require 'yaml'
require 'erbook/template'

module ERBook
  class Document
    # Data from the format specification file.
    attr_reader :format

    # All root nodes in the document.
    attr_reader :roots

    # All nodes in the document.
    attr_reader :nodes

    # All nodes in the document arranged by node type.
    attr_reader :nodes_by_type

    ##
    # @param [String] format
    #   Either the short-hand name of a built-in format
    #   or the path to a format specification file.
    #
    # @param [String] input_text
    #   The body of the input document.
    #
    # @param [String] input_file
    #   Name of the file from which the input document originated.
    #
    # @param [Hash] options
    #   Additional method parameters:
    #
    #   [boolean] :unindent =>
    #     If true, all node content is unindented hierarchically.
    #
    def initialize format, input_text, input_file, options = {}
      # process format specification
        @format_file = format.to_s

        File.file? @format_file or
          @format_file = File.join(ERBook::FORMATS_DIR, @format_file + '.yaml')

        begin
          @format = YAML.load_file(@format_file)
          @format[:file] = File.expand_path(@format_file)
          @format[:name] = File.basename(@format_file).sub(/\..*?$/, '')

          if @format.key? 'code'
            eval @format['code'].to_s, TOPLEVEL_BINDING, "#{@format_file}:code"
          end

        rescue Exception
          error "Could not load format specification file #{@format_file.inspect}"
        end

        @node_defs = @format['nodes']

      # process input document
        begin
          # create sandbox for input evaluation
            template = Template.new(input_file, input_text, options[:unindent])

            @template_vars = {
              :@format        => @format,
              :@roots         => @roots = [], # root nodes of all trees
              :@nodes         => @nodes = [], # all nodes in the forest
              :@nodes_by_type => @nodes_by_type = Hash.new {|h,k| h[k] = [] },
              :@stack         => [], # stack for all nodes
            }.each_pair {|k,v| template.instance_variable_set(k, v) }

            class << template
              private

              # Handles the method call from a node
              # placeholder in the input document.
              def __node__ node_type, *node_args, &node_content
                node = Node.new(
                  :type => node_type,
                  :defn => @format['nodes'][node_type],
                  :args => node_args,
                  :children => [],

                  # omit erbook internals from the stack trace
                  :trace => caller.reject {|t|
                    [$0, ERBook::INSTALL].any? {|f| t.index(f) == 0 }
                  }
                )
                @nodes << node
                @nodes_by_type[node.type] << node

                # calculate occurrence number for this node
                if node.defn['number']
                  @count ||= Hash.new {|h,k| h[k] = []}
                  node.number = (@count[node.type] << node).length
                end

                # assign node family
                if parent = @stack.last
                  parent.children << node
                  node.parent = parent
                  node.depth = parent.depth
                  node.depth += 1 if node.defn['depth']

                  # calculate latex-style index number for this node
                  if node.defn['index']
                    ancestry = @stack.reverse.find {|n| n.defn['index'] }.index
                    branches = node.parent.children.select {|n| n.index }

                    node.index = [ancestry, branches.length + 1].join('.')
                  end
                else
                  @roots << node
                  node.parent = nil
                  node.depth = 0

                  # calculate latex-style index number for this node
                  if node.defn['index']
                    branches = @roots.select {|n| n.index }
                    node.index = (branches.length + 1).to_s
                  end
                end

                # assign node content
                if block_given?
                  @stack.push node
                  content = content_from_block(node, &node_content)
                  @stack.pop

                  digest = Document.digest(content)
                  self.buffer << digest
                else
                  content = nil
                  digest = Document.digest(node.object_id)
                end

                node.content = content
                node.digest = digest

                digest
              end
            end

            @node_defs.each_key do |type|
              # XXX: using a string because define_method()
              #      does not accept a block until Ruby 1.9
              file, line = __FILE__, __LINE__ + 1
              template.instance_eval %{
                def #{type} *node_args, &node_content
                  __node__ #{type.inspect}, *node_args, &node_content
                end
              }, file, line
            end

          # evaluate the input & build the document tree
            @processed_document = template.instance_eval { result binding }

          # chain block-level nodes together for local navigation
            block_nodes = @nodes.reject {|n| @node_defs[n.type]['inline'] }

            require 'enumerator'
            block_nodes.each_cons(2) do |a, b|
              a.next_node = b
              b.prev_node = a
            end

          # replace node placeholders with their corresponding output
            expander = lambda do |n, buf|
              # calculate node output
              source = "#{@format_file}:nodes:#{n.type}:output"
              n.output = Template.new(
                source, @node_defs[n.type]['output'].to_s.chomp
              ).render_with(@template_vars.merge(:@node => n))

              # expand all child nodes in this node's output
              n.children.each {|c| expander[c, n.output] }

              # replace this node's placeholder with its output in the buffer
              buf[n.digest] = @node_defs[n.type]['silent'] ? '' : n.output
            end

            @roots.each {|n| expander[n, @processed_document] }

        rescue Exception
          puts input_text # so the user can debug line numbers in the stack trace
          error "Could not process input document #{input_file.inspect}"
        end
    end

    ##
    # Returns the output of this document.
    #
    def to_s
      Template.new("#{@format_file}:output", @format['output'].to_s).
      render_with(@template_vars.merge(:@content => @processed_document))
    end

    require 'ostruct'
    class Node < OpenStruct
      # deprecated in Ruby 1.8; removed in Ruby 1.9
      undef id if respond_to? :id
      undef type if respond_to? :type

      # Returns the output of this node.
      def to_s
        output
      end
    end

    require 'digest/sha1'
    ##
    # Returns a digest of the given string that
    # will not be altered by String#to_xhtml.
    #
    def Document.digest input
      Digest::SHA1.hexdigest(input.to_s).

      # XXX: surround all digits with alphabets so
      #      Maruku doesn't change them into HTML
      gsub(/\d/, 'z\&z')
    end

    private

    ##
    # Prints the given message and raises the given error.
    #
    def error message, error = $!
      STDERR.printf "%s:\n\n", message
      raise error
    end
  end
end