Bash_Scripts/Misc/Templater.bash

#!/usr/bin/env bash

echo_rgb() {
	# Echo a colored string to the terminal based on rgb values
	#
	# Positional Arguments:
	#
	#   message <type: string> <position: 1> <required: true>
	#     - The message to be printed to stdout
	#   red <type: int> <position: 2> <required: true>
	#     - The red value from 0 to 255
	#   green <type: int> <position: 3> <required: true>
	#     - The green value from 0 to 255
	#   blue <type: int> <position: 4> <required: true>
	#     - The blue value from 0 to 255
	#
	# Usage:
	#   echo_rgb "Yep" 10 8 30
	#
	# POSIX Compliant:
	#   N/A
	#

	local red
	local green
	local blue
	local input

	input="${1}"
	red="${2}"
	green="${3}"
	blue="${4}"

	printf "\e[0;38;2;%s;%s;%sm%s\e[m\n" "${red}" "${green}" "${blue}" "${input}"
}

log() {
	# Print a message and send it to stdout or stderr depending upon log level, also configurable with debug etc.
	#
	# Arguments:
	#   level <type: string> <position: 1> <required: true>
	#     - The log level, defined within a case check in this function
	#   message <type: string> <position: 2> <required: true>
	#     - The info message
	#   line_number <type: int> <position: 3> <required: false>
	#     - The line number of the calling function (${LINNO})
	#
	# Usage:
	#   log "info" "Could not find that directory"
	#
	# POSIX Compliant:
	#   Yes
	#

	local FORMAT
	FORMAT="[$(echo_rgb "$(date +%Y-%m-%dT%H:%M:%S)" 180 140 255)]"

	# Convert the level to uppercase
	local level
	level=$(echo "${1}" | tr '[:lower:]' '[:upper:]')

	local message
	message="${2}"

	case "${level}" in
	INFO)
		# Output all info log levels to stdout
		printf "${FORMAT}[$(echo_rgb "INFO" 0 140 255)] %s\n" "${message}" >&1
		return 0
		;;
	WARN | WARNING)
		# Output all warning log levels to stdout
		printf "${FORMAT}[$(echo_rgb "WARNING" 255 255 0)] %s\n" "${message}" >&1
		return 0
		;;
	DEBUG)
		# Output all debug log levels to stdout
		if [ "${DEBUG}" ]; then
			printf "${FORMAT}[$(echo_rgb "DEBUG" 0 160 110)] %s\n" "${message}" >&1
		fi
		return 0
		;;
	ERROR)
		# Output all error log levels to stderr
		printf "${FORMAT}[$(echo_rgb "ERROR" 255 0 0)] %s\n" "${message}" >&2
		return 0
		;;
	# Further log levels can be added by extending this switch statement with more comparisons

	*) # Default case, no matches
		# Returns non-zero code as an improper log option was passed, this helps with using `set -e`
		printf "${FORMAT}[ERROR] %s\n" "Invalid log level passed, received level \"${level}\" with message \"${message}\"" >&2
		return 1
		;;
	esac
}

trim() {
	local input="${1}"

	while [[ "${input}" == " "* ]]; do
		input="${input## }"
	done

	while [[ "${input}" == *" " ]]; do
		input="${input%% }"
	done

	echo "${input}"
}

# Get a temp working file so we don't pollute directories
TEMP_FILE="$(mktemp)"

# Set the Contents directory to the env variable, script set, or to their .contents file in the user home
CONTENTS_DIRECTORY="${CONTENTS_DIRECTORY:=\
				$(mkdir -p "${HOME}/.contents" && echo "${HOME}/.contents")}"

EXIT_ON_ERROR=0

REPEAT=1
WRITE_TEMPLATE_MANUALLY_SET=1
WRITE_TEMPLATE_TO=""

declare -A template_handlers

template_handlers=(
	["FILE"]="file_handler"
	["WRITE-TO"]="write_to_handler"
	["TEMPLATE"]="template_handler"
	["VAR"]="var_handler"
	["EVAL"]="eval_handler"
)

write_content() {
	local content
	local leading_spaces
	content="${1}"
	leading_spaces="${2}"

	local string_builder
	string_builder=""

	for ((i = 1; i <= leading_spaces; i++)); do
		string_builder="${string_builder} "
	done
	string_builder="${string_builder}${content}"
	_write_to_buffer "${string_builder}"
}

