resolves #62 assign document header attributes; add output file option

- parse the document header and assign any attributes defined there
- add an output file option for writing the output directly to a file

scripts/asciidoc-coalescer.rb

@@ -1,26 +1,62 @@
-# This script coalesces the AsciiDoc source into a single file by resolving all
-# preprocessor directives, in particular include directives.
+#!/usr/bin/env ruby
+
+# This script coalesces the AsciiDoc content from a document master into a
+# single output file. It does so by resolving all preprocessor directives in
+# the document, and in any files which are included. The resolving of include
+# directives is likely of most interest to users of this script.
+#
+# This script works by using Asciidoctor's PreprocessorReader to read and
+# resolve all the lines in the specified input file. The script then writes the
+# result to the output.
+#
+# The script only recognizes attributes passed in as options or those defined
+# in the document header. It does not currently process attributes defined in
+# other, arbitrary locations within the document.
 
 # TODO
-# - add option to write cli attributes into header of document
-# - add option to write output to file
+# - add cli option to write attributes passed to cli to header of document
+# - escape all preprocessor directives after lines are processed (these are preprocessor directives that were escaped in the input)
 
 require 'asciidoctor'
 require 'optparse'
 
-options = { attributes: [] }
+options = { attributes: [], output: '-' }
 OptionParser.new do |opts|
   opts.banner = 'Usage: ruby asciidoc-coalescer.rb [OPTIONS] FILE'
   opts.on('-a', '--attribute key[=value]', 'A document attribute to set in the form of key[=value]') do |a|
     options[:attributes] << a
   end
+  opts.on('-o', '--output FILE', 'Write output to FILE instead of stdout.') do |o|
+    options[:output] = o
+  end
 end.parse!
 
 unless (source_file = ARGV.shift)
   warn 'Please specify an AsciiDoc source file to coalesce.'
   exit 1
 end
 
-doc = Asciidoctor.load_file source_file, safe: :safe, parse: false, attributes: options[:attributes]
+unless (output_file = options[:output]) == '-'
+  if (output_file = File.expand_path output_file) == (File.expand_path source_file)
+    warn 'Source and output cannot be the same file.'
+    exit 1
+  end
+end
+
+# NOTE first, resolve attributes defined at the end of the document header
+# QUESTION can we do this in a single load?
+doc = Asciidoctor.load_file source_file, safe: :unsafe, header_only: true, attributes: options[:attributes]
+# NOTE quick and dirty way to get the attributes set or unset by the document header
+header_attr_names = (doc.instance_variable_get :@attributes_modified).to_a
+header_attr_names.each {|k| doc.attributes[%(#{k}!)] = '' unless doc.attr? k }
+
+doc = Asciidoctor.load_file source_file, safe: :unsafe, parse: false, attributes: doc.attributes
+# FIXME also escape ifdef, ifndef, ifeval and endif directives
+# FIXME do this more carefully by reading line by line; if input differs by output by leading backslash, restore original line
 lines = doc.reader.read.gsub(/^include::(?=.*\[\]$)/m, '\\include::')
-puts lines
+
+if output_file == '-'
+  puts lines
+else
+  File.open(output_file, 'w') {|f| f.write lines }
+end