"""Provides the IsoLineEmitter."""
import numpy as np

from ribs._utils import check_batch_shape, check_shape
from ribs.emitters._emitter_base import EmitterBase


class IsoLineEmitter(EmitterBase):
    """Emits solutions by leveraging correlations between existing elites.

    If the archive is empty and ``initial_solutions`` is set, a call to
    :meth:`ask` will return ``initial_solutions``. If ``initial_solutions`` is
    not set, we draw solutions from an isotropic Gaussian distribution centered
    at ``x0`` with standard deviation ``iso_sigma``. Otherwise, to generate each
    new solution, the emitter selects a pair of elites :math:`x_i` and
    :math:`x_j` and samples from

    .. math::

        x_i + \\sigma_{iso} \\mathcal{N}(0,\\mathcal{I}) +
            \\sigma_{line}(x_j - x_i)\\mathcal{N}(0,1)

    This emitter is based on the Iso+LineDD operator presented in `Vassiliades
    2018 <https://arxiv.org/abs/1804.03906>`_.

    Args:
        archive (ribs.archives.ArchiveBase): Archive of solutions, e.g.,
            :class:`ribs.archives.GridArchive`.
        iso_sigma (float): Scale factor for the isotropic distribution used to
            generate solutions.
        line_sigma (float): Scale factor for the line distribution used when
            generating solutions.
        x0 (array-like): Center of the Gaussian distribution from which to
            sample solutions when the archive is empty. Must be 1-dimensional.
            This argument is ignored if ``initial_solutions`` is set.
        initial_solutions (array-like): An (n, solution_dim) array of solutions
            to be used when the archive is empty. If this argument is None, then
            solutions will be sampled from a Gaussian distribution centered at
            ``x0`` with standard deviation ``iso_sigma``.
        bounds (None or array-like): Bounds of the solution space. Solutions are
            clipped to these bounds. Pass None to indicate there are no bounds.
            Alternatively, pass an array-like to specify the bounds for each
            dim. Each element in this array-like can be None to indicate no
            bound, or a tuple of ``(lower_bound, upper_bound)``, where
            ``lower_bound`` or ``upper_bound`` may be None to indicate no bound.
        batch_size (int): Number of solutions to return in :meth:`ask`.
        seed (int): Value to seed the random number generator. Set to None to
            avoid a fixed seed.
    Raises:
        ValueError: There is an error in x0 or initial_solutions.
        ValueError: There is an error in the bounds configuration.
    """

    def __init__(self,
                 archive,
                 *,
                 iso_sigma=0.01,
                 line_sigma=0.2,
                 x0=None,
                 initial_solutions=None,
                 bounds=None,
                 batch_size=64,
                 seed=None):
        EmitterBase.__init__(
            self,
            archive,
            solution_dim=archive.solution_dim,
            bounds=bounds,
        )

        self._rng = np.random.default_rng(seed)
        self._batch_size = batch_size
        self._iso_sigma = archive.dtypes["solution"](iso_sigma)
        self._line_sigma = archive.dtypes["solution"](line_sigma)
        self._x0 = None
        self._initial_solutions = None

        if x0 is None and initial_solutions is None:
            raise ValueError("Either x0 or initial_solutions must be provided.")
        if x0 is not None and initial_solutions is not None:
            raise ValueError(
                "x0 and initial_solutions cannot both be provided.")

        if x0 is not None:
            self._x0 = np.array(x0, dtype=archive.dtypes["solution"])
            check_shape(self._x0, "x0", archive.solution_dim,
                        "archive.solution_dim")
        elif initial_solutions is not None:
            self._initial_solutions = np.asarray(
                initial_solutions, dtype=archive.dtypes["solution"])
            check_batch_shape(self._initial_solutions, "initial_solutions",
                              archive.solution_dim, "archive.solution_dim")

    @property
    def x0(self):
        """numpy.ndarray: Center of the Gaussian distribution from which to
        sample solutions when the archive is empty (if initial_solutions is not
        set)."""
        return self._x0

    @property
    def initial_solutions(self):
        """numpy.ndarray: The initial solutions which are returned when the
        archive is empty (if x0 is not set)."""
        return self._initial_solutions

    @property
    def iso_sigma(self):
        """float: Scale factor for the isotropic distribution used to
        generate solutions when the archive is not empty."""
        return self._iso_sigma

    @property
    def line_sigma(self):
        """float: Scale factor for the line distribution used when generating
        solutions."""
        return self._line_sigma

    @property
    def batch_size(self):
        """int: Number of solutions to return in :meth:`ask`."""
        return self._batch_size

    def _clip(self, solutions):
        """Clips solutions to the bounds of the solution space."""
        return np.clip(solutions, self.lower_bounds, self.upper_bounds)

    def ask(self):
        """Generates ``batch_size`` solutions.

        If the archive is empty and ``initial_solutions`` is set, a call to
        :meth:`ask` will return ``initial_solutions``. If ``initial_solutions``
        is not set, we draw solutions from an isotropic Gaussian distribution
        centered at ``x0`` with standard deviation ``iso_sigma``. Otherwise, to
        generate each new solution, the emitter selects a pair of elites
        :math:`x_i` and :math:`x_j` and samples from

        .. math::

            x_i + \\sigma_{iso} \\mathcal{N}(0,\\mathcal{I}) +
                \\sigma_{line}(x_j - x_i)\\mathcal{N}(0,1)

        Returns:
            If the archive is not empty, ``(batch_size, solution_dim)`` array --
            contains ``batch_size`` new solutions to evaluate. If the archive is
            empty, we return ``initial_solutions``, which might not have
            ``batch_size`` solutions.
        """
        if self.archive.empty and self._initial_solutions is not None:
            return self._clip(self.initial_solutions)

        if self.archive.empty:
            # Note: Since the parents are all `x0`, the `directions` below will
            # all be 0.
            parents = np.repeat(self.x0[None],
                                repeats=2 * self.batch_size,
                                axis=0)
        else:
            parents = self.archive.sample_elites(2 *
                                                 self.batch_size)["solution"]

        parents = parents.reshape(2, self.batch_size, self.solution_dim)
        elites = parents[0]
        directions = parents[1] - parents[0]

        iso_gaussian = self._rng.normal(
            scale=self.iso_sigma,
            size=(self.batch_size, self.solution_dim),
        ).astype(elites.dtype)
        line_gaussian = self._rng.normal(
            scale=self.line_sigma,
            size=(self.batch_size, 1),
        ).astype(elites.dtype)

        solutions = elites + iso_gaussian + line_gaussian * directions

        return self._clip(solutions)