_write_to_buffer() {
	log "debug" "Received content to write to buffer:
	${1}"
	printf "%s\n" "${1}" >>"${TEMP_FILE}"
	log "debug" "Finished writing content to buffer"
}

var_handler() {
	local variable="${1}"
	local leading_spaces="${2}"
	while IFS=$'\n' read -r line; do
		write_content "${line}" "${leading_spaces}"
	done <<<"${variable}"
}

eval_handler() {
	local eval_statement="${1}"
	local leading_spaces="${2}"
	while IFS=$'\n' read -r line; do
		write_content "${line}" "${leading_spaces}"
	done <<<"$(eval "${eval_statement}")"
}

template_handler() {
	local template_file
	template_file="${1}"

	local leading_spaces
	leading_spaces="${2}"
	# Check that the given file is not an absolute path
	if [[ ! "${template_file:0:1}" == "/" ]]; then
		template_file="${CONTENTS_DIRECTORY}/${template_file}"
	fi
	if [[ ! -f "${template_file}" ]]; then
		log "error" "The given template file \"${template_file}\" does not exist"
		return 1
	fi

	file_handler "${template_file}" "${leading_spaces}"
	REPEAT=0
}

file_handler() {
	local file
	file="${1}"

	local leading_spaces
	leading_spaces="${2}"

	# Check that the given file is not an absolute path
	if [[ ! "${file:0:1}" == "/" ]] && [[ ! -f "${file}" ]]; then
		file="${CONTENTS_DIRECTORY}/${file}"
	fi

	if [[ ! -f "${file}" ]]; then
		log "error" "The given file \"${file}\" does not exist"
		return 1
	fi

	while IFS=$'\n' read -r line; do
		write_content "${line}" "${leading_spaces}"
	done <"${file}"
}

write_to_handler() {
	local write_path
	write_path=${1}

	log "debug" "Received write path \"${write_path}\""
	if [[ ! "${write_path:0:1}" == "/" ]]; then
		log "error" "Given write path was invalid, received \"${write_path}\", the path must be an absolute path"
		return 1
	fi

	if [[ -d "${write_path}" ]]; then
		log "error" "Given write path was invalid, received \"${write_path}\", the path must be a path to an output file (doesn't have to exist), not a directory"
		return 1
	fi
	# This means that it was NOT manually set, 0 is true in shell
	if (("${WRITE_TEMPLATE_MANUALLY_SET}" == 1)); then
		WRITE_TEMPLATE_TO=${write_path}
	fi
}

parse_template_extracted() {
	local tmpl_extracted
	tmpl_extracted="${1}"

	local full_line
	full_line="${2}"

	local num_leading_spaces
	num_leading_spaces=$(awk -F"[ ]" '{for(i=1;i<=NF && ($i=="");i++);print ""i-1""}' <<<"${full_line}")

	# Basic checks to ensure template is correct, first not empty, second that an '=' was passed to give type specifier
	# third is to ensure only one equals sign is passed
	if [[ -z "${tmpl_extracted}" ]]; then
		log "error" "Template passed was empty... ignoring"
		return 1
	elif [[ ! "${tmpl_extracted}" = *"="* ]]; then
		log "error" "Template line passed was of an invalid format, missing = specifier, assumed type is missing as well"
		return 1
	elif [ "$(echo "${tmpl_extracted}" | grep -o "=" | wc -l)" -gt 1 ]; then
		log "error" "Template line passed had too many \"=\", there should only be 1"
		return 1
	fi

	local var_type
	var_type="$(trim "$(echo "${tmpl_extracted}" | cut -d "=" -f1)")"

	# Shellcheck incorrectly reads the below line
	# shellcheck disable=SC2116
	var_type="$(echo "${var_type^^}")"

	local var_arg
	var_arg="$(trim "$(echo "${tmpl_extracted}" | cut -d "=" -f 2-)")"

	local handler_to_use
	handler_to_use="${template_handlers[${var_type}]}"

	if [[ -z "${handler_to_use}" ]]; then
		log "error" "Invalid handler found, no such handler \"${var_type}\" exists as a handler"
		return 1
	else
		log "debug" "Using handler \"${handler_to_use}\""
		if ! eval "${handler_to_use}" "${var_arg}" "${num_leading_spaces}"; then
			log "error" "Arguments passed for \"${var_type}\" were invalid, check the argument"
			return 1
		fi
		log "debug" "Finished using handler \"${handler_to_use}\""
	fi
}

output_finished_template() {
	log "debug" "Outputting finished template"
	mkdir -p "$(dirname "${WRITE_TEMPLATE_TO}")"
	# We want globbing here
	# shellcheck disable=SC2086
	if [[ -z "${WRITE_TEMPLATE_TO}" ]]; then
		log "error" "Was never given a path to write the template to, check your template file or explicitly specify an output location"
		exit 1
	else
		mv "${TEMP_FILE}" ${WRITE_TEMPLATE_TO}
	fi
}

parse_template_line() {
	local line
	line="${1}"

	local tmpl_extracted
	if [[ "${line}" = *\{#%*%#\}* ]]; then
		tmpl_extracted="${line#*\{#%}"
		tmpl_extracted="${tmpl_extracted%\%#\}*}"
		tmpl_extracted="$(trim "${tmpl_extracted}")"

