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])