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# pylint: disable=invalid-name
"""ROI pool operator"""
import tvm
from ...util import get_const_tuple

@tvm.target.generic_func
def roi_pool_nchw(data, rois, pooled_size, spatial_scale):
    """ROI pool operator in NCHW layout.

    Parameters
    ----------
    data : tvm.Tensor
        4-D with shape [batch, channel, height, width]

    rois : tvm.Tensor
        2-D with shape [num_roi, 5]. The last dimension should be in format of
        [batch_index, w_start, h_start, w_end, h_end]

    pooled_size : int or list/tuple of two ints
        output size, or [out_height, out_width]

    spatial_scale : float
        Ratio of input feature map height (or w) to raw image height (or w). Equals the reciprocal
        of total stride in convolutional layers, which should be in range (0.0, 1.0]

    Returns
    -------
    output : tvm.Tensor
        4-D with shape [num_roi, channel, pooled_size, pooled_size]
    """
    dtype = rois.dtype
    _, channel, height, width = get_const_tuple(data.shape)
    num_roi, _ = get_const_tuple(rois.shape)

    if isinstance(pooled_size, int):
        pooled_size_h = pooled_size_w = pooled_size
    else:
        pooled_size_h, pooled_size_w = pooled_size

    def _pool(i, c, ph, pw):
        roi = rois[i]
        batch_index = roi[0].astype('int32')
        roi_start_w, roi_start_h, roi_end_w, roi_end_h = roi[1], roi[2], roi[3], roi[4]

        roi_start_h = tvm.round(roi_start_h * spatial_scale).astype('int32')
        roi_start_w = tvm.round(roi_start_w * spatial_scale).astype('int32')
        roi_end_h = tvm.round(roi_end_h * spatial_scale).astype('int32')
        roi_end_w = tvm.round(roi_end_w * spatial_scale).astype('int32')

        # force malformed ROIs to be 1x1
        roi_h = tvm.max(roi_end_h - roi_start_h + 1, tvm.const(1, 'int32'))
        roi_w = tvm.max(roi_end_w - roi_start_w + 1, tvm.const(1, 'int32'))

        bin_h = roi_h.astype(dtype) / pooled_size_h
        bin_w = roi_w.astype(dtype) / pooled_size_w

        # use epsilon to prevent floating point precision loss in floor/ceil
        epsilon = tvm.const(0.00001, dtype)
        hstart = tvm.floor(ph * bin_h + epsilon).astype('int32')
        wstart = tvm.floor(pw * bin_w + epsilon).astype('int32')
        hend = tvm.ceil((ph + 1) * bin_h - epsilon).astype('int32')
        wend = tvm.ceil((pw + 1) * bin_w - epsilon).astype('int32')
        hstart = tvm.min(tvm.max(hstart + roi_start_h, 0), height)
        wstart = tvm.min(tvm.max(wstart + roi_start_w, 0), width)
        hend = tvm.min(tvm.max(hend + roi_start_h, 0), height)
        wend = tvm.min(tvm.max(wend + roi_start_w, 0), width)

        non_empty = tvm.all(hstart < hend, wstart < wend)
        min_value = lambda dtype: tvm.if_then_else(non_empty, tvm.min_value(dtype),
                                                   tvm.const(0.0, dtype))
        # pylint: disable=unnecessary-lambda
        _max = tvm.comm_reducer(lambda x, y: tvm.make._OpMax(x, y), min_value, name='max')
        rh = tvm.reduce_axis((0, hend - hstart), 'rh')
        rw = tvm.reduce_axis((0, wend - wstart), 'rw')
        return _max(data[batch_index, c, hstart+rh, wstart+rw], axis=[rh, rw])

    return tvm.compute((num_roi, channel, pooled_size_h, pooled_size_w), _pool, tag="pool,roi_pool")
