#!/bin/sh

src="$1"
dest="$2"
tmp=/tmp/`basename $0`.tmp.$$

if [ -z "$dest" ]; then
	dest="/dev/fd/1"
elif [ "$src" == "$dest" ]; then
	cp "$src" "$src.orig" || exit 1
fi

awk '
function dump_hunk()
{
	if (!hunk) {
		return;
	}

	if (!hsrc_line)
		foffset = 1;

#	if (hsuffix !~ /\n$/) {
#		hsuffix = hsuffix "\n";
#	}
	printf("@@ -%d,%d +%d,%d %s\n", -hsrc_line, hsrc_count,
		-hsrc_line + foffset, hdest_count, hsuffix);

	if (hunchanged + hdel + hadd != hlines) {
		fflush();
		printf("%s %d: Warning: Unchanged %d deleted %d added %d != lines %d\n",
			FILENAME, FNR, hunchanged, hdel, hadd, hlines) > "/dev/stderr";
	}

	if (hunchanged + hdel != hsrc_count) {
		fflush();
		printf("%s %d: Warning: Unchanged %d deleted %d != hsrc_count %d\n",
			FILENAME, FNR, hunchanged, hdel, hsrc_count) > "/dev/stderr";
	}

	if (hunchanged + hadd != hdest_count) {
		fflush();
		printf("%s %d: Warning: Unchanged %d added %d != hdest_count %d\n",
			FILENAME, FNR, hunchanged, hadd, hdest_count) > "/dev/stderr";
	}

	for (i = 0; i < hlines; i++) {
		print hline[i];
		delete hline[i];
	}

	foffset += hdest_count - hsrc_count;
	hsrc_line = 0;
	hsrc_count = 0;
	hdest_line = 0;
	hdest_count = 0;
	hsuffix = "";

	hunchanged = hadd = hdel = 0;
	hlines = 0;
	hunk = 0;
}

/^(diff|====)/ {
	dump_hunk();
	print;
	foffset = 0;
	next;
}

/^@@/ {
	dump_hunk();
	n = split($2, a, /,/);
	hsrc_line = a[1]+0;
	hsrc_oldcount = a[2]+0;
	hsrc_count = 0;
	if (n != 2 || hsrc_line > 0 || hsrc_oldcount < 0) {
		fflush();
		printf("%s %d: Error: Corrupt hunk header (n %d hsrc_line %d hsrc_oldcount %d)\n",
			FILENAME, FNR, n, hsrc_line, hsrc_count) > "/dev/stderr";
	}

	n = split($3, a, /,/);
	hdest_line = a[1]+0;
	hdest_oldcount = a[2]+0;
	hdest_count = 0;
	if (n != 2 || hdest_line < 0 || hdest_oldcount < 0) {
		fflush();
		printf("%s %d: Error: Corrupt hunk header (hdest_line %d hdest_oldcount %d)\n",
			FILENAME, FNR, hdest_line, hdest_oldcount) > "/dev/stderr";
	}

	hsuffix = $0;
	sub(/^@@.*@@/, "@@", hsuffix);

	hlines = 0;
	hunk = 1;
	next;
}

(!hunk) || /^#/ {
	print;
	next;
}

/^-/ {
	hdel++;
	hsrc_count++;
}

/^+/ {
	hadd++;
	hdest_count++;
}

/^ / {
	hunchanged++;
	hsrc_count++;
	hdest_count++;
}

/^$/ || /^[^-+ ]/ {
	fflush();
	printf("%s %d: Warning: badly formatted line\n",
		FILENAME, FNR) > "/dev/stderr";
	exit(255);
##	hadd++;
##	hdest_count++;
#	next;
}

{
	hline[hlines++] = $0;
}

END {
	dump_hunk()
}
' "$src" > "$tmp" && mv "$tmp" "$dest"