#!/usr/bin/env bash

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

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

script_editor="" ; readonly script_editor  # Script editor


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

Purpose: Create new systemd timer.

Variables to set:
    script_editor
        Program to use for editing files.

        By default, the script will respect your environment's ${fb}EDITOR${fr}
        value. If this value is not configured, you can set
        ${fb}script_editor${fr} to your editor of choice."

    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

    # Override EDITOR with script_editor
    if [[ "${script_editor}" ]]; then
        EDITOR="${script_editor}"
    fi
    # Verify that an editor is set
    if ! [[ "${EDITOR}" || "${script_editor}" ]]; then
        # Prompt user to set required variable and exit
        err_msg="\nSet either ${fb}EDITOR${fr} or ${fb}script_editor${fr} "
        err_msg+='before running the script again.'
        echo -e "${err_msg}" 1>&2
        exit 1
    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}"
}


# .timer unit creation function
timer_matter() {
    {
        echo '[Unit]'
        echo -e "Description=${timer_description}\\n"
        echo '[Timer]'
        echo "${timer_directive}"
        echo -e 'Persistent=true\n'
        echo '[Install]'
        echo 'WantedBy=timers.target'
    } > "${HOME}/.config/systemd/user/${unit_name}.timer"
}


# .service unit creation function
service_matter() {
    {
        echo '[Unit]'
        echo -e "Description=${service_description}\\n"
        echo '[Service]'
        echo "ExecStart=${service_command}"
    } > "${HOME}/.config/systemd/user/${unit_name}.service"
}


# Function to pause script
pause() {
    echo ''
    read -n 1 -rs -p 'Press any key to continue...'
    echo ''
}


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

    run_init_cks

    # Create systemd user unit directory, and parent directories,
    # if they do not exist
    if ! "${HOME}/.config/systemd/user" > '/dev/null' 2>&1; then
        mkdir -p "${HOME}/.config/systemd/user"
    fi

    # Output systemd directives reference
    sysd_ref='\nsystemd Directives Reference\nhttps://www.freedesktop.org/'
    sysd_ref+='software/systemd/man/systemd.directives.html'
    echo -e "${sysd_ref}"

    # Get unit name
    echo ''
    read -p 'Enter unit name: ' -r unit_name
    unit_name="$(clean_name "${unit_name}")"  # Sanitize input

    # Gather .timer unit description
    read -p 'Enter .timer description: ' -r timer_description
    timer_description="${timer_description//[^a-zA-Z0-9 ,]/}"  # Sanitize input

    # Gather .timer unit directive
    read -p 'Enter .timer directive: ' -r timer_directive
    timer_directive="${timer_directive//[^a-zA-Z0-9 =]/}"  # Sanitize input

    # Gather .service unit description
    read -p 'Enter .service description: ' -r service_description
    # Sanitize input
    service_description="${service_description//[^a-zA-Z0-9 ,]/}"

    # Gather .service unit command
    read -p 'Enter .service command: ' -r service_command

    timer_matter  # Create .timer unit

    service_matter  # Create .service unit

    while true; do
        # Present option to open units in editor
        echo ''
        read -p 'Open units in editor? (y or n): ' -r edit
        
        if [[ "${edit}" == 'y' || "${edit}" == 'n' ]]; then
            break
        elif [[ "${edit}" == 'q' ]]; then
            exit 0
        else
            err_msg='\nInvalid input. Try again or enter q to quit.'
            echo -e "${err_msg}" 1>&2
        fi
    done

    # Open units in editor
    if [[ "${edit}" == 'y' ]]; then
        "${EDITOR}" "${HOME}/.config/systemd/user/${unit_name}.timer" \
            "${HOME}/.config/systemd/user/${unit_name}.service"
        pause
    fi

    # Enable and start units
    systemctl --user enable --now "${unit_name}.timer"

    # Check units' status
    systemctl --user status "${unit_name}.timer" "${unit_name}.service"
}


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

exit 0  # Exit script with successful exit status