		log "debug" "Extracted a template: ${tmpl_extracted}"
		# Check for non zero status codes and parse the extracted template
		if ! parse_template_extracted "${tmpl_extracted}" "${line}"; then
			return 1
		fi
		log "debug" "Finished extracting template: ${tmpl_extracted}"
	else
		write_content "${line}" "0"
	fi
}

read_template() {
	local read_file
	local line
	local line_num
	line_num=1
	read_file="${1}"
	log "info" "Parsing template file \"${read_file}\""
	while IFS=$'\n' read -r line; do
		# Check for non zero status code
		if ! parse_template_line "${line}"; then
			log "error" "Invalid template passed from \"${read_file}\", check line ${line_num}"
			if (("${EXIT_ON_ERROR}" == 0)); then
				exit 1
			fi
		fi
		line_num=$((line_num + 1))
	done <"${read_file}"
}

templater() {
	local read_file
	read_file="${1}"
	[[ ! -f "${read_file}" ]] &&
		log "error" "$(important "${read_file}") does not exist!" &&
		return 1

	read_template "${read_file}"

	if (("${REPEAT}" == 0)); then
		REPEAT=1
		log "debug" "Repeat set to 0, repeating on the finished file located at ${TEMP_FILE}"
		mv "${TEMP_FILE}" "${TEMP_FILE}-repeat"
		main "-t" "${TEMP_FILE}-repeat"
	else
		log "info" "Finished parsing template file \"${read_file}\""
		log "info" "Writing finished template..."
		output_finished_template
		log "info" "Finished writing template for \"${read_file}\" to \"${WRITE_TEMPLATE_TO}\""
	fi
}

arg_required() {
	echo_rgb "${1}" 255 183 0
}

arg_optional() {
	echo_rgb "${1}" 117 255 255
}

arg_description() {
	echo_rgb "${@}" 220 190 255
}

usage() {
	# Print out usage instructions for the local script
	#
	# Arguments:
	#   None
	#
	# Usage:
	#   usage
	#
	# POSIX Compliant:
	#   Yes
	#
	cat <<EOF
Usage: $(basename ${0}) [OPTIONS]
  $(arg_required "REQUIRED")
  $(arg_optional "OPTIONAL")

  $(arg_required "--template-file") <templateFile: string> | $(arg_required "-t") <templateFile: string>
    $(arg_description "A template file to parse and apply rules for

    Example:
      --template-file example.tmpl")

  $(arg_optional "--contents-dir") <contentsDirectory: string> | $(arg_optional "-c") <contentsDirectory: string>
    $(arg_description "The files that contain contents read by the templates.

    By default this is set to ~/.contents/ if unset, to set via variable you can either use this argument or pass
    export CONTENTS_DIRECTORY=\`your contents directory\`

    Example:
      --contents-dir ~/Desktop/contents")

  $(arg_optional "--output-to") <outputFile: string> | $(arg_optional "-o") <outputFile: string>
    $(arg_description "The file to output the applied template to, this can be set within a template, but can be overriden with this option

    Example:
      --output-to myfile.out")

  $(arg_optional "--no-exit") | $(arg_optional "-n")
    $(arg_description "Do not exit on any errors, continue executing

    Example:
      --no-exit")
EOF

}

main() {
	# Parse input arguments
	#
	# Arguments:
	#   Consult the `usage` function
	#
	# Usage:
	#   parse_args "$@"
	#     - All arguments should be ingested by parse_args first for variable setting
	#
	# POSIX Compliant:
	#   Yes
	#
	local template_file

	while :; do
		case ${1} in
		-h | -\? | --help)
			usage # Display a usage synopsis.
			exit
			;;
		--) # End of all options.
			break
			;;
		-t | --template-file)
			shift
			template_file="${1}"
			[[ ! -f "${template_file}" ]] &&
				log "error" "The given template file \"${template_file}\" does not exist" &&
				exit 1
			log "info" "Set template file to \"${template_file}\""
			;;
		-c | --contents-dir)
			shift
			CONTENTS_DIRECTORY="${1}"
			[[ ! -d "${CONTENTS_DIRECTORY}" ]] &&
				log "error" "\"${CONTENTS_DIRECTORY}\" is an invalid path, contents directory must be an absolute path" &&
				exit 1
			log "info" "Set contents directory to \"${CONTENTS_DIRECTORY}\""
			;;
		-o | --output-to)
			shift
			WRITE_TEMPLATE_MANUALLY_SET=0
			WRITE_TEMPLATE_TO="${1}"
			;;
		-n | --no-exit)
			EXIT_ON_ERROR=1
			log "info" "No longer exiting on errors."
			;;
		-?*)
			printf 'Unknown option: %s\n' "$1" >&2
			usage
			exit 1
			;;
		*) # Default case: No more options, so break out of the loop.
			break ;;
		esac
		shift
	done
	[[ -z "${template_file}" ]] &&
		log "error" "No template file provided, exiting! Check \`-h\` for help." &&
		exit 1
	templater "${template_file}"
}

main "$@"