galyleo.sh

#!/usr/bin/env sh
# ======================================================================
#
# NAME
#
#     galyleo.sh
#
# DESCRIPTION
#
#     A shell utility to help you launch Jupyter notebooks in a simple,
#     secure way.
#
# USAGE
#
# DEPENDENCIES
#
#     jupyter
#     jupyterlab
#     satellite - https://github.com/sdsc-hpc-training-org/satellite
#
# TODO
#
#     Add support for non-jupyter-based web services; 
#       e.g., Spark and TensorBoard; VNC
#
# AUTHOR(S)
#
#     Marty Kandes, Ph.D.
#     Senior Computational & Data Science Research Specialist
#     High-Performance Computing User Services Group
#     Data-Enabled Scientific Computing Division
#     San Diego Supercomputer Center
#     University of California, San Diego
#
# LAST UPDATED
#
#     Monday, March 17th, 2025
#
# ----------------------------------------------------------------------

# Declare a global environment variable to set the installation location
# of galyleo. DO NOT leave as PWD when deployed in production. In the
# future, may include a Makefile with a PREFIX option to install
# correctly and set this variable. e.g., https://github.com/oyvinev/log.sh
declare -xr GALYLEO_INSTALL_DIR="${PWD}"

# Declare a global environment variable to set the galyleo cache
# directory, which will hold all output files generated by galyleo.
# e.g., Slurm batch job scripts, Slurm standard output files, etc.

declare -xr GALYLEO_CACHE_DIR="${HOME}/.galyleo"

# Declare a set of global environment variables used to identify a
# specific execution of galyleo. e.g., used to label a unique id of the
# generated batch job script.

declare -xr CURRENT_LOCAL_TIME="$(date +'%Y%m%dT%H%M%S%z')"
declare -xir CURRENT_UNIX_TIME="$(date +'%s')"
declare -xir RANDOM_ID="${RANDOM}"

# Source all shell libraries required for galyleo.
source "${GALYLEO_INSTALL_DIR}/lib/slog.sh"

# Source the galyleo configuration file. If it does not exist yet, then
# one must be created with the galyleo configure command. A galyleo.conf
# file must be created prior to end-user use of its launch capabilities.
if [[ ! -f "${GALYLEO_INSTALL_DIR}/galyleo.conf" ]]; then
  slog warning -m 'galyleo.conf file does not exist yet.'
else
  source "${GALYLEO_INSTALL_DIR}/galyleo.conf"
  if [[ "${?}" -ne 0 ]]; then
    slog error -m 'Failed to source galyleo.conf file.'
    exit 1
  fi
fi

# ----------------------------------------------------------------------
# galyleo_launch
#
#   Launches a Jupyter notebook server on a remote system. There will be
#   several modes of operation that are supported with the 'launch'
#   command. However, only the 'local' launch mode is available at this
#   time. i.e., 'local' -> no SSH involved.
#
# Globals:
#
#   GALYLEO_CACHE_DIR
#   SLOG_LEVEL
#
# Arguments:
#
#   -A | --account <account>
#   -R | --reservation <reservation>
#   -p | --partition <partition>
#   -q | --qos <qos>
#   -N | --nodes <nodes>
#   -c | --cpus <cpus_per_task>
#   -m | --memory <memory_per_node> (in units of GB)
#   -g | --gpus <gpus>
#      | --gres <gres>
#   -t | --time-limit <time_limit>
#   -C | --constraint <constraint>
#   -i | --interface <jupyter_interface>
#   -d | --notebook-dir <jupyter_notebook_dir>
#      | --scratch-dir <local_scratch_dir>
#   -e | --env-modules <env_modules>
#      | --append-modulepath <append_modpath>
#   -s | --sif <singularity_image_file>
#   -B | --bind <singularity_bind_mounts>
#      | --nv
#      | --conda-init <conda_init>
#      | --conda-env <conda_env>
#      | --conda-yml <conda_yml>
#      | --conda-version <conda_version>
#      | --mamba
#      | --cache
#      | --spark-home <spark_home>
#      | --disable-checklist
#      | --checklist-timeout <checklist_timeout>
#   -Q | --quiet
#
# Returns:
#
#   True  (0) if the launch was successful.
#   False (1) if the launch failed and/or was halted.
#
# ----------------------------------------------------------------------
function galyleo_launch() {

  # Declare galyleo launch mode variable and set its default to 'local'.
  local mode='local'

  # Declare input variables associated with scheduler.
  local account=''
  local reservation=''
  local partition="${GALYLEO_DEFAULT_PARTITION}"
  local qos=''
  local -i nodes=1
  local -i ntasks_per_node=1
  local -i cpus_per_task="${GALYLEO_DEFAULT_CPUS}"
  local -i memory_per_node="${GALYLEO_DEFAULT_MEMORY}"
  local gpus=''
  local gres=''
  local time_limit="${GALYLEO_DEFAULT_TIME_LIMIT}"
  local constraint=''

  # Declare input variables associated with Jupyter runtime environment.
  local jupyter_interface="${GALYLEO_DEFAULT_JUPYTER_INTERFACE}"
  local jupyter_notebook_dir=''

  # Declare input variables associated with system architecture.
  local local_scratch_dir="${GALYLEO_DEFAULT_LOCAL_SCRATCH_DIR}"

  # Declare input variables associated with environment modules.
  local env_modules=''

  # Declare directories that append MODULEPATH environment variable
  local append_modpath=''

  # Declare input variables associated with Singularity containers.
  local singularity_image_file=''
  local singularity_bind_mounts=''
  local singularity_gpu_type=''

  # Declare input variables associated with conda environments.
  local conda_init=''
  local conda_env=''
  local conda_yml=''
  local conda_version='latest'
  local conda_mamba='false'
  local conda_cache='false'

  # Declare input variables associated with auxillary applications. e.g. Spark, Tensorboard
  local spark_home=''

  # Declare input variables associated with error checking.
  local disable_checklist='false'
  local -i checklist_timeout=10

  # Declare internal galyelo_launch variables not affected by input variables.
  local job_name="galyleo-${CURRENT_LOCAL_TIME}-${CURRENT_UNIX_TIME}-${RANDOM_ID}"
  local -i job_id=-1
  local http_response=''
  local -i http_status_code=-1

