"""Quantum attention mechanism implementation."""

from typing import List, Optional, Tuple

import numpy as np
import qiskit
from qiskit import ClassicalRegister, QuantumCircuit, QuantumRegister


class QuantumAttention:
    """Implements quantum attention mechanism for enhanced feature processing."""

    def __init__(self, n_qubits: int = 4):
        """Initialize quantum attention with specified number of qubits.

        Args:
            n_qubits: Number of qubits to use in the quantum circuit
        """
        self.n_qubits = n_qubits
        self.qr = QuantumRegister(n_qubits)
        self.cr = ClassicalRegister(n_qubits)
        self.circuit = QuantumCircuit(self.qr, self.cr)

    def apply_attention(self, features: np.ndarray) -> np.ndarray:
        """Apply quantum attention mechanism to input features.

        Args:
            features: Input feature array to process

        Returns:
            Processed features with quantum attention applied
        """
        # Normalize features
        features = self._normalize_features(features)

        # Encode features into quantum states
        self._encode_features(features)

        # Apply quantum attention operations
        self._apply_attention_ops()

        # Measure and return results
        return self._measure_results()

    def _normalize_features(self, features: np.ndarray) -> np.ndarray:
        """Normalize input features to prepare for quantum encoding.

        Args:
            features: Raw input features

        Returns:
            Normalized features
        """
        return features / np.linalg.norm(features)

    def _encode_features(self, features: np.ndarray) -> None:
        """Encode normalized features into quantum states.

        Args:
            features: Normalized features to encode
        """
        for i, feature in enumerate(features):
            if i < self.n_qubits:
                angle = np.arccos(feature)
                self.circuit.ry(angle, self.qr[i])

    def _apply_attention_ops(self) -> None:
        """Apply quantum operations implementing the attention mechanism."""
        # Apply Hadamard gates to create superposition
        self.circuit.h(self.qr)

        # Apply controlled operations between qubits
        for i in range(self.n_qubits - 1):
            self.circuit.cx(self.qr[i], self.qr[i + 1])

        # Apply phase rotations
        for i in range(self.n_qubits):
            self.circuit.rz(np.pi / 4, self.qr[i])

    def _measure_results(self) -> np.ndarray:
        """Measure quantum circuit and process results.

        Returns:
            Processed measurement results
        """
        self.circuit.measure(self.qr, self.cr)

        # Execute circuit and get counts
        backend = qiskit.Aer.get_backend("qasm_simulator")
        job = qiskit.execute(self.circuit, backend, shots=1000)
        result = job.result()
        counts = result.get_counts(self.circuit)

        # Process and return measurement results
        processed_results = np.zeros(self.n_qubits)
        total_shots = sum(counts.values())

        for bitstring, count in counts.items():
            for i, bit in enumerate(reversed(bitstring)):
                if bit == "1":
                    processed_results[i] += count / total_shots

        return processed_results
