#! /usr/bin/env python3
# encoding: utf-8

import glob
import re
import sys

def is_a_version(token):
	"""
	Returns True iff token is a portage version spec (i.e. contains only numbers or ".").
	"""
	
	for A in token:
		a = ord(A)
		if not (0x30 <= a <= 0x39 or a == 0x2e):
			return False
	
	return True

def strip_version(atom):
	"""
	Removes the =version-123 spec from a portage atom.
	
	Works like 99% of the time. Good enough for the girls I go out with.
	"""
	
	parts = atom[1:].split("-")
	wanted = []
	
	for part in parts:
		if is_a_version(part):
			break
		
		wanted.append(part)
	
	return "-".join(wanted)

def grep(exp, filename):
	with open(filename) as f:
		matches = re.findall(exp, f.read())
	
	return matches

def find_reverse_deps(deps, version=True):
	all_dep_files = glob.glob("/var/db/pkg/*/*/*DEPEND")
	
	regexp = "(%s)[^:]*:[^/]+/[^=]+=" %("|".join(deps))
	matching_files = set(f for f in all_dep_files if grep(regexp, f))
	atoms = {"=" + f[12:].rsplit("/", 1)[0] for f in matching_files}
	
	if not version:
		atoms = {strip_version(a) for a in atoms}
	
	return atoms

if __name__ == "__main__":
	if len(sys.argv) > 1:
		if sys.argv[1] == "-v":
			version = False
			targets = sys.argv[2:]
		else:
			version = True
			targets = sys.argv[1:]
		
		atoms = find_reverse_deps(targets, version)
		print(" ".join(sorted(atoms)))
	else:
		print("Usage: %s DEPENDENCY [more DEPENDENCIES...]" %(sys.argv[0]))
		print("Finds all reverse deps of DEPENDENCY")
		
		sys.exit(1)