# This code is part of Qiskit.
#
# (C) Copyright IBM 2023.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.


"""Tests for Clifford synthesis methods."""

import unittest
from test import combine
from ddt import ddt

import numpy as np

from qiskit.test import QiskitTestCase
from qiskit.quantum_info.operators import Clifford
from qiskit.quantum_info import random_clifford
from qiskit.synthesis.clifford import synth_clifford_layers, synth_clifford_depth_lnn
from qiskit.synthesis.linear.linear_circuits_utils import check_lnn_connectivity


@ddt
class TestCliffordDecomposeLayers(QiskitTestCase):
    """Tests for clifford advanced decomposition functions."""

    @combine(num_qubits=[4, 5, 6, 7])
    def test_decompose_clifford(self, num_qubits):
        """Create layer decomposition for a Clifford U, and check that it
        results in an equivalent Clifford."""
        rng = np.random.default_rng(1234)
        samples = 10
        for _ in range(samples):
            cliff = random_clifford(num_qubits, seed=rng)
            circ = synth_clifford_layers(cliff, validate=True)
            cliff_target = Clifford(circ)
            self.assertEqual(cliff, cliff_target)
            # Verify the layered structure
            self.assertEqual(circ.data[0].operation.name, "S2")
            self.assertEqual(circ.data[1].operation.name, "CZ")
            self.assertEqual(circ.data[2].operation.name, "CX_dg")
            self.assertEqual(circ.data[3].operation.name, "H2")
            self.assertEqual(circ.data[4].operation.name, "S1")
            self.assertEqual(circ.data[5].operation.name, "CZ")
            self.assertEqual(circ.data[6].operation.name, "H1")
            self.assertEqual(circ.data[7].operation.name, "Pauli")

    @combine(num_qubits=[4, 5, 6, 7])
    def test_decompose_lnn_depth(self, num_qubits):
        """Test layered decomposition for linear-nearest-neighbour (LNN) connectivity."""
        rng = np.random.default_rng(1234)
        samples = 10
        for _ in range(samples):
            cliff = random_clifford(num_qubits, seed=rng)
            circ = synth_clifford_depth_lnn(cliff)
            # Check that the Clifford circuit 2-qubit depth is bounded by 7*n+2
            depth2q = (circ.decompose()).depth(
                filter_function=lambda x: x.operation.num_qubits == 2
            )
            self.assertTrue(depth2q <= 7 * num_qubits + 2)
            # Check that the Clifford circuit has linear nearest neighbour connectivity
            self.assertTrue(check_lnn_connectivity(circ.decompose()))
            cliff_target = Clifford(circ)
            self.assertEqual(cliff, cliff_target)


if __name__ == "__main__":
    unittest.main()