  # Read in command-line options and assign input variables to local
  # variables.
  while (("${#}" > 0)); do
    case "${1}" in
      --mode )
        mode="${2}"
        shift 2
        ;;
      -A | --account )
        account="${2}"
        shift 2
        ;;
      -R | --reservation )
        reservation="${2}"
        shift 2
        ;;
      -p | --partition )
        partition="${2}"
        shift 2
        ;;
      -q | --qos )
        qos="${2}"
        shift 2
        ;;
      -N | --nodes )
        nodes="${2}"
        shift 2
        ;;
      -n | --ntasks-per-node )
        ntasks_per_node="${2}"
        shift 2
        ;;
      -c | --cpus | --cpus-per-task )
        cpus_per_task="${2}"
        shift 2
        ;;
      -m | -M | --memory | --memory-per-node )
        memory_per_node="${2}"
        shift 2
        ;;
      -g | -G | --gpus )
        gpus="${2}"
        shift 2
        ;;
      --gres )
        gres="${2}"
        shift 2
        ;;
      -t | --time-limit )
        time_limit="${2}"
        shift 2
        ;;
      -C | --constraint )
        constraint="${2}"
        shift 2
        ;;
      -i | --interface )
        jupyter_interface="${2}"
        shift 2
        ;;
      -j | --jupyter )
        jupyter_interface="${2}"
        shift 2
        ;;
      -d | --notebook-dir )
        jupyter_notebook_dir="${2}"
        shift 2
        ;;
      --scratch-dir )
        local_scratch_dir="${2}"
        shift 2
        ;;
      -e | --env-modules )
        env_modules="${2}"
        shift 2
        ;;
      --append-modulepath)
        append_modpath="${2}"
        shift 2
        ;;
      -s | --sif )
        singularity_image_file="${2}"
        shift 2
        ;;
      -B | --bind )
        singularity_bind_mounts="${2}"
        shift 2
        ;;
      --nv )
        singularity_gpu_type='nv'
        shift 1
        ;;
      --rocm )
        singularity_gpu_type='rocm'
        shift 1
        ;;
      --conda-init )
        conda_init="${2}"
        shift 2
        ;;
      --conda-env )
        conda_env="${2}"
        shift 2
        ;;
      --conda-yml )
        conda_yml="${2}"
        shift 2
        ;;
      --conda-version )
        conda_version="${2}"
        shift 2
        ;;
      --mamba )
        conda_mamba='true'
        shift 1
        ;;
      --cache )
        conda_cache='true'
        shift 1
        ;;
      --spark-home )
        spark_home="${2}"
        shift 2
        ;;
      --disable-checklist )
        disable_checklist='true'
        shift 1
        ;;
      --checklist-timeout )
        checklist_timeout="${2}"
        shift 2
        ;;
      -Q | --quiet )
        SLOG_LEVEL=0
        shift 1
        ;;
      *)
        slog error -m "Command-line option ${1} not recognized or not supported."
        return 1
    esac
  done

  # Print all command-line options read in for launch to standard output.
  slog output -m 'Preparing galyleo for launch into Jupyter orbit ...'
  slog output -m 'Listing all launch parameters ...'
  slog output -m '  command-line options       : values'
  slog output -m "    -A | --account           : ${account}"
  slog output -m "    -R | --reservation       : ${reservation}"
  slog output -m "    -p | --partition         : ${partition}"
  slog output -m "    -q | --qos               : ${qos}"
  slog output -m "    -N | --nodes             : ${nodes}"
  slog output -m "    -c | --cpus              : ${cpus_per_task}"
  slog output -m "    -m | --memory            : ${memory_per_node} GB"
  slog output -m "    -g | --gpus              : ${gpus}"
  slog output -m "       | --gres              : ${gres}"
  slog output -m "    -t | --time-limit        : ${time_limit}"
  slog output -m "    -C | --constraint        : ${constraint}"
  slog output -m "    -i | --interface         : ${jupyter_interface}"
  slog output -m "    -d | --notebook-dir      : ${jupyter_notebook_dir}"
  slog output -m "       | --scratch-dir       : ${local_scratch_dir}"
  slog output -m "    -e | --env-modules       : ${env_modules}"
  slog output -m "       | --append-modulepath : ${append_modpath}"
  slog output -m "    -s | --sif               : ${singularity_image_file}"
  slog output -m "    -B | --bind              : ${singularity_bind_mounts}"
  slog output -m "       | --nv                : ${singularity_gpu_type}"
  slog output -m "       | --conda-init        : ${conda_init}"
  slog output -m "       | --conda-env         : ${conda_env}"
  slog output -m "       | --conda-yml         : ${conda_yml}"
  slog output -m "       | --conda-version     : ${conda_version}"
  slog output -m "       | --mamba             : ${conda_mamba}"
  slog output -m "       | --cache             : ${conda_cache}"
  slog output -m "       | --spark-home        : ${spark_home}"
  slog output -m "       | --disable-checklist : ${disable_checklist}"
  slog output -m "       | --checklist-timeout : ${checklist_timeout} s"
  slog output -m "    -Q | --quiet             : ${SLOG_LEVEL}"

  # Start pre-launch checklist.
  if [[ "${disable_checklist}" == 'false' ]]; then

    # Check if the user specified a Jupyter user interface. If the user
    # did not specify a user interface, then set JupyterLab ('lab') as the
    # default interface.
    if [[ -z "${jupyter_interface}" ]]; then
      jupyter_interface='lab'
    fi

    # Check if a valid Jupyter user interface was specified. At
    # present, the only two valid user interfaces are JupyterLab ('lab')
    # OR Jupyter Notebook ('notebook'). If an invalid interface name is
    # provided by the user, then halt the launch.
    case "${jupyter_interface}" in
      'lab' )
        ;;
      'notebook' )
        ;;
      'voila' )
        ;;
      *)
      slog error -m "Not a valid Jupyter user interface: ${jupyter_interface}"
      slog error -m "Only --interface lab OR --interface notebook OR --interface voila are allowed."
      return 1
    esac

    # Check if the user specified a working directory for their Jupyter
    # notebook session. If the user did not specify a working directory,
    # then set the working directory to the user's $HOME directory.
    if [[ -z "${jupyter_notebook_dir}" ]]; then
      jupyter_notebook_dir="${HOME}"
    fi

    # Check if the Jupyter notebook directory exists. If it does not
    # exist, then halt the launch.
    if [[ ! -d "${jupyter_notebook_dir}" ]]; then
      slog error -m "Jupyter notebook directory does not exist: ${jupyter_notebook_dir}"
      return 1
    fi
 
    # Check if the user has write permissions within the Jupyter notebook
    # directory. If the user does not have write permissions, then halt
    # the launch.
    if [[ ! -w "${jupyter_notebook_dir}" ]]; then
      slog error -m "Jupyter notebook directory exists, but you do not have write permissions: ${jupyter_notebook_dir}"
      return 1
    fi

    # Check if any directories to be append to MODULEPATH exist and
    # are accessible. If they are not, then halt the launch.
    if [[ -n "${append_modpath}" ]]; then
      for mpath_name in $(sed 's/,/ /g' <<< "$append_modpath"); do
        if [[ ! -d "${mpath_name}" ]] || [[ ! -r "${mpath_name}" ]]; then
          slog error -m "directory to append MODULE path not found: ${mpath_name}"
          return 1
        fi
      done
    fi

    # Check if all environment modules specified by the user, if any, are
    # available and can be loaded successfully. If not, then halt the launch.
    if [[ -n "${env_modules}" ]]; then
      IFS=','
      read -r -a modules <<< "${env_modules}"
      IFS=$' \t\n'
      for module in "${modules[@]}"; do
        module load "${module}"
        if [[ $? -ne 0 ]]; then
          slog error -m "module not found: ${module}"
          return 1
        fi
      done
    fi

