# -*- coding: utf-8 -*-

# Copyright 2017, IBM.
#
# This source code is licensed under the Apache License, Version 2.0 found in
# the LICENSE.txt file in the root directory of this source tree.

# pylint: disable=invalid-name

"""
Pauli Y (bit-phase-flip) gate.
"""
from qiskit.circuit import CompositeGate
from qiskit.circuit import Gate
from qiskit.circuit import QuantumCircuit
from qiskit.circuit import QuantumRegister
from qiskit.circuit.decorators import _op_expand
from qiskit.qasm import pi
from qiskit.extensions.standard.u3 import U3Gate


class YGate(Gate):
    """Pauli Y (bit-phase-flip) gate."""

    def __init__(self):
        """Create new Y gate."""
        super().__init__("y", 1, [])

    def _define(self):
        definition = []
        q = QuantumRegister(1, "q")
        rule = [
            (U3Gate(pi, pi/2, pi/2), [q[0]], [])
        ]
        for inst in rule:
            definition.append(inst)
        self.definition = definition

    def inverse(self):
        """Invert this gate."""
        return YGate()  # self-inverse


@_op_expand(1)
def y(self, q):
    """Apply Y to q."""
    return self.append(YGate(), [q], [])


QuantumCircuit.y = y
CompositeGate.y = y
