paperless-ngx/docs/development.md

# Development

This section describes the steps you need to take to start development
on paperless-ngx.

Check out the source from github. The repository is organized in the
following way:

- `main` always represents the latest release and will only see
  changes when a new release is made.
- `dev` contains the code that will be in the next release.
- `feature-X` contain bigger changes that will be in some release, but
  not necessarily the next one.

When making functional changes to paperless, _always_ make your changes
on the `dev` branch.

Apart from that, the folder structure is as follows:

- `docs/` - Documentation.
- `src-ui/` - Code of the front end.
- `src/` - Code of the back end.
- `scripts/` - Various scripts that help with different parts of
  development.
- `docker/` - Files required to build the docker image.

## Contributing to Paperless

Maybe you've been using Paperless for a while and want to add a feature
or two, or maybe you've come across a bug that you have some ideas how
to solve. The beauty of open source software is that you can see what's
wrong and help to get it fixed for everyone!

Before contributing please review our [code of
conduct](https://github.com/paperless-ngx/paperless-ngx/blob/main/CODE_OF_CONDUCT.md)
and other important information in the [contributing
guidelines](https://github.com/paperless-ngx/paperless-ngx/blob/main/CONTRIBUTING.md).

## Code formatting with pre-commit Hooks

To ensure a consistent style and formatting across the project source,
the project utilizes a Git [pre-commit]{.title-ref} hook to perform some
formatting and linting before a commit is allowed. That way, everyone
uses the same style and some common issues can be caught early on. See
below for installation instructions.

Once installed, hooks will run when you commit. If the formatting isn't
quite right or a linter catches something, the commit will be rejected.
You'll need to look at the output and fix the issue. Some hooks, such
as the Python formatting tool [black]{.title-ref}, will format failing
files, so all you need to do is [git add]{.title-ref} those files again
and retry your commit.

## Initial setup and first start

After you forked and cloned the code from github you need to perform a
first-time setup. To do the setup you need to perform the steps from the
following chapters in a certain order:

1.  Install prerequisites + pipenv as mentioned in
    `[Bare metal route](/setup#bare_metal)

2.  Copy `paperless.conf.example` to `paperless.conf` and enable debug
    mode.

3.  Install the Angular CLI interface:

    ```shell-session
    $ npm install -g @angular/cli
    ```

4.  Install pre-commit

    ```shell-session
    pre-commit install
    ```

5.  Create `consume` and `media` folders in the cloned root folder.

    ```shell-session
    mkdir -p consume media
    ```

6.  You can now either \...

    - install redis or

    - use the included scripts/start-services.sh to use docker to fire
      up a redis instance (and some other services such as tika,
      gotenberg and a database server) or

    - spin up a bare redis container

      > ```shell-session
      > docker run -d -p 6379:6379 --restart unless-stopped redis:latest
      > ```

7.  Install the python dependencies by performing in the src/ directory.

    ```shell-session
    pipenv install --dev
    ```

> - Make sure you're using python 3.9.x or lower. Otherwise you might
>   get issues with building dependencies. You can use
>   [pyenv](https://github.com/pyenv/pyenv) to install a specific
>   python version.

8.  Generate the static UI so you can perform a login to get session
    that is required for frontend development (this needs to be done one
    time only). From src-ui directory:

    ```shell-session
    npm install .
    ./node_modules/.bin/ng build --configuration production
    ```

9.  Apply migrations and create a superuser for your dev instance:

    ```shell-session
    python3 manage.py migrate
    python3 manage.py createsuperuser
    ```

10. Now spin up the dev backend. Depending on which part of paperless
    you're developing for, you need to have some or all of them
    running.

> ```shell-session
> python3 manage.py runserver & python3 manage.py document_consumer & celery --app paperless worker
> ```

11. Login with the superuser credentials provided in step 8 at
    `http://localhost:8000` to create a session that enables you to use
    the backend.

Backend development environment is now ready, to start Frontend
development go to `/src-ui` and run `ng serve`. From there you can use
`http://localhost:4200` for a preview.

## Back end development

The backend is a django application. PyCharm works well for development,
but you can use whatever you want.

Configure the IDE to use the src/ folder as the base source folder.
Configure the following launch configurations in your IDE:

- python3 manage.py runserver
- celery \--app paperless worker
- python3 manage.py document_consumer

To start them all:

```shell-session
python3 manage.py runserver & python3 manage.py document_consumer & celery --app paperless worker
```

Testing and code style:

- Run `pytest` in the src/ directory to execute all tests. This also
  generates a HTML coverage report. When runnings test, paperless.conf
  is loaded as well. However: the tests rely on the default
  configuration. This is not ideal. But for now, make sure no settings
  except for DEBUG are overridden when testing.

