class Bundler::PubGrub::Strategy

def initialize(source)
  @source = source
  @root_package = Package.root
  @root_version = Package.root_version
  @version_indexes = Hash.new do |h,k|
    if k == @root_package
      h[k] = { @root_version => 0 }
    else
      h[k] = @source.all_versions_for(k).each.with_index.to_h
    end
  end
end

def most_preferred_version_of(package, range)
  versions = @source.versions_for(package, range)
  indexes = @version_indexes[package]
  versions.min_by { |version| indexes[version] }
end

def next_package_and_version(unsatisfied)
  package, range = next_term_to_try_from(unsatisfied)
  [package, most_preferred_version_of(package, range)]
end

def next_term_to_try_from(unsatisfied)
  unsatisfied.min_by do |package, range|
    matching_versions = @source.versions_for(package, range)
    higher_versions = @source.versions_for(package, range.upper_invert)
    [matching_versions.count <= 1 ? 0 : 1, higher_versions.count]
  end
end