# GNU GPLv3, see LICENSE

import os
import random
from unittest import TestCase

from gf256 import _gfmul,evaluate
from shamira import generateRaw,generate
from condensed import *


class TestCondensed(TestCase):
	_urandom=os.urandom

	@classmethod
	def setUpClass(cls):
		random.seed(17)
		os.urandom=lambda n: bytes(random.randint(0,255) for i in range(n))

	@classmethod
	def tearDownClass(cls):
		os.urandom=cls._urandom

	def testGfmul(self):
		for a in range(256):
			for b in range(256):
				self.assertEqual(_gfmul(a,b), gfmul(a,b))

	def testGetConstantCoef(self):
		self.assertEqual(getConstantCoef((1,1),(2,2),(3,3)), 0)

		random.seed(17)
		randomMatches=0
		for i in range(10):
			k=random.randint(2,255)

			# exact
			res=self.checkCoefsMatch(k,k)
			self.assertEqual(res[0], res[1])

			# overdetermined
			res=self.checkCoefsMatch(k,256)
			self.assertEqual(res[0], res[1])

			# underdetermined => random
			res=self.checkCoefsMatch(k,k-1)
			if res[0]==res[1]:
				randomMatches+=1
		self.assertLess(randomMatches, 2) # with a chance (255/256)**10=0.96 there should be no match

	def checkCoefsMatch(self,k,m):
		coefs=[random.randint(0,255) for i in range(k)]
		points=[(j, evaluate(coefs,j)) for j in range(1,256)]
		random.shuffle(points)
		return (getConstantCoef(*points[:m]), coefs[0])

	def testGenerateReconstructRaw(self):
		for (k,n) in [(2,3), (254,254)]:
			shares=generateRaw(b"abcd",k,n)
			random.shuffle(shares)
			self.assertEqual(reconstructRaw(*shares[:k]), b"abcd")
			self.assertNotEqual(reconstructRaw(*shares[:k-1]), b"abcd")

	def testGenerateReconstruct(self):
		for secret in ["abcde","ěščřžý"]:
			for (k,n) in [(2,3), (254,254)]:
				with self.subTest(sec=secret,k=k,n=n):
					shares=generate(secret,k,n)
					random.shuffle(shares)
					self.assertEqual(reconstruct(*shares[:k]), secret)
					try:
						self.assertNotEqual(reconstruct(*shares[:k-1]), secret)
					except UnicodeDecodeError:
						pass
		shares=generate(b"\xfeaa",2,3)
		with self.assertRaises(UnicodeDecodeError):
			reconstruct(*shares)

	def testDecode(self):
		with self.assertRaises(ValueError):
			decode("AAA")
			decode("1.")
			decode(".AAA")
			decode("1AAA")
			decode("1.AAAQEAY")
			decode("1.AAAQEAy=")
			decode("256.AAAQEAY=")
		self.assertEqual(decode("2.AAAQEAY="), (2,b"\x00\x01\x02\x03"))