# Copyright (c) 2017-present, Facebook, Inc.
#
# 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.
##############################################################################
#
# Based on:
# --------------------------------------------------------
# Fast R-CNN
# Copyright (c) 2015 Microsoft
# Licensed under The MIT License [see LICENSE for details]
# Written by Sergey Karayev
# --------------------------------------------------------

cimport cython
import numpy as np
cimport numpy as np

DTYPE = np.float32
ctypedef np.float32_t DTYPE_t

@cython.boundscheck(False)
def bbox_overlaps(
        np.ndarray[DTYPE_t, ndim=2] boxes,
        np.ndarray[DTYPE_t, ndim=2] query_boxes):
    """
    Parameters
    ----------
    boxes: (N, 4) ndarray of float
    query_boxes: (K, 4) ndarray of float
    Returns
    -------
    overlaps: (N, K) ndarray of overlap between boxes and query_boxes
    """
    cdef unsigned int N = boxes.shape[0]
    cdef unsigned int K = query_boxes.shape[0]
    cdef np.ndarray[DTYPE_t, ndim=2] overlaps = np.zeros((N, K), dtype=DTYPE)
    cdef DTYPE_t iw, ih, box_area
    cdef DTYPE_t ua
    cdef unsigned int k, n
    with nogil:
        for k in range(K):
            box_area = (
                (query_boxes[k, 2] - query_boxes[k, 0] + 1) *
                (query_boxes[k, 3] - query_boxes[k, 1] + 1)
            )
            for n in range(N):
                iw = (
                    min(boxes[n, 2], query_boxes[k, 2]) -
                    max(boxes[n, 0], query_boxes[k, 0]) + 1
                )
                if iw > 0:
                    ih = (
                        min(boxes[n, 3], query_boxes[k, 3]) -
                        max(boxes[n, 1], query_boxes[k, 1]) + 1
                    )
                    if ih > 0:
                        ua = float(
                            (boxes[n, 2] - boxes[n, 0] + 1) *
                            (boxes[n, 3] - boxes[n, 1] + 1) +
                            box_area - iw * ih
                        )
                        overlaps[n, k] = iw * ih / ua
    return overlaps
