"""
Verifiable Delay Function (VDF) implementation for Astreum.

This module provides functionality for computing and verifying VDFs,
which are used in the consensus mechanism to create artificial time delays.
"""

import time
import hashlib
from typing import Optional
from .constants import VDF_DIFFICULTY


def compute_vdf(input_data: bytes, difficulty: Optional[int] = None) -> bytes:
    """
    Compute VDF output for given input data.
    
    Args:
        input_data: Input data for VDF
        difficulty: VDF difficulty level (if None, uses default)
        
    Returns:
        VDF output
    """
    if difficulty is None:
        difficulty = VDF_DIFFICULTY
        
    # Simple VDF implementation
    # In a real implementation, this would be a proper VDF algorithm
    # like Wesolowski VDF or Pietrzak VDF
    
    # For this implementation, we'll use a simple hash-based time delay
    result = input_data
    for _ in range(difficulty):
        result = hashlib.sha256(result).digest()
        
    return result


def verify_vdf(input_data: bytes, output: bytes, difficulty: Optional[int] = None) -> bool:
    """
    Verify VDF computation.
    
    Args:
        input_data: Input data for VDF
        output: Purported VDF output
        difficulty: VDF difficulty level (if None, uses default)
        
    Returns:
        True if output is valid, False otherwise
    """
    if difficulty is None:
        difficulty = VDF_DIFFICULTY
        
    # Compute expected output and compare
    expected = compute_vdf(input_data, difficulty)
    return expected == output


def validate_block_vdf(block_number: int, previous_hash: bytes, vdf_proof: bytes) -> bool:
    """
    Validate the VDF proof for a block.
    
    Args:
        block_number: Block number
        previous_hash: Hash of previous block
        vdf_proof: VDF proof to validate
        
    Returns:
        True if VDF proof is valid, False otherwise
    """
    # Skip VDF validation for genesis block
    if block_number == 0:
        return True
        
    # Compute expected input for the VDF
    vdf_input = previous_hash
    
    # Verify the VDF
    return verify_vdf(vdf_input, vdf_proof)
