# Contributions are very welcome

If you would like to contribute a new diagnostic and recipe or a new feature, please discuss your idea with the development team before getting started, to avoid double work and/or disappointment later. A good way to do this is to open an [issue on GitHub](https://github.com/ESMValGroup/ESMValTool/issues). This is also a good way to get help.

If you have a bug to report, please do so using the [issues tab on the ESMValTool github repository](https://github.com/ESMValGroup/ESMValTool/issues).

To get started developing, follow the instructions below. More detailed instructions can be found in the [manual](https://esmvaltool.readthedocs.io) under Developer's Guide.

## Getting started

To install in development mode, follow these instructions.

-   [Download and install conda](https://conda.io/projects/conda/en/latest/user-guide/install/linux.html) (this should be done even if the system in use already has a preinstalled version of conda, as problems have been reported with NCL when using such a version)
-   To make the `conda` command availble, add `source <prefix>/etc/profile.d/conda.sh` to your `.bashrc` file and restart your shell. If using (t)csh shell, add `source <prefix>/etc/profile.d/conda.csh` to your `.cshrc`/`.tcshrc` file instead.
-   Update conda: `conda update -y conda`
-   Clone the ESMValTool public github repository: `git clone git@github.com:ESMValGroup/ESMValTool`, or one of the private github repositories (e.g. `git clone git@github.com:ESMValGroup/ESMValTool-private`)
-   Go to the esmvaltool directory: `cd ESMValTool`
-   Create the esmvaltool conda environment `conda env create --name esmvaltool --file environment.yml`
-   Activate the esmvaltool environment: `conda activate esmvaltool`
-   Install in development mode: `pip install -e '.[develop]'`. If you are installing behind a proxy that does not trust the usual pip-urls you can declare them with the option `--trusted-host`, e.g. `pip install --trusted-host=pypi.python.org --trusted-host=pypi.org --trusted-host=files.pythonhosted.org -e .[develop]`
-   If you want to use R diagnostics, run `Rscript esmvaltool/install/R/setup.R` to install the R dependences. Note that if you only want to run the lint test for R scripts you will have to install the `lintr` package. You can do that by running `Rscript esmvaltool/install/R/setup_devutils.R`.
-   If you want to use Julia diagnostics, first install Julia as described below in section "Installing Julia", then run `julia esmvaltool/install/Julia/setup.jl` to install the Julia dependences. Install Julia dependences after R dependences if you plan to use both.
-   Test that your installation was succesful by running `esmvaltool -h`.
-   If you log into a cluster or other device via `ssh` and your origin machine sends the `locale` environment via the `ssh` connection, make sure the environment is set correctly, specifically `LANG` and `LC_ALL` are set correctly (for GB English UTF-8 encoding these variables must be set to `en_GB.UTF-8`; you can set them by adding `export LANG=en_GB.UTF-8` and `export LC_ALL=en_GB.UTF-8` in your origin or login machines' `.profile`)
-   Do not run `conda update --update-all` in the `esmvaltool` environment since that will update some packages that are pinned to specific versions for the correct functionality of the environment.

## Using the development version of the ESMValTool Core package

If you need the latest developments of the ESMValTool Core package,
you can install that into the same conda environment:

-   Clone the ESMValTool Core github repository: `git clone git@github.com:ESMValGroup/ESMValCore`)
-   Go to the esmvalcore directory: `cd ESMValCore`
-   Update the esmvaltool conda environment `conda env update --name esmvaltool --file environment.yml`
-   Activate the esmvaltool environment: `conda activate esmvaltool`
-   Install `esmvalcore` in development mode: `pip install -e '.[develop]'`.

## Installing Julia

To run Julia diagnostics you will have to install Julia; the safest way is to use the official pre-built executable and link it in the conda environment:

-   Get the tarball (for v1.0.3 in this case): `wget https://julialang-s3.julialang.org/bin/linux/x64/1.0/julia-1.0.3-linux-x86_64.tar.gz`
-   Unpack the tarball: `tar xfz julia-*-linux-x86_64.tar.gz`
-   Symlink the Julia executable into the conda environment: `ln -s $PWD/julia-*/bin/julia $HOME/$ANACONDA/envs/esmvaltool/bin` (here `$ANACONDA` represents the name of your `anaconda` or `miniconda` directory, most commonly `anaconda3` or `miniconda3`)
-   Check executable location: `which julia`
-   Check Julia startup: `julia --help`
-   Optionally install the Julia diagnostics dependencies: `julia esmvaltool/install/Julia/setup.jl`

Note that sometimes, if you are under a firewall, the installation of Julia diagnostics dependencies may fail due to failure of cloning the references in `$HOME/.julia/registries/General`. To fix this issue you will have to touch the registry files: `touch $HOME/.julia/environments/v1.0/Manifest.toml && touch $HOME/.julia/environments/v1.0/Project.toml` and manually git clone the references: `git clone https://github.com/JuliaRegistries/General.git $HOME/.julia/registries/General`.

