# encoding: utf-8

module Prawn
  class Document
    # @group Stable API

    # Lazily instantiates a Prawn::Outline object for document. This is used as point of entry
    # to methods to build the outline tree for a document's table of contents.
    def outline
      @outline ||= Outline.new(self)
    end
  end

  # The Outline class organizes the outline tree items for the document.
  # Note that the prev and parent instance variables are adjusted while navigating
  # through the nested blocks. These variables along with the presence or absense
  # of blocks are the primary means by which the relations for the various
  # OutlineItems and the OutlineRoot are set. Unfortunately, the best way to
  # understand how this works is to follow the method calls through a real example.
  #
  # Some ideas for the organization of this class were gleaned from name_tree. In
  # particular the way in which the OutlineItems are finally rendered into document
  # objects in PdfObject through a hash.
  #
  class Outline
    # @private
    attr_accessor :parent, :prev, :document, :items

    def initialize(document)
      @document = document
      @parent = root
      @prev = nil
      @items = {}
    end

    # @group Stable API

    # Returns the current page number of the document
    def page_number
      @document.page_number
    end

    # Defines/Updates an outline for the document.
    # The outline is an optional nested index that appears on the side of a PDF
    # document usually with direct links to pages. The outline DSL is defined by nested
    # blocks involving two methods: section and page; see the documentation on those methods
    # for their arguments and options. Note that one can also use outline#update
    # to add more sections to the end of the outline tree using the same syntax and scope.
    #
    # The syntax is best illustrated with an example:
    #
    # Prawn::Document.generate(outlined_document.pdf) do
    #   text "Page 1. This is the first Chapter. "
    #   start_new_page
    #   text "Page 2. More in the first Chapter. "
    #   start_new_page
    #   outline.define do
    #     section 'Chapter 1', :destination => 1, :closed => true do
    #       page :destination => 1, :title => 'Page 1'
    #       page :destination => 2, :title => 'Page 2'
    #     end
    #   end
    #   start_new_page do
    #   outline.update do
    #     section 'Chapter 2', :destination =>  2, do
    #       page :destination => 3, :title => 'Page 3'
    #     end
    #   end
    # end
    #
    def define(&block)
      instance_eval(&block)  if block
    end

    alias :update :define

    # Inserts an outline section to the outline tree (see outline#define).
    # Although you will probably choose to exclusively use outline#define so
    # that your outline tree is contained and easy to manage, this method
    # gives you the option to insert sections to the outline tree at any point
    # during document generation. This method allows you to add a child subsection
    # to any other item at any level in the outline tree.
    # Currently the only way to locate the place of entry is with the title for the
    # item. If your title names are not unique consider using define_outline.
    # The method takes the following arguments:
    #   title: a string that must match an outline title to add the subsection to
    #   position: either :first or :last(the default) where the subsection will be placed relative
    #      to other child elements. If you need to position your subsection in between
    #      other elements then consider using #insert_section_after
    #   block: uses the same DSL syntax as outline#define, for example:
    #
    # Consider using this method inside of outline.update if you want to have the outline object
    # to be scoped as self (see #insert_section_after example).
    #
    #   go_to_page 2
    #   start_new_page
    #   text "Inserted Page"
    #   outline.add_subsection_to :title => 'Page 2', :first do
    #     outline.page :destination => page_number, :title => "Inserted Page"
    #   end
    #
    def add_subsection_to(title, position = :last, &block)
      @parent = items[title]
      raise Prawn::Errors::UnknownOutlineTitle,
        "\n No outline item with title: '#{title}' exists in the outline tree" unless @parent
      @prev = position == :first ? nil : @parent.data.last
      nxt = position == :first ? @parent.data.first : nil
      insert_section(nxt, &block)
    end

    # Inserts an outline section to the outline tree (see outline#define).
    # Although you will probably choose to exclusively use outline#define so
    # that your outline tree is contained and easy to manage, this method
    # gives you the option to insert sections to the outline tree at any point
    # during document generation. Unlike outline.add_section, this method allows
    # you to enter a section after any other item at any level in the outline tree.
    # Currently the only way to locate the place of entry is with the title for the
    # item. If your title names are not unique consider using define_outline.
    # The method takes the following arguments:
    #   title: the title of other section or page to insert new section after
    #   block: uses the same DSL syntax as outline#define, for example:
    #
    #   go_to_page 2
    #   start_new_page
    #   text "Inserted Page"
    #   update_outline do
    #     insert_section_after :title => 'Page 2' do
    #       page :destination => page_number, :title => "Inserted Page"
    #     end
    #   end
    #
    def insert_section_after(title, &block)
      @prev = items[title]
      raise Prawn::Errors::UnknownOutlineTitle,
        "\n No outline item with title: '#{title}' exists in the outline tree" unless @prev
      @parent = @prev.data.parent
      nxt = @prev.data.next
      insert_section(nxt, &block)
    end