    # Check if Singularity is available within the software environment
    # specified by the user. If it is not available, then halt the launch.
    if [[ -n "${singularity_image_file}" ]]; then
      singularity --version > /dev/null
      if [[ "${?}" -ne 0 ]]; then
        slog error -m "No singularity executable was found within the software environment."
        return 1
      fi
    fi

    # Check if the user specified a URI to a container stored in a
    # registry, or a path to a Singularity container already stored on
    # a local filesystem. If the user specified a path to the container
    # and the file does not exist, then halt the launch. Note: We cannot
    # currently check if the URI is valid prior to job launch.
    if [[ -n "${singularity_image_file}" ]]; then
      grep -E '^docker://|^library://|^oras://' <<< "${singularity_image_file}"
      if [[ "${?}" -eq 0 ]]; then
        slog output -m "Detected URI for container image: ${singularity_image_file}"
      else
        if [[ ! -f "${singularity_image_file}" ]]; then
          slog error -m "Singularity image file does not exist: ${singularity_image_file}"
          return 1
        fi
      fi
    fi

    # Check if jupyter is already installed within the container
    # specified by the user. If it is not already installed, then halt
    # the launch.
    if [[ -f "${singularity_image_file}" ]]; then
      timeout "${checklist_timeout}" singularity exec "${singularity_image_file}" jupyter "${jupyter_interface}" --version > /dev/null
      if [[ "${?}" -ne 0 ]]; then
        slog error -m "Either no jupyter executable was found within the singularity container OR the process used to check for the jupyter executable within the container may have hung and then timed out."
        return 1
      fi
    fi

    # Check if the conda environment specified by the user can be
    # initialized and activated successfully. If it can be, then check
    # if jupyter is already installed. If not, then halt the launch.
    if [[ -n "${conda_env}" ]] && [[ -z "${conda_yml}" ]]; then
      if [[ -n "${conda_init}" ]]; then
        source "${conda_init}"
      else
        source ~/.bashrc
      fi
      conda activate "${conda_env}"
      if [[ "${?}" -ne 0 ]]; then
        slog error -m "conda environment could not be activated: ${conda_env}"
        return 1
      fi
      jupyter "${jupyter_interface}" --version > /dev/null
      if [[ "${?}" -ne 0 ]]; then
        slog error -m "No jupyter executable was found within the conda  environment: ${conda_env}"
        return 1
      fi
    elif [[ -z "${conda_env}" ]] && [[ -n "${conda_yml}" ]]; then
      if [[ ! -f "${conda_yml}" ]]; then
        slog error -m "conda environment.yml file not found: ${conda_yml}"
        return 1
      fi
    elif [[ -n "${conda_env}" ]] && [[ -n "${conda_yml}" ]]; then
      slog error -m "--conda-env and --conda-yml options should no longer be used together."
      return 1
    fi

  fi
  # End pre-launch checklist.

  # Request a subdomain connection token from reverse proxy service. If the 
  # reverse proxy service returns an HTTP/S error, then halt the launch.
  http_response="$(curl -s -w %{http_code} https://manage.${GALYLEO_REVERSE_PROXY_FQDN}/getlink.cgi -o -)"
  slog output -m "${http_response}"
  http_status_code="$(echo ${http_response} | awk '{print $NF}')"
  if (( "${http_status_code}" != 200 )); then
    slog error -m "Unable to connect to the Satellite reverse proxy service: ${http_status_code}"
    return 1
  fi

  # Extract the reverse proxy connection token and export it as a
  # read-only environment variable.
  declare -xr REVERSE_PROXY_TOKEN="$(echo ${http_response} | awk 'NF>1{printf $((NF-1))}' -)"

  # Generate an authentication token to be used for first-time 
  # connections to the Jupyter notebook server and export it as a 
  # read-only environment variable.
  declare -xr JUPYTER_TOKEN="$(openssl rand -hex 16)"

  # Change present working directory to GALYLEO_CACHE_DIR. Generate and
  # store all Jupyter launch scripts and standard output files in the
  # GALYLEO_CACHE_DIR. Users should not need to access these files when
  # the service is working properly. They will generally only be useful
  # for debugging purposes by SDSC staff. A cleanup function to clear
  # the cache will be provided. We will eventually do some default
  # purging of older files to prevent cache buildup.
  if [[ ! -d "${GALYLEO_CACHE_DIR}" ]]; then
    mkdir -p "${GALYLEO_CACHE_DIR}"
    chmod u+rwx "${GALYLEO_CACHE_DIR}"
    chmod g-rwx "${GALYLEO_CACHE_DIR}"
    chmod o-rwx "${GALYLEO_CACHE_DIR}"
    if [[ "${?}" -ne 0 ]]; then
      slog error -m "Failed to create GALYLEO_CACHE_DIR: ${GALYLEO_CACHE_DIR}"
      return 1
    fi
  fi
  cd "${GALYLEO_CACHE_DIR}"

  # Generate a Jupyter launch script.
  slog output -m 'Generating Jupyter launch script ...'
  if [[ ! -f "${job_name}.sh" ]]; then

    slog append -f "${job_name}.sh" -m '#!/usr/bin/env sh'
    slog append -f "${job_name}.sh" -m ''
    slog append -f "${job_name}.sh" -m "#SBATCH --job-name=${job_name}"
    if [[ -n "${account}" ]]; then
      slog append -f "${job_name}.sh" -m "#SBATCH --account=${account}"
    else
      slog error -m 'No account specified. Every job must be charged to an account.'
      rm "${job_name}.sh"
      return 1
    fi
    if [[ -n "${reservation}" ]]; then
      slog append -f "${job_name}.sh" -m "#SBATCH --reservation=${reservation}"
    fi
    if [[ -n "${qos}" ]]; then
      slog append -f "${job_name}.sh" -m "#SBATCH --qos=${qos}"
    fi
    slog append -f "${job_name}.sh" -m "#SBATCH --partition=${partition}"
    slog append -f "${job_name}.sh" -m "#SBATCH --nodes=${nodes}"
    slog append -f "${job_name}.sh" -m "#SBATCH --ntasks-per-node=${ntasks_per_node}"
    slog append -f "${job_name}.sh" -m "#SBATCH --cpus-per-task=${cpus_per_task}"
    if [[ -n "${gpus}" && -z "${gres}" ]]; then
      slog append -f "${job_name}.sh" -m "#SBATCH --gpus=${gpus}"
    elif [[ -z "${gpus}" && -n "${gres}" ]]; then
      slog append -f "${job_name}.sh" -m "#SBATCH --gres=${gres}"
    fi
    if (( "${memory_per_node}" > 0 )); then
      slog append -f "${job_name}.sh" -m "#SBATCH --mem=${memory_per_node}G"
    fi
    slog append -f "${job_name}.sh" -m "#SBATCH --time=${time_limit}"
    if [[ -n "${constraint}" ]]; then
      slog append -f "${job_name}.sh" -m "#SBATCH --constraint=${constraint}"
    fi
    slog append -f "${job_name}.sh" -m "#SBATCH --no-requeue"
    slog append -f "${job_name}.sh" -m "#SBATCH --export=ALL"
    slog append -f "${job_name}.sh" -m "#SBATCH --output=%x.o%j.%N"
    slog append -f "${job_name}.sh" -m ''

