require 'action_view/helpers/tag_helper'

module ActionView
  module Helpers
    # Provides functionality for working with JavaScript in your views.
    # 
    # == Ajax, controls and visual effects
    # 
    # * For information on using Ajax, see 
    #   ActionView::Helpers::PrototypeHelper.
    # * For information on using controls and visual effects, see
    #   ActionView::Helpers::ScriptaculousHelper.
    #
    # == Including the JavaScript libraries into your pages
    #
    # Rails includes the Prototype JavaScript framework and the Scriptaculous
    # JavaScript controls and visual effects library.  If you wish to use
    # these libraries and their helpers (ActionView::Helpers::PrototypeHelper
    # and ActionView::Helpers::ScriptaculousHelper), you must do one of the
    # following:
    #
    # * Use <tt><%= javascript_include_tag 'prototype' %></tt>: As above, but 
    #   will only include the Prototype core library, which means you are able
    #   to use all basic AJAX functionality. For the Scriptaculous-based 
    #   JavaScript helpers, like visual effects, autocompletion, drag and drop 
    #   and so on, you should use the method described above.
    #
    # For documentation on +javascript_include_tag+ see 
    # ActionView::Helpers::AssetTagHelper.
    module JavaScriptHelper
      # Returns a link that will trigger a JavaScript +function+ using the 
      # onclick handler and return false after the fact.
      #
      # The +function+ argument can be omitted in favor of an +update_page+
      # block, which evaluates to a string when the template is rendered
      # (instead of making an Ajax request first).      
      #
      # Examples:
      #   link_to_function "Greeting", "alert('Hello world!')"
      #     Produces:
      #       <a onclick="alert('Hello world!'); return false;" href="#">Greeting</a>
      #
      #   link_to_function(image_tag("delete"), "if (confirm('Really?')) do_delete()")
      #     Produces:
      #       <a onclick="if (confirm('Really?')) do_delete(); return false;" href="#">
      #         <img src="/images/delete.png?" alt="Delete"/>
      #       </a>
      def link_to_function(name, *args, &block)
        html_options = args.extract_options!.symbolize_keys
        function = args[0] || ''

        function = update_page(&block) if block_given?
        content_tag(
          "a", name, 
          html_options.merge({ 
            :href => html_options[:href] || "#", 
            :onclick => (html_options[:onclick] ? "#{html_options[:onclick]}; " : "") + "#{function}; return false;" 
          })
        )
      end
      
      # Returns a button that'll trigger a JavaScript +function+ using the 
      # onclick handler.
      #
      # The +function+ argument can be omitted in favor of an +update_page+
      # block, which evaluates to a string when the template is rendered
      # (instead of making an Ajax request first).      
      #
      # Examples:
      #   button_to_function "Greeting", "alert('Hello world!')"
      #   button_to_function "Delete", "if (confirm('Really?')) do_delete()"
      def button_to_function(name, *args, &block)
        html_options = args.extract_options!.symbolize_keys
        function = args[0] || ''

        function = update_page(&block) if block_given?
        tag(:input, html_options.merge({ 
          :type => "button", :value => name, 
          :onclick => (html_options[:onclick] ? "#{html_options[:onclick]}; " : "") + "#{function};" 
        }))
      end

      # Escape carrier returns and single and double quotes for JavaScript segments.
      def escape_javascript(javascript)
        (javascript || '').gsub('\\','\0\0').gsub('</','<\/').gsub(/\r\n|\n|\r/, "\\n").gsub(/["']/) { |m| "\\#{m}" }
      end

      # Returns a JavaScript tag with the +content+ inside. Example:
      #   javascript_tag "alert('All is good')"
      #
      # Returns:
      #   <script type="text/javascript">
      #   //<![CDATA[
      #   alert('All is good')
      #   //]]>
      #   </script>
      #
      # +html_options+ may be a hash of attributes for the <script> tag. Example:
      #   javascript_tag "alert('All is good')", :defer => 'defer' 
      #   # => <script defer="defer" type="text/javascript">alert('All is good')</script>
      #
      # Instead of passing the content as an argument, you can also use a block
      # in which case, you pass your +html_options+ as the first parameter.
      #   <% javascript_tag :defer => 'defer' do -%>
      #     alert('All is good')
      #   <% end -%>
      def javascript_tag(content_or_options_with_block = nil, html_options = {}, &block)
        if block_given?
          html_options = content_or_options_with_block if content_or_options_with_block.is_a?(Hash)
          content = capture(&block)
        else
          content = content_or_options_with_block
        end

        javascript_tag = content_tag("script", javascript_cdata_section(content), html_options.merge(:type => Mime::JS))
        
        if block_given? && block_is_within_action_view?(block)
          concat(javascript_tag, block.binding)
        else
          javascript_tag
        end
      end

      def javascript_cdata_section(content) #:nodoc:
        "\n//#{cdata_section("\n#{content}\n//")}\n"
      end
      
    protected
      def options_for_javascript(options)
        '{' + options.map {|k, v| "#{k}:#{v}"}.sort.join(', ') + '}'
      end
      
      def array_or_string_for_javascript(option)
        js_option = if option.kind_of?(Array)
          "['#{option.join('\',\'')}']"
        elsif !option.nil?
          "'#{option}'"
        end
        js_option
      end

    private
      def block_is_within_action_view?(block)
        eval("defined? _erbout", block.binding)
      end
    end
  end
end