# This code is part of Qiskit.
#
# (C) Copyright IBM 2017.
#
# 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 https://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.

"""Two-pulse single-qubit gate."""

from __future__ import annotations

import cmath
import copy as _copy
import math
from cmath import exp

import numpy
from qiskit.circuit.controlledgate import ControlledGate
from qiskit.circuit.gate import Gate
from qiskit.circuit.parameterexpression import ParameterValueType
from qiskit._accelerate.circuit import StandardGate


class UGate(Gate):
    r"""Generic single-qubit rotation in terms of ZYZ Euler angles.

    The action of this gate can be related to the standard ZYZ Euler decomposition by

    .. math::

        U(\theta, \phi, \lambda) = P(\phi) R_Y(\theta) P(\lambda) 
        = e^{i\frac{\phi + \lambda}{2}} R_Z(\phi) R_Y(\theta) R_Z(\lambda).

    Can be applied to a :class:`~qiskit.circuit.QuantumCircuit`
    with the :meth:`~qiskit.circuit.QuantumCircuit.u` method.

    Circuit symbol:

    .. code-block:: text

             ┌──────────┐
        q_0: ┤ U(ϴ,φ,λ) ├
             └──────────┘

    Matrix representation:

    .. math::

        \newcommand{\rotationangle}{\frac{\theta}{2}}

        U(\theta, \phi, \lambda) =
        \begin{pmatrix}
            \cos\left(\rotationangle\right) & -e^{i\lambda}\sin\left(\rotationangle\right) \\
            e^{i\phi}\sin\left(\rotationangle\right) & e^{i(\phi+\lambda)}\cos\left(\rotationangle\right)
        \end{pmatrix}

    .. note::

        The matrix representation shown here is the same as in the `OpenQASM 3.0 specification
        <https://openqasm.com/language/gates.html#built-in-gates>`_,
        which differs from the `OpenQASM 2.0 specification
        <https://doi.org/10.48550/arXiv.1707.03429>`_ by a global phase of
        :math:`e^{i(\phi+\lambda)/2}`.

    Examples:

    .. math::

        U\left(\theta, -\frac{\pi}{2}, \frac{\pi}{2}\right) = RX(\theta)

    .. math::

        U(\theta, 0, 0) = RY(\theta)
    """

    _standard_gate = StandardGate.U

    def __init__(
        self,
        theta: ParameterValueType,
        phi: ParameterValueType,
        lam: ParameterValueType,
        label: str | None = None,
    ):
        r"""
        Args:
            theta: The angle :math:`\theta` corresponding to the :math:`R_Y(\theta)` rotation.
            phi: The angle :math:`\phi` corresponding to the :math:`R_Z(\phi)` rotation.
            lam: The angle :math:`\lambda` corresponding to the :math:`R_Z(\lambda)` rotation.
            label: An optional label for the gate.
        """
        super().__init__("u", 1, [theta, phi, lam], label=label)

    def inverse(self, annotated: bool = False):
        r"""Return inverted U gate.

        :math:`U(\theta,\phi,\lambda)^{\dagger} =U(-\theta,-\lambda,-\phi))`

        Args:
            annotated: when set to ``True``, this is typically used to return an
                :class:`.AnnotatedOperation` with an inverse modifier set instead of a concrete
                :class:`.Gate`. However, for this class this argument is ignored as the
                inverse of this gate is always a :class:`.UGate` with inverse parameter values.

        Returns:
            UGate: inverse gate.
        """
        return UGate(-self.params[0], -self.params[2], -self.params[1])

    def control(
        self,
        num_ctrl_qubits: int = 1,
        label: str | None = None,
        ctrl_state: str | int | None = None,
        annotated: bool | None = None,
    ):
        """Return a controlled version of the U gate.

        For a single control qubit, the controlled gate is implemented as :class:`.CUGate`,
        regardless of the value of `annotated`.

        For more than one control qubit,
        the controlled gate is implemented as :class:`.ControlledGate` when ``annotated``
        is ``False``, and as :class:`.AnnotatedOperation` when ``annotated`` is ``True``.
        When ``annotated`` is ``None``, it is interpreted as ``True`` when the gate has free
        parameters (in which case the gate cannot be synthesized at the construction time),
        and as ``False`` otherwise.

        Args:
            num_ctrl_qubits: Number of controls to add. Defaults to ``1``.
            label: Optional gate label. Ignored if the controlled gate is implemented as an
                annotated operation.
            ctrl_state: The control state of the gate, specified either as an integer or a bitstring
                (e.g. ``"110"``). If ``None``, defaults to the all-ones state ``2**num_ctrl_qubits - 1``.
            annotated: Indicates whether the controlled gate should be implemented as a controlled gate
                or as an annotated operation.

