Now with cleaner variable interpolation

shell.nix

# On Nixos running this from the project folder with nix-shell will create a shell with all the necessary dependencies
# and run postgresql in an ephemeral mode for development.

{ pkgs ? import <nixpkgs> {} }:
pkgs.mkShell {
  nativeBuildInputs = with pkgs; [
    elixir_1_18
    elixir-ls
    erlang
    rebar3
    nodejs
    yarn
    fish
    gnumake
    postgresql
  ];

  # Environment variables
  MIX_ENV = "dev";
  NIX_ENFORCE_PURITY = "0"; # Without this bcrypt does not compile
  IEX_FILE = "${builtins.getEnv "PWD"}/.iex.exs";
  PROJECT_DIR = "/tmp/indie";
  PGPORT = "5432"; # Use quotes to ensure consistency in shell environments

  # Hook to automatically switch to Fish when entering the shell
  shellHook = ''
    # Environment variables that need interpolation
    export PGDATA=$PROJECT_DIR/data
    export PGLOCKDIR=$PROJECT_DIR/lock
    export PGLOG=$PROJECT_DIR/postgress.log  

    alias quit="killall -s KILL postgres && exit"
  
    red() { echo -e "\e[31m🚀 $1\e[0m"; }
    green() { echo -e "\e[32m🚀 $1\e[0m"; }

    iexfile() {
    # Create the .iex.exs file if it doesn't exist
    if [ ! -f "$IEX_FILE" ]; then
      red "Creating .iex.exs with common aliases..."
      cat <<EOF > "$IEX_FILE"
        IEx.configure(auto_reload: true)

        alias Indie.Repo
        alias Indie.Accounts.{User, Address}
        alias Indie.Commerce.Order
        alias Indie.Domains.Domain
EOF
    else
      green ".iex.exs already exists!"
    fi
    }

    

    get_dependencies () {
      # Run mix deps.get and mix deps.compile if necessary
      green "Getting Dependencies"
      [ ! -d "deps" ] && red "Running mix deps.get" && mix deps.get
      [ ! -d "_build" ] && red "Running mix deps.compile" && mix deps.compile
    }


    cleanup () {
      # Ensure the custom directories exist
      green "Cleaning and setting up ephemeral directories"
      rm -r $PGDATA
      mkdir -p $PGDATA
      mkdir -p $PGLOCKDIR
      chmod 700 $PGDATA
      chmod 700 $PGLOCKDIR
    }


    run_postgres () {
      green "Running Postgress"
      pg_ctl initdb -o "-U postgres"
      pg_ctl -D $PGDATA -l $PGLOG -o "-p $PGPORT -h localhost -k $PGLOCKDIR" start
    }

    populate_db () {
      green "Populating database"
      mix ecto.reset
    }

    dev () {
      iex -S mix phx.server 
    }
    
    iexfile
    get_dependencies
    cleanup
    run_postgres
    populate_db

    #trap 'killall -s KILL postgres && echo Postgress is now DEAD 🥳!' EXIT
  '';
}