action.yml

name: 'Switch into Nix Shell'
description: 'Switch into a Nix shell and export environment variables to subsequent steps.'
author: 'Lukas Mertens'
inputs:
  nix_args:
    description: 'Additional arguments to pass to nix print-dev-env.'
    required: false
    default: ''
  install_nix:
    description: 'Whether to install Nix. Set to false if Nix is already installed.'
    required: false
    default: 'true'
runs:
  using: 'composite'
  steps:
    - name: Install Nix
      if: ${{ inputs.install_nix == 'true' }}
      uses: cachix/install-nix-action@v27

    - name: Switch into Nix Shell
      shell: bash
      run: |
        set -xe

        # Function to save environment variables to a file
        save_env() {
          compgen -e | while read -r var; do
            value="${!var}"
            # Replace newlines with \n for comparison
            escaped_value=$(printf '%s' "$value" | sed ':a;N;$!ba;s/\n/\\n/g')
            echo "${var}=${escaped_value}"
          done | sort > "$1"
        }

        before_env=$(mktemp)
        after_env=$(mktemp)
        diff_env=$(mktemp)

        # Save initial environment
        save_env "$before_env"

        # Load Nix environment
        nix_dev_env_script=$(mktemp)
        nix print-dev-env ${{ inputs.nix_args }} > "$nix_dev_env_script"
        source "$nix_dev_env_script"

        # Save environment after loading Nix
        save_env "$after_env"

        # Find differences
        diff "$before_env" "$after_env" | grep '^>' | sed 's/^> //' > "$diff_env" || true

        # Add changed variables to GITHUB_ENV
        while IFS='=' read -r name value; do
          # Unescape newlines
          unescaped_value=$(printf '%s' "$value" | sed 's/\\n/\n/g')

          echo "${name}<<EOF" >> "$GITHUB_ENV"
          echo "$unescaped_value" >> "$GITHUB_ENV"
          echo "EOF" >> "$GITHUB_ENV"
        done < "$diff_env"

        echo "Environment variables added to GITHUB_ENV:"
        cat "$diff_env"

branding:
  icon: 'terminal'
  color: 'blue'