= reverse_asciidoctor

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Based on https://github.com/xijo/reverse_markdown

Transforms HTML into asciidoctor.

== Requirements

. http://nokogiri.org/[Nokogiri]
. Ruby 1.9.3 or higher

== Installation

Install the gem

[source,console]
----
[sudo] gem install reverse_asciidoctor
----

or add it to your Gemfile

[source,ruby]
----
gem 'reverse_asciidoctor'
----

== Usage

=== Ruby

You can convert HTML content as string or Nokogiri document:

[source,ruby]
----
input  = '<strong>feelings</strong>'
result = ReverseAsciidoctor.convert input
result.inspect # " *feelings* "
----

=== Commandline

It's also possible to convert HTML files to AsciiDoc markup using the binary:

[source,console]
----
$ bin/reverse_asciidoctor file.html > file.adoc
$ cat file.html | bin/reverse_asciidoctor > file.adoc
----

In addition, the `bin/w2a` script (adapted from the `bin/w2m` script in 
https://github.com/benbalter/word-to-markdown[Ben Balter's word-to-markdown])
extracts HTML from Word docx documents, and converts it to Asciidoc.

[source,console]
----
$ bundle exec bin/w2a document.docx > document.adoc
----

The script presumes that LibreOffice has already been installed: it uses LibreOffice's
export to XHTML. LibreOffice's export of XHTML is superior to the native Microsoft Word export
to HTML: it exports lists (which Word keeps as paragraphs), and it exports OOMML into MathML.
On the other hand, the LibreOffice export relies on default styling being used in the
document, and it may not cope with ordered lists or headings with customised appearance.
For best results, reset the styles in the document you're converting to those in
the default Normal.dot template.

If you wish to convert the MathML in the document to AsciiMath, run the script with the
`--mathml2asciimath` option:

[source,console]
----
$ bundle exec bin/w2a --mathml2asciimath document.docx > document.adoc
----

Note that some information in OOMML is not preserved in the export to MathML from LibreOffice;
in particular, font shifts such as double-struck fonts.

Note that the LibreOffice exporter does seem to drop some text (possibly associated with
MathML); use with caution.

== Features

As a port of reverse_markdown, reverse_asciidoctor shares its features:

* Module based - if you miss a tag, just add it
* Can deal with nested lists 
* Inline and block code is supported
* Supports blockquote

It supports the following html tags supported by reverse_markdown:

* `a`
* `blockquote`
* `br`
* `code`, `tt` (added: `kbd`, `samp`, `var`)
* `div`, `article`
* `em`, `i` (added: `cite`)
* `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `hr`
* `img` 
* `li`, `ol`, `ul` (added: `dir`)
* `p`, `pre`
* `strong`, `b`
* `table`, `td`, `th`, `tr`

[NOTE]
====
* reverse_asciidoctor does *not* support `del` or `strike`, because Asciidoctor out of the box does not
* As with reverse_markdown, `pre` is only treated as sourcecode if it is contained in a `div@class = highlight-` element, or has a `@brush` attribute naming the language (Confluence).
* The gem does not support `p@align`, because Asciidoctor doesn't
====

In addition, it supports:

* `aside`
* `audio`, `video` (with `@src` attributes)
* `figure`, `figcaption` 
* `mark`
* `q`
* `sub`, `sup`
* `@id` anchors
* `blockquote@cite`
* `img/@width`, `img/@height`
* `ol/@style`, `ol/@start`, `ol/@reversed`, `ul/@type`
* `td/@colspan`, `td/@rowspan`, `td@/align`, `td@/valign`
* `table/caption`, `table/@width`, `table/@frame` (partial), `table/@rules` (partial)
* Lists and paragraphs within cells
** Not tables within cells: Asciidoctor cannot deal with nested tabls

It also supports MathML... sort of.

* Asciidoctor supports AsciiMath and LaTeX for stem expressions. HTML uses MathML.
The gem will recognise MathML expressions in HTML, and will wrap them in Asciidoctor
`stem:[ ]` macros. The result of this gem is not actually legal Asciidoctor for stem:
Asciidoctor will presumably
think this is AsciiMath in the `stem:[ ]` macro, try to pass it into MathJax as
AsciiMath, and fail. But of course, MathJax has no problem with MathML, and some postprocessing
on the Asciidoctor output can ensure that the MathML is treated by MathJax (or whatever else
uses the output) as such; so this is still much better than nothing for stem processing.
** On the other hand, if you are using this gem in the context of https://www.metanorma.com[Metanorma],
Metanorma Asciidoctor accepts MathML as a native mathematical format. So you do not need
to convert the MathML to AsciiMath.
** The gem will optionally invoke the https://github.com/metanorma/mathml2asciimath
gem, to convert MathML to AsciiMath. The conversion is not perfect, and will need to be
post-edited; but it's a lot better than nothing.

The gem does not support:

* `col`, `colgroup`
* `source`, `picture`
* `bdi`, `bdo`, `ruby`, `rt`, `rp`, `wbr`
* `frame`, `frameset`, `iframe`, `noframes`, `noscript`, `script`, `input`, `output`, `progress`
* `map`, `canvas`, `dialog`, `embed`, `object`, `param`, `svg`, `track`
* `fieldset`, `button`, `datalist`, `form`, `label`, `legend`, `menu`, `menulist`, `optgroup`, `option`, `select`, `textarea`
* `big`, `dfn`, `font`, `s`, `small`, `span`, `strike`, `u`
* `center`
* `data`, `meter`
* `del`, `ins`
* `footer`, `header`, `main`, `nav`, `details`, `section`, `summary`, `template`


== Configuration

The following options are available:

* `unknown_tags` (default `pass_through`) - how to handle unknown tags. Valid options are:
** `pass_through` - Include the unknown tag completely into the result
** `drop` - Drop the unknown tag and its content
** `bypass` - Ignore the unknown tag but try to convert its content
** `raise` - Raise an error to let you know
* `tag_border` (default `' '`) - how to handle tag borders. valid options are:
** `' '` - Add whitespace if there is none at tag borders.
** `''` - Do not not add whitespace.
* `mathml2asciimath` - if `true`, will use the https://github.com/metanorma/mathml2asciimath gem
to convert MathML to AsciiMath

=== As options

Just pass your chosen configuration options in after the input. The given options will last for this operation only.

[source,ruby]
----
ReverseAsciidoctor.convert(input, unknown_tags: :raise, mathml2asciimath: true)
----

=== Preconfigure

Or configure it block style on a initializer level. These configurations will last for all conversions until they are set to something different.

[source,ruby]
----
ReverseAsciidoctor.config do |config|
  config.unknown_tags     = :bypass
  config.mathml2asciimath  = true
  config.tag_border  = ''
end
----


== Related stuff

* https://github.com/xijo/reverse_markdown[Xijo's original reverse_markdown gem]
* https://github.com/xijo/reverse_markdown/wiki/Write-your-own-converter[Write custom converters] - Wiki entry about how to write your own converter
* https://github.com/harlantwood/html_massage[html_massage] - A gem by Harlan T. Wood to convert regular sites into markdown using reverse_markdown
* https://github.com/benbalter/word-to-markdown[word-to-markdown] - Convert word docs into markdown while using reverse_markdown, by Ben Balter
* https://github.com/asciidocfx/HtmlToAsciidoc[HtmlToAsciidoc] - Javascript regexp-based converter of HTML to Asciidoctor
* https://asciidoctor.org/docs/user-manual/[The Asciidoctor User Manual]