#!/bin/bash

# @author: <sylvain.herledan@hrafnagud.info>
# @date: 2017-06-06

set -o nounset
set -o errexit
set -o pipefail

readonly PROGNAME="$(basename "${0}")";
readonly PROGDIR="$(readlink -f "$(dirname "${0}")")";
readonly ARGS="${@}";

readonly PYTHON_VERSION_PATH="$(mktemp)";
readonly PIP_INSTALL_SCRIPT="$(mktemp)";

cleanup()
{
  local rc=$?;  # Keep original return code

  rm -f "${PYTHON_VERSION_PATH}"
  rm -f "${PIP_INSTALL_SCRIPT}"
  exit ${rc}
}

get_python_version()
{
  local python="${1}"; shift;
  local version_path="${1}"; shift;

  # Redirecting stderr to stdout is necessary because older versions
  # of Python printed to stderr
  "${python}" --version 2>&1 \
    | cut -d\  -f2 \
    > "${version_path}"
}

venv_install_method()
{
  local python="${1}"; shift;
  local env_dir="${1}"; shift;

  "${python}" -m venv "${env_dir}"

  set +o nounset
  source "${env_dir}/bin/activate"
  set -o nounset

  pip install --upgrade pip

  set +o nounset
  deactivate
  set -o nounset
}

pip_install_method()
{
  local python="${1}"; shift;
  local env_dir="${1}"; shift;
  local version="${1:-}"; shift;
  local opts='';

  [ -n "${version}" ] && version="/${version}"
  wget "https://bootstrap.pypa.io/pip${version}/get-pip.py" \
       -O "${PIP_INSTALL_SCRIPT}"
  "${python}" "${PIP_INSTALL_SCRIPT}" --isolated \
                                      --prefix="${env_dir}" \
                                      --ignore-installed \
                                      --no-cache

  # WARNING: for some reason it is not possible to force
  # the script to build from source (with --no-binary setuptools,pip)
  # due to an unsupported --no-user option in the install procedure.
  # So it is better to check that the installed binary is compatible
  # with the local system (notably the SSL library which may cause
  # issues when downloading packages from HTTPS).
}

install_environment()
{

  get_python_version "${python}" "${PYTHON_VERSION_PATH}"
  local major="$(cat "${PYTHON_VERSION_PATH}" | cut -d. -f1)";
  local minor="$(cat "${PYTHON_VERSION_PATH}" | cut -d. -f2)";
  local num=$((${minor} + 10 * ${major}));

  if [ ${num} -gt 33 ];
  then
    set +o errexit
    "${python}" -m ensurepip --help 2>&1 >/dev/null
    local rc=$?
    set -o errexit

    if [ 0 -eq ${rc} ];
    then
      venv_install_method "${python}" "${env_dir}"
    else
      pip_install_method "${python}" "${env_dir}" "${major}.${minor}"
      install_virtualenv "${python}" "${env_dir}"
    fi
  elif [ ${num} -eq 27 ];
  then
    pip_install_method "${python}" "${env_dir}" "${major}.${minor}"
    install_virtualenv "${python}" "${env_dir}"
  else
    >&2 echo "Unsupported Python version"
    exit 1
  fi

  mkdir -p "${env_dir}/cache"
  cat > "${env_dir}/pip.conf" << EOF
[global]
cache-dir=${env_dir}/cache
EOF
}

install_virtualenv()
{
  local python="${1}"; shift;
  local env_dir="${1}"; shift;
  local _pkg_dir="$(find "${env_dir}/lib" -mindepth 2 -maxdepth 2 \
                                          -name "site-packages")";
  local pkg_dir="$(readlink -f "${_pkg_dir}")";

  echo "Install virtual env"

  # Install virtualenv
  PYTHONPATH="${pkg_dir}" \
  "${env_dir}/bin/pip" install --prefix="${env_dir}" \
                               --ignore-installed \
                               --no-cache \
                               --no-binary virtualenv \
                               virtualenv


  PIP_CACHE_DIR="${env_dir}/cache" \
  PIP_IGNORE_INSTALLED=true \
  PYTHONPATH="${pkg_dir}" \
  "${python}" -m virtualenv "${env_dir}"
}

main()
{
  local python="${1}"; shift;
  local _install_dir="${1}"; shift;
  local install_dir="$(readlink -f "${_install_dir}")";
  local env_dir="${install_dir}/env";

  trap 'cleanup' INT TERM EXIT

  install_environment "${python}" "${env_dir}"

  trap - INT TERM EXIT
  echo 'Environment ready'
}

main ${ARGS}
exit 0