format

#!/usr/bin/env bash

set -euo pipefail

function main() {
	local skip_lines_backref="" prev_file_contents="" next_file_contents=""

	if ! command -v shfmt &> /dev/null
	then
		echo "!!! Install shfmt first: brew install shfmt !!!"
		exit 1
	fi

	for file in "$@"
	do
		# First, auto-format with shfmt (https://github.com/mvdan/sh):
		shfmt -w -kp -ci -sr "${file}"

		# Move "then" and "do" keywords onto separate lines for readability:
		perl -0777 -pe 's/; then\n(\s+)(\s)(\S)/\n\1then\n\1\2\3/g;' -i "${file}"
		perl -0777 -pe 's/; do\n(\s+)(\s)(\S)/\n\1do\n\1\2\3/g;' -i "${file}"

		# Add surrounding spaces to $(...) and ((...)) expressions for readability:
		skip_lines_backref='(?<!(?:=~|s\/|# |echo).{1,250})'
		next_file_contents="$( cat "${file}" )"
		while [[ "${prev_file_contents}" != "${next_file_contents}" ]]
		do
			prev_file_contents="$( cat "${file}" )"
			perl -0777 -pe \
				"s/${skip_lines_backref}"'(\$|\()\(([^\(\)\s])/\1\( \2/g' \
				-i "${file}"
			# ^ Add space after $( and (( when they aren't followed by space already,
			#   skipping lines which contain regex match, sed pattern, comments, or echos.
			perl -0777 -pe \
				"s/${skip_lines_backref}"'(?<=(?:\$\(|\(\().{1,250})([^\(\)\s])\)/\1 \)/g' \
				-i "${file}"
			# ^ Add space before ) and )) when they aren't preceeded by space already,
			#   skipping lines which contain regex match, sed pattern, comments, or echos.
			#   Only do this when $( or (( occurs before these char sequences earlier in line.
			perl -0777 -pe "s/${skip_lines_backref}"'\) +/\) /g' -i "${file}"
			# ^ If the above spacing changes result in multiple spaces after ), reduce to one.
			perl -0777 -pe "s/${skip_lines_backref}"'\(\(\(/\(\( \(/g' -i "${file}"
			perl -0777 -pe "s/${skip_lines_backref}"'\)\)\)/\) \)\)/g' -i "${file}"
			# ^ Refine spacing of nested (( (...) )) and (( ((...)) )) expressions.
			perl -0777 -pe "s/${skip_lines_backref}"' \( / \(/g' -i "${file}"
			perl -0777 -pe \
				"s/${skip_lines_backref}"'(?<!(?:\$\()[^\(\)]{1,250}) \) /\) /g' \
				-i "${file}"
			# ^ Remove extra spacing inside (...) expressions.
			next_file_contents="$( cat "${file}" )"
		done

		# Remove trailing space from all lines in all files:
		perl -0777 -pe 's/\s+$//g' -i "${file}"

		# Ensure every file has a trailing newline:
		if [[ -n "$( tail -c1 "${file}" )" ]]
		then
			echo >> "${file}"
		fi
	done
}

main "$@"