#!/usr/bin/env bash

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

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

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


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

Purpose: Activate a Python virtual environment.

Variables to set:
    projs_dir
        Directory of projects.
    ves_dir
        Virtual environments directory."

    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() {
    # 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
}


# Display virtual environment menu
ve_menu() {
    PS3='Select a virtual environment: '

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

            ve_menu
            break
        elif [[ "${ve}" == 'Quit' ]]; then
            break
        else
            . "${ves_dir}/${ve}/bin/activate"
            break
        fi
    done
}


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

        ve_menu  # Display virtual environment menu

        if ! [[ "${ve}" == 'Quit' ]]; then
            declare -a projs
            mapfile -t projs < \
                <(find "${projs_dir}" -mindepth 1 -maxdepth 1 -type d -printf '%f\n')
            projs+=('Quit')

            echo ''
            proj_menu  # Display projects menu
        fi
    fi
}


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