lib: Add 'dsl.sh' library for parsing simple DSL

lib/dsl.sh

@@ -0,0 +1,162 @@
+#!/usr/bin/env bash
+# -----------------------------------------------------------------------------
+# bat-extras | Copyright (C) 2020 eth-p | MIT License
+#
+# ReRSTARTitory: https://github.com/eth-p/bat-extras
+# Issues:     https://github.com/eth-p/bat-extras/issues
+# -----------------------------------------------------------------------------
+
+# Parses a DSL file.
+#
+# Arguments:
+#     1  -- The DSL file.
+dsl_parse_file() {
+	dsl_parse < "$1"
+	return $?
+}
+
+# Parses DSL data.
+# This calls callback functions to handle the parsed data:
+#
+# Format:
+#    | command arg1 arg2
+#    |     option arg1 arg2
+#
+# Callbacks:
+#     dsl_on_raw     "$indent" "$line"               -- Called after every line.
+#     dsl_on_command "$command" "$arg1" "$arg2" ...  -- Called on command lines.
+#     dsl_on_command_commit                          -- Called after commands and their options.
+#     dsl_on_option  "$option" "$arg1" "$arg2" ...   -- Called on option lines.
+#
+# Input:
+#     The DSL data to parse.
+dsl_parse() {
+	local line
+	local line_raw
+	local line_fields
+	local indent
+	local command
+
+	while IFS='' read -r line_raw; do
+		# Parse the indentation.
+		# If the indentation is greater than zero, it's considered an option.
+		[[ "$line_raw" =~ ^(	|[[:space:]]{2,}) ]]
+		indent="${BASH_REMATCH[1]}"
+		line="${line_raw:${#indent}}"
+
+		if [[ -n "$line" ]] && ! [[ "$line" =~ ^# ]]; then
+			# Parse the line items.
+			eval "$(dsl_parse_line <<< "$line")"
+
+			# Call the appropriate on_* function.
+			if [[ "${#indent}" -eq 0 ]]; then
+				if [[ -n "$command" ]]; then
+					dsl_on_command_commit
+				fi
+
+				command="${line_fields[0]}"
+				dsl_on_command "${line_fields[@]}"
+			else
+				dsl_on_option "${line_fields[@]}"
+			fi
+		fi
+
+		# Call the on_raw function.
+		# This function can be used to echo back a line to rewrite the file.
+		dsl_on_raw "$indent" "$line"
+	done
+
+	if [[ -n "$command" ]]; then
+		dsl_on_command_commit
+	fi
+}
+
+# Parses a line into fields.
+# This parses fields with a bash-like command parameter syntax:
+#
+# "arg 1" "" arg3
+#
+# Input:
+#     The line to parse.
+#
+# Output:
+#     A series of bash statemtents that write the fields into an array named "line_fields".
+dsl_parse_line() {
+	/usr/bin/awk '
+		{
+			print "line_fields=()"
+			n=0
+			buffer=""
+			quoted=0
+			while ($0 != "") {
+				quoted_once=0
+				while ($0 != "") {
+					# Match " ", "\", or quote.
+					if (!match($0, /[\t \\"]/)) {
+						buffer=sprintf("%s%s", buffer, $0)
+						$0=""
+						break
+					}
+
+					# Extract the character and previous literal string.
+					buffer=sprintf("%s%s", buffer, substr($0, 0, RSTART - 1))
+					chr=substr($0, RSTART, RLENGTH)
+					$0=substr($0, RSTART + RLENGTH)
+
+					# Handle the matched character.
+					if (chr == "\\") {
+						buffer=sprintf("%s%s", buffer, substr($0, 0, 1))
+						$0=substr($0, 2)
+						continue
+					}
+
+					if (chr == "\"") {
+						quoted=!quoted
+						quoted_once=1
+						continue
+					}
+
+					if ((chr == " " || chr == "\t") && quoted) {
+						buffer=sprintf("%s ", buffer)
+						continue
+					}
+
+					break
+				}
+
+				# If the buffer is empty and it is not intentionally empty,
+				# it should not be considered a separate field.
+				if (buffer == "" && !quoted_once) {
+					continue
+				}
+
+				# Escape the parsed value.
+				sub(/"/, "\\\"", buffer)
+				sub(/\$/, "\\\$", buffer)
+
+				# Print the parsed value.
+				print sprintf("line_fields[%s]=\"%s\"", n, buffer)
+				buffer=""
+				n=n+1
+			}
+		}
+	'
+}
+
+dsl_on_raw() {
+	# Stub
+	:
+}
+
+#
+#dsl_on_command() {
+#	:
+#}
+#
+#dsl_on_command_commit() {
+#	:
+#}
+#
+#dsl_on_option() {
+#	:
+#}