module Markdown

  class Env
    def self.home
      path = if( ENV['HOME'] || ENV['USERPROFILE'] )
               ENV['HOME'] || ENV['USERPROFILE']
             elsif( ENV['HOMEDRIVE'] && ENV['HOMEPATH'] )
               "#{ENV['HOMEDRIVE']}#{ENV['HOMEPATH']}"
             else
               begin
                 File.expand_path('~')
               rescue
                 if File::ALT_SEPARATOR
                   'C:/'
                 else
                   '/'
                 end
               end
             end
      
      puts "env home=>#{path}<"
      path
    end
    
    def self.markdown_lib
      ENV['MARKDOWN_LIB']
    end    
  end # class Env

  class Props

    attr_reader :path
    attr_reader :parent
    
    def initialize( hash, path, parent=nil)
      @hash   = hash
      @path   = path
      @parent = parent
    end
    
    def self.load_file( path, parent=nil )
      h = YAML.load_file( path )
      puts "dump of >#{path}<:"      
      pp h    # todo: add debug flag (turn off for default)
      Props.new( h, path, parent )
    end
    
    def [](key)  get( key );  end
    
    def fetch(key, default)
      value = get( key )
      value.nil? ? default : value
    end

private
    def get( key )
      value = @hash[ key.to_s ]
      # if not found try lookup in parent hash
      (value.nil? && parent) ? parent[key] : value
    end
    
  end # class props


  class Config

# note: only kramdown is listed as a dependency in gem specs (because it's Ruby only and, thus, easy to install)
#  if you want to use other markdown libs install the required/desired lib e.g.
#  use  gem install rdiscount for rdiscount and so on
#
# also note for now the first present markdown library gets used
#  the search order is first come, first serve, that is: rdiscount, rpeg-markdown, maruku, bluecloth, kramdown (fallback, always present)

#  DEFAULTS = {
#    'libs' => [ 'pandoc-ruby',
#                'rdiscount',
#                'rpeg-markdown',
#                'maruku',
#                'bluecloth',
#                'kramdown' ] }

# note: make kramdown default engine
DEFAULTS = { 'libs' => [ 'kramdown' ] }

  
    def initialize
      @props = @props_default = Props.new( DEFAULTS, 'DEFAULTS' )

      # check for user settings (markdown.yml) in home folder 

      ## todo/fix: use join path???
      ## todo: use .markdown.yml?? or differnt name ??
      props_home_file = "#{Env.home}/markdown.yml"      
      if File.exists?( props_home_file )
        puts "Loading settings from '#{props_home_file}'..."
        @props = @props_home = Props.load_file( props_home_file, @props )
      end
      
      # check for user settings (markdown.yml) in working folder 
    
      props_work_file = "./markdown.yml"
      if File.exists?( props_work_file )
        puts "Loading settings from '#{props_work_file}'..."
        @props = @props_work = Props.load_file( props_work_file, @props )
      end

      @libs   = []
      @mn     = nil   # markdown converter method name (mn) e.g. kramdown_to_html
      
      require_markdown_libs()      
    end

    def known_markdown_libs
      # returns an array of known markdown engines e.g.
      # [ 'pandoc-ruby', 'rdiscount', 'rpeg-markdown', 'maruku', 'bluecloth', 'kramdown' ]
    
      ## todo: allow single lib para instead of libs    
      ##  todo: allow ENV setting markdown_[select]_lib=xxxx
    
      ## todo/fix: use lookup with config parent cascade
    
    
      ## lookup order
      ## 1)  env variable MARKDOWN_LIB
      ## 2)  lib property (single markdown engine)
      ## 3)  libs property (first-come first-serve markdown engine list)

      user_lib = Env.markdown_lib || @props.fetch( 'lib', nil )      

      if user_lib.nil?         
        user_libs = @props.fetch( 'libs', nil )
      else
        [ user_lib ]  # return as array (wrap single lib entry)  
      end      
    end

      
    def require_markdown_libs

      # check for available markdown libs/gems
      # try to require each lib and remove any not installed

      known_markdown_libs.each do |lib|
        begin
          require lib
          @libs << lib
        rescue LoadError => ex
          ## todo: use logger.debug  instead of puts        
          puts "Markdown library #{lib} not found. Use gem install #{lib} to install."
        end
      end

      puts "  Found #{@libs.length} Markdown libraries: #{@libs.join(', ')}"
    end

    def markdown_lib
      @libs.first
    end
    
    def markdown_to_html_method
      lib  = @libs.first
      opts = @props.fetch( lib, {} )
      method = opts.fetch( 'converter', "#{lib.downcase}_to_html" )  # default to <lib>_to_html if converter prop not found    
      method.tr('-','_').to_sym
    end      

  end # class Config
end # module Markdown