#!/usr/bin/env python3
"""
Brute-forcer for Guess the Seed.

Usage:
  python3 solve.py http://127.0.0.1:9000

What it does:
 - Fetches /api/observed to retrieve observed tokens and the time window
 - Brute-forces candidate seeds in the inclusive window to find the seed that
   reproduces the observed tokens in order
 - Predicts the next token (the required one) and prints it
 - Optionally attempts to fetch /flag?token=<predicted> and prints the response
"""
import sys
import requests
import hashlib
import random
import time

def token_from_seed(s):
    rnd = random.Random(int(s))
    val = rnd.getrandbits(64)
    h = hashlib.sha256(str(val).encode()).hexdigest()[:16]
    return h

if len(sys.argv) < 2:
    print("Usage: python3 solve.py http://host:port")
    sys.exit(1)

base = sys.argv[1].rstrip("/")
api = base + "/api/observed"
print("[*] Fetching observed tokens from", api)
r = requests.get(api, timeout=5)
r.raise_for_status()
j = r.json()
observed = j["observed"]
ws = int(j["window_start"])
we = int(j["window_end"])
print("[*] Observed tokens:", observed)
print("[*] Window:", ws, we)

found = False
match_seed = None
# Brute force seed candidates in window
for seed in range(ws, we+1):
    ok = True
    for idx, obs in enumerate(observed):
        cand = token_from_seed(seed + idx)
        if cand != obs:
            ok = False
            break
    if ok:
        match_seed = seed
        print("[+] Found matching seed:", seed)
        found = True
        break

if not found:
    print("[-] No seed found in window.")
    sys.exit(1)

pred = token_from_seed(match_seed + len(observed))
print("[*] Predicted next token:", pred)
# Attempt to fetch flag
flag_url = f"{base}/flag?token={pred}"
print("[*] Requesting flag from:", flag_url)
r2 = requests.get(flag_url, timeout=5)
print("[*] Response:", r2.status_code)
print(r2.text)