from matplotlib import pyplot as plt
import numpy as np
from matplotlib.animation import FuncAnimation

# graphing parameters

font = {'size':16}
fig,ax = plt.subplots()
plt.rcParams['savefig.facecolor'] = '#c0c0c0'
plt.rc('font', **font)
marker_style = dict(linestyle = 'none', markersize = 10, markeredgecolor = 'k')
ax.set_aspect(1)
(min_plot, max_plot) = (0, 10)
bar_extent = 0.4
height_above_bar = 0.4

# input data

left_points = [1, 3]
right_points = [6, 6.5, 8.3]
divisions = (3.7, 4.5, 5.2)

def slope(point):
	if point<divisions[1]:
		slope = 1/(point - max(left_points))
	else:
		slope = 1/(min(right_points) - point)
	return slope

# get handles to animated features

plane, = ax.plot((min_plot, max_plot),
	(slope(divisions[0])*(min_plot - divisions[0]), slope(divisions[0])*(max_plot - divisions[0])),
	lw = 3, color = ('0.5'), zorder = -1)
ann1 = ax.annotate('', xy = (divisions[0], -bar_extent), xytext = (divisions[0], bar_extent),
		arrowprops = {'arrowstyle':'-', 'lw':5, 'color':'0.5'},
		va = 'center', zorder = -1)
ann2 = ax.annotate('A', xy = (0, 0), xytext = (divisions[0], bar_extent + height_above_bar),
		ha = 'center', va = 'center', zorder = -1)
ann1.set_animated(True)
ann2.set_animated(True)

# arrange the static features and axes

ax.plot([max(left_points)] + [min(right_points)],(-1,1), marker="o", linestyle = 'none', markersize = 25, markerfacecolor = 'None', markeredgecolor = 'k')
ax.annotate('', xy = (max_plot, 0), xytext = (-.05, 0),
	arrowprops = {'arrowstyle':'->', 'lw':1, 'facecolor':'k'},
	va = 'center', zorder = -1) 
ax.annotate('$x$', xy = (0, 0), xytext = (max_plot + 0.2, 0), va = 'center') 
ax.annotate('$y$', xy = (0, 0), xytext = (0, 2), ha = 'center') 
ax.annotate('', xy = (0, 1.7), xytext = (0, -1.7),
	arrowprops = {'arrowstyle':'<->', 'lw':1, 'facecolor':'k'},
	va = 'center')
plt.box(on = None)
ax.spines['bottom'].set_position('zero')
ax.spines['bottom'].set_color('none')
ax.spines['left'].set_position('zero')
ax.spines['left'].set_color('none')
ax.spines['left'].set_linewidth(1)
ax.spines['bottom'].set_linewidth(1)
plt.xticks(np.arange(2, 9, 2), fontsize = 10)
plt.yticks(np.arange(-1, 2, 1), fontsize = 10)
ax.plot(left_points, np.zeros(len(left_points)) - 1, marker = "^",
	markerfacecolor = 'red', **marker_style)
ax.plot(right_points,np.zeros(len(right_points)) + 1, marker = "s",
	markerfacecolor = 'blue', **marker_style)
plt.xlim([-1, 11])
plt.ylim([-2.3, 2.7])

# set animation parameters, initial states, and expected motion paths

frame_number = 50
darken_margin = 0.1

def init():
	return plane, ann1, ann2

def update(i):
	point = divisions[2] - abs(frame_number/2 - i)/(frame_number/2)*(divisions[2] - divisions[0])
	plane.set_ydata((slope(point)*(0 - point), slope(point)*(10 - point)))
	plane.set_color('k' if abs(point - divisions[1]) < darken_margin else '0.5')
	ann1.set_position((point, bar_extent))
	ann1.xy = (point, -bar_extent)
	ann1.arrow_patch.set_color('k' if abs(point - divisions[1]) < darken_margin else '0.5')
	ann2_text = 'B' if abs(point - divisions[1]) < darken_margin else ('A' if abs(point - divisions[0]) < darken_margin
	 else ('C' if abs(point - divisions[2]) < darken_margin else ''))
	ann2.set_text(ann2_text)
	ann2.set_position((point, bar_extent + height_above_bar))
	ann2.set_color('k' if abs(point - divisions[1]) < darken_margin else '0.5')
	return plane, ann1, ann2

# implement the animation and save the results

anim = FuncAnimation(fig, update, frames = np.arange(0, frame_number),interval = 100, init_func = init, blit = True)
anim.save('graph.gif', dpi = 200, writer = 'imagemagick')
plt.show()