import hashlib
import secrets
from datetime import timedelta

from django.utils import timezone

from infrasynth.shared.settings_utils import get_setting

from ..models import ALTCHAChallenge


class ALTCHAService:
    """Proof-of-work challenge for anti-spam protection."""

    def create_challenge(self) -> dict:
        difficulty = get_setting("INFRASYNTH_SECURITY", "ALTCHA_DIFFICULTY", 10000)
        expiry_seconds = get_setting("INFRASYNTH_SECURITY", "ALTCHA_CHALLENGE_EXPIRY_SECONDS", 300)
        challenge_id = secrets.token_hex(32)
        salt = secrets.token_hex(16)
        expires_at = timezone.now() + timedelta(seconds=expiry_seconds)

        ALTCHAChallenge.objects.create(
            challenge_id=challenge_id,
            salt=salt,
            difficulty=difficulty,
            expires_at=expires_at,
        )

        return {
            "challenge_id": challenge_id,
            "salt": salt,
            "difficulty": difficulty,
            "algorithm": "SHA-256",
        }

    def verify(self, challenge_id: str, solution: str, number: int) -> bool:
        try:
            challenge = ALTCHAChallenge.objects.get(challenge_id=challenge_id, is_verified=False)
        except ALTCHAChallenge.DoesNotExist:
            return False

        if challenge.expires_at < timezone.now():
            return False

        expected = hashlib.sha256(f"{challenge.salt}{number}".encode()).hexdigest()
        if solution != expected:
            return False

        challenge.is_verified = True
        challenge.save(update_fields=["is_verified"])
        return True

    def compute_solution(self, salt: str, difficulty: int) -> tuple[str, int]:
        number = 0
        while True:
            h = hashlib.sha256(f"{salt}{number}".encode()).hexdigest()
            if h.startswith("0" * (difficulty // 10000)):
                return h, number
            number += 1