    slog append -f "${job_name}.sh" -m 'declare -xr GALYLEO_LAUNCH_DIR="${SLURM_SUBMIT_DIR}"'
    slog append -f "${job_name}.sh" -m "declare -xr LOCAL_SCRATCH_DIR=${local_scratch_dir}"
    slog append -f "${job_name}.sh" -m ''

    slog append -f "${job_name}.sh" -m 'declare -xr JUPYTER_RUNTIME_DIR="${HOME}/.jupyter/runtime"'
    slog append -f "${job_name}.sh" -m 'declare -xi JUPYTER_PORT=-1'
    slog append -f "${job_name}.sh" -m 'declare -xir LOWEST_EPHEMERAL_PORT=49152'
    slog append -f "${job_name}.sh" -m 'declare -i random_ephemeral_port=-1'
    slog append -f "${job_name}.sh" -m ''

    # Choose an open ephemeral port at random.
    slog append -f "${job_name}.sh" -m 'while (( "${JUPYTER_PORT}" < 0 )); do'
    slog append -f "${job_name}.sh" -m '  while (( "${random_ephemeral_port}" < "${LOWEST_EPHEMERAL_PORT}" )); do'
    slog append -f "${job_name}.sh" -m '    random_ephemeral_port="$(od -An -N 2 -t u2 -v < /dev/urandom)"'
    slog append -f "${job_name}.sh" -m '  done'
    slog append -f "${job_name}.sh" -m '  ss -nutlp | cut -d : -f2 | grep "^${random_ephemeral_port})" > /dev/null'
    slog append -f "${job_name}.sh" -m '  if [[ "${?}" -ne 0 ]]; then'
    slog append -f "${job_name}.sh" -m '    JUPYTER_PORT="${random_ephemeral_port}"'
    slog append -f "${job_name}.sh" -m '  fi'
    slog append -f "${job_name}.sh" -m 'done'
    slog append -f "${job_name}.sh" -m ''

    # Reset module environment to default set.
    slog append -f "${job_name}.sh" -m 'module reset'

    # Append MODULEPATH with user specified directories
    if [[ -n "$append_modpath" ]]; then
      append_modpath=$(sed 's/,/:/g' <<< "$append_modpath")
      slog append -f "${job_name}.sh" -m 'export MODULEPATH=${MODULEPATH}:'"${append_modpath}"
    fi

    # Load environment modules specified by the user.
    if [[ -n "${env_modules}" ]]; then
      IFS=','
      read -r -a modules <<< "${env_modules}"
      unset IFS
      for module in "${modules[@]}"; do
        slog append -f "${job_name}.sh" -m  "module load ${module}"
      done
    fi

    # Activate a pre-installed conda environment specified by the user.
    if [[ -n "${conda_env}" ]] && [[ -z "${conda_yml}" ]] && [[ -z "${singularity_image_file}" ]]; then
      if [[ -n "${conda_init}" ]]; then
        slog append -f "${job_name}.sh" -m "source ${conda_init}"
      else
        slog append -f "${job_name}.sh" -m 'source ~/.bashrc'
      fi
      slog append -f "${job_name}.sh" -m "conda activate ${conda_env}"
    fi

    # Create and/or activate a dynamically generated conda environment specified by the user.
    if [[ -z "${conda_env}" ]] && [[ -n "${conda_yml}" ]] && [[ -z "${singularity_image_file}" ]]; then
      conda_env="$(grep name: ${OLDPWD}/${conda_yml} | awk '{print $2}')"
      if [[ ! -d "${GALYLEO_CACHE_DIR}/${conda_env}" ]]; then
        mkdir -p "${GALYLEO_CACHE_DIR}/${conda_env}"
      fi
      cp "${OLDPWD}/${conda_yml}" "${GALYLEO_CACHE_DIR}/${conda_env}/${conda_yml}"
      cd "${GALYLEO_CACHE_DIR}/${conda_env}"
      md5sum -c "${conda_env}.md5" > /dev/null
      if [[ "${?}" -eq 0 ]]; then # unpack existing conda environment
        cd "${GALYLEO_CACHE_DIR}"
        slog append -f "${job_name}.sh" -m 'cd "${LOCAL_SCRATCH_DIR}"'
        slog append -f "${job_name}.sh" -m "cp ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_env}.tar.gz ./"
        slog append -f "${job_name}.sh" -m "mkdir -p ${conda_env}"
        slog append -f "${job_name}.sh" -m "tar -xf ${conda_env}.tar.gz -C ${conda_env}"
        slog append -f "${job_name}.sh" -m "source ${conda_env}/bin/activate"
        slog append -f "${job_name}.sh" -m 'conda-unpack'
      else # re/build (and cache) the conda environment
        cd "${GALYLEO_CACHE_DIR}"
        slog append -f "${job_name}.sh" -m 'cd "${LOCAL_SCRATCH_DIR}"'
        slog append -f "${job_name}.sh" -m "cp ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_yml} ./"
        slog append -f "${job_name}.sh" -m "wget https://repo.anaconda.com/miniconda/Miniconda3-${conda_version}-Linux-x86_64.sh"
        slog append -f "${job_name}.sh" -m "chmod +x Miniconda3-${conda_version}-Linux-x86_64.sh"
        slog append -f "${job_name}.sh" -m 'export CONDA_INSTALL_PATH="${LOCAL_SCRATCH_DIR}/miniconda3"'
        slog append -f "${job_name}.sh" -m 'export CONDA_ENVS_PATH="${CONDA_INSTALL_PATH}/envs"'
        slog append -f "${job_name}.sh" -m 'export CONDA_PKGS_DIRS="${CONDA_INSTALL_PATH}/pkgs"'
        slog append -f "${job_name}.sh" -m "./Miniconda3-${conda_version}-Linux-x86_64.sh -b -p \"\${CONDA_INSTALL_PATH}\""
        slog append -f "${job_name}.sh" -m 'source "${CONDA_INSTALL_PATH}/etc/profile.d/conda.sh"'
        slog append -f "${job_name}.sh" -m 'conda activate base'
        if [[ "${conda_mamba}" == 'true' ]]; then
          slog append -f "${job_name}.sh" -m 'conda install -y mamba -n base -c conda-forge'
          slog append -f "${job_name}.sh" -m "mamba env create --file ${conda_yml}"
        else
          slog append -f "${job_name}.sh" -m "conda env create --file ${conda_yml}"
        fi
        if [[ "${conda_cache}" == 'true' ]]; then
          slog append -f "${job_name}.sh" -m 'conda install -y conda-pack -c conda-forge'
          slog append -f "${job_name}.sh" -m "conda pack -n ${conda_env} -o ${conda_env}.tar.gz"
          slog append -f "${job_name}.sh" -m "cp ${conda_env}.tar.gz ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_env}.tar.gz"
          slog append -f "${job_name}.sh" -m "md5sum ${conda_yml} > ${conda_env}.md5"
          slog append -f "${job_name}.sh" -m "cp ${conda_env}.md5 ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_env}.md5"
          slog append -f "${job_name}.sh" -m "cp Miniconda3-${conda_version}-Linux-x86_64.sh ${GALYLEO_CACHE_DIR}/${conda_env}/Miniconda3-${conda_version}-Linux-x86_64.sh"
        fi
        slog append -f "${job_name}.sh" -m "conda activate ${conda_env}"
      fi
    fi
    slog append -f "${job_name}.sh" -m ''

