"""
(C) Steven Byrnes, 2014-2016. This code is released under the MIT license
http://opensource.org/licenses/MIT

This code runs in Python 2.7 or 3.3. It requires imagemagick to be installed;
that's how it assembles images into animated GIFs.
"""

from __future__ import division

import pygame as pg
from numpy import cos, pi, sin, linspace

import subprocess, os
directory_now = os.path.dirname(os.path.realpath(__file__))

frames_in_anim = 100
animation_loop_seconds = 5 #time in seconds for animation to loop one cycle

bgcolor = (255,255,255) #background is white
ecolor = (0,0,0) #electrons are black
wire_color = (200,200,200) # wire color is light gray
arrow_color = (140,0,0)

# pygame draws pixel-art, not smoothed. Therefore I am drawing it
# bigger, then smoothly shrinking it down
img_height = 180
img_width = 900
final_height = 60
final_width = 300

# ~23 megapixel limit for wikipedia animated gifs
assert final_height * final_width * frames_in_anim < 22e6

#transmission line thickness, and y-coordinate of the top of each wire
tl_thickness = 27
tl_top_y = 40
tl_bot_y = img_height - tl_top_y - tl_thickness + 2

wavelength = 1.1 * img_width

e_radius = 4

# dimensions of triangular arrow head (this is for the longest arrows; it's
# scaled down when the arrow is too small)
arrowhead_base = 9
arrowhead_height = 15
# width of the arrow line
arrow_width = 6

# number of electrons spread out over the transmission line (top plus bottom)
num_electrons = 100
# max_e_displacement is defined here as a multiple of the total electron path length
# (roughly twice the width of the image, because we're adding top + bottom)
max_e_displacement = 1/60

num_arrows = 20
max_arrow_halflength = 22

def tup_round(tup):
    """round each element of a tuple to nearest integer"""
    return tuple(int(round(x)) for x in tup)

def draw_arrow(surf, x, tail_y, head_y):
    """
    draw a vertical arrow. Coordinates do not need to be integers
    """
    # calculate dimensions of the triangle; it's scaled down for short arrows
    if abs(head_y - tail_y) >= 1.5 * arrowhead_height:
        h = arrowhead_height
        b = arrowhead_base
    else:
        h = abs(head_y - tail_y) / 1.5
        b = arrowhead_base * h / arrowhead_height

    if tail_y < head_y:
        # downward arrow
        triangle = [tup_round((x, head_y)),
                    tup_round((x - b, head_y - h)),
                    tup_round((x + b, head_y - h))]
        triangle_middle_y = head_y - h/2
    else:
        # upward arrow
        triangle = [tup_round((x, head_y)),
                    tup_round((x - b, head_y + h)),
                    tup_round((x + b, head_y + h))]
        triangle_middle_y = head_y + h/2
    pg.draw.line(surf, arrow_color, tup_round((x, tail_y)), tup_round((x, triangle_middle_y)), arrow_width)
    pg.draw.polygon(surf, arrow_color, triangle, 0)

def e_path(param, phase_top_left):
    """
    as param goes 0 to 1, this returns {'pos': (x, y), 'phase':phi},
    where (x,y) is the coordinates of the corresponding point on the electron
    dot path, and phi is the phase for an electron at that point on the path.
    phase_top_left is phase of the left side of the top wire.
    """
    # d is a vertical offset between the electrons and the wires
    d = tl_thickness - e_radius - 2
    # pad is how far to extend the transmission line beyond the image borders
    # (since those electrons may enter the image a bit)
    pad = 36
    path_length = 2*(img_width + 2*pad)
    howfar = param * path_length

    # move right across top transmission line
    if howfar <= path_length / 2:
        x = howfar - pad
        y = tl_top_y + d
        phase = phase_top_left + 2 * pi * x / wavelength
        return {'pos':(x,y), 'phase':phase}
    # ...then move left across the bottom transmission line
    x = path_length - howfar - pad
    y = tl_bot_y + tl_thickness - d
    phase = phase_top_left + 2 * pi * x / wavelength
    return {'pos':(x,y), 'phase':phase}

def main():
    #Make and save a drawing for each frame
    filename_list = [os.path.join(directory_now, 'temp' + str(n) + '.png')
                         for n in range(frames_in_anim)]

    for frame in range(frames_in_anim):
        phase_top_left = -2 * pi * frame / frames_in_anim

        #initialize surface
        surf = pg.Surface((img_width,img_height))
        surf.fill(bgcolor);

        #draw transmission line
        pg.draw.rect(surf, wire_color, [0, tl_top_y, img_width, tl_thickness])
        pg.draw.rect(surf, wire_color, [0, tl_bot_y, img_width, tl_thickness])

        #draw electrons. Remember, "param" is an abstract coordinate that goes
        #from 0 to 1 as the electron position goes right across the top wire
        #then left across the bottom wire
        equilibrium_params = linspace(0, 1, num=num_electrons)
        phases = [e_path(a, phase_top_left)['phase'] for a in equilibrium_params]
        now_params = [equilibrium_params[i] + sin(phases[i]) * max_e_displacement
                           for i in range(num_electrons)]
        coords = [e_path(a, phase_top_left)['pos'] for a in now_params]
        for coord in coords:
            pg.draw.circle(surf, ecolor, tup_round(coord), e_radius)

        #draw arrows
        arrow_params = linspace(0, 0.5, num=num_arrows)
        for i in range(len(arrow_params)):
            a = arrow_params[i]
            arrow_x = e_path(a, phase_top_left)['pos'][0]
            arrow_phase = e_path(a, phase_top_left)['phase']
            head_y = img_height/2 + max_arrow_halflength * cos(arrow_phase)
            tail_y = img_height/2 - max_arrow_halflength * cos(arrow_phase)
            draw_arrow(surf, arrow_x, tail_y, head_y)

        #shrink the surface to its final size, and save it
        shrunk_surface = pg.transform.smoothscale(surf, (final_width, final_height))
        pg.image.save(shrunk_surface, filename_list[frame])

    seconds_per_frame = animation_loop_seconds / frames_in_anim
    frame_delay = str(int(seconds_per_frame * 100))
    # Use the "convert" command (part of ImageMagick) to build the animation
    command_list = ['convert', '-delay', frame_delay, '-loop', '0'] + filename_list + ['anim.gif']
    subprocess.call(command_list, cwd=directory_now)
    # Earlier, we saved an image file for each frame of the animation. Now
    # that the animation is assembled, we can (optionally) delete those files
    if True:
        for filename in filename_list:
            os.remove(filename)

main()