require 'uri'

require 'eymiha/url/url_exception'

module Eymiha

  # A UrlNormalizer normalizes URLs. They are validated using the URI class
  # except when they can be identified as file resources. When so, if the
  # designated file's name starts with a slash (or a drive identifier
  # followed by a slash on a windows box) the path is used verbatim. If not,
  # the named file is assumed to be relative to a caller-supplied base
  # directory.
  class UrlNormalizer
    
    @@using_pc_filesystem = Config::CONFIG['target_vendor'] == "pc"
    
    @@relative_base = nil
    
    # Returns true if the given relative_base is valid. It should start and
    # end with a slash (or start with a drive designator and a slash and end
    # with a slash on a PC).
    def self.valid_relative_base? relative_base
      ((@@using_pc_filesystem and (relative_base =~ /^[A-Za-z]:\//)) or
       (!@@using_pc_filesystem and (relative_base =~ /^\//))) and
        (relative_base =~ /\/$/)
    end
    
    # Sets and returns the default directory for normalizing relative file
    # resources. The directory is validated prior to assignment - if invalid
    # a UrlException will be raised.
    def self.relative_base=(relative_base)
      if valid_relative_base? relative_base
        @@relative_base = relative_base
      else
        raise UrlException, "Invalid relative file base '#{relative_base}'"
      end
    end
    
    # Returns the default directory for normalizing relative file resources.
    def self.relative_base
      @@relative_base
    end
    
    attr_reader :relative_base
    
    # Creates a new instance using the default direcory for normalizing
    # relative file resources.
    def initialize()
      @relative_base = @@relative_base
    end
    
    # Returns a normalized URL relative to the given base if it is a
    # relative file resource.
    def normalize(url,relative_base=nil)
      self.relative_base = relative_base if relative_base
      (self.class.file_url? url) ? normalize_file(url) : URI.parse(url).to_s
    end
    
    # Returns true if the given URL is a file resource.
    def self.file_url? url
      (url =~ /^file:/) or
        (url =~ /^\//) or
        ((url =~ /^[A-Za-z]:/) and @@using_pc_filesystem) or
        !(url =~ /:/)
    end
    
    # Normalizes and returns a relative or absolute URL file resource.
    def normalize_file file_url
      "file://#{normalize_file_path((file_url =~ /file:\/\//) ? $' : file_url)}"
    end
    
    # Sets and Returns the directory for normalizing relative file resources.
    # The directory is validated prior to assignment - if invalid a
    # UrlException will be raised.
    def relative_base=(relative_base)
      if self.class.valid_relative_base? relative_base
        @relative_base = relative_base
      else
        raise UrlException, "Invalid relative file base '#{relative_base}'"
      end
    end
    
    # Returns true if the given URL file resource is absolute.
    def self.absolute_file_path? file_url
      @@using_pc_filesystem ?
        ((file_url =~ /^[A-Za-z]:\//) or (file_url =~ /^\//)) :
        (!(file_url =~ /^[A-Za-z]:/) and (file_url =~ /^\//))
    end

    # grafts on the drive designator for an absolute file if not present and
    # on a pc filesystem
    def self.absolute_file_path file_url
      (@@using_pc_filesystem && (file_url =~ /^\//)) ?
        "C:#{file_url}" : file_url
    end
    
    # Returns an absolute path for the given URL file resource. This is either
    # the incoming URL if absolute, or the URL anchored at the relative base
    # if relative.
    def normalize_file_path file_url
      if self.class.absolute_file_path? file_url
        self.class.absolute_file_path file_url
      elsif @relative_base != nil
        "#{relative_base}#{file_url}"
      else
        raise UrlException, "no relative file base was configured"
      end
    end
    
  end
    
end