    # Configure and startup a standalone Spark cluster.
    if [[ -n "${spark_home}" ]]; then
      slog append -f "${job_name}.sh" -m "export SPARK_HOME=${spark_home}"
      slog append -f "${job_name}.sh" -m 'export SPARK_MASTER_HOST="$(hostname -s).${GALYLEO_DNS_DOMAIN}"'
      slog append -f "${job_name}.sh" -m 'export SPARK_MASTER_PORT=7777'
      slog append -f "${job_name}.sh" -m "export SPARK_DAEMON_MEMORY='8g'"
      slog append -f "${job_name}.sh" -m "export SPARK_WORKER_CORES=${cpus_per_task}"
      slog append -f "${job_name}.sh" -m "export SPARK_WORKER_MEMORY=${memory_per_node}g"
      slog append -f "${job_name}.sh" -m 'export SPARK_CACHE_DIR="${HOME}/.spark/${SLURM_JOB_ID}"'
      slog append -f "${job_name}.sh" -m 'export SPARK_CONF_DIR="${SPARK_CACHE_DIR}/conf"'
      slog append -f "${job_name}.sh" -m 'export SPARK_LOG_DIR="${SPARK_CACHE_DIR}/logs"'
      slog append -f "${job_name}.sh" -m 'export SPARK_WORKER_DIR="${SPARK_CACHE_DIR}/work"'
      slog append -f "${job_name}.sh" -m 'export SPARK_LOCAL_DIRS="${LOCAL_SCRATCH_DIR}"'
      slog append -f "${job_name}.sh" -m 'export PATH="${SPARK_HOME}/bin:${PATH}"'
      slog append -f "${job_name}.sh" -m 'export PATH="${SPARK_HOME}/sbin:${PATH}"'
      slog append -f "${job_name}.sh" -m 'export PYSPARK_PYTHON="$(which python)"'
      slog append -f "${job_name}.sh" -m 'export PYTHONPATH=$(ZIPS=("$SPARK_HOME"/python/lib/*.zip); IFS=:; echo "${ZIPS[*]}"):$PYTHONPATH'

      slog append -f "${job_name}.sh" -m 'mkdir -p "${SPARK_CONF_DIR}"'

      slog append -f "${job_name}.sh" -m 'echo "#!/usr/bin/env bash" > "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_HOME=${SPARK_HOME}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_MASTER_HOST=${SPARK_MASTER_HOST}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_MASTER_PORT=${SPARK_MASTER_PORT}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_DAEMON_MEMORY=${SPARK_DAEMON_MEMORY}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_WORKER_CORES=${SPARK_WORKER_CORES}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_WORKER_MEMORY=${SPARK_WORKER_MEMORY}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_CACHE_DIR=${SPARK_CACHE_DIR}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_CONF_DIR=${SPARK_CONF_DIR}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_LOG_DIR=${SPARK_LOG_DIR}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_WORKER_DIR=${SPARK_WORKER_DIR}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export SPARK_LOCAL_DIRS=${SPARK_LOCAL_DIRS}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export PATH=${PATH}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export PYSPARK_PYTHON=${PYSPARK_PYTHON}" >> "${SPARK_CONF_DIR}/spark-env.sh"'
      slog append -f "${job_name}.sh" -m 'echo "export PYTHONPATH=${PYTHONPATH}" >> "${SPARK_CONF_DIR}/spark-env.sh"'

      slog append -f "${job_name}.sh" -m 'start-master.sh'

      slog append -f "${job_name}.sh" -m 'readarray -t spark_workers <<< "$(scontrol show hostnames ${SLURM_NODELIST})"'
      #slog append -f "${job_name}.sh" -m 'for spark_worker in "${spark_workers[@]}"; do'
      #slog append -f "${job_name}.sh" -m '  echo "${spark_worker}.${GALYLEO_DNS_DOMAIN}" >> "${SPARK_CONF_DIR}/workers"'
      #slog append -f "${job_name}.sh" -m 'done'

      #slog append -f "${job_name}.sh" -m 'start-all.sh'

      slog append -f "${job_name}.sh" -m 'for spark_worker in "${spark_workers[@]}"; do'
      slog append -f "${job_name}.sh" -m '  ssh "${spark_worker}" "source ${SPARK_CONF_DIR}/spark-env.sh; start-worker.sh spark://${SPARK_MASTER_HOST}:${SPARK_MASTER_PORT} --host ${spark_worker}.${GALYLEO_DNS_DOMAIN}"'
      slog append -f "${job_name}.sh" -m 'done'

      #slog append -f "${job_name}.sh" -m 'for spark_worker in "${spark_workers[@]}"; do'
      #slog append -f "${job_name}.sh" -m '  srun --nodes=1 --nodelist="${spark_worker}" --ntasks=1 start-worker.sh spark://${SPARK_MASTER_HOST}:${SPARK_MASTER_PORT} --host ${spark_worker}.eth.cluster'
      #slog append -f "${job_name}.sh" -m 'done'

      #slog append -f "${job_name}.sh" -m "srun --nodes=\${SLURM_NNODES} --ntasks=\${SLURM_NNODES} --ntasks-per-node=1 start-worker.sh spark://\${SPARK_MASTER_HOST}:\${SPARK_MASTER_PORT} --host "
      slog append -f "${job_name}.sh" -m ''
    fi

    # Change job working directory (from GALYLEO_CACHE_DIR) to jupyter_notebook_dir.
    slog append -f "${job_name}.sh" -m "cd ${jupyter_notebook_dir}"
    slog append -f "${job_name}.sh" -m ''

    # Locally cache a container stored in a remote container registry
    if [[ -n "${singularity_image_file}" ]]; then
      grep -E '^docker://|^library://|^oras://' <<< "${singularity_image_file}" > /dev/null
      if [[ "${?}" -eq 0 ]]; then
        slog append -f "${job_name}.sh" -m "singularity exec ${singularity_image_file} cat /etc/os-release"
      fi
    fi