- Coding style is enforced by the Git pre-commit hooks. These will
  ensure your code is formatted and do some linting when you do a [git
  commit]{.title-ref}.

- You can also run `black` manually to format your code

  !!! note

      The line length rule E501 is generally useful for getting multiple
      source files next to each other on the screen. However, in some
      cases, its just not possible to make some lines fit, especially
      complicated IF cases. Append `# NOQA: E501` to disable this check
      for certain lines.

## Front end development

The front end is built using Angular. In order to get started, you need
`npm`. Install the Angular CLI interface with

```shell-session
$ npm install -g @angular/cli
```

and make sure that it's on your path. Next, in the src-ui/ directory,
install the required dependencies of the project.

```shell-session
$ npm install
```

You can launch a development server by running

```shell-session
$ ng serve
```

This will automatically update whenever you save. However, in-place
compilation might fail on syntax errors, in which case you need to
restart it.

By default, the development server is available on
`http://localhost:4200/` and is configured to access the API at
`http://localhost:8000/api/`, which is the default of the backend. If
you enabled DEBUG on the back end, several security overrides for
allowed hosts, CORS and X-Frame-Options are in place so that the front
end behaves exactly as in production. This also relies on you being
logged into the back end. Without a valid session, The front end will
simply not work.

Testing and code style:

- The frontend code (.ts, .html, .scss) use `prettier` for code
  formatting via the Git `pre-commit` hooks which run automatically on
  commit. See
  [above](#code-formatting-with-pre-commit-hooks) for installation. You can also run this via cli with a
  command such as

  ```shell-session
  $ git ls-files -- '*.ts' | xargs pre-commit run prettier --files
  ```

- Frontend testing uses jest and cypress. There is currently a need
  for significantly more frontend tests. Unit tests and e2e tests,
  respectively, can be run non-interactively with:

  ```shell-session
  $ ng test
  $ npm run e2e:ci
  ```

  Cypress also includes a UI which can be run from within the `src-ui`
  directory with

  ```shell-session
  $ ./node_modules/.bin/cypress open
  ```

In order to build the front end and serve it as part of django, execute

```shell-session
$ ng build --prod
```

This will build the front end and put it in a location from which the
Django server will serve it as static content. This way, you can verify
that authentication is working.

## Localization

Paperless is available in many different languages. Since paperless
consists both of a django application and an Angular front end, both
these parts have to be translated separately.

### Front end localization

- The Angular front end does localization according to the [Angular
  documentation](https://angular.io/guide/i18n).
- The source language of the project is "en_US".
- The source strings end up in the file "src-ui/messages.xlf".
- The translated strings need to be placed in the
  "src-ui/src/locale/" folder.
- In order to extract added or changed strings from the source files,
  call `ng xi18n --ivy`.

Adding new languages requires adding the translated files in the
"src-ui/src/locale/" folder and adjusting a couple files.

1.  Adjust "src-ui/angular.json":

    ```json
    "i18n": {
        "sourceLocale": "en-US",
        "locales": {
            "de": "src/locale/messages.de.xlf",
            "nl-NL": "src/locale/messages.nl_NL.xlf",
            "fr": "src/locale/messages.fr.xlf",
            "en-GB": "src/locale/messages.en_GB.xlf",
            "pt-BR": "src/locale/messages.pt_BR.xlf",
            "language-code": "language-file"
        }
    }
    ```

2.  Add the language to the available options in
    "src-ui/src/app/services/settings.service.ts":

    ```typescript
    getLanguageOptions(): LanguageOption[] {
        return [
            {code: "en-us", name: $localize`English (US)`, englishName: "English (US)", dateInputFormat: "mm/dd/yyyy"},
            {code: "en-gb", name: $localize`English (GB)`, englishName: "English (GB)", dateInputFormat: "dd/mm/yyyy"},
            {code: "de", name: $localize`German`, englishName: "German", dateInputFormat: "dd.mm.yyyy"},
            {code: "nl", name: $localize`Dutch`, englishName: "Dutch", dateInputFormat: "dd-mm-yyyy"},
            {code: "fr", name: $localize`French`, englishName: "French", dateInputFormat: "dd/mm/yyyy"},
            {code: "pt-br", name: $localize`Portuguese (Brazil)`, englishName: "Portuguese (Brazil)", dateInputFormat: "dd/mm/yyyy"}
            // Add your new language here
        ]
    }
    ```

    `dateInputFormat` is a special string that defines the behavior of
    the date input fields and absolutely needs to contain "dd", "mm"
    and "yyyy".

