#                       Data Parallel Control (dpctl)
#
#  Copyright 2020-2021 Intel Corporation
#
#  Licensed under the Apache License, Version 2.0 (the "License");
#  you may not use this file except in compliance with the License.
#  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
#  Unless required by applicable law or agreed to in writing, software
#  distributed under the License is distributed on an "AS IS" BASIS,
#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#  See the License for the specific language governing permissions and
#  limitations under the License.
import operator

import numpy as np

import dpctl.memory as dpm
import dpctl.tensor as dpt


def contract_iter2(shape, strides1, strides2):
    p = np.argsort(np.abs(strides1))[::-1]
    sh = [operator.index(shape[i]) for i in p]
    disp1 = 0
    disp2 = 0
    st1 = []
    st2 = []
    contractable = True
    for i in p:
        this_stride1 = operator.index(strides1[i])
        this_stride2 = operator.index(strides2[i])
        if this_stride1 < 0 and this_stride2 < 0:
            disp1 += this_stride1 * (shape[i] - 1)
            this_stride1 = -this_stride1
            disp2 += this_stride2 * (shape[i] - 1)
            this_stride2 = -this_stride2
        if this_stride1 < 0 or this_stride2 < 0:
            contractable = False
        st1.append(this_stride1)
        st2.append(this_stride2)
    while contractable:
        changed = False
        k = len(sh) - 1
        for i in range(k):
            step1 = st1[i + 1]
            jump1 = st1[i] - (sh[i + 1] - 1) * step1
            step2 = st2[i + 1]
            jump2 = st2[i] - (sh[i + 1] - 1) * step2
            if jump1 == step1 and jump2 == step2:
                changed = True
                st1[i:-1] = st1[i + 1 :]
                st2[i:-1] = st2[i + 1 :]
                sh[i] *= sh[i + 1]
                sh[i + 1 : -1] = sh[i + 2 :]
                sh = sh[:-1]
                st1 = st1[:-1]
                st2 = st2[:-1]
                break
        if not changed:
            break
    return (sh, st1, disp1, st2, disp2)


def has_memory_overlap(x1, x2):
    m1 = dpm.as_usm_memory(x1)
    m2 = dpm.as_usm_memory(x2)
    if m1.sycl_device == m2.sycl_device:
        p1_beg = m1._pointer
        p1_end = p1_beg + m1.nbytes
        p2_beg = m2._pointer
        p2_end = p2_beg + m2.nbytes
        return p1_beg > p2_end or p2_beg < p1_end
    else:
        return False


def copy_to_numpy(ary):
    if type(ary) is not dpt.usm_ndarray:
        raise TypeError
    h = ary.usm_data.copy_to_host().view(ary.dtype)
    itsz = ary.itemsize
    strides_bytes = tuple(si * itsz for si in ary.strides)
    offset = ary.__sycl_usm_array_interface__.get("offset", 0) * itsz
    return np.ndarray(
        ary.shape,
        dtype=ary.dtype,
        buffer=h,
        strides=strides_bytes,
        offset=offset,
    )


def copy_from_numpy(np_ary, usm_type="device", queue=None):
    "Copies numpy array `np_ary` into a new usm_ndarray"
    # This may peform a copy to meet stated requirements
    Xnp = np.require(np_ary, requirements=["A", "O", "C", "E"])
    if queue:
        ctor_kwargs = {"queue": queue}
    else:
        ctor_kwargs = dict()
    Xusm = dpt.usm_ndarray(
        Xnp.shape,
        dtype=Xnp.dtype,
        buffer=usm_type,
        buffer_ctor_kwargs=ctor_kwargs,
    )
    Xusm.usm_data.copy_from_host(Xnp.reshape((-1)).view("u1"))
    return Xusm


def copy_from_numpy_into(dst, np_ary):
    if not isinstance(np_ary, np.ndarray):
        raise TypeError("Expected numpy.ndarray, got {}".format(type(np_ary)))
    src_ary = np.broadcast_to(np.asarray(np_ary, dtype=dst.dtype), dst.shape)
    for i in range(dst.size):
        mi = np.unravel_index(i, dst.shape)
        host_buf = np.array(src_ary[mi], ndmin=1).view("u1")
        usm_mem = dpm.as_usm_memory(dst[mi])
        usm_mem.copy_from_host(host_buf)


class Dummy:
    def __init__(self, iface):
        self.__sycl_usm_array_interface__ = iface


def copy_same_dtype(dst, src):
    if type(dst) is not dpt.usm_ndarray or type(src) is not dpt.usm_ndarray:
        raise TypeError

    if dst.shape != src.shape:
        raise ValueError

    if dst.dtype != src.dtype:
        raise ValueError

    # check that memory regions do not overlap
    if has_memory_overlap(dst, src):
        tmp = copy_to_numpy(src)
        copy_from_numpy_into(dst, tmp)
        return

    if (dst.flags & 1) and (src.flags & 1):
        dst_mem = dpm.as_usm_memory(dst)
        src_mem = dpm.as_usm_memory(src)
        dst_mem.copy_from_device(src_mem)
        return

