import numpy as np
import pytest
from qiskit.quantum_info import Statevector
from reachy_bloch.circuit_library import get_circuit
from reachy_bloch.executor import QuantumExecutor, StepResult

S2 = 1 / np.sqrt(2)

def test_bell_yields_four_steps():
    qc = get_circuit("bell_state").qc  # H, CX, measure, measure
    steps = list(QuantumExecutor().step_through(qc))
    assert len(steps) == 4
    assert all(isinstance(s, StepResult) for s in steps)

def test_bell_statevector_after_cx_is_correct():
    qc = get_circuit("bell_state").qc
    steps = list(QuantumExecutor().step_through(qc))
    sv = steps[1].statevector  # the CX step
    assert sv is not None
    expected = Statevector([S2, 0, 0, S2])
    assert sv.equiv(expected)

def test_measure_steps_have_outcome_and_no_statevector():
    qc = get_circuit("bell_state").qc
    steps = list(QuantumExecutor(seed=7).step_through(qc))
    measures = [s for s in steps if s.measurement is not None]
    assert len(measures) == 2
    for m in measures:
        assert m.measurement in {"0", "1"}
        assert m.statevector is None

def test_bell_measurements_are_correlated():
    # Entangled Bell pair must collapse together: both qubits always match.
    qc = get_circuit("bell_state").qc
    for seed in range(20):
        outcomes = [
            s.measurement
            for s in QuantumExecutor(seed=seed).step_through(qc)
            if s.measurement is not None
        ]
        assert outcomes[0] == outcomes[1], f"seed {seed}: {outcomes} not correlated"

def test_gate_labels_present():
    qc = get_circuit("hadamard_demo").qc
    labels = [s.gate_label for s in QuantumExecutor().step_through(qc)]
    assert labels[0].lower().startswith("h")
    assert "measure" in labels[-1].lower()

from qiskit import QuantumCircuit

def test_more_than_two_qubits_refused():
    qc = QuantumCircuit(3)
    qc.h(0)
    with pytest.raises(ValueError, match="1 and 2 qubit"):
        list(QuantumExecutor().step_through(qc))