"""
Utils for dealing with arrays.
"""
import sys
from itertools import product
from copy import copy
from numbers import Integral

import numpy as np
from scipy.sparse import coo_matrix

from openmdao.core.constants import INT_DTYPE


def shape_to_len(shape):
    """
    Compute length given a shape tuple.

    For realistic-dimension arrays, looping over the shape tuple is much faster than np.prod.

    Parameters
    ----------
    shape : tuple
        Numpy shape tuple.

    Returns
    -------
    int
        Length of multidimensional array.
    """
    if shape is None:
        return None

    length = 1
    if not isinstance(shape, Integral):
        for dim in shape:
            length *= dim

    return length


def evenly_distrib_idxs(num_divisions, arr_size):
    """
    Return evenly distributed entries for the given array size.

    Given a number of divisions and the size of an array, chop the array up
    into pieces according to number of divisions, keeping the distribution
    of entries as even as possible.

    Parameters
    ----------
    num_divisions : int
        Number of parts to divide the array into.
    arr_size : int
        Number of entries in the array.

    Returns
    -------
    tuple
        A tuple of (sizes, offsets), where sizes and offsets contain values for all
        divisions.
    """
    base, leftover = divmod(arr_size, num_divisions)
    sizes = np.full(num_divisions, base, dtype=INT_DTYPE)

    # evenly distribute the remainder across size-leftover procs,
    # instead of giving the whole remainder to one proc
    sizes[:leftover] += 1

    offsets = np.zeros(num_divisions, dtype=INT_DTYPE)
    offsets[1:] = np.cumsum(sizes)[:-1]

    return sizes, offsets


def take_nth(rank, size, seq):
    """
    Iterate returning every nth value.

    Return an iterator over the sequence that returns every
    nth element of seq based on the given rank within a group of
    the given size.  For example, if size = 2, a rank of 0 returns
    even indexed elements and a rank of 1 returns odd indexed elements.

    Parameters
    ----------
    rank : int
        MPI rank of this process.
    size : int
        Size of the array we're taking nth entries from.
    seq : iter
        Iterator containing the values being returned.

    Yields
    ------
    generator
    """
    assert(rank < size)
    it = iter(seq)
    while True:
        for proc in range(size):
            if rank == proc:
                try:
                    yield next(it)
                except StopIteration:
                    return
            else:
                try:
                    next(it)
                except StopIteration:
                    return


def convert_neg(arr, size):
    """
    Convert any negative indices into their positive equivalent.

    This only works for a 1D array.

    Parameters
    ----------
    arr : ndarray
        Array having negative indices converted.
    size : int
        Dimension of the array.

    Returns
    -------
    ndarray
        The converted array.
    """
    arr[arr < 0] += size
    return arr


def array_viz(arr, prob=None, of=None, wrt=None, stream=sys.stdout):
    """
    Display the structure of a boolean array in a compact form.

    If prob, of, and wrt are supplied, print the name of the response alongside
    each row and print the names of the design vars, aligned with each column, at
    the bottom.

    Parameters
    ----------
    arr : ndarray
        Array being visualized.
    prob : Problem or None
        Problem object.
    of : list of str or None
        Names of response variables used in derivative calculation.
    wrt : list of str or None
        Names of design variables used in derivative calculation.
    stream : file-like
        Stream where output will be written.
    """
    if len(arr.shape) != 2:
        raise RuntimeError("array_viz only works for 2d arrays.")

    if prob is not None:
        if of is None:
            of = prob.driver._get_ordered_nl_responses()
        if wrt is None:
            wrt = list(prob.driver._designvars)

    if prob is None or of is None or wrt is None:
        for r in range(arr.shape[0]):
            for c in range(arr.shape[1]):
                if arr[r, c]:
                    stream.write('x')
                else:
                    stream.write('.')
            stream.write(' %d\n' % r)
    else:

        row = 0
        for res in of:
            for r in range(row, row + prob.driver._responses[res]['size']):
                col = 0
                for dv in wrt:
                    for c in range(col, col + prob.driver._designvars[dv]['size']):
                        if arr[r, c]:
                            stream.write('x')
                        else:
                            stream.write('.')
                    col = c + 1
                stream.write(' %d  %s\n' % (r, res))
            row = r + 1

        start = 0
        for name in wrt:
            tab = ' ' * start
            stream.write('%s|%s\n' % (tab, name))
            start += prob.driver._designvars[name]['size']


def array_connection_compatible(shape1, shape2):
    """
    Return True if the two arrays shapes are compatible.

    Array shapes are compatible if the underlying data has the same size and is
    stored in the same contiguous order for the two shapes.