    # Create and/or activate a dynamically generated conda environment
    # within a container specified by the user.
    if [[ -z "${conda_env}" ]] && [[ -n "${conda_yml}" ]] && [[ -n "${singularity_image_file}" ]]; then
      conda_env="$(grep name: ${OLDPWD}/${conda_yml} | awk '{print $2}')"
      if [[ ! -d "${GALYLEO_CACHE_DIR}/${conda_env}" ]]; then
        mkdir -p "${GALYLEO_CACHE_DIR}/${conda_env}"
      fi
      cp "${OLDPWD}/${conda_yml}" "${GALYLEO_CACHE_DIR}/${conda_env}/${conda_yml}"
      cd "${GALYLEO_CACHE_DIR}/${conda_env}"
      md5sum -c "${conda_env}.md5" > /dev/null
      if [[ "${?}" -ne 0 ]]; then # re/build (and cache) the conda environment within container
        cd "${GALYLEO_CACHE_DIR}"
        slog append -f "${job_name}.sh" -m 'export CONDA_INSTALL_PATH="${LOCAL_SCRATCH_DIR}/miniconda3"'
        slog append -f "${job_name}.sh" -m 'export CONDA_ENVS_PATH="${CONDA_INSTALL_PATH}/envs"'
        slog append -f "${job_name}.sh" -m 'export CONDA_PKGS_DIRS="${CONDA_INSTALL_PATH}/pkgs"'
        slog append -f "${job_name}.sh" -m 'cd "${LOCAL_SCRATCH_DIR}"'
        slog append -f "${job_name}.sh" -m "cp ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_yml} ./"
        slog append -f "${job_name}.sh" -m "wget https://repo.anaconda.com/miniconda/Miniconda3-${conda_version}-Linux-x86_64.sh"
        slog append -f "${job_name}.sh" -m "chmod +x Miniconda3-${conda_version}-Linux-x86_64.sh"
        slog append -f "${job_name}.sh" -m 'singularity instance start --bind ${LOCAL_SCRATCH_DIR} \'
        if [[ -n "${singularity_gpu_type}" ]]; then
          slog append -f "${job_name}.sh" -m "  --${singularity_gpu_type} \\"
        fi
        slog append -f "${job_name}.sh" -m "  ${singularity_image_file} ${job_name}"
        slog append -f "${job_name}.sh" -m "singularity exec instance://${job_name} ./Miniconda3-${conda_version}-Linux-x86_64.sh -b -p \"\${CONDA_INSTALL_PATH}\""

        slog append -f 'setup-conda.sh' -m '#!/usr/bin/env bash'
        slog append -f 'setup-conda.sh' -m ''
        slog append -f 'setup-conda.sh' -m 'source "${CONDA_INSTALL_PATH}/etc/profile.d/conda.sh"'
        slog append -f 'setup-conda.sh' -m 'conda activate base'
        if [[ "${conda_mamba}" == 'true' ]]; then
          slog append -f 'setup-conda.sh' -m 'conda install -y mamba -n base -c conda-forge'
          slog append -f 'setup-conda.sh' -m "mamba env create -y -f ${conda_yml}"
        else
          slog append -f 'setup-conda.sh' -m "conda env create -y -f ${conda_yml}"
        fi
        if [[ "${conda_cache}" == 'true' ]]; then
          slog append -f 'setup-conda.sh' -m 'conda install -y conda-pack -c conda-forge'
          slog append -f 'setup-conda.sh' -m "conda pack -n ${conda_env} -o ${conda_env}.tar.gz"
          slog append -f 'setup-conda.sh' -m "cp ${conda_env}.tar.gz ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_env}.tar.gz"
          slog append -f 'setup-conda.sh' -m "md5sum ${conda_yml} > ${conda_env}.md5"
          slog append -f 'setup-conda.sh' -m "cp ${conda_env}.md5 ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_env}.md5"
        fi
        slog append -f "${job_name}.sh" -m "cp ${GALYLEO_CACHE_DIR}/setup-conda.sh ./"
        slog append -f "${job_name}.sh" -m "chmod +x setup-conda.sh"
        slog append -f "${job_name}.sh" -m "singularity exec instance://${job_name} ./setup-conda.sh"
      else # unpack existing conda environment within container
        slog append -f "${job_name}.sh" -m 'cd "${LOCAL_SCRATCH_DIR}"'
        slog append -f "${job_name}.sh" -m "cp ${GALYLEO_CACHE_DIR}/${conda_env}/${conda_env}.tar.gz ./"
        slog append -f "${job_name}.sh" -m "mkdir -p ${conda_env}"
        slog append -f "${job_name}.sh" -m "tar -xf ${conda_env}.tar.gz -C ${conda_env}"
        slog append -f "${job_name}.sh" -m 'singularity instance start --bind ${LOCAL_SCRATCH_DIR} \'
        if [[ -n "${singularity_gpu_type}" ]]; then
          slog append -f "${job_name}.sh" -m "  --${singularity_gpu_type} \\"
        fi
        slog append -f "${job_name}.sh" -m "  ${singularity_image_file} ${job_name}"
        slog append -f "${job_name}.sh" -m "singularity exec instance://${job_name} bash -c 'source ${conda_env}/bin/activate; conda-unpack'"
      fi
    fi

    if [[ -n "${conda_env}" ]] && [[ -n "${conda_yml}" ]] && [[ -n "${singularity_image_file}" ]]; then
      slog append -f "${job_name}.sh" -m "singularity exec instance://${job_name} pwd"
      slog append -f "${job_name}.sh" -m "singularity exec instance://${job_name} bash -c 'source \"\${CONDA_INSTALL_PATH}/etc/profile.d/conda.sh\"; conda activate ${conda_env}; jupyter ${jupyter_interface} --ip=\"\$(hostname -s).${GALYLEO_DNS_DOMAIN}\" --notebook-dir=${jupyter_notebook_dir} --port=\"\${JUPYTER_PORT}\" --NotebookApp.allow_origin=* --KernelManager.transport=ipc --no-browser;'"
      slog append -f "${job_name}.sh" -m 'if [[ "${?}" -ne 0 ]]; then'
      slog append -f "${job_name}.sh" -m "  echo 'ERROR: Failed to launch Jupyter.'"
      slog append -f "${job_name}.sh" -m '  exit 1'
      slog append -f "${job_name}.sh" -m 'fi'
    fi

    # Run singularity exec command and its command-line options
    # specified by the user.
    if [[ -z "${conda_env}" ]] && [[ -z "${conda_yml}" ]] && [[ -n "${singularity_image_file}" ]]; then
      slog append -f "${job_name}.sh" -m 'singularity exec \'
      if [[ -n "${singularity_bind_mounts}" ]]; then
        slog append -f "${job_name}.sh" -m "  --bind ${singularity_bind_mounts} \\"
      fi
      if [[ -n "${singularity_gpu_type}" ]]; then
        slog append -f "${job_name}.sh" -m "  --${singularity_gpu_type} \\"
      fi
      slog append -f "${job_name}.sh" -m "  ${singularity_image_file} \\"
    fi

