# Copyright (C) 2011 RightScale, Inc, All Rights Reserved Worldwide.
#
# THIS PROGRAM IS CONFIDENTIAL AND PROPRIETARY TO RIGHTSCALE
# AND CONSTITUTES A VALUABLE TRADE SECRET. Any unauthorized use,
# reproduction, modification, or disclosure of this program is
# strictly prohibited. Any use of this program by an authorized
# licensee is strictly subject to the terms and conditions,
# including confidentiality obligations, set forth in the applicable
# License Agreement between RightScale.com, Inc. and
# the licensee

require 'rbconfig'

module RightConf

  class Platform

    include Singleton


    # Generic platform family
    #
    # === Return
    # family(Symbol):: One of :linux, :windows or :darwin
    def family
      @family ||= case RbConfig::CONFIG['host_os']
                  when /mswin|win32|dos|mingw|cygwin/i then :windows
                  when /darwin/i then :darwin
                  when /linux/i then :linux
                  end
    end

    # Is current platform linux?
    #
    # === Return
    # true:: If current platform is linux
    # false:: Otherwise
    def linux?
      return family == :linux
    end

    # Is current platform darwin?
    #
    # === Return
    # true:: If current platform is darwin
    # false:: Otherwise
    def darwin?
      return family == :darwin
    end
    # Is current platform windows?
    #
    # === Return
    # true:: If current platform is Windows
    # false:: Otherwise
    def windows?
      return family == :windows
    end

    # Call platform specific implementation of method whose symbol is returned
    # by the passed in block. Arguments are passed through.
    # e.g.
    #
    #   Platform.dispatch(2) { :echo }
    #
    # will result in 'echo_linux(2)' being executed in self if running on linux,
    # 'echo_windows(2)' if running on Windows and 'echo_darwin(2)' if on 
    # Mac OS X. Note that the method is run in the instance of the caller.
    #
    # === Parameters
    # args:: Pass-through arguments
    #
    # === Block
    # Given block should not take any argument and return a symbol for the 
    # method that should be called
    #
    # === Return
    # res(ObjecT):: Result returned by platform specific implementation
    def dispatch(*args, &blk)
      raise "Platform.dispatch requires a block" unless blk
      binding = blk.binding.eval('self')
      meth = blk.call
      target = dispatch_candidates(meth).detect do |candidate|
        binding.respond_to?(candidate)
      end
      raise "No platform dispatch target found in #{binding.class} for " + 
            "'#{meth.inspect}', tried " + dispatch_candidates(meth).join(', ') unless target
      binding.__send__(target, *args)
    end

    protected

    # Load platform specific implementation
    def initialize
      require File.expand_path(File.join(File.dirname(__FILE__), 'platforms', family.to_s))
      init
    end

    # Candidate platform specific methods for given prefix
    # Ordered by most platform specific to most generic
    #
    # === Parameters
    # prefix(String):: Method prefix
    #
    # === Return
    # candidates(Array):: List of potential candidates
    def dispatch_candidates(prefix)
      candidates = ["#{prefix}_#{family}_#{flavor}_#{release}",
                    "#{prefix}_#{family}_#{flavor}",
                    "#{prefix}_#{family}"]
      candidates.map(&:to_sym)
    end

  end
end