    Parameters
    ----------
    shape1 : tuple of int
        Shape of the first array.
    shape2 : tuple of int
        Shape of the second array.

    Returns
    -------
    bool
        True if the two shapes are compatible for connection, else False.
    """
    ashape1 = np.asarray(shape1, dtype=INT_DTYPE)
    ashape2 = np.asarray(shape2, dtype=INT_DTYPE)

    size1 = shape_to_len(ashape1)
    size2 = shape_to_len(ashape2)

    # Shapes are not connection-compatible if size is different
    if size1 != size2:
        return False

    nz1 = np.where(ashape1 > 1)[0]
    nz2 = np.where(ashape2 > 1)[0]

    if len(nz1) > 0:
        fundamental_shape1 = ashape1[np.min(nz1): np.max(nz1) + 1]
    else:
        fundamental_shape1 = np.ones((1,))

    if len(nz2) > 0:
        fundamental_shape2 = ashape2[np.min(nz2): np.max(nz2) + 1]
    else:
        fundamental_shape2 = np.ones((1,))

    return np.all(fundamental_shape1 == fundamental_shape2)


def tile_sparse_jac(data, rows, cols, nrow, ncol, num_nodes):
    """
    Assemble arrays necessary to define a COO sparse jacobian for a vectorized component.

    These arrays can also be passed to csc_matrix or csr_matrix to create CSC and CSR sparse
    matrices.

    Parameters
    ----------
    data : ndarray
        Array of values.
    rows : index array
        Array of row indices.
    cols : index array
        Array of column indices.
    nrow : int
        Number of rows in sub jacobian.
    ncol : int
        Number of columns in sub jacobian.
    num_nodes : int
        Number of vectorized copies to tile.

    Returns
    -------
    ndarray, ndarray, ndarray
        Arrays to define a COO sparse jacobian of size num_nodes*nrow by num_nodes*ncol.
    """
    nnz = len(rows)

    if np.isscalar(data):
        data = data * np.ones(nnz)

    if not np.isscalar(nrow):
        nrow = shape_to_len(nrow)

    if not np.isscalar(ncol):
        ncol = shape_to_len(ncol)

    repeat_arr = np.repeat(np.arange(num_nodes), nnz)

    data = np.tile(data, num_nodes)
    rows = np.tile(rows, num_nodes) + repeat_arr * nrow
    cols = np.tile(cols, num_nodes) + repeat_arr * ncol

    return data, rows, cols


def _global2local_offsets(global_offsets):
    """
    Given existing global offsets, return a copy with offsets localized to each process.

    Parameters
    ----------
    global_offsets : dict
        Arrays of global offsets keyed by vec_name and deriv direction.

    Returns
    -------
    dict
        Arrays of local offsets keyed by vec_name and deriv direction.
    """
    offsets = {}
    for type_ in global_offsets:
        goff = global_offsets[type_]
        offsets[type_] = goff.copy()
        if goff[0].size > 0:
            # adjust offsets to be local in each process
            offsets[type_] -= goff[:, 0].reshape((goff.shape[0], 1))

    return offsets


def get_input_idx_split(full_idxs, inputs, outputs, use_full_cols, is_total):
    """
    Split an array of indices into vec outs + ins into two arrays of indices into outs and ins.

    Parameters
    ----------
    full_idxs : ndarray
        Indices into the full array (which could be outs + ins or just ins).
    inputs : Vector
        Inputs vector.
    outputs : Vector
        Outputs vector.
    use_full_cols : bool
        If True,  full idxs are into the full outs + ins vector.
    is_total : bool
        If True, total derivatives are being computed and wrt vector is the outputs vector.

    Returns
    -------
    list of tuples
        Each tuple is of the form (array, idxs).
    """
    assert len(full_idxs) > 0, "Empty index array passed to get_input_idx_split."
    full_idxs = np.asarray(full_idxs)
    if use_full_cols:
        out_size = len(outputs)
        out_idxs = full_idxs[full_idxs < out_size]
        in_idxs = full_idxs[full_idxs >= out_size] - out_size
        full = [(outputs, out_idxs), (inputs, in_idxs)]
        return [(vec, inds) for vec, inds in full if inds.size > 0]
    elif is_total:
        return [(outputs, full_idxs)]
    else:
        return [(inputs, full_idxs)]


def _flatten_src_indices(src_indices, shape_in, shape_out, size_out):
    """
    Convert src_indices into a flat, non-negative form.

    Parameters
    ----------
    src_indices : ndarray
        Array of src_indices.  Can be flat or multi-dimensional.
    shape_in : tuple
        Shape of the input variable.
    shape_out : tuple
        Shape of the output variable.
    size_out : int
        Size of the output variable.

