module_loader

#!/bin/bash

############################################# LICENCE ##############################################

#   Copyright (C) 2018, Ivan Balevic

#   This file is part of the "Bash Modules" project, a collection
#   of Bash scripts that provides additional functionality.
#
#   "Bash Modules" is free software: you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   "Bash Modules" is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
#   GNU General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with "Bash Modules". If not, see <http://www.gnu.org/licenses/>.

########################################### DESCRIPTION ############################################

#   This script contains "load_modules" function that should be used for sourcing of bash modules.

####################################### AVAILABLE FUNCTIONS ########################################

#   load_modules    ->  Sources the requested modules if they aren't sourced already.

########################################### REQUIREMENTS ###########################################

# If path to modules isn't provided, assume that modules are in the same directory as this script.
BASH_MODULES_PATH="${BASH_MODULES_PATH:-"$(realpath "$(dirname "${BASH_SOURCE[0]}")")"}"

######################################### DEFAULT SETTINGS #########################################

# If this script is sourced by the module, then that module should by default be counted as sourced.
[[ "${BASH_SOURCE[1]}" =~ _module$ ]] && export "$(basename ${BASH_SOURCE[1]^^})_LOADED"

############################################ FUNCTIONS #############################################

# load_modules [${1} ... ${N}]
#
#   Description                 ->  Source bash modules [${1} ... ${N}] if they aren't sourced yet.
#                                   The variable with name coresponding to the successfully sourced
#                                   module will be exported afterwards to prevent later attempts to
#                                   load the same module again.
#
#   [${1} ... ${N}]             ->  Names of the bash modules that need to be sourced.
#                                   The suffix "_module" may be excluded from the module name.
#
#   <=  BASH_MODULES_PATH       ->  The path where this function will look for requested modules.
#
#   =>  ${X}[_MODULE]_LOADED    ->  For each loaded module, variable like this is exported:
#                                   ${X}='color_module' =>  COLOR_MODULE_LOADED
#                                   ${X}='debug'        =>  DEBUG_MODULE_LOADED
#                                   ${X}='decorative'   =>  DECORATIVE_MODULE_LOADED
#
#   return                      ->  Exit with 1 if sourcing of any module fails.
#                                   Return 0 otherwise.
#
function load_modules()
{
    local module_name module_loaded_flag
    for module_name in "${@}"; do
        # Remove the suffix "_module" from the current module name.
        module_name="${module_name//_module/}"

        # Generate the variable name that should indicate if this module is sourced already.
        module_loaded_flag="${module_name^^}_MODULE_LOADED"

        # If the generated variable name doesn't exist already, export it and source the module.
        if ! declare -p "${module_loaded_flag}" &> /dev/null; then
            export "${module_loaded_flag}"
            source "${BASH_MODULES_PATH}/${module_name}_module" || exit 1
        fi
    done
}