler" && other_bundler_required
        o << "This Gemfile requires a different version of Bundler.\n"
        o << "Perhaps you need to update Bundler by running `gem install bundler`?"
      end
    # origin is nil if the required gem and version cannot be found in any of
    # the specified sources
    else
      # if the gem cannot be found because of a version conflict between lockfile and gemfile,
      # print a useful error that suggests running `bundle update`, which may fix things
      #
      # @base is a SpecSet of the gems in the lockfile
      # conflict is the name of the gem that could not be found
      if locked = @base[conflict].first
        o << "Bundler could not find compatible versions for gem #{conflict.inspect}:\n"
        o << "  In snapshot (Gemfile.lock):\n"
        o << "    #{clean_req(locked)}\n\n"
        o << "  In Gemfile:\n"
        required_by = requirement.required_by
        o << gem_message(requirement, required_by)
        o << "Running `bundle update` will rebuild your snapshot from scratch, using only\n"
        o << "the gems in your Gemfile, which may resolve the conflict.\n"
      # the rest of the time, the gem cannot be found because it does not exist in the known sources
      else
        if requirement.required_by.first
          o << "Could not find gem '#{clean_req(requirement)}', which is required by "
          o << "gem '#{clean_req(requirement.required_by.first)}', in any of the sources."
        else
          o << "Could not find gem '#{clean_req(requirement)} in any of the sources\n"
        end
      end
    end
    o
  end
end