        Returns:
            A controlled version of this gate.
        """
        if num_ctrl_qubits == 1:
            gate = CUGate(
                self.params[0],
                self.params[1],
                self.params[2],
                0,
                label=label,
                ctrl_state=ctrl_state,
            )
            gate.base_gate.label = self.label
        else:
            gate = super().control(
                num_ctrl_qubits=num_ctrl_qubits,
                label=label,
                ctrl_state=ctrl_state,
                annotated=annotated,
            )
        return gate

    def __array__(self, dtype=None, copy=None):
        """Return a numpy.array for the U gate."""
        if copy is False:
            raise ValueError("unable to avoid copy while creating an array as requested")
        theta, phi, lam = (float(param) for param in self.params)
        cos = math.cos(theta / 2)
        sin = math.sin(theta / 2)
        return numpy.array(
            [
                [cos, -exp(1j * lam) * sin],
                [exp(1j * phi) * sin, exp(1j * (phi + lam)) * cos],
            ],
            dtype=dtype or complex,
        )

    def __eq__(self, other):
        if isinstance(other, UGate):
            return self._compare_parameters(other)
        return False


class _CUGateParams(list):
    # This awful class is to let `CUGate.params` have its keys settable (as
    # `QuantumCircuit.assign_parameters` requires), while accounting for the problem that `CUGate`
    # was defined to have a different number of parameters to its `base_gate`, which breaks
    # `ControlledGate`'s assumptions, and would make most parametric `CUGate` objects invalid.
    #
    # It's constructed only as part of the `CUGate.params` getter, and given that the general
    # circuit model assumes that that's a directly mutable list that _must_ be kept in sync with the
    # gate's requirements, we don't need this to support arbitrary mutation, just enough for
    # `QuantumCircuit.assign_parameters` to work.

    __slots__ = ("_gate",)

    def __init__(self, gate):
        super().__init__(gate._params)
        self._gate = gate

    def __setitem__(self, key, value):
        super().__setitem__(key, value)
        self._gate._params[key] = value
        # Magic numbers: CUGate has 4 parameters, UGate has 3, with the last of CUGate's missing.
        if isinstance(key, slice):
            # We don't need to worry about the case of the slice being used to insert extra / remove
            # elements because that would be "undefined behavior" in a gate already, so we're
            # within our rights to do anything at all.
            for i, base_key in enumerate(range(*key.indices(4))):
                if base_key < 0:
                    base_key = 4 + base_key
                if base_key < 3:
                    self._gate.base_gate.params[base_key] = value[i]
        else:
            if key < 0:
                key = 4 + key
            if key < 3:
                self._gate.base_gate.params[key] = value


class CUGate(ControlledGate):
    r"""Controlled-U gate (4-parameter two-qubit gate).

    This is a controlled version of the U gate (generic single qubit rotation),
    including a possible global phase :math:`e^{i\gamma}` of the U gate.

    Can be applied to a :class:`~qiskit.circuit.QuantumCircuit`
    with the :meth:`~qiskit.circuit.QuantumCircuit.cu` method.

    Circuit symbol:

    .. code-block:: text

        q_0: ──────■──────
             ┌─────┴──────┐
        q_1: ┤ U(ϴ,φ,λ,γ) ├
             └────────────┘

    Matrix representation:

    .. math::

        \newcommand{\rotationangle}{\frac{\theta}{2}}

        CU(\theta, \phi, \lambda, \gamma)\ q_0, q_1 =
            I \otimes |0\rangle\langle 0| +
            e^{i\gamma} U(\theta,\phi,\lambda) \otimes |1\rangle\langle 1| =
            \begin{pmatrix}
                1 & 0 & 0 & 0 \\
                0 & e^{i\gamma}\cos(\rotationangle) &
                0 & -e^{i(\gamma + \lambda)}\sin(\rotationangle) \\
                0 & 0 & 1 & 0 \\
                0 & e^{i(\gamma+\phi)}\sin(\rotationangle) &
                0 & e^{i(\gamma+\phi+\lambda)}\cos(\rotationangle)
            \end{pmatrix}

    .. note::

        In Qiskit's convention, higher qubit indices are more significant
        (little endian convention). In many textbooks, controlled gates are
        presented with the assumption of more significant qubits as control,
        which in our case would be q_1. Thus a textbook matrix for this
        gate will be:

        .. code-block:: text

                 ┌────────────┐
            q_0: ┤ U(ϴ,φ,λ,γ) ├
                 └─────┬──────┘
            q_1: ──────■───────

        .. math::