    # Run the Jupyter (or Voila) server process in the backgroud.
    if [[ "${jupyter_interface}" == 'voila' ]]; then
      slog append -f "${job_name}.sh" -m "voila --Voila.ip=\"\$(hostname -s).${GALYLEO_DNS_DOMAIN}\" --port=\"\${JUPYTER_PORT}\" --Voila.tornado_settings=allow_origin='*' --no-browser &"
      slog append -f "${job_name}.sh" -m 'if [[ "${?}" -ne 0 ]]; then'
      slog append -f "${job_name}.sh" -m "  echo 'ERROR: Failed to launch Voila.'"
      slog append -f "${job_name}.sh" -m '  exit 1'
      slog append -f "${job_name}.sh" -m 'fi'
      slog append -f "${job_name}.sh" -m ''
    else
      slog append -f "${job_name}.sh" -m "jupyter ${jupyter_interface} --ip=\"\$(hostname -s).${GALYLEO_DNS_DOMAIN}\" --notebook-dir='${jupyter_notebook_dir}' --port=\"\${JUPYTER_PORT}\" --NotebookApp.allow_origin='*' --KernelManager.transport='ipc' --no-browser &"
      slog append -f "${job_name}.sh" -m 'if [[ "${?}" -ne 0 ]]; then'
      slog append -f "${job_name}.sh" -m "  echo 'ERROR: Failed to launch Jupyter.'"
      slog append -f "${job_name}.sh" -m '  exit 1'
      slog append -f "${job_name}.sh" -m 'fi'
      slog append -f "${job_name}.sh" -m ''
    fi

    # Redeem the connection token from reverse proxy service to enable
    # proxy mapping.
    slog append -f "${job_name}.sh" -m 'curl "https://manage.${GALYLEO_REVERSE_PROXY_FQDN}/redeemtoken.cgi?token=${REVERSE_PROXY_TOKEN}&port=${JUPYTER_PORT}"'
    slog append -f "${job_name}.sh" -m ''

    # Wait for the Jupyter server to be shutdown by the user.
    slog append -f "${job_name}.sh" -m 'wait'
    slog append -f "${job_name}.sh" -m ''

    # If a standalone Spark cluster may be running, then shut it down.
    if [[ -n "${spark_home}" ]]; then
      slog append -f "${job_name}.sh" -m 'stop-all.sh'
      slog append -f "${job_name}.sh" -m ''
    fi

    # Revoke the connection token from reverse proxy service once the
    # Jupyter server has been shutdown.
    slog append -f "${job_name}.sh" -m 'curl "https://manage.${GALYLEO_REVERSE_PROXY_FQDN}/destroytoken.cgi?token=${REVERSE_PROXY_TOKEN}"'

  else

    slog error -m 'Jupyter launch script already exists. Cannot overwrite.'
    return 1

  fi

  # Submit Jupyter launch script to Slurm scheduler.
  job_id="$(sbatch ${job_name}.sh | grep -o '[[:digit:]]*')"
  if [[ "${?}" -ne 0 ]]; then
    slog error -m 'Failed job submission to Slurm.'
    http_response="$(curl -s https://manage.${GALYLEO_REVERSE_PROXY_FQDN}/destroytoken.cgi?token=${REVERSE_PROXY_TOKEN})"
    slog output -m "${http_response}"
    return 1
  else
    slog output -m "Submitted Jupyter launch script to Slurm. Your SLURM_JOB_ID is ${job_id}."
  fi

  # Associate batch job id to the connection token from the reverse proxy service.
  http_response="$(curl -s https://manage.${GALYLEO_REVERSE_PROXY_FQDN}/linktoken.cgi?token=${REVERSE_PROXY_TOKEN}\&jobid=${job_id})"
  slog output -m "${http_response}"

  # Always print to standard output the URL where the Jupyter notebook 
  # server may be accessed by the user.
  slog output -m 'Please copy and paste the HTTPS URL provided below into your web browser.'
  slog output -m 'Do not share this URL with others. It is the password to your Jupyter notebook session.'
  slog output -m 'Your Jupyter notebook session will begin once compute resources are allocated to your job by the scheduler.'
  echo "https://${REVERSE_PROXY_TOKEN}.${GALYLEO_REVERSE_PROXY_FQDN}/?token=${JUPYTER_TOKEN}"

  return 0

}

# ----------------------------------------------------------------------
# galyleo_configure
#
#   Sets the GALYLEO_INSTALL_DIR to a fixed, absolute path and creates a
#   global configuration file (galyleo.conf), where system-specifc
#   deployment variables like the fully-qualified domain name of the
#   Satellite reverse proxy server and the default Slurm partition for
#   all galyleo launches can be set.
#
# Globals:
#
#   GALYLEO_INSTALL_DIR
#
# Arguments:
#
#   -r | --reverse-proxy <reverse_proxy_fqdn>
#   -D | --dns-domain <dns_domain>
#   -s | --scheduler <scheduler>
#   -p | --partition <partition>
#   -c | --cpus <cpus_per_task>
#   -m | --memory <memory_per_node> (in units of GB)
#   -t | --time-limit <time_limit>
#   -i | --interface <jupyter_interface>
#      | --scratch-dir <local_scratch_dir>
#
# Returns:
#
#   True (0) if galyleo was configured successfully.
#   False (1) if galyleo configuration failed.
#
# ----------------------------------------------------------------------
function galyleo_configure() {

  # Declare local variables associated with reverse proxy service.
  local reverse_proxy_fqdn='expanse-user-content.sdsc.edu'
  local dns_domain='eth.cluster'

  # Declare default variables associated with scheduler.
  local scheduler='slurm'
  local partition='shared'
  local -i cpus_per_task=1
  local -i memory_per_node=1
  local time_limit='00:30:00'

  # Declare default variables associated with Jupyter runtime environment.
  local jupyter_interface='lab'

  # Declare input variables associated with system architecture.
  local local_scratch_dir='/tmp'

  # Read in command-line options and assign input variables to local
  # variables.
  while (("${#}" > 0)); do
    case "${1}" in
      -r | --reverse-proxy )
        reverse_proxy_fqdn="${2}"
        shift 2
        ;;
      -D | --dns-domain )
        dns_domain="${2}"
        shift 2
        ;;
      -s | --scheduler )
        scheduler="${2}"
        shift 2
        ;;
      -p | --partition )
        partition="${2}"
        shift 2
        ;;
      -c | --cpus )
        cpus_per_task="${2}"
        shift 2
        ;;
      -m | --memory )
        memory_per_node="${2}"
        ;;
      -t | --time-limit )
        time_limit="${2}"
        shift 2
        ;;
      -i | --interface )
        jupyter_interface="${2}"
        shift 2
        ;;
      -j | --jupyter )
        jupyter_interface="${2}"
        shift 2
        ;;
      --scratch-dir )
        local_scratch_dir="${2}"
        shift 2
        ;;
      *)
        slog error -m "Command-line option ${1} not recognized or not supported."
        return 1
    esac
  done

