"""Block class representing a single record in the blockchain.

Each block stores transaction information (owner, amount, operation type) and
a cryptographic hash linking it to the previous block. Provides serialization
methods for computing hashes and maintaining blockchain integrity.

Authors: Andre Grassi de Jesus, Ricardo Faria
Last Modified: Nov. 14 2025
"""

import json
from typing import Optional

from models.operation import Operation


class Block:
    """A register in the block chain.

    Attributes:
        owner_name (str): The name of the client that did the operation
        registered.
        amount (float): The amount of minicoins involved in the operation.
        operation (Operation): The action that the client did.
        hash_b (bytes): The hash of the block. It's initialized as None and
        must be computed and set by the server with Hash class.
    """

    def __init__(
        self,
        owner_name: str,
        amount: float,
        operation: Operation,
    ):
        if amount <= 0:
            raise ValueError("amount must be positive.")

        if owner_name is None:
            raise ValueError("owner_name can't be None")

        self.owner_name = owner_name
        self.amount = amount
        self.operation = operation
        self.hash_b: bytes = None

    def serialize(self) -> bytes:
        """Transforms the Block in a JSON object for hashing."""
        json_s = json.dumps(self.to_dict(), sort_keys=True)
        return json_s.encode("utf-8")

    def to_dict(self) -> dict:
        """Transforms the Block into a dictionary for serialization."""
        return {
            "owner_name": self.owner_name,
            "amount": self.amount,
            "operation": self.operation.value,
        }

    def __repr__(self):
        if self.hash_b is None:
            hash_hex = "None"
        else:
            hash_hex = self.hash_b.hex()[:3]

        return f"Block {self.owner_name} {self.operation.value} {self.amount} hash={hash_hex}"