text: # This code is part of Qiskit.
  #
  # (C) Copyright IBM 2017, 2018.
  #
  # 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.
  
  """Test the CX Direction  pass"""
  import unittest
  from math import pi
  
  from qiskit import ClassicalRegister, QuantumRegister, QuantumCircuit
  from qiskit.circuit.library import U2Gate
  from qiskit.transpiler import TranspilerError
  from qiskit.transpiler import CouplingMap
  from qiskit.transpiler.passes import CXDirection
  from qiskit.converters import circuit_to_dag
  from qiskit.test import QiskitTestCase
  
  
  class TestCXDirection(QiskitTestCase):
      """ Tests the CXDirection pass."""
  
      def test_no_cnots(self):
          """ Trivial map in a circuit without entanglement
           qr0:---[H]---
  
           qr1:---[H]---
  
           qr2:---[H]---
  
           CouplingMap map: None
          """
          qr = QuantumRegister(3, 'qr')
          circuit = QuantumCircuit(qr)
          circuit.h(qr)
          coupling = CouplingMap()
          dag = circuit_to_dag(circuit)
  
          pass_ = CXDirection(coupling)
          after = pass_.run(dag)
  
          self.assertEqual(dag, after)
  
      def test_direction_error(self):
          """ The mapping cannot be fixed by direction mapper
           qr0:---------
  
           qr1:---(+)---
                   |
           qr2:----.----
  
           CouplingMap map: [2] <- [0] -> [1]
          """
          qr = QuantumRegister(3, 'qr')
          circuit = QuantumCircuit(qr)
          circuit.cx(qr[1], qr[2])
          coupling = CouplingMap([[0, 1], [0, 2]])
          dag = circuit_to_dag(circuit)
  
          pass_ = CXDirection(coupling)
  
          with self.assertRaises(TranspilerError):
              pass_.run(dag)
  
      def test_direction_correct(self):
          """ The CX is in the right direction
           qr0:---(+)---
                   |
           qr1:----.----
  
           CouplingMap map: [0] -> [1]
          """
          qr = QuantumRegister(2, 'qr')
          circuit = QuantumCircuit(qr)
          circuit.cx(qr[0], qr[1])
          coupling = CouplingMap([[0, 1]])
          dag = circuit_to_dag(circuit)
  
          pass_ = CXDirection(coupling)
          after = pass_.run(dag)
  
          self.assertEqual(dag, after)
  
      def test_direction_flip(self):
          """ Flip a CX
           qr0:----.----
                   |
           qr1:---(+)---
  
           CouplingMap map: [0] -> [1]
  
           qr0:-[H]-(+)-[H]--
                     |
           qr1:-[H]--.--[H]--
          """
          qr = QuantumRegister(2, 'qr')
          circuit = QuantumCircuit(qr)
          circuit.cx(qr[1], qr[0])
          coupling = CouplingMap([[0, 1]])
          dag = circuit_to_dag(circuit)
  
          expected = QuantumCircuit(qr)
          expected.append(U2Gate(0, pi), [qr[0]])
          expected.append(U2Gate(0, pi), [qr[1]])
          expected.cx(qr[0], qr[1])
          expected.append(U2Gate(0, pi), [qr[0]])
          expected.append(U2Gate(0, pi), [qr[1]])
  
          pass_ = CXDirection(coupling)
          after = pass_.run(dag)
  
          self.assertEqual(circuit_to_dag(expected), after)
  
      def test_flip_with_measure(self):
          """
           qr0: -(+)-[m]-
                  |   |
           qr1: --.---|--
                      |
           cr0: ------.--
  
           CouplingMap map: [0] -> [1]
  
           qr0: -[H]--.--[H]-[m]-
                      |       |
           qr1: -[H]-(+)-[H]--|--
                              |
           cr0: --------------.--
          """
          qr = QuantumRegister(2, 'qr')
          cr = ClassicalRegister(1, 'cr')
  
          circuit = QuantumCircuit(qr, cr)
          circuit.cx(qr[1], qr[0])
          circuit.measure(qr[0], cr[0])
          coupling = CouplingMap([[0, 1]])
          dag = circuit_to_dag(circuit)
  
          expected = QuantumCircuit(qr, cr)
          expected.append(U2Gate(0, pi), [qr[0]])
          expected.append(U2Gate(0, pi), [qr[1]])
          expected.cx(qr[0], qr[1])
          expected.append(U2Gate(0, pi), [qr[0]])
          expected.append(U2Gate(0, pi), [qr[1]])
          expected.measure(qr[0], cr[0])
  
          pass_ = CXDirection(coupling)
          after = pass_.run(dag)
  
          self.assertEqual(circuit_to_dag(expected), after)
  
      def test_preserves_conditions(self):
          """Verify CXDirection preserves conditional on CX gates.
  
                          ┌───┐      ┌───┐
          q_0: |0>───■────┤ X ├───■──┤ X ├
                   ┌─┴─┐  └─┬─┘ ┌─┴─┐└─┬─┘
          q_1: |0>─┤ X ├────■───┤ X ├──■──
                   └─┬─┘    │   └───┘
                  ┌──┴──┐┌──┴──┐
           c_0: 0 ╡ = 0 ╞╡ = 0 ╞══════════
                  └─────┘└─────┘
          """
  
          qr = QuantumRegister(2, 'q')
          cr = ClassicalRegister(1, 'c')
  
          circuit = QuantumCircuit(qr, cr)
          circuit.cx(qr[0], qr[1]).c_if(cr, 0)
          circuit.cx(qr[1], qr[0]).c_if(cr, 0)
  
          circuit.cx(qr[0], qr[1])
          circuit.cx(qr[1], qr[0])
  
          coupling = CouplingMap([[0, 1]])
          dag = circuit_to_dag(circuit)
  
          expected = QuantumCircuit(qr, cr)
          expected.cx(qr[0], qr[1]).c_if(cr, 0)
  
          # Ordering of u2 is important because DAG comparison will consider
          # different conditional order on a creg to be a different circuit.
          # See https://github.com/Qiskit/qiskit-terra/issues/3164
          expected.append(U2Gate(0, pi), [[qr[1], qr[0]]]).c_if(cr, 0)
          expected.cx(qr[0], qr[1]).c_if(cr, 0)
          expected.append(U2Gate(0, pi), [[qr[1], qr[0]]]).c_if(cr, 0)
  
          expected.cx(qr[0], qr[1])
          expected.append(U2Gate(0, pi), [[qr[1], qr[0]]])
          expected.cx(qr[0], qr[1])
          expected.append(U2Gate(0, pi), [[qr[1], qr[0]]])
  
          pass_ = CXDirection(coupling)
          after = pass_.run(dag)
  
          self.assertEqual(circuit_to_dag(expected), after)
  
  
  if __name__ == '__main__':
      unittest.main()
  