    Returns
    -------
    ndarray
        The flattened src_indices.
    """
    if len(shape_out) == 1 or shape_in == src_indices.shape:
        return convert_neg(src_indices.ravel(), size_out)

    entries = [list(range(x)) for x in shape_in]
    cols = np.vstack([src_indices[i] for i in product(*entries)])
    dimidxs = [convert_neg(cols[:, i], shape_out[i]) for i in range(cols.shape[1])]
    return np.ravel_multi_index(dimidxs, shape_out)


def sizes2offsets(size_array):
    """
    For a given array of sizes, return an array of offsets.

    Offsets will be computed using a flattened version of size_array and then
    reshaped to match the shape of size_array.

    Parameters
    ----------
    size_array : ndarray
        Array of sizes.

    Returns
    -------
    ndarray
        Array of offsets.
    """
    offsets = np.zeros(size_array.size, dtype=size_array.dtype)
    offsets[1:] = np.cumsum(size_array.flat)[:-1]
    return offsets.reshape(size_array.shape)


def abs_complex(x):
    """
    Compute the absolute value of a complex-stepped vector.

    Rather than taking a Euclidian norm, simply negate the values that are less than zero.

    Parameters
    ----------
    x : ndarray
        Input array.

    Returns
    -------
    ndarray
        Complex-step absolute value of the array.
    """
    idx_neg = np.where(x < 0)
    x[idx_neg] = -x[idx_neg]
    return x


def dv_abs_complex(x, x_deriv):
    """
    Compute the complex-step derivative of the absolute value function and its derivative.

    Parameters
    ----------
    x : ndarray
        Input array, used for determining which elements to negate.
    x_deriv : ndarray
        Incominng partial derivative array, may have one additional dimension.

    Returns
    -------
    ndarray
        Absolute value applied to x.
    ndarray
        Absolute value applied to x_deriv.
    """
    idx_neg = np.where(x < 0)

    # Special case when x is (1, ) and x_deriv is (1, n).
    if len(x_deriv.shape) == 1:
        if idx_neg[0].size != 0:
            return -x, -x_deriv

    x[idx_neg] = -x[idx_neg]
    x_deriv[idx_neg] = -x_deriv[idx_neg]

    return x, x_deriv


def rand_sparsity(shape, density_ratio, dtype=bool):
    """
    Return a random boolean COO matrix of the given shape with given percent density.

    Row and column indices are generated using random integers so some duplication
    is possible, resulting in a matrix with somewhat lower density than specified.

    Parameters
    ----------
    shape : tuple
        Desired shape of the matrix.
    density_ratio : float
        Approximate ratio of nonzero to zero entries in the desired matrix.
    dtype : type
        Specifies type of the values in the returned matrix.

    Returns
    -------
    coo_matrix
        A COO matrix with approximately the nonzero density desired.
    """
    assert len(shape) == 2, f"shape must be a size 2 tuple but {shape} was given"

    nrows, ncols = shape

    nnz = int(nrows * ncols * density_ratio)

    data = np.ones(nnz, dtype=dtype)
    rows = np.random.randint(0, nrows, nnz)
    cols = np.random.randint(0, ncols, nnz)

    coo = coo_matrix((data, (rows, cols)), shape=shape)

    # get rid of dup rows/cols
    coo.sum_duplicates()

    return coo


def sparse_subinds(orig, inds):
    """
    Compute new rows or cols resulting from applying inds on top of an existing sparsity pattern.

    This only comes into play when we have an approx total jacobian where some dv/resp have
    indices.

    Parameters
    ----------
    orig : ndarray
        Either row or col indices (part of a subjac sparsity pattern).
    inds : ndarray or list
        Sub-indices introduced when adding a desvar or response.

    Returns
    -------
    ndarray
        New compressed rows or cols.
    ndarray
        Mask array that can be used to update subjac value and corresponding index array to orig.
    """
    mask = np.zeros(orig.size, dtype=bool)
    for i in inds:
        mask |= orig == i
    newsp = orig[mask]

    # replace the index with the 'compressed' index after we've masked out entries
    for r, i in enumerate(np.sort(inds)):
        newsp[newsp == i] = r

    return newsp, mask


def identity_column_iter(column):
    """
    Yield the given column with a 1 in each position.

    This is useful if you don't want to allocate memory for the full sized identity matrix.
    Note that this reuses the column array and assumes that the column array has not
    been modified outside of this function.

    Parameters
    ----------
    column : ndarray
        The array that will contain a column of the 'virtual' identity matrix.

    Yields
    ------
    ndarray
        A column of the identity matrix.
    """
    column[:] = 0
    for i in range(column.size):
        column[i - 1] = 0
        column[i] = 1
        yield column