            \newcommand{\rotationangle}{\frac{\theta}{2}}
            CU(\theta, \phi, \lambda, \gamma)\ q_1, q_0 =
            |0\rangle\langle 0| \otimes I +
            e^{i\gamma}|1\rangle\langle 1| \otimes U(\theta,\phi,\lambda) =
            \begin{pmatrix}
            1 & 0 & 0 & 0 \\
            0 & 1 & 0 & 0 \\
            0 & 0 & e^{i\gamma} \cos(\rotationangle) & -e^{i(\gamma + \lambda)}\sin(\rotationangle) \\
            0 & 0 &
            e^{i(\gamma + \phi)}\sin(\rotationangle) & e^{i(\gamma + \phi+\lambda)}\cos(\rotationangle)
            \end{pmatrix}
    """

    _standard_gate = StandardGate.CU

    def __init__(
        self,
        theta: ParameterValueType,
        phi: ParameterValueType,
        lam: ParameterValueType,
        gamma: ParameterValueType,
        label: str | None = None,
        ctrl_state: int | str | None = None,
        *,
        _base_label=None,
    ):
        """Create new CU gate."""
        super().__init__(
            "cu",
            2,
            [theta, phi, lam, gamma],
            num_ctrl_qubits=1,
            label=label,
            ctrl_state=ctrl_state,
            base_gate=UGate(theta, phi, lam, label=_base_label),
        )

    def _define(self):
        """Default definition"""

        from qiskit.circuit import QuantumCircuit

        #          ┌──────┐    ┌──────────────┐
        # q_0: ────┤ P(γ) ├────┤ P(λ/2 + φ/2) ├──■────────────────────────────■────────────────
        #      ┌───┴──────┴───┐└──────────────┘┌─┴─┐┌──────────────────────┐┌─┴─┐┌────────────┐
        # q_1: ┤ P(λ/2 - φ/2) ├────────────────┤ X ├┤ U(-0/2,0,-λ/2 - φ/2) ├┤ X ├┤ U(0/2,φ,0) ├
        #      └──────────────┘                └───┘└──────────────────────┘└───┘└────────────┘

        self.definition = QuantumCircuit._from_circuit_data(
            StandardGate.CU._get_definition(self.params), legacy_qubits=True
        )

    def inverse(self, annotated: bool = False):
        r"""Return inverted CU gate.

        :math:`CU(\theta,\phi,\lambda,\gamma)^{\dagger} = CU(-\theta,-\phi,-\lambda,-\gamma))`

        Args:
            annotated: when set to ``True``, this is typically used to return an
                :class:`.AnnotatedOperation` with an inverse modifier set instead of a concrete
                :class:`.Gate`. However, for this class this argument is ignored as the inverse
                of this gate is always a :class:`.CUGate` with inverse parameter
                values.

        Returns:
            CUGate: inverse gate.
        """
        return CUGate(
            -self.params[0],
            -self.params[2],
            -self.params[1],
            -self.params[3],
            ctrl_state=self.ctrl_state,
        )

    def __array__(self, dtype=None, copy=None):
        """Return a numpy.array for the CU gate."""
        if copy is False:
            raise ValueError("unable to avoid copy while creating an array as requested")
        theta, phi, lam, gamma = (float(param) for param in self.params)
        cos = math.cos(theta / 2)
        sin = math.sin(theta / 2)
        a = cmath.exp(1j * gamma) * cos
        b = -cmath.exp(1j * (gamma + lam)) * sin
        c = cmath.exp(1j * (gamma + phi)) * sin
        d = cmath.exp(1j * (gamma + phi + lam)) * cos
        if self.ctrl_state:
            return numpy.array(
                [[1, 0, 0, 0], [0, a, 0, b], [0, 0, 1, 0], [0, c, 0, d]], dtype=dtype
            )
        else:
            return numpy.array(
                [[a, 0, b, 0], [0, 1, 0, 0], [c, 0, d, 0], [0, 0, 0, 1]], dtype=dtype
            )

    @property
    def params(self):
        return _CUGateParams(self)

    @params.setter
    def params(self, parameters):
        # We need to skip `ControlledGate` in the inheritance tree, since it defines
        # that all controlled gates are `(1-|c><c|).1 + |c><c|.base` for control-state `c`, which
        # this class does _not_ satisfy (so it shouldn't really be a `ControlledGate`).
        super(ControlledGate, type(self)).params.fset(self, parameters)
        self.base_gate.params = parameters[:-1]

    def __deepcopy__(self, memo=None):
        # We have to override this because `ControlledGate` doesn't copy the `_params` list,
        # assuming that `params` will be a view onto the base gate's `_params`.
        memo = memo if memo is not None else {}
        out = super().__deepcopy__(memo)
        out._params = _copy.deepcopy(out._params, memo)
        return out

    def __eq__(self, other):
        return (
            isinstance(other, CUGate)
            and self.ctrl_state == other.ctrl_state
            and self._compare_parameters(other)
        )
