require 'pathname'

module Sass
  module Importers
    # The default importer, used for any strings found in the load path.
    # Simply loads Sass files from the filesystem using the default logic.
    class Filesystem < Base

      attr_accessor :root

      # Creates a new filesystem importer that imports files relative to a given path.
      #
      # @param root [String] The root path.
      #   This importer will import files relative to this path.
      def initialize(root)
        @root = root
      end

      # @see Base#find_relative
      def find_relative(name, base, options)
        _find(File.dirname(base), name, options)
      end

      # @see Base#find
      def find(name, options)
        _find(@root, name, options)
      end

      # @see Base#mtime
      def mtime(name, options)
        file, s = find_real_file(@root, name)
        File.mtime(file) if file
      rescue Errno::ENOENT
        nil
      end

      # @see Base#key
      def key(name, options)
        [self.class.name + ":" + File.dirname(File.expand_path(name)),
          File.basename(name)]
      end

      # @see Base#to_s
      def to_s
        @root
      end

      def hash
        @root.hash
      end

      def eql?(other)
        root.eql?(other.root)
      end

      protected

      # If a full uri is passed, this removes the root from it
      # otherwise returns the name unchanged
      def remove_root(name)
        root = @root.end_with?('/') ? @root : @root + '/'
        if name.index(root) == 0
          name[root.length..-1]
        else
          name
        end
      end

      # A hash from file extensions to the syntaxes for those extensions.
      # The syntaxes must be `:sass` or `:scss`.
      #
      # This can be overridden by subclasses that want normal filesystem importing
      # with unusual extensions.
      #
      # @return [{String => Symbol}]
      def extensions
        {'sass' => :sass, 'scss' => :scss}
      end

      # Given an `@import`ed path, returns an array of possible
      # on-disk filenames and their corresponding syntaxes for that path.
      #
      # @param name [String] The filename.
      # @return [Array(String, Symbol)] An array of pairs.
      #   The first element of each pair is a filename to look for;
      #   the second element is the syntax that file would be in (`:sass` or `:scss`).
      def possible_files(name)
        dirname, basename, extname = split(name)
        sorted_exts = extensions.sort
        syntax = extensions[extname]

        return [["#{dirname}/{_,}#{basename}.#{extensions.invert[syntax]}", syntax]] if syntax
        sorted_exts.map {|ext, syn| ["#{dirname}/{_,}#{basename}.#{ext}", syn]}
      end


      REDUNDANT_DIRECTORY = %r{#{Regexp.escape(File::SEPARATOR)}\.#{Regexp.escape(File::SEPARATOR)}}
      # Given a base directory and an `@import`ed name,
      # finds an existant file that matches the name.
      #
      # @param dir [String] The directory relative to which to search.
      # @param name [String] The filename to search for.
      # @return [(String, Symbol)] A filename-syntax pair.
      def find_real_file(dir, name)
        for (f,s) in possible_files(remove_root(name))
          path = (dir == ".") ? f : "#{dir}/#{f}"
          if full_path = Dir[path].first
            full_path.gsub!(REDUNDANT_DIRECTORY,File::SEPARATOR)
            return full_path, s
          end
        end
        nil
      end

      # Splits a filename into three parts, a directory part, a basename, and an extension
      # Only the known extensions returned from the extensions method will be recognized as such.
      def split(name)
        extension = nil
        dirname, basename = File.dirname(name), File.basename(name)
        if basename =~ /^(.*)\.(#{extensions.keys.map{|e| Regexp.escape(e)}.join('|')})$/
          basename = $1
          extension = $2
        end
        [dirname, basename, extension]
      end

      private

      def _find(dir, name, options)
        full_filename, syntax = find_real_file(dir, name)
        return unless full_filename && File.readable?(full_filename)

        options[:syntax] = syntax
        options[:filename] = full_filename
        options[:importer] = self
        Sass::Engine.new(File.read(full_filename), options)
      end

      def join(base, path)
        Pathname.new(base).join(path).to_s
      end
    end
  end
end
