"""
Generate base anchors on index 0
"""
from __future__ import print_function
import sys
import numpy as np

def anchors_plane(height, width, stride, base_anchors):
    """
    Parameters
    ----------
    height: height of plane
    width:  width of plane
    stride: stride ot the original image
    anchors_base: (A, 4) a base set of anchors
    Returns
    -------
    all_anchors: (height, width, A, 4) ndarray of anchors spreading over the plane
    """
    A = base_anchors.shape[0]
    all_anchors = np.zeros((height, width, A, 4), dtype=int)
    iw = 0
    ih = 0
    k = 0
    sh = 0
    sw = 0
    for iw in range(width):
        sw = iw * stride
        for ih in range(height):
            sh = ih * stride
            for k in range(A):
                all_anchors[ih, iw, k, 0] = base_anchors[k, 0] + sw
                all_anchors[ih, iw, k, 1] = base_anchors[k, 1] + sh
                all_anchors[ih, iw, k, 2] = base_anchors[k, 2] + sw
                all_anchors[ih, iw, k, 3] = base_anchors[k, 3] + sh
    return all_anchors    

def generate_anchors(base_size=16, ratios=[0.5, 1, 2],
                     scales=2 ** np.arange(3, 6), stride=16, dense_anchor=False):
    """
    Generate anchor (reference) windows by enumerating aspect ratios X
    scales wrt a reference (0, 0, 15, 15) window.
    """

    base_anchor = np.array([1, 1, base_size, base_size]) - 1
    ratio_anchors = _ratio_enum(base_anchor, ratios)
    anchors = np.vstack([_scale_enum(ratio_anchors[i, :], scales)
                         for i in range(ratio_anchors.shape[0])])
    if dense_anchor:
      assert stride%2==0
      anchors2 = anchors.copy()
      anchors2[:,:] += int(stride/2)
      anchors = np.vstack( (anchors, anchors2) )
    #print('GA',base_anchor.shape, ratio_anchors.shape, anchors.shape)
    return anchors

def generate_anchors_fpn(cfg, dense_anchor=False):
    #assert(False)
    """
    Generate anchor (reference) windows by enumerating aspect ratios X
    scales wrt a reference (0, 0, 15, 15) window.
    """
    RPN_FEAT_STRIDE = []
    for k in cfg:
      RPN_FEAT_STRIDE.append( int(k) )
    RPN_FEAT_STRIDE = sorted(RPN_FEAT_STRIDE, reverse=True)
    anchors = []
    for k in RPN_FEAT_STRIDE:
      v = cfg[str(k)]
      bs = v['BASE_SIZE']
      __ratios = np.array(v['RATIOS'])
      __scales = np.array(v['SCALES'])
      stride = int(k)
      #print('anchors_fpn', bs, __ratios, __scales, file=sys.stderr)
      r = generate_anchors(bs, __ratios, __scales, stride, dense_anchor)
      #print('anchors_fpn', r.shape, file=sys.stderr)
      anchors.append(r)

    return anchors

def _whctrs(anchor):
    """
    Return width, height, x center, and y center for an anchor (window).
    """

    w = anchor[2] - anchor[0] + 1
    h = anchor[3] - anchor[1] + 1
    x_ctr = anchor[0] + 0.5 * (w - 1)
    y_ctr = anchor[1] + 0.5 * (h - 1)
    return w, h, x_ctr, y_ctr


def _mkanchors(ws, hs, x_ctr, y_ctr):
    """
    Given a vector of widths (ws) and heights (hs) around a center
    (x_ctr, y_ctr), output a set of anchors (windows).
    """

    ws = ws[:, np.newaxis]
    hs = hs[:, np.newaxis]
    anchors = np.hstack((x_ctr - 0.5 * (ws - 1),
                         y_ctr - 0.5 * (hs - 1),
                         x_ctr + 0.5 * (ws - 1),
                         y_ctr + 0.5 * (hs - 1)))
    return anchors


def _ratio_enum(anchor, ratios):
    """
    Enumerate a set of anchors for each aspect ratio wrt an anchor.
    """

    w, h, x_ctr, y_ctr = _whctrs(anchor)
    size = w * h
    size_ratios = size / ratios
    ws = np.round(np.sqrt(size_ratios))
    hs = np.round(ws * ratios)
    anchors = _mkanchors(ws, hs, x_ctr, y_ctr)
    return anchors


def _scale_enum(anchor, scales):
    """
    Enumerate a set of anchors for each scale wrt an anchor.
    """

    w, h, x_ctr, y_ctr = _whctrs(anchor)
    ws = w * scales
    hs = h * scales
    anchors = _mkanchors(ws, hs, x_ctr, y_ctr)
    return anchors
