require 'sass/engine'

module Sass
  # This module contains methods to aid in using Sass
  # as a stylesheet-rendering plugin for various systems.
  # Currently Rails/ActionController and Merb are supported out of the box.
  module Plugin
    class << self
      @@options = {
        :css_location       => './public/stylesheets',
        :always_update      => false,
        :always_check       => true,
        :full_exception     => true
      }
      @@checked_for_updates = false

      # Whether or not Sass has *ever* checked if the stylesheets need updates
      # (in this Ruby instance).
      def checked_for_updates
        @@checked_for_updates
      end

      # Gets various options for Sass. See README.rdoc for details.
      #--
      # TODO: *DOCUMENT OPTIONS*
      #++
      def options
        @@options
      end

      # Sets various options for Sass.
      def options=(value)
        @@options.merge!(value)
      end

      # Get the options ready to be passed to the Sass::Engine
      def engine_options(additional_options = {})
        opts = options.dup.merge(additional_options)
        opts[:load_paths] = load_paths(opts)
        opts
      end

      # Checks each stylesheet in <tt>options[:css_location]</tt>
      # to see if it needs updating,
      # and updates it using the corresponding template
      # from <tt>options[:templates]</tt>
      # if it does.
      def update_stylesheets
        return if options[:never_update]

        @@checked_for_updates = true
        template_locations.zip(css_locations).each do |template_location, css_location|

          Dir.glob(File.join(template_location, "**", "*.sass")).each do |file|
            # Get the relative path to the file with no extension
            name = file.sub(template_location + "/", "")[0...-5]

            if !forbid_update?(name) && (options[:always_update] || stylesheet_needs_update?(name, template_location, css_location))
              update_stylesheet(name, template_location, css_location)
            end
          end
        end
      end

      private

      def update_stylesheet(name, template_location, css_location)
        css = css_filename(name, css_location)
        File.delete(css) if File.exists?(css)

        filename = template_filename(name, template_location)
        engine = Engine.new(File.read(filename), engine_options(:css_filename => css, :filename => filename))
        result = begin
                   engine.render
                 rescue Exception => e
                   exception_string(e)
                 end

        # Create any directories that might be necessary
        mkpath(css_location, name)

        # Finally, write the file
        File.open(css, 'w') do |file|
          file.print(result)
        end
      end
      
      # Create any successive directories required to be able to write a file to: File.join(base,name)
      def mkpath(base, name)
        dirs = [base]
        name.split(File::SEPARATOR)[0...-1].each { |dir| dirs << File.join(dirs[-1],dir) }
        dirs.each { |dir| Dir.mkdir(dir) unless File.exist?(dir) }
      end

      def load_paths(opts = options)
        (opts[:load_paths] || []) + template_locations
      end
      
      def template_locations
        location = (options[:template_location] || File.join(options[:css_location],'sass'))
        if location.is_a?(String)
          [location]
        else
          location.to_a.map { |l| l.first }
        end
      end
      
      def css_locations
        if options[:template_location] && !options[:template_location].is_a?(String)
          options[:template_location].to_a.map { |l| l.last }
        else
          [options[:css_location]]
        end
      end

      def exception_string(e)
        if options[:full_exception]
          e_string = "#{e.class}: #{e.message}"

          if e.is_a? Sass::SyntaxError
            e_string << "\non line #{e.sass_line}"

            if e.sass_filename
              e_string << " of #{e.sass_filename}"

              if File.exists?(e.sass_filename)
                e_string << "\n\n"

                min = [e.sass_line - 5, 0].max
                begin
                  File.read(e.sass_filename).rstrip.split("\n")[
                    min .. e.sass_line + 5
                  ].each_with_index do |line, i|
                    e_string << "#{min + i + 1}: #{line}\n"
                  end
                rescue
                  e_string << "Couldn't read sass file: #{e.sass_filename}"
                end
              end
            end
          end
          <<END
/*
#{e_string}

Backtrace:\n#{e.backtrace.join("\n")}
*/
body:before {
  white-space: pre;
  font-family: monospace;
  content: "#{e_string.gsub('"', '\"').gsub("\n", '\\A ')}"; }
END
          # Fix an emacs syntax-highlighting hiccup: '
        else
          "/* Internal stylesheet error */"
        end
      end

      def template_filename(name, path)
        "#{path}/#{name}.sass"
      end

      def css_filename(name, path)
        "#{path}/#{name}.css"
      end

      def forbid_update?(name)
        name.sub(/^.*\//, '')[0] == ?_
      end

      def stylesheet_needs_update?(name, template_path, css_path)
        css_file = css_filename(name, css_path)
        template_file = template_filename(name, template_path)
        if !File.exists?(css_file)
          return true
        else
          css_mtime = File.mtime(css_file)
          File.mtime(template_file) > css_mtime ||
            dependencies(template_file).any?(&dependency_updated?(css_mtime))
        end
      end

      def dependency_updated?(css_mtime)
        lambda do |dep|
          File.mtime(dep) > css_mtime ||
            dependencies(dep).any?(&dependency_updated?(css_mtime))
        end
      end

      def dependencies(filename)
        File.readlines(filename).grep(/^@import /).map do |line|
          line[8..-1].split(',').map do |inc|
            Sass::Engine.find_file_to_import(inc.strip, [File.dirname(filename)] + load_paths)
          end
        end.flatten.grep(/\.sass$/)
      end
    end
  end
end

require 'sass/plugin/rails' if defined?(ActionController)
require 'sass/plugin/merb'  if defined?(Merb::Plugins)