This extension provides a CodeMirror overlay mode to highlight incorrectly
spelled words in Markdown and Raw cells:

![screenshot.png](./screenshot.png)

It was inspired in part by
[NextStepWebs/codemirror-spell-checker](https://github.com/NextStepWebs/codemirror-spell-checker/blob/78773ebdd6c8cf8acd043342023636ae345ca0f3/src/js/spell-checker.js)
at the
[suggestion](https://github.com/ipython-contrib/jupyter_contrib_nbextensions/issues/521)
of [@JanSchulz](https://github.com/JanSchulz).


Spellchecking
-------------
The actual spellchecking is performed by the
[Typo.js](https://github.com/cfinke/Typo.js) library, which is included as a
dependency, with its own license.
Typo.js allows the use of
[hunspell](https://en.wikipedia.org/wiki/Hunspell)-style dictionaries in a
javascript-based spellchecker.


Dictionaries
------------

The dictionaries used by the extension are fetched according to the parameters.
To keep this repository lightweight, no dictionaries are incuded, and by
default the extension fetches an `en_US` dictionary from a cdn.
However, you can also add your own dictionaries for other languages, or to
remove dependency on the cdn.
To use your own dictionary, you'll need to alter the `.aff` and `.dic` urls in
the extension config.
The urls can be relative (for files on your jupyter server) or absolute (for
files hosted elsewhere, e.g. on a cdn like the defaults).

This is probably easiest to understand with some explicit examples.
Let's say I want to install a `de_DE` dictionary.
I can get the hunspell files from anywhere I like, but in this example I'm
going to use ones listed in the
[chromium source distribution](https://chromium.googlesource.com/chromium/deps/hunspell_dictionaries/+/master),
which includes quite a lot of different languages.
I place my dictionary `.aff` and `.dic` files inside the nbextension, such that
the directory structure looks like the following:

```
spellchecker/
	README.md
	config.yaml
	main.css
	main.js
	screenshot.png
	typo/
		LICENSE.txt
		typo.js
		dictionaries/
			de_DE.aff
			de_DE.dic
```

Then, I need to set the urls in the config to give the location of the
dictinaries relative to the `spellchecker/main.js` file and starting with `./`.
So, in this case, I would use `./typo/dictionaries/de_DE.aff` and
`./typo/dictionaries/de_DE.dic`.

If you've installed the nbextension in the usual place (that is, the per-user
`jupyter_data_dir()` as done by the repo installation script), you can use the
following python snippet with the appropriate language code to fetch and save
the appropriate files, and configure the extension to use the newly-installed
language:

```python
from __future__ import print_function
import os.path
import sys
import base64
from jupyter_core.paths import jupyter_data_dir
from notebook.services.config import ConfigManager

try:
    from urllib.request import urlopen # Py3
    from urllib.parse import urljoin
except ImportError:
    from urllib import urlopen # Py2
    from urlparse import urljoin

cm = ConfigManager()

remote_base_url = 'https://chromium.googlesource.com/chromium/deps/hunspell_dictionaries/+/master'
local_base_url = os.path.join(jupyter_data_dir(), 'nbextensions', 'spellchecker', 'typo', 'dictionaries')

lang_code = 'de_DE'

for ext in ('dic', 'aff'):
    dict_fname = lang_code + '.' + ext
    remote_path = remote_base_url + '/' + dict_fname + '?format=TEXT'
    local_path = os.path.join(local_base_url, dict_fname)

    print('saving {!r}\n    to {!r}'.format(remote_path, local_path))
    with open(local_path, 'wb') as loc_file:
        base64.decode(urlopen(remote_path), loc_file)
    rel_path = './typo/dictionaries/' + dict_fname
    cm.update('notebook', {'spellchecker': {ext + '_url': rel_path}})

cm.update('notebook', {'spellchecker': {'lang_code': lang_code}})
```

The above is also included as part of the nbextension, and should be
[available here](./download_new_dict.py).


Internals
---------
Any mispelled word has the css class `cm-spell-error` applied to it, so you can
customize their styling in cutom.css if you'd like.
