"""A seeded random generator that is the same on every Python: xoshiro256** seeded through splitmix64 from a SHA-256
of the seed and a name. `sub(name)` gives an independent stream, so changing how many posts are drawn never reshuffles
the follow graph."""
import hashlib

MASK = (1 << 64) - 1


def _rotl(x, k):
	return ((x << k) | (x >> (64 - k))) & MASK


def _splitmix(state):
	while True:
		state = (state + 0x9E3779B97F4A7C15) & MASK
		z = state
		z = ((z ^ (z >> 30)) * 0xBF58476D1CE4E5B9) & MASK
		z = ((z ^ (z >> 27)) * 0x94D049BB133111EB) & MASK
		yield z ^ (z >> 31)


class Rng:
	def __init__(self, seed, name="root"):
		self.seed = seed
		self.name = name
		digest = hashlib.sha256(f"{seed}/{name}".encode()).digest()
		mix = _splitmix(int.from_bytes(digest[:8], "little"))
		self.s = [next(mix) for _ in range(4)]

	def sub(self, name):
		return Rng(self.seed, f"{self.name}/{name}")

	def next64(self):
		s = self.s
		result = (_rotl((s[1] * 5) & MASK, 7) * 9) & MASK
		t = (s[1] << 17) & MASK
		s[2] ^= s[0]
		s[3] ^= s[1]
		s[1] ^= s[2]
		s[0] ^= s[3]
		s[2] ^= t
		s[3] = _rotl(s[3], 45)
		return result

	def random(self):
		return (self.next64() >> 11) / float(1 << 53)

	def below(self, n):
		"""An integer in [0, n)."""
		if n <= 0:
			raise ValueError("below() needs n > 0")
		limit = MASK - (MASK % n)
		while True:
			x = self.next64()
			if x < limit:
				return x % n

	def between(self, lo, hi):
		"""An integer in [lo, hi]."""
		return lo + self.below(hi - lo + 1)

	def chance(self, p):
		return self.random() < p

	def choice(self, seq):
		return seq[self.below(len(seq))]

	def weighted(self, weights):
		"""A key of {key: weight}, keys taken in sorted order so the draw does not depend on dict order."""
		keys = sorted(k for k, w in weights.items() if w > 0)
		total = sum(weights[k] for k in keys)
		x = self.random() * total
		for k in keys:
			x -= weights[k]
			if x < 0:
				return k
		return keys[-1]

	def shuffle(self, items):
		items = list(items)
		for i in range(len(items) - 1, 0, -1):
			j = self.below(i + 1)
			items[i], items[j] = items[j], items[i]
		return items

	def sample(self, seq, k):
		return self.shuffle(seq)[:max(0, min(k, len(seq)))]

	def span(self, pair):
		"""A value drawn from [lo, hi] given as a two-item list, or the value itself."""
		if isinstance(pair, (list, tuple)):
			return self.between(pair[0], pair[1])
		return pair