#!/usr/bin/env bash

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

dot_files_src='' ; readonly dot_files_src  # Set dot file directory source
deb_prefix='' ; readonly deb_prefix  # Set Debian prefix
fed_prefix='' ; readonly fed_prefix  # Set Fedora prefix
scripts_dir_src='' ; readonly scripts_dir_src  # Set scripts directory source
# Set scripts directory destination for new system
scripts_dir_dest="" ; readonly scripts_dir_dest

# Create required variables array
required_vars=(
    'dot_files_src'
    'deb_prefix'
    'fed_prefix'
    'scripts_dir_src'
    'scripts_dir_dest'
) ; readonly required_vars


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

Purpose: Configure a Debian or Fedora GNU/Linux shell environment.

Variables to set:
    deb_prefix
        The string prefix that has been chosen to specify files with
        Debian-specific dot file content (e.g., dbn_).
    dot_files_src
        The name of the directory that contains the files that serve as the
        basis for the new system's dot files (e.g., dot_files/).
    fed_prefix
        The string prefix that has been chosen to specify files with
        Fedora-specific dot file content (e.g., fda_).
    scripts_dir_dest
        The destination directory on the new system to copy scripts to.
    scripts_dir_src
        The name of the directory that contains the scripts to be copied to
        the new system (e.g., scripts/)."

    echo "${help_msg}"
}


# Verify object exists and is a directory
val_extant_dir() {
    local to_test
    to_test="${1}"
    [[ -d "${to_test}" ]] ; echo "${?}"
}


# Define starting point for execution of the program
main() {
    # Parse arguments
    parsed_args="$(getopt \
        -n "${0##*/}" \
        -o h \
        --long help \
        -- "${@}")"

    inv_ents="${?}"  # Check for invalid entries
    if [[ "${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

    # 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+=("${required_var}")
        fi
    done
    # Exit script if variables are not set
    if [[ "${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
        exit 1
    fi

    abs_path="$(realpath "${0}")"  # Get absolute path of script
    # Get absolute path of script configuration directory
    dir_path="${abs_path%/*}"

    cd "${dir_path}" || exit 1  # Change to directory script is running from

    # Filter out extraneous files, customize command prompt
    if grep -iq 'debian' '/etc/os-release'; then
        # Loop through each .txt file in dot_files_src
        for f in ./${dot_files_src}/*; do
            # Filter out Fedora-specific files
            if ! [[ "${f}" =~ ${dot_files_src}/${fed_prefix}.+ ]]; then
                f_base="${f%.txt}"
                # Remove Debian prefix from filename
                if [[ "${f_base}" =~ ${dot_files_src}/${deb_prefix}+ ]]; then
                    f_base="${f_base/${deb_prefix}/}"
                fi
                # Create file basename
                f_base="${f_base##*/}"
                # Append file content
                cat "${f}" >> "${HOME}/.${f_base}"
            fi
        done
    elif grep -iq 'fedora' '/etc/os-release'; then
        for f in ./${dot_files_src}/*; do
            if ! [[ "${f}" =~ ${dot_files_src}/${deb_prefix}.+ ]]; then
                f_base="${f%.txt}"
                if [[ "${f_base}" =~ ${dot_files_src}/${fed_prefix}.+ ]]; then
                    f_base="${f_base/${fed_prefix}/}"
                fi
                f_base="${f_base##*/}"
                cat "${f}" >> "${HOME}/.${f_base}"
            fi
        done
    else
        err_msg='\nUnable to verify supported GNU/Linux '
        err_msg+='distribution.'
        echo -e "${err_msg}" 1>&2
        exit 1
    fi

    pass_or_fail="$(val_extant_dir "${scripts_dir_dest}")"
    if [[ "${pass_or_fail}" -ne 0 ]]; then
        mkdir "${scripts_dir_dest}"  # Create script directory
    fi
    # Copy over scripts
    for f in ${dir_path}/${scripts_dir_src}/*; do
        cp -f "${f}" "${scripts_dir_dest}"
    done
    chmod -R 700 "${scripts_dir_dest}"  # Make scripts executable

    # Display log out message
    echo -e '\nLog out and log in to see changes take effect.'
}


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

exit 0  # Exit script with successful exit status