#!/usr/bin/awk -E
# Copyright 2017 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Usage: bitrule [number_of_characters_to_ignore_at_start

function usage() {
	print "usage: bitrule [n_chars_to_ignore_at_line_start]" >"/dev/stderr"
	exiting=1; exit
}

function repeat(s, n,   r, i) {
	for (i = 0; i < n; ++i)
		r = r " "
	return r
}

BEGIN {
	ignore_leading = "none"

	if (ARGC > 2)
		usage()
	else if (ARGC == 2) {
		ignore_leading = ARGV[1]
		delete ARGV[1]  # don't treat it as a file
		if (ignore_leading < 0)
			usage()
	}
}

# Track the maximum length of the lines.
length($0) > max_length { max_length = length($0) }

# Detect lines beginning in '0b', '0x' or '0o'. These are binary representations
# of numbers and shouldn't have the rule extend through their prefix.
/^0[box].*/ { is_prefixed = 1 }

{ print }

END {
	if (exiting)
		exit exiting

	top = max_length - 1

	if (ignore_leading != "none") {
		prefix = repeat(" ", ignore_leading)
		top -= ignore_leading
	} else if (is_prefixed) {
		prefix = "  "
		top -= 2
	}

	# Print the ruler.
	printf(prefix)
	for (i = top; i >= 0; --i)
		printf(i % 4 ? "'" : "|")
	printf("\n")

	# Print the numbers.
	printf("%s%s", prefix, repeat("x", top % 4))
	for (i = int(top / 4) * 4; i >= 0; i -= 4)
		printf("%-4d", i)
	printf("\n")
}