    # See outline#define above for documentation on how this is used in that context
    #
    # Adds an outine section to the outline tree.
    # Although you will probably choose to exclusively use outline#define so
    # that your outline tree is contained and easy to manage, this method
    # gives you the option to add sections to the outline tree at any point
    # during document generation. When not being called from within another #section block
    # the section will be added at the top level after the other root elements of the outline.
    # For more flexible placement try using outline#insert_section_after and/or
    # outline#add_subsection_to
    # Takes the following arguments:
    #   title: the outline text that appears for the section.
    #   options: destination - optional integer defining the page number for a destination link
    #                          to the top of the page (using a :FIT destination).
    #                 - or an array with a custom destination (see the #dest_* methods of the
    #                   PDF::Destination module)
    #            closed - whether the section should show its nested outline elements.
    #                   - defaults to false.
    #            block: more nested subsections and/or page blocks
    #
    # example usage:
    #
    #   outline.section 'Added Section', :destination => 3 do
    #     outline.page :destionation => 3, :title => 'Page 3'
    #   end
    def section(title, options = {}, &block)
      add_outline_item(title, options, &block)
    end

    # See Outline#define above for more documentation on how it is used in that context
    #
    # Adds a page to the outline.
    # Although you will probably choose to exclusively use outline#define so
    # that your outline tree is contained and easy to manage, this method also
    # gives you the option to add pages to the root of outline tree at any point
    # during document generation. Note that the page will be added at the
    # top level after the other root outline elements. For more flexible placement try
    # using outline#insert_section_after and/or outline#add_subsection_to.
    #
    # Takes the following arguments:
    #     options:
    #            title - REQUIRED. The outline text that appears for the page.
    #            destination - optional integer defining the page number for a destination link
    #                          to the top of the page (using a :FIT destination).
    #                 - or an array with a custom destination (see the #dest_* methods of the
    #                   PDF::Destination module)
    #            closed - whether the section should show its nested outline elements.
    #                   - defaults to false.
    # example usage:
    #
    #   outline.page :title => "Very Last Page"
    # Note: this method is almost identical to section except that it does not accept a block
    # thereby defining the outline item as a leaf on the outline tree structure.
    def page(options = {})
      if options[:title]
        title = options[:title]
      else
        raise Prawn::Errors::RequiredOption,
          "\nTitle is a required option for page"
      end
      add_outline_item(title, options)
    end

    private

    # The Outline dictionary (12.3.3) for this document.  It is
    # lazily initialized, so that documents that do not have an outline
    # do not incur the additional overhead.
    def root
      document.state.store.root.data[:Outlines] ||= document.ref!(PDF::Core::OutlineRoot.new)
    end

    def add_outline_item(title, options, &block)
      outline_item = create_outline_item(title, options)
      set_relations(outline_item)
      increase_count
      set_variables_for_block(outline_item, block)
      block.call if block
      reset_parent(outline_item)
    end

    def create_outline_item(title, options)
      outline_item = PDF::Core::OutlineItem.new(title, parent, options)

      case options[:destination]
      when Integer
        page_index = options[:destination] - 1
        outline_item.dest = [document.state.pages[page_index].dictionary, :Fit]
      when Array
        outline_item.dest = options[:destination]
      end

      outline_item.prev = prev if @prev
      items[title] = document.ref!(outline_item)
    end

    def set_relations(outline_item)
      prev.data.next = outline_item if prev
      parent.data.first = outline_item unless prev
      parent.data.last = outline_item
    end

    def increase_count
      counting_parent = parent
      while counting_parent
        counting_parent.data.count += 1
        if counting_parent == root
          counting_parent = nil
        else
          counting_parent = counting_parent.data.parent
        end
      end
    end

    def set_variables_for_block(outline_item, block)
      self.prev = block ? nil : outline_item
      self.parent = outline_item if block
    end

    def reset_parent(outline_item)
      if parent == outline_item
        self.prev = outline_item
        self.parent = outline_item.data.parent
      end
    end

    def insert_section(nxt, &block)
      last = @parent.data.last
      if block
        block.call
      end
      adjust_relations(nxt, last)
      reset_root_positioning
    end

    def adjust_relations(nxt, last)
      if nxt
        nxt.data.prev = @prev
        @prev.data.next = nxt
        @parent.data.last = last
      end
    end

    def reset_root_positioning
      @parent = root
      @prev = root.data.last
    end
  end
end