from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister, execute, Aer
from qiskit.circuit.library import XGate, RZGate, CXGate, CCXGate, U2Gate

def quantum_xor(circuit, a, b, output):
    """Quantum XOR gate using CNOTs."""
    circuit.cx(a, output)
    circuit.cx(b, output)

def quantum_and(circuit, a, b, output, ancilla):
    """Quantum AND gate using Toffoli gate."""
    circuit.ccx(a, b, ancilla)
    circuit.cx(ancilla, output)
    circuit.reset(ancilla)

def right_rotate(circuit, qubits, rotation):
    """Performs a right rotation on a register."""
    for _ in range(rotation):
        circuit.swap(qubits[0], qubits[-1])
        qubits.insert(0, qubits.pop())

def quantum_adder(circuit, a, b, output, carry):
    """Quantum full-adder for bitwise addition."""
    for i in range(len(a)):
        quantum_xor(circuit, a[i], b[i], output[i])
        # Implementing carry is a complex process and would involve more auxiliary qubits

def initialize_constants(circuit, qubits):
    """Initializes SHA-256 constants into the first part of a quantum register."""
    # SHA-256 constants, first 32 bits of the fractional parts of the square roots of the first 8 primes
    constants = [
        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
        0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
    ]
    for idx, const in enumerate(constants):
        for bit_pos in range(32):
            if const & (1 << bit_pos):
                circuit.x(qubits[idx*32 + bit_pos])

def main_compression_loop(circuit, message_schedule, working_vars):
        # Implements the main loop of SHA-256 with quantum gates.
    for i in range(64):
        # Ch, Maj, sum0, sum1 are functions that need quantum implementations
        # These are placeholders and would be implemented similarly to the example functions above
        pass

def sha256_quantum():
    """Constructs a full SHA-256 quantum circuit."""
    # For simplicity, assume a single 512-bit message block
    num_qubits = 8 * 32 + 512  # 8x32 for initial hash values, 512 for message schedule
    qr = QuantumRegister(num_qubits, 'qr')
    cr = ClassicalRegister(256, 'cr')  # Output is 256 bits
    circuit = QuantumCircuit(qr, cr)

    # Initialize constants and hash values
    initialize_constants(circuit, qr[:8*32])  # Initial hash values
    # Message schedule would be loaded here

    # Main compression loop
    main_compression_loop(circuit, qr[8*32:], qr[:8*32])

    # Measure the output hash into classical bits
    circuit.measure(qr[:256], cr)

    return circuit

circuit = sha256_quantum()
simulator = Aer.get_backend('qasm_simulator')
result = execute(circuit, backend=simulator, shots=1).result()
counts = result.get_counts()
print(counts)