    # simplify strides
    sh_i, dst_st, dst_disp, src_st, src_disp = contract_iter2(
        dst.shape, dst.strides, src.strides
    )
    # sh_i, dst_st, dst_disp, src_st, src_disp = (
    #    dst.shape, dst.strides, 0, src.strides, 0
    # )
    src_iface = src.__sycl_usm_array_interface__
    dst_iface = dst.__sycl_usm_array_interface__
    src_iface["shape"] = tuple()
    src_iface.pop("strides", None)
    dst_iface["shape"] = tuple()
    dst_iface.pop("strides", None)
    dst_disp = dst_disp + dst_iface.get("offset", 0)
    src_disp = src_disp + src_iface.get("offset", 0)
    for i in range(dst.size):
        mi = np.unravel_index(i, sh_i)
        dst_offset = dst_disp
        src_offset = src_disp
        for j, dst_stj, src_stj in zip(mi, dst_st, src_st):
            dst_offset = dst_offset + j * dst_stj
            src_offset = src_offset + j * src_stj
        dst_iface["offset"] = dst_offset
        src_iface["offset"] = src_offset
        msrc = dpm.as_usm_memory(Dummy(src_iface))
        mdst = dpm.as_usm_memory(Dummy(dst_iface))
        mdst.copy_from_device(msrc)


def copy_same_shape(dst, src):
    if src.dtype == dst.dtype:
        copy_same_dtype(dst, src)

    # check that memory regions do not overlap
    if has_memory_overlap(dst, src):
        tmp = copy_to_numpy(src)
        tmp = tmp.astype(dst.dtype)
        copy_from_numpy_into(dst, tmp)
        return

    # simplify strides
    sh_i, dst_st, dst_disp, src_st, src_disp = contract_iter2(
        dst.shape, dst.strides, src.strides
    )
    # sh_i, dst_st, dst_disp, src_st, src_disp = (
    #    dst.shape, dst.strides, 0, src.strides, 0
    # )
    src_iface = src.__sycl_usm_array_interface__
    dst_iface = dst.__sycl_usm_array_interface__
    src_iface["shape"] = tuple()
    src_iface.pop("strides", None)
    dst_iface["shape"] = tuple()
    dst_iface.pop("strides", None)
    dst_disp = dst_disp + dst_iface.get("offset", 0)
    src_disp = src_disp + src_iface.get("offset", 0)
    for i in range(dst.size):
        mi = np.unravel_index(i, sh_i)
        dst_offset = dst_disp
        src_offset = src_disp
        for j, dst_stj, src_stj in zip(mi, dst_st, src_st):
            dst_offset = dst_offset + j * dst_stj
            src_offset = src_offset + j * src_stj
        dst_iface["offset"] = dst_offset
        src_iface["offset"] = src_offset
        msrc = dpm.as_usm_memory(Dummy(src_iface))
        mdst = dpm.as_usm_memory(Dummy(dst_iface))
        tmp = msrc.copy_to_host().view(src.dtype)
        tmp = tmp.astype(dst.dtype)
        mdst.copy_from_host(tmp.view("u1"))


def copy_from_usm_ndarray_to_usm_ndarray(dst, src):
    if type(dst) is not dpt.usm_ndarray or type(src) is not dpt.usm_ndarray:
        raise TypeError

    if dst.ndim == src.ndim and dst.shape == src.shape:
        copy_same_shape(dst, src)

    try:
        common_shape = np.broadcast_shapes(dst.shape, src.shape)
    except ValueError:
        raise ValueError

    if dst.size < src.size:
        raise ValueError

    if len(common_shape) > dst.ndim:
        ones_count = len(common_shape) - dst.ndim
        for k in range(ones_count):
            if common_shape[k] != 1:
                raise ValueError
        common_shape = common_shape[ones_count:]

    if src.ndim < len(common_shape):
        new_src_strides = (0,) * (len(common_shape) - src.ndim) + src.strides
        src_same_shape = dpt.usm_ndarray(
            common_shape, dtype=src.dtype, buffer=src, strides=new_src_strides
        )
    else:
        src_same_shape = src

    copy_same_shape(dst, src_same_shape)


def astype(usm_ary, newdtype, order="K", casting="unsafe", copy=True):
    """
    astype(usm_array, new_dtype, order="K", casting="unsafe", copy=True)

    Returns a copy of the array, cast to a specified type.

    A view can be returned, if possible, when `copy=False` is used.
    """
    if not isinstance(usm_ary, dpt.usm_ndarray):
        return TypeError(
            "Expected object of type dpt.usm_ndarray, got {}".format(
                type(usm_ary)
            )
        )
    ary_dtype = usm_ary.dtype
    target_dtype = np.dtype(newdtype)
    if not np.can_cast(ary_dtype, target_dtype, casting=casting):
        raise TypeError(
            "Can not cast from {} to {} according to rule {}".format(
                ary_dtype, newdtype, casting
            )
        )
    c_contig = usm_ary.flags & 1
    f_contig = usm_ary.flags & 2
    needs_copy = copy or not (ary_dtype == target_dtype)
    if not needs_copy and (order != "K"):
        needs_copy = (c_contig and order not in ["A", "C"]) or (
            f_contig and order not in ["A", "F"]
        )
    if needs_copy:
        copy_order = "C"
        if order == "C":
            pass
        elif order == "F":
            copy_order = order
        elif order == "A":
            if usm_ary.flags & 2:
                copy_order = "F"
        elif order == "K":
            if usm_ary.flags & 2:
                copy_order = "F"
        R = dpt.usm_ndarray(
            usm_ary.shape,
            dtype=target_dtype,
            buffer=usm_ary.usm_type,
            order=copy_order,
            buffer_ctor_kwargs={"queue": usm_ary.sycl_queue},
        )
        if order == "K" and (not c_contig and not f_contig):
            original_strides = usm_ary.strides
            ind = sorted(
                range(usm_ary.ndim),
                key=lambda i: abs(original_strides[i]),
                reverse=True,
            )
            new_strides = tuple(R.strides[ind[i]] for i in ind)
            R = dpt.usm_ndarray(
                usm_ary.shape,
                dtype=target_dtype,
                buffer=R.usm_data,
                strides=new_strides,
            )
        copy_from_usm_ndarray_to_usm_ndarray(R, usm_ary)
        return R
    else:
        return usm_ary
