#!/bin/bash
set -e

# The location of the br2-external tree, once validated.
declare BR2_EXT

main() {
    local OPT OPTARG
    local br2_ext ofile

    while getopts :ho: OPT; do
        case "${OPT}" in
        h)  help; exit 0;;
        o)  ofile="${OPTARG}";;
        :)  error "option '%s' expects a mandatory argument\n" "${OPTARG}";;
        \?) error "unknown option '%s'\n" "${OPTARG}";;
        esac
    done
    # Forget options; keep only positional args
    shift $((OPTIND-1))

    # Accept 0 or 1 br2-external tree.
    if [ ${#} -gt 1 ]; then
        error "only zero or one br2-external tree allowed.\n"
    fi

    br2_ext="${1}"

    if [ -z "${ofile}" ]; then
        error "no output file specified (-o)\n"
    fi

    do_validate "${br2_ext}"

    do_kconfig >"${ofile}"
}

# Validates the br2-external tree passed as argument. Makes it cannonical
# and store it in global variable BR2_EXT.
do_validate() {
    local br2_ext="${1}"

    # No br2-external tree is valid
    if [ -z "${br2_ext}" ]; then
        return
    fi

    if [ ! -d "${br2_ext}" ]; then
        error "'%s': no such file or directory\n" "${br2_ext}"
    fi
    if [ ! -r "${br2_ext}" -o ! -x "${br2_ext}" ]; then
        error "'%s': permission denied\n" "${br2_ext}"
    fi

    BR2_EXT="$(cd "${br2_ext}"; pwd -P )"
}

# Generate the kconfig snippet for the br2-external tree.
do_kconfig() {
    printf '#\n# Automatically generated file; DO NOT EDIT.\n#\n'
    printf '\n'

    if [ -z "${BR2_EXT}" ]; then
        printf '# No br2-external tree defined.\n'
        return
    fi

    printf 'config BR2_EXTERNAL\n'
    printf '\tstring\n'
    printf '\tdefault "%s"\n' "${BR2_EXT}"
    printf '\n'
    printf 'menu "User-provided options"\n'
    printf '\n'
    printf 'source "%s/Config.in"\n' "${BR2_EXT}"
    printf '\n'
    printf "endmenu # User-provided options\n"
}

help() {
    cat <<-_EOF_
	Usage:
	    ${my_name} -o FILE PATH

	${my_name} generates the kconfig snippet to include the configuration
	options specified in the br2-external tree passed as positional argument.

	Options:
	    -o FILE
	        FILE in which to generate the kconfig snippet.

	Returns:
	    0   If no error
	    !0  If any error
	_EOF_
}

error() { local fmt="${1}"; shift; printf "%s: ${fmt}" "${my_name}" "${@}" >&2; exit 1; }

my_name="${0##*/}"
main "${@}"