# t_fireflies.py

# t_fireflies.py

import turtle
import colorsys
import random
import math

screen = turtle.Screen()
screen.setup(500,500)
screen.title("Fireflies")
turtle.hideturtle()
turtle.speed(0)
turtle.tracer(0,0)

# Constants
H_YELLOWGREEN = 0.22 # constant: hue value of yellow green color.
V_DARK = 0.1 # constant: brightness value of initial dark state
V_BRIGHT = 1 # constant: brightness value of the brightest state
FPS = 30 # constant: refresh about 30 times per second
TIMER_VALUE = 1000//FPS # the timer value in milliseconds for timer events
LIGHTUP_TIME = 1 # constant: 1 second light up and dim
SPEED = 20 # 100 units per second
CLOSE_ENOUGH = 16 # if distance squared to target is less than 16, then it is close enough.
                    # make sure that this number is greater than SPEED/FPS squared
N = 100 # Number of fireflies

# Variables
fireflies = [] # list of firefly turtles
v = [] # list of brightness values
glow = [float(str(z*0.01)[:4]) for z in range(0,100,5)]
glow += [1]+glow[::-1]
CYCLE = len(glow) # costant: cycle for firefly to light up
phase = [] # list of phases
current_xpos = [] # list of current x coordinate
current_ypos = [] # list of current y coordinate
target_xpos = [] # list of target x coordinate
target_ypos = [] # list of target y coordinate

if 1: # initialze_fireflies
    for i in range(N):
        fireflies.append(turtle.Turtle()) # Add a turtle to the firefly turtle list
        v.append(V_DARK) # set them DARK first. The update function will update it to the correct value
        phase.append(random.randint(0,CYCLE)) # phase is random from 0 to CYCLE
        current_xpos.append(random.uniform(-210,210)) # Let them go anywhere on screen
        current_ypos.append(random.uniform(-210,210))
        target_xpos.append(random.uniform(-210,210))
        target_ypos.append(random.uniform(-210,210))

    for firefly in fireflies: # initialize these turtles
        firefly.hideturtle()
        firefly.up()

# this function computes brightness based on phase

def update_brightness():
    global phase,v
    for i in range(N):
        phase[i] = (phase[i]+1)%CYCLE # increase the phase
        v[i] = glow[phase[i]] # compute the brightness based on phase

def update_position():
    global current_xpos,current_ypos,target_xpos,target_ypos
    for i in range(N):
        # move towards target steps
        # figure out angle to target first
        angle_to_target = math.atan2(target_ypos[i]-current_ypos[i],target_xpos[i]-current_xpos[i])
        # compute changes to current position based on the angle and distance to move.
        current_xpos[i] += 5*math.cos(angle_to_target)
        current_ypos[i] += 5*math.sin(angle_to_target)
        # check to see if close enough to target.
        dist_to_target_squared = (current_xpos[i]-target_xpos[i])**2 + (current_ypos[i]-target_ypos[i])**2
        if dist_to_target_squared < CLOSE_ENOUGH: # close enough, set new target
            target_xpos[i] = random.randint(-210,210) # target x coordinate, random location
            target_ypos[i] = random.randint(-210,210) # target y coordinate, random location

def draw():
    global v,fireflies,current_xpos,current_ypos
    for i in range(N):
        fireflies[i].clear() # clear the current drawing
        color = colorsys.hsv_to_rgb(H_YELLOWGREEN,1,v[i]) # use colorsys to convert HSV to RGB color
        fireflies[i].color(color)
        fireflies[i].goto(current_xpos[i],current_ypos[i])
        fireflies[i].dot(10)

screen.bgcolor('black')
while True:
    update_brightness()
    update_position()
    draw() # draw forever
    screen.update()