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"""Implementation of flatiter."""

import dpnp


class flatiter:
    def __init__(self, X):
        if type(X) is not dpnp.ndarray:
            raise TypeError(
                "Argument must be of type dpnp.ndarray, got {}".format(type(X))
            )
        self.arr_ = X
        self.size_ = X.size
        self.i_ = 0

    def _multiindex(self, i):
        nd = self.arr_.ndim
        if nd == 0:
            if i == 0:
                return ()
            raise KeyError
        elif nd == 1:
            return (i,)
        sh = self.arr_.shape
        i_ = i
        multi_index = [0] * nd
        for k in reversed(range(1, nd)):
            si = sh[k]
            q = i_ // si
            multi_index[k] = i_ - q * si
            i_ = q
        multi_index[0] = i_
        return tuple(multi_index)

    def __getitem__(self, key):
        idx = getattr(key, "__index__", None)
        if not callable(idx):
            raise TypeError(key)
        i = idx()
        mi = self._multiindex(i)
        return self.arr_.__getitem__(mi)

    def __setitem__(self, key, val):
        idx = getattr(key, "__index__", None)
        if not callable(idx):
            raise TypeError(key)
        i = idx()
        mi = self._multiindex(i)
        return self.arr_.__setitem__(mi, val)

    def __iter__(self):
        return self

    def __next__(self):
        if self.i_ < self.size_:
            val = self.__getitem__(self.i_)
            self.i_ = self.i_ + 1
            return val
        else:
            raise StopIteration
