import numpy as np

from matplotlib.widgets import PolygonSelector
from matplotlib.path import Path


class SelectFromCollection:
  """
  Select indices from a matplotlib collection using `PolygonSelector`.

  Selected indices are saved in the `ind` attribute. This tool fades out the
  points that are not part of the selection (i.e., reduces their alpha
  values). If your collection has alpha < 1, this tool will permanently
  alter the alpha values.

  Note that this tool selects collection objects based on their *origins*
  (i.e., `offsets`).

  Parameters
  ----------
  ax : `~matplotlib.axes.Axes`
    Axes to interact with.
  collection : `matplotlib.collections.Collection` subclass
    Collection you want to select from.
  alpha_other : 0 <= float <= 1
    To highlight a selection, this tool sets all selected points to an
    alpha value of 1 and non-selected points to *alpha_other*.
  """

  def __init__(self, ax, collection, alpha_other=0.3):
    self.canvas = ax.figure.canvas
    self.collection = collection
    self.alpha_other = alpha_other

    self.xys = collection.get_offsets()
    self.Npts = len(self.xys)

    # Ensure that we have separate colors for each object
    self.fc = collection.get_facecolors()
    if len(self.fc) == 0:
      raise ValueError('Collection must have a facecolor')
    elif len(self.fc) == 1:
      self.fc = np.tile(self.fc, (self.Npts, 1))

    self.poly = PolygonSelector(ax, self.onselect)
    self.ind = []

  def onselect(self, verts):
    path = Path(verts)
    self.ind = np.nonzero(path.contains_points(self.xys))[0]
    self.fc[:, -1] = self.alpha_other
    self.fc[self.ind, -1] = 1
    self.collection.set_facecolors(self.fc)
    self.canvas.draw_idle()

  def disconnect(self):
    self.poly.disconnect_events()
    self.fc[:, -1] = 1
    self.collection.set_facecolors(self.fc)
    self.canvas.draw_idle()


if __name__ == '__main__':
  import matplotlib.pyplot as plt

  fig, ax = plt.subplots()
  grid_size = 5
  grid_x = np.tile(np.arange(grid_size), grid_size)
  grid_y = np.repeat(np.arange(grid_size), grid_size)
  pts = ax.scatter(grid_x, grid_y)

  selector = SelectFromCollection(ax, pts)

  print("Select points in the figure by enclosing them within a polygon.")
  print("Press the 'esc' key to start a new polygon.")
  print("Try holding the 'shift' key to move all of the vertices.")
  print("Try holding the 'ctrl' key to move a single vertex.")

  plt.show()

  selector.disconnect()

  # After figure is closed print the coordinates of the selected points
  print('\nSelected points:')
  print(selector.xys[selector.ind])