#!/usr/bin/env bash
set -euo pipefail

# replicate_venv.sh
# Export and recreate a Python virtual environment across machines.
#
# Quick start:
# 1) On source machine:
#      ./Scripts/replicate_venv.sh export --venv /path/to/.venv --out .venv-lock
# 2) Copy .venv-lock and this script to target machine.
# 3) On target machine:
#      ./Scripts/replicate_venv.sh recreate --venv .venv --from .venv-lock --python python3
#
# The lock folder contains:
# - requirements.txt        pip freeze output (all Python libraries)
# - python-version.txt      full Python version from source venv
# - platform.txt            source OS/platform info
# - bootstrap.txt           recreation command and dependency notes

usage() {
  cat <<'EOF'
Usage:
  replicate_venv.sh export   --venv <source_venv_path> [--out <lock_dir>]
  replicate_venv.sh recreate --venv <target_venv_path> [--from <lock_dir>] [--python <python_cmd>]

Options:
  --venv   Path to source/target virtual environment directory.
  --out    Export destination directory (default: .venv-lock).
  --from   Input lock directory (default: .venv-lock).
  --python Python command to create new venv (default: python3).
  -h, --help  Show this help.

Quick Start:
  Source machine:
    ./Scripts/replicate_venv.sh export --venv /path/to/.venv --out .venv-lock

  Target machine:
    ./Scripts/replicate_venv.sh recreate --venv .venv --from .venv-lock --python python3

Dependencies required on target machine:
  1. Python 3 with venv support.
  2. Internet access to install pip packages from requirements.txt (or access to your package mirror).
  3. Build tools for packages that compile native extensions (when needed by your requirements).

Notes:
  - This script recreates Python package dependencies; it does not install system packages for you.
  - It will warn if source and target Python versions differ.
EOF
}

abort() {
  echo "Error: $*" >&2
  exit 1
}

require_cmd() {
  command -v "$1" >/dev/null 2>&1 || abort "Required command not found: $1"
}

ensure_python_has_venv() {
  local python_cmd="$1"
  "$python_cmd" -c 'import venv' >/dev/null 2>&1 || abort "Python does not include the venv module. Install Python with venv support and retry."
}

ensure_python_has_pip_bootstrap() {
  local python_cmd="$1"
  "$python_cmd" -m ensurepip --upgrade >/dev/null 2>&1 || true
}

find_venv_python() {
  local venv_path="$1"
  if [[ -x "$venv_path/bin/python" ]]; then
    echo "$venv_path/bin/python"
  elif [[ -x "$venv_path/Scripts/python.exe" ]]; then
    # Windows-style venv path support.
    echo "$venv_path/Scripts/python.exe"
  else
    abort "Could not find Python inside virtualenv at: $venv_path"
  fi
}

mode="${1:-}"
[[ -n "$mode" ]] || { usage; exit 1; }
shift || true

case "$mode" in
  export)
    venv_path=""
    out_dir=".venv-lock"

    while [[ $# -gt 0 ]]; do
      case "$1" in
        --venv)
          venv_path="${2:-}"
          shift 2
          ;;
        --out)
          out_dir="${2:-}"
          shift 2
          ;;
        -h|--help)
          usage
          exit 0
          ;;
        *)
          abort "Unknown option for export: $1"
          ;;
      esac
    done

    [[ -n "$venv_path" ]] || abort "Missing required --venv for export"
    [[ -d "$venv_path" ]] || abort "Venv path does not exist: $venv_path"

    py_bin="$(find_venv_python "$venv_path")"

    mkdir -p "$out_dir"
    "$py_bin" -m pip freeze > "$out_dir/requirements.txt"
    "$py_bin" -c 'import platform; print(platform.python_version())' > "$out_dir/python-version.txt"
    "$py_bin" -c 'import platform; print(platform.platform())' > "$out_dir/platform.txt"
    cat > "$out_dir/bootstrap.txt" <<'EOF'
Recreate command:
  ./Scripts/replicate_venv.sh recreate --venv .venv --from .venv-lock --python python3

Dependencies needed on target machine:
  - Python 3 with venv module enabled
  - Network access (or internal package mirror) for pip installs
  - Build toolchain for any packages requiring native compilation

If Python differs from source version, recreate may still work but package compatibility can vary.
EOF

    echo "Export complete."
    echo "Lock dir: $out_dir"
    echo "Files: $out_dir/requirements.txt, $out_dir/python-version.txt, $out_dir/platform.txt, $out_dir/bootstrap.txt"
    ;;

  recreate)
    target_venv=""
    from_dir=".venv-lock"
    python_cmd="python3"

    while [[ $# -gt 0 ]]; do
      case "$1" in
        --venv)
          target_venv="${2:-}"
          shift 2
          ;;
        --from)
          from_dir="${2:-}"
          shift 2
          ;;
        --python)
          python_cmd="${2:-}"
          shift 2
          ;;
        -h|--help)
          usage
          exit 0
          ;;
        *)
          abort "Unknown option for recreate: $1"
          ;;
      esac
    done

    [[ -n "$target_venv" ]] || abort "Missing required --venv for recreate"
    [[ -f "$from_dir/requirements.txt" ]] || abort "Missing lock file: $from_dir/requirements.txt"

    require_cmd "$python_cmd"
    ensure_python_has_venv "$python_cmd"
    ensure_python_has_pip_bootstrap "$python_cmd"

    if [[ -d "$target_venv" ]]; then
      abort "Target venv already exists at $target_venv. Remove it first or use a different path."
    fi

    "$python_cmd" -m venv "$target_venv"
    py_bin="$(find_venv_python "$target_venv")"

    "$py_bin" -m pip --version >/dev/null 2>&1 || abort "pip is unavailable in the target venv. Ensure your Python installation supports ensurepip."
    "$py_bin" -m pip install --upgrade pip setuptools wheel
    "$py_bin" -m pip install -r "$from_dir/requirements.txt"

    if [[ -f "$from_dir/python-version.txt" ]]; then
      source_ver="$(cat "$from_dir/python-version.txt")"
      target_ver="$($py_bin -c 'import platform; print(platform.python_version())')"
      if [[ "$source_ver" != "$target_ver" ]]; then
        echo "Warning: Source Python version ($source_ver) differs from target ($target_ver)."
      fi
    fi

    echo "Recreate complete at: $target_venv"
    ;;

  -h|--help)
    usage
    ;;

  *)
    abort "Unknown mode: $mode"
    ;;
esac