3.  Import and register the Angular data for this locale in
    "src-ui/src/app/app.module.ts":

    ```typescript
    import localeDe from '@angular/common/locales/de'
    registerLocaleData(localeDe)
    ```

### Back end localization

A majority of the strings that appear in the back end appear only when
the admin is used. However, some of these are still shown on the front
end (such as error messages).

- The django application does localization according to the [django
  documentation](https://docs.djangoproject.com/en/3.1/topics/i18n/translation/).
- The source language of the project is "en_US".
- Localization files end up in the folder "src/locale/".
- In order to extract strings from the application, call
  `python3 manage.py makemessages -l en_US`. This is important after
  making changes to translatable strings.
- The message files need to be compiled for them to show up in the
  application. Call `python3 manage.py compilemessages` to do this.
  The generated files don't get committed into git, since these are
  derived artifacts. The build pipeline takes care of executing this
  command.

Adding new languages requires adding the translated files in the
"src/locale/" folder and adjusting the file
"src/paperless/settings.py" to include the new language:

```python
LANGUAGES = [
    ("en-us", _("English (US)")),
    ("en-gb", _("English (GB)")),
    ("de", _("German")),
    ("nl-nl", _("Dutch")),
    ("fr", _("French")),
    ("pt-br", _("Portuguese (Brazil)")),
    # Add language here.
]
```

## Building the documentation

The documentation is built using material-mkdocs, see their [documentation](https://squidfunk.github.io/mkdocs-material/reference/). If you want to build the documentation locally, this is how you do it:

1.  Install python dependencies.

    ```shell-session
    $ cd /path/to/paperless
    $ pipenv install --dev
    ```

2.  Build the documentation

    ```shell-session
    $ cd /path/to/paperless
    $ pipenv mkdocs build
    ```

## Building the Docker image

The docker image is primarily built by the GitHub actions workflow, but
it can be faster when developing to build and tag an image locally.

To provide the build arguments automatically, build the image using the
helper script `build-docker-image.sh`.

Building the docker image from source:

> ```shell-session
> ./build-docker-image.sh Dockerfile -t <your-tag>
> ```

## Extending Paperless

Paperless does not have any fancy plugin systems and will probably never
have. However, some parts of the application have been designed to allow
easy integration of additional features without any modification to the
base code.

### Making custom parsers

Paperless uses parsers to add documents to paperless. A parser is
responsible for:

- Retrieve the content from the original
- Create a thumbnail
- Optional: Retrieve a created date from the original
- Optional: Create an archived document from the original

Custom parsers can be added to paperless to support more file types. In
order to do that, you need to write the parser itself and announce its
existence to paperless.

The parser itself must extend `documents.parsers.DocumentParser` and
must implement the methods `parse` and `get_thumbnail`. You can provide
your own implementation to `get_date` if you don't want to rely on
paperless' default date guessing mechanisms.

```python
class MyCustomParser(DocumentParser):

    def parse(self, document_path, mime_type):
        # This method does not return anything. Rather, you should assign
        # whatever you got from the document to the following fields:

        # The content of the document.
        self.text = "content"

        # Optional: path to a PDF document that you created from the original.
        self.archive_path = os.path.join(self.tempdir, "archived.pdf")

        # Optional: "created" date of the document.
        self.date = get_created_from_metadata(document_path)

    def get_thumbnail(self, document_path, mime_type):
        # This should return the path to a thumbnail you created for this
        # document.
        return os.path.join(self.tempdir, "thumb.png")
```

If you encounter any issues during parsing, raise a
`documents.parsers.ParseError`.

The `self.tempdir` directory is a temporary directory that is guaranteed
to be empty and removed after consumption finished. You can use that
directory to store any intermediate files and also use it to store the
thumbnail / archived document.

After that, you need to announce your parser to paperless. You need to
connect a handler to the `document_consumer_declaration` signal. Have a
look in the file `src/paperless_tesseract/apps.py` on how that's done.
The handler is a method that returns information about your parser:

```python
def myparser_consumer_declaration(sender, **kwargs):
    return {
        "parser": MyCustomParser,
        "weight": 0,
        "mime_types": {
            "application/pdf": ".pdf",
            "image/jpeg": ".jpg",
        }
    }
```

- `parser` is a reference to a class that extends `DocumentParser`.
- `weight` is used whenever two or more parsers are able to parse a
  file: The parser with the higher weight wins. This can be used to
  override the parsers provided by paperless.
- `mime_types` is a dictionary. The keys are the mime types your
  parser supports and the value is the default file extension that
  paperless should use when storing files and serving them for
  download. We could guess that from the file extensions, but some
  mime types have many extensions associated with them and the python
  methods responsible for guessing the extension do not always return
  the same value.