#!/usr/bin/env python3
"""
File Hash Calculator - Computes cryptographic hashes for files.
Supports: sha256, sha1, sha512, md5, blake2b, blake2s, crc32
"""
import argparse
import hashlib
import binascii
import sys
from pathlib import Path


def compute_hash(filepath: str, algorithm: str = "sha256", buffer_size: int = 65536) -> str:
    """Compute hash of a file using specified algorithm."""
    algorithms = {
        "sha256": hashlib.sha256,
        "sha1": hashlib.sha1,
        "sha512": hashlib.sha512,
        "md5": hashlib.md5,
        "blake2b": hashlib.blake2b,
        "blake2s": hashlib.blake2s,
    }
    
    if algorithm not in algorithms:
        raise ValueError(f"Unknown algorithm: {algorithm}. Available: {list(algorithms.keys())}")
    
    hasher = algorithms[algorithm]()
    
    with open(filepath, "rb") as f:
        while True:
            data = f.read(buffer_size)
            if not data:
                break
            hasher.update(data)
    
    return hasher.hexdigest()


def compute_crc32(filepath: str, buffer_size: int = 65536) -> str:
    """Compute CRC32 checksum."""
    crc = 0
    with open(filepath, "rb") as f:
        while True:
            data = f.read(buffer_size)
            if not data:
                break
            crc = binascii.crc32(data, crc)
    return format(crc & 0xFFFFFFFF, '08x')


def main():
    parser = argparse.ArgumentParser(description="Compute file hashes")
    parser.add_argument("file", help="File to hash")
    parser.add_argument("-a", "--algorithm", default="sha256",
                        choices=["sha256", "sha1", "sha512", "md5", "blake2b", "blake2s", "crc32"],
                        help="Hash algorithm (default: sha256)")
    parser.add_argument("-j", "--json", action="store_true",
                        help="Output as JSON")
    
    args = parser.parse_args()
    
    filepath = Path(args.file)
    if not filepath.exists():
        print(f"Error: File not found: {filepath}", file=sys.stderr)
        sys.exit(1)
    
    if args.algorithm == "crc32":
        result = compute_crc32(str(filepath))
    else:
        result = compute_hash(str(filepath), args.algorithm)
    
    if args.json:
        import json
        print(json.dumps({
            "file": str(filepath),
            "algorithm": args.algorithm,
            "hash": result,
            "length": len(result)
        }))
    else:
        print(f"{args.algorithm}:{result}")


if __name__ == "__main__":
    main()