#!/usr/bin/awk -f

BEGIN {
	isatty = system("test -t 1") == "0"
	retcode = 0
}

function color(code, s) {
	if (isatty) {
		return "\033[" code "m" s "\033[0m"
	}
	return s
}
function red(s) { return color("31", s) }
function green(s) { return color("32", s) }
function magenta(s) { return color("35", s) }
function cyan(s) { return color("36", s) }
function bg_red(s) { return color("41", s) }
function hl_ws(s, pattern) {
	gsub(pattern, bg_red("&"), s)
	# convert tab characters to 8 spaces to allow coloring
	gsub(/\t/, "        ", s)
	return s
}

/ +\t+/ {
	retcode = 1
	print magenta(FILENAME) cyan(":") green(FNR) cyan(":") \
		hl_ws($0, " +\\t+") red("<-- space(s) followed by tab(s)")
}

/[ \t]+$/ {
	retcode = 1
	print magenta(FILENAME) cyan(":") green(FNR) cyan(":") \
		hl_ws($0, "[ \\t]+$") red("<-- trailing whitespace")
}

ENDFILE {
	# will only match on GNU awk, ignored on non-GNU versions
	if ($0 ~ /^[ \t]*$/) {
		retcode = 1
		print magenta(FILENAME) cyan(": ") red("trailing new line(s)")
	} else if (RT != "\n") {
		retcode = 1
		print magenta(FILENAME) cyan(": ") red("no new line at end of file")
	}
}

END {
	exit retcode
}