#!/usr/bin/env bash

#############
# Variables #
#############
# Define formatting variables
fb="$(tput bold)"
fr="$(tput sgr0)"

name_regex='[^a-zA-Z0-9]'  # Define name regular expression

# Set virtual environments directory
ves_dir=""
# Set projects directory
projs_dir=""

# Create required modules array
req_mods=('pip' 'venv')

# Create required variables array
required_vars=(
    'projs_dir'
    'ves_dir'
)


#############
# Functions #
#############
display_usage() {
    local help_msg  # Define local variable
    help_msg="Usage: . '${0}'

Purpose: Create a new Python virtual environment.

Requires:
    pip3
        pip is the package installer for Python.
    python3-venv (Debian)
        This package contains the venv module for the Python language
        (default python3 version).

Variables to set:
    projs_dir
        Directory of projects.
    ves_dir
        Directory to create virtual environment in."

    echo "${help_msg}"
}


# Parse arguments
parse_args() {
    local parsed_args inv_ents

    parsed_args="$(getopt \
        -n "${0##*/}" \
        -o h \
        --long help \
        -- "${@}")"

    # Check for invalid entries
    inv_ents="${?}" ; readonly inv_ents
    if [[ "${inv_ents}" -ne 0 ]]; then
        echo ''
        display_usage
        exit 1
    fi

    # Set positional parameters using parsed argument string
    eval set -- "${parsed_args}"

    # Evaluate options
    while true; do
        case "${1}" in
            '-h' | '--help')
                display_usage
                exit 0
                ;;
            '--')
                ## End of options
                shift
                break
                ;;
        esac
    done
}


# Run initialization checks
run_init_cks() {
    local err_msg mis_mods req_mod

    # Verify script was loaded via . command
    if ! [[ "${BASH_SOURCE[0]}" != "${0}" ]]; then
        echo -e "\nRerun script using the ${fb}.${fr} command." 1>&2 &&
            exit 1
    fi

    # Create missing modules array
    declare -a mis_mods
    # Verify that required modules are installed
    for req_mod in "${req_mods[@]}"; do
        if ! python3 -c "import ${req_mod}" > '/dev/null' 2>&1; then
            mis_mods+=("${req_mod}")
        fi
    done
    # Display error message if modules are missing
    if [[ "${mis_mods[*]}" ]]; then
        err_msg='\nInstall the following Python module(s) before '
        err_msg+='running the script again:'
        echo -e "${err_msg}\n${fb}${mis_mods[*]}${fr}" 1>&2
    fi
}


# Sanitize name
clean_name() {
    local cleaned
    # Replace most non-alphanumeric characters with underscores
    cleaned="${1//${name_regex}/_}"
    # Squeeze underscores and lowercase name
    cleaned="$(echo -n "${cleaned}" | tr -s '_' | tr '[:upper:]' '[:lower:]')"
    echo "${cleaned}"
}


# Display projects menu
proj_menu() {
    PS3='Select a project: '

    select proj in "${projs[@]}"; do
        if ! [[ "${proj}" ]]; then
            echo -e '\nPlease enter a valid menu selection.\n' 1>&2

            proj_menu
            break
        elif [[ "${proj}" == 'Quit' ]]; then
            break
        else
            cd "${projs_dir}/${proj}" || exit 1
            break
        fi
    done
}


# Define starting point for execution of the program
main() {
    parse_args "${@}"

    run_init_cks

    # Create unset variables array
    declare -a unset_vars
    # Verify that required variables are set
    for required_var in "${required_vars[@]}"; do
        if ! [[ "${!required_var}" ]]; then
            unset_vars+=("${required_var}")
        fi
    done
    # Display error message if variables are not set
    if [[ "${unset_vars[*]}" ]]; then
        err_msg='\nSet the following variable(s) before '
        err_msg+='running the script again:'
        echo -e "${err_msg}\n${fb}${unset_vars[*]}${fr}" 1>&2
    else
        # Capture virtual environment name
        echo ''
        read -p 'Enter virtual environment name: ' -r ve_name
        ve_name="$(clean_name "${ve_name}")"  # Sanitize input

        # Set virtual environment directory path
        ve_dir="${ves_dir}/${ve_name}"

        # If specified directory does not already exist
        if ! [[ -d "${ve_dir}" ]]; then
            # Create virtual environment, upgrade its version of pip and setuptools
            python3 -m venv --upgrade-deps "${ve_dir}"

            # Activate virtual environment and install wheel
            . "${ve_dir}/bin/activate" &&
                python3 -m pip install wheel

            msg="\nSuccessfully created ${fb}${ve_dir}${fr} "
            msg+="virtual environment."
            echo -e "${msg}\n"

            # Declare projects indexed array
            declare -a projs
            # Define projects array
            mapfile -t projs < \
                <(find "${projs_dir}" -mindepth 1 -maxdepth 1 -type d -printf '%f\n')
            projs+=('Quit')  # Add quit option to projects array

            proj_menu  # Display projects menu
        else
            echo -e "\n${fb}${ve_dir}${fr} already exists."
        fi
    fi
}


###########
# Program #
###########
main "${@}"  # Start program