## Running tests

Go to the directory where the repository is cloned and run `python setup.py test --installation`. Tests will also be run automatically by [CircleCI](https://circleci.com/gh/ESMValGroup/ESMValTool).

## Code style

To increase the readability and maintainability or the ESMValTool source code, we aim to adhere to best practices and coding standards. All pull requests are reviewed and tested by one or more members of the core development team. For code in all languages, it is highly recommended that you split your code up in functions that are short enough to view without scrolling.

### Python

The standard document on best practices for Python code is [PEP8](https://www.python.org/dev/peps/pep-0008/) and there is [PEP257](https://www.python.org/dev/peps/pep-0257/) for documentation. We make use of [numpy style docstrings](https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_numpy.html) to document Python functions that are visible on [readthedocs](https://esmvaltool.readthedocs.io).

Most formatting issues in Python code can be fixed automatically by running the commands

    isort some_file.py

to sort the imports in the standard way and

    yapf -i some_file.py

to add/remove whitespace as required by the standard.

To check if your code adheres to the standard, go to the directory where the repository is cloned, e.g. `cd ESMValTool`.
and run

    prospector esmvaltool/diag_scripts/your_diagnostic/your_script.py

Run

    python setup.py lint

to see the warnings about the code style of the entire project.

We use `pycodestyle` on CircleCI to automatically check that there are no formatting mistakes and Codacy for monitoring (Python) code quality. Running prospector locally will give you quicker and sometimes more accurate results.

### NCL

Because there is no standard best practices document for NCL, we use [PEP8](https://www.python.org/dev/peps/pep-0008/) for NCL code as well, with some minor adjustments to accomodate for differences in the languages. The most important difference is that for NCL code the indentation should be 2 spaces instead of 4.

### R

Best practices for R code are described in [The tidyverse style guide](https://style.tidyverse.org/). We check adherence to this style guide by using [lintr](https://cran.r-project.org/web/packages/lintr/index.html) on CircleCI. Please use [styler](https://styler.r-lib.org/) to automatically format your code according to this style guide. In the future we would also like to make use of [goodpractice](https://cran.r-project.org/web/packages/goodpractice/index.html) to assess the quality of R code.

### YAML

Please use `yamllint` to check that your YAML files do not contain mistakes.

## Documentation

### What should be documented

Any code documentation that is visible on [readthedocs](https://esmvaltool.readthedocs.io) should be well written and adhere to the standards for documentation for the respective language. Recipes should have a page in the _Recipes_ section on readthedocs. This is also the place to document recipe options for the diagnostic scripts used in those recipes. Note that there is no need to write extensive documentation for functions that are not visible on readthedocs. However, adding a one line docstring describing what a function does is always a good idea.

### How to build the documentation locally

Go to the directory where the repository is cloned and run

    python setup.py build_sphinx -Ea

Make sure that your newly added documentation builds without warnings or errors.

## Pull requests and code review

New development should preferably be done in a new git branch in the main ESMValTool github repository. However, for scientists requiring confidentiality, private repositories are available. It is recommended that you open a pull request early (in draft mode), as this will cause CircleCI to run the unit tests and Codacy to analyse your code. It's also easier to get help from other developers if your code is visible in a pull request.

You can view the results of the automatic checks below your pull request. If one of the tests shows a red cross instead of a green approval sign, please click the link and try to solve the issue. Note that this kind of automated checks make it easier to review code, but they are not flawless, so occasionally Codacy will report false positives.

### Diagnostic script contributions

A pull request with diagnostic code should preferably not introduce new Codacy issues. However, we understand that there is a limit to how much time can be spend on polishing code, so up to 10 new (non-trivial) issues is still an acceptable amount.

### List of authors

If you make a (significant) contribution to ESMValTool, please add your name to the list of authors in CITATION.cff and regenerate the file .zenodo.json by running the command

    pip install cffconvert
    cffconvert --ignore-suspect-keys --outputformat zenodo --outfile .zenodo.json