#! /usr/bin/env python3

"""This program demonstrates basic generation of a canvas: it makes a
list of random city coordinates, then draws them (with paths) on the
canvas.
"""

import random
import math

## we use the tkinter widget set; this seems to come automatically
## with python3 on ubuntu 16.04, but on some systems one might need to
## install a package with a name like python3-tk
from tkinter import *

canvas_width = 640
canvas_height = 480
n_cities = 25

def main():
    ## prepare a basic canvas
    root = Tk()
    w = Canvas(root, 
               width=canvas_width,
               height=canvas_height)
    w.pack()       # boiler-plate: we always call pack() on tk windows
    city_list = make_random_cities(0, canvas_width-1, 0, 
                                   canvas_height-1, n_cities)
    draw_city_path(w, city_list)
    write_info_at_bottom(w, canvas_width, canvas_height, city_list)
    mainloop()

def draw_city_path(w, city_list):
    """draws lines between the cities"""
    for city in city_list:
        draw_city(w, city[0], city[1])
    draw_city(w, city_list[0][0], city_list[0][1], color='green', name='Home')
    ## now draw lines between them
    for i in range(len(city_list)-1):
        w.create_line(city_list[i][0], city_list[i][1], 
                      city_list[i+1][0], city_list[i+1][1])
    ## now draw a line that goes from the last city back to our home
    w.create_line(city_list[-1][0], city_list[-1][1], 
                  city_list[0][0], city_list[0][1])


def make_random_cities(xmin, xmax, ymin, ymax, n_cities):
    """returns a list of randomly placed cities in the given rectangle"""
    city_list = []
    for i in range(n_cities):
        x = random.randint(xmin, xmax)
        y = random.randint(ymin, ymax)
        city_list.append((x, y))
    return city_list

def draw_city(w, x, y, color='yellow', name=None):
    """draws a city; if a name is given also writes the name of it"""
    w.create_oval(x-5, y-5, x+5, y+5, fill=color)
    ## if a name was given, write in the name
    if name:
        w.create_text(x, y+10, text=name)

def write_info_at_bottom(w, width, height, city_list):
    n_cities = len(city_list)
    total_distance = path_length(city_list)
    w.create_text(width/2, height-40, text='n_cities: %d' % n_cities, 
                  fill='red')
    w.create_text(width/2, height-20,
                  text='total_distance: %g' % total_distance, fill='red')

def distance(c1, c2):
   x1 = c1[0]
   y1 = c1[1]
   x2 = c2[0]
   y2 = c2[1]
   r = math.sqrt((x2-x1)**2 + (y2-y1)**2)
   return r

def path_length(city_list):
    total_length = 0
    for i in range(n_cities-1):   ## iterate up to the second-last city
        c1 = city_list[i]
        c2 = city_list[i+1]
        length = distance(c1, c2)
        total_length += length
    ## now add in the path length required to get back home
    total_length += distance(city_list[-1], city_list[0])
    return length

main()