# OpenFOAM nix shell environment

## Usage

With `direnv` installed and active (`eval $"(direnv hook bash)"`) the 
environment loads itself when you enter this directory or any below it.
Simulations can be placed inside the `sims` directory. The `sims` 
directory is ignored by git. If you change branches your simulations 
should stay untouched. However it may lead to confusion if you have
simulation results from one OpenFOAM version and then change to another.
Clone this repository again for each OpenFOAM version you want to use to
not confuse yourself ;-)

## Requirements

### nix with flakes
On `nixos` flakes can be enabled by adding the following to your system
configuration:

``` nix
nix.settings.experimental-features = [ "nix-command" "flakes" ];
```

On other systems add the following to your `/etc/nix/nix.conf`:

``` conf
experimental-features = nix-command flakes
```

### direnv

After installing `direnv` it has to be loaded. Maybe add the hook to your
shellrc:

``` sh
echo 'eval "$(direnv hook bash)"' >> ~/.bashrc
```

See https://direnv.net/docs/hook.html for more information.
You'll need to `allow` the current directory:

``` sh
direnv allow
```

## Update nixpkgs

From within this directory run

``` sh
nix flake update
```

to pin to the latest `nixpkgs` version.

## Update OpenFOAM version

The OpenFOAM derivation is defined in `pkgs/openfoam/default.nix`. Edit the
variables in the `let` block at the top of the file and replace the 
`"sha256-..."` string with an empty string. The first build will then fail 
and give you the correct sha hash. Replace the empty string with it.

## Add different OpenFOAM release

There are branches for each OpenFOAM release. The main branch has always the 
latest version. If you want to add a new one:

- create a new branch to hold the current version (e.g. openfoam-12)
- update the repository path in `pkgs/openfoam/default.nix` by editing the
  parameters in the `let` block.
- adjust the `patches`, `postPatch`, `configurePhase`, `buildPhase` and 
  `installPhase` if required

Reevaluating `envrc` will build the new OpenFOAM (this may take a while (expect
 up to 1h).