  # If the galyleo configuration file already exists, do not let the
  # galyleo configure command reconfigure and overwrite it. This is
  # intended to force the original configuration file owner --- e.g.,
  # the system administrator who deployed galyleo --- to manually
  # remove the existing configuration file first. If the configuration
  # file does not exist yet, then create it.
  if [[ -f "${GALYLEO_INSTALL_DIR}/galyleo.conf" ]]; then

    slog error -m 'galyleo.conf cannot be overwritten with this command.'
    return 1

  else

     slog output -m 'Setting GALYLEO_INSTALL_DIR ... '

     sed -i "s|\"\${PWD}\"|'${PWD}'|" 'galyleo.sh'

     slog output -m 'Creating galyleo.conf file ... '

     slog append -f 'galyleo.conf' -m '#!/usr/bin/env sh'
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_REVERSE_PROXY_FQDN='${reverse_proxy_fqdn}'"
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_DNS_DOMAIN='${dns_domain}'"
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_SCHEDULER='${scheduler}'"
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_DEFAULT_PARTITION='${partition}'"
     slog append -f 'galyleo.conf' -m "declare -xir GALYLEO_DEFAULT_CPUS='${cpus_per_task}'"
     slog append -f 'galyleo.conf' -m "declare -xir GALYLEO_DEFAULT_MEMORY='${memory_per_node}'"
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_DEFAULT_TIME_LIMIT='${time_limit}'"
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_DEFAULT_JUPYTER_INTERFACE='${jupyter_interface}'"
     slog append -f 'galyleo.conf' -m "declare -xr  GALYLEO_DEFAULT_LOCAL_SCRATCH_DIR='${local_scratch_dir}'"

  fi

  slog output -m 'galyleo configuration complete.'

  return 0

}

# ----------------------------------------------------------------------
# galyleo_clean
#
#   Clean up the GALYLEO_CACHE_DIR. 
#
# Globals:
#
#   None
#
# Arguments:
#
#   None
#
# Returns:
#
#   True (0) always.
#
# ----------------------------------------------------------------------
function galyleo_clean() {

  rm -rf "${GALYLEO_CACHE_DIR}"

  return 0

}

# ----------------------------------------------------------------------
# galyleo_help
#
#   Provides usage information to help users run galyleo.
#
# Globals:
#
#   None
#
# Arguments:
#
#   None
#
# Returns:
#
#   True (0) always.
#
# ----------------------------------------------------------------------
function galyleo_help() {

  slog output -m 'USAGE: galyleo launch [command-line option] {value}'
  slog output -m '  command-line options  : (default) values'
  slog output -m "    -A | --account           : ${account}"
  slog output -m "    -R | --reservation       : ${reservation}"
  slog output -m "    -p | --partition         : ${partition}"
  slog output -m "    -q | --qos               : ${qos}"
  slog output -m "    -N | --nodes             : ${nodes}"
  slog output -m "    -c | --cpus              : ${cpus_per_task}"
  slog output -m "    -m | --memory            : ${memory_per_node} GB"
  slog output -m "    -g | --gpus              : ${gpus}"
  slog output -m "       | --gres              : ${gres}"
  slog output -m "    -t | --time-limit        : ${time_limit}"
  slog output -m "    -C | --constraint        : ${constraint}"
  slog output -m "    -i | --interface         : ${jupyter_interface}"
  slog output -m "    -d | --notebook-dir      : ${jupyter_notebook_dir}"
  slog output -m "       | --scratch-dir       : ${local_scratch_dir}"
  slog output -m "    -e | --env-modules       : ${env_modules}"
  slog output -m "    --append-modulepath      : ${append_modpath}"
  slog output -m "    -s | --sif               : ${singularity_image_file}"
  slog output -m "    -B | --bind              : ${singularity_bind_mounts}"
  slog output -m "       | --nv                : ${singularity_gpu_type}"
  slog output -m "       | --conda-init        : ${conda_init}"
  slog output -m "       | --conda-env         : ${conda_env}"
  slog output -m "       | --conda-yml         : ${conda_yml}"
  slog output -m "       | --conda-version     : ${conda_version}"
  slog output -m "       | --mamba             : ${conda_mamba}"
  slog output -m "       | --cache             : ${conda_cache}"
  slog output -m "       | --spark-home        : ${spark_home}"
  slog output -m "       | --disable-checklist : ${disable_checklist}"
  slog output -m "       | --checklist-timeout : ${checklist_timeout} s"
  slog output -m "    -Q | --quiet             : ${SLOG_LEVEL}"

  return 0

}

# ----------------------------------------------------------------------
# galyleo
#
#   This is the main function used to control the execution of galyleo
#   and its auxiliary functions.
#
# Globals:
#
#   @
#
# Arguments:
#
#   @
#
# Returns:
#
#   True  (0) if galyleo executed successfully without issue.
#   False (1) if galyleo failed to execute properly.
#
# ----------------------------------------------------------------------
function galyleo() {

  # Define local variables.
  local galyleo_command

  # Assign default values to local variables.
  galyleo_command=''

  # If at least one command-line argument was provided by the user, then
  # start parsing the command-line arguments. Otherwise, throw an error.
  if (( "${#}" > 0 )); then
 
    # Read in the first command-line argument, which is expected to be 
    # the main command issued by the user.
    galyleo_command="${1}"
    shift 1

    # Determine if the command provided by user is a valid. If it is a
    # valid command, then execute that command. Otherwise, throw an error.
    if [[ "${galyleo_command}" = 'launch' ]]; then

      galyleo_launch "${@}"
      if [[ "${?}" -ne 0 ]]; then
        slog error -m 'galyleo_launch command failed.'
        exit 1
      fi

    elif [[ "${galyleo_command}" = 'configure' ]]; then

      galyleo_configure "${@}"
      if [[ "${?}" -ne 0 ]]; then
        slog error -m 'galyleo_configure command failed.'
        exit 1
      fi

    elif [[ "${galyleo_command}" = 'clean' ]]; then
    
      galyleo_clean
      if [[ "${?}" -ne 0 ]]; then
        slog error -m 'galyleo_clean command failed.'
        exit 1
      fi

    elif [[ "${galyleo_command}" = 'help' || \
            "${galyleo_command}" = '-h' || \
            "${galyleo_command}" = '--help' ]]; then

      galyleo_help
      if [[ "${?}" -ne 0 ]]; then
        slog error -m 'galyleo_help command failed.'
        exit 1
      fi
    
    else
    
      slog error -m 'Command not recognized or not supported.'
      exit 1

    fi

  else

    slog error -m 'No command-line arguments were provided.'
    exit 1

  fi
  
  exit 0

}

# ----------------------------------------------------------------------

galyleo "${@}"

# ======================================================================