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# The python_helper is used in the Formula class when the user calls
# `python`, `python2` or `python3`.

module Python
  # This method has a dual nature. For one, it takes a &block and sets up
  # the ENV such that a Python, as defined in the requirements, is the default.
  # If there are multiple `PythonInstalled` requirements, the block is evaluated
  # once for each Python. This makes it possible to easily support 2.x and
  # 3.x Python bindings without code duplication in formulae.
  # If you need to special case stuff, set :allowed_major_versions.
  # Second, inside the block, a formula author may call this method to access
  # certain convienience methods for the currently selected Python, e.g.
  # `python.site_packages`.
  def python_helper(options={:allowed_major_versions => [2, 3]}, &block)
    if !block_given? and !@current_python.nil?
      # We are already inside of a `python do ... end` block, so just return
      # the current_python or false if the version.major is not allowed.
      if options[:allowed_major_versions].include?(@current_python.version.major)
        @current_python
      else
        false
      end
    else
      # Look for PythonInstalled requirements for this formula
      python_reqs = requirements.select{ |r| r.kind_of?(PythonInstalled) }
      if python_reqs.empty?
        raise "If you use python in the formula, you have to add `depends_on :python` (or :python3)!"
      end
      # Now select those that are satisfied and matching the version.major
      python_reqs = python_reqs.select do |p|
        p.satisfied? &&
        options[:allowed_major_versions].include?(p.version.major) &&
        if p.optional? || p.recommended?
          self.build.with?(p.name)
        else
          true
        end
      end

      # Allow to use an else-branch like so: `if python do ... end; else ... end`
      return false if python_reqs.empty?

      # Sort by version, so the older 2.x will be used first and if no
      # block_given? then 2.x is preferred because it is returned.
      # Further note, having 3.x last allows us to run `2to3 --write .`
      # which modifies the sources in-place (for some packages that need this).
      python_reqs.sort_by{ |py| py.version }.map do |py|
        # Now is the time to set the site_packages to the correct value
        py.site_packages = lib/py.xy/'site-packages'
        if !block_given?
          return py
        else
          puts "brew: Python block (#{py.binary})..." if ARGV.verbose? && ARGV.debug?
          # Ensure env changes are only temporary
          begin
            old_env = ENV.to_hash
            # In order to install into the Cellar, the dir must exist and be in the
            # PYTHONPATH. This will be executed in the context of the formula
            # so that lib points to the HOMEBREW_PREFIX/Cellar/<formula>/<version>/lib
            puts "brew: Appending to PYTHONPATH: #{py.site_packages}" if ARGV.verbose?
            mkdir_p py.site_packages
            ENV.append 'PYTHONPATH', py.site_packages, ':'
            ENV['PYTHON'] = py.binary
            ENV.prepend 'CMAKE_INCLUDE_PATH', py.incdir, ':'
            ENV.prepend 'PKG_CONFIG_PATH', py.pkg_config_path, ':' if py.pkg_config_path
            ENV.prepend 'PATH', py.binary.dirname, ':' unless py.from_osx?
            ENV.prepend 'LDFLAGS', "-F#{py.framework}" if py.brewed?
            # Track the state of the currently selected python for this block,
            # so if this python_helper is called again _inside_ the block, we can
            # just return the right python (see `else`-branch a few lines down):
            @current_python = py
            res = instance_eval(&block)
            @current_python = nil
            res
          ensure
            ENV.replace(old_env)
          end
        end
      end
    end
  end  # enf of python_helper method

end