require 'time'

##
# A ChangeLog file parser.
#
# This parser converts a ChangeLog into an RDoc::Markup::Document.  When
# viewed as HTML a ChangeLog page will have an entry for each day's entries in
# the sidebar table of contents.
#
# This parser is meant to parse the MRI ChangeLog, but can be used to parse any
# {GNU style Change
# Log}[http://www.gnu.org/prep/standards/html_node/Style-of-Change-Logs.html].

class RDoc::Parser::ChangeLog < RDoc::Parser

  include RDoc::Parser::Text

  parse_files_matching(/(\/|\\|\A)ChangeLog[^\/\\]*\z/)

  ##
  # Attaches the +continuation+ of the previous line to the +entry_body+.
  #
  # Continued function listings are joined together as a single entry.
  # Continued descriptions are joined to make a single paragraph.

  def continue_entry_body entry_body, continuation
    return unless last = entry_body.last

    if last =~ /\)\s*\z/ and continuation =~ /\A\(/ then
      last.sub!(/\)\s*\z/, ',')
      continuation.sub!(/\A\(/, '')
    end

    if last =~ /\s\z/ then
      last << continuation
    else
      last << ' ' << continuation
    end
  end

  ##
  # Creates an RDoc::Markup::Document given the +groups+ of ChangeLog entries.

  def create_document groups
    doc = RDoc::Markup::Document.new
    doc.omit_headings_below = 2
    doc.file = @top_level

    doc << RDoc::Markup::Heading.new(1, File.basename(@file_name))
    doc << RDoc::Markup::BlankLine.new

    groups.sort_by do |day,| day end.reverse_each do |day, entries|
      doc << RDoc::Markup::Heading.new(2, day.dup)
      doc << RDoc::Markup::BlankLine.new

      doc.concat create_entries entries
    end

    doc
  end

  ##
  # Returns a list of ChangeLog entries an RDoc::Markup nodes for the given
  # +entries+.

  def create_entries entries
    out = []

    entries.each do |entry, items|
      out << RDoc::Markup::Heading.new(3, entry)
      out << RDoc::Markup::BlankLine.new

      out << create_items(items)
    end

    out
  end

  ##
  # Returns an RDoc::Markup::List containing the given +items+ in the
  # ChangeLog

  def create_items items
    list = RDoc::Markup::List.new :NOTE

    items.each do |item|
      item =~ /\A(.*?(?:\([^)]+\))?):\s*/

      title = $1
      body = $'

      paragraph = RDoc::Markup::Paragraph.new body
      list_item = RDoc::Markup::ListItem.new title, paragraph
      list << list_item
    end

    list
  end

  ##
  # Groups +entries+ by date.

  def group_entries entries
    entries.group_by do |title, _|
      begin
        Time.parse(title).strftime '%Y-%m-%d'
      rescue NoMethodError, ArgumentError
        time, = title.split '  ', 2
        Time.parse(time).strftime '%Y-%m-%d'
      end
    end
  end

  ##
  # Parses the entries in the ChangeLog.
  #
  # Returns an Array of each ChangeLog entry in order of parsing.
  #
  # A ChangeLog entry is an Array containing the ChangeLog title (date and
  # committer) and an Array of ChangeLog items (file and function changed with
  # description).
  #
  # An example result would be:
  #
  #    [ 'Tue Dec  4 08:33:46 2012  Eric Hodel  <drbrain@segment7.net>',
  #      [ 'README.EXT:  Converted to RDoc format',
  #        'README.EXT.ja:  ditto']]

  def parse_entries
    entries = []
    entry_name = nil
    entry_body = []

    @content.each_line do |line|
      case line
      when /^\s*$/ then
        next
      when /^\w.*/ then
        entries << [entry_name, entry_body] if entry_name

        entry_name = $&

        begin
          time = Time.parse entry_name
          # HACK Ruby 1.8 does not raise ArgumentError for Time.parse "Other"
          entry_name = nil unless entry_name =~ /#{time.year}/
        rescue NoMethodError
          time, = entry_name.split '  ', 2
          time = Time.parse time
        rescue ArgumentError
          entry_name = nil
        end

        entry_body = []
      when /^(\t| {8})?\*\s*(.*)/ then # "\t* file.c (func): ..."
        entry_body << $2
      when /^(\t| {8})?\s*(\(.*)/ then # "\t(func): ..."
        entry = $2

        if entry_body.last =~ /:/ then
          entry_body << entry
        else
          continue_entry_body entry_body, entry
        end
      when /^(\t| {8})?\s*(.*)/ then
        continue_entry_body entry_body, $2
      end
    end

    entries << [entry_name, entry_body] if entry_name

    entries.reject! do |(entry,_)|
      entry == nil
    end

    entries
  end

  ##
  # Converts the ChangeLog into an RDoc::Markup::Document

  def scan
    entries = parse_entries
    grouped_entries = group_entries entries

    doc = create_document grouped_entries

    @top_level.comment = doc

    @top_level
  end

end