#!/usr/bin/env python3
#
# Draw a circle surrounded by other circles
#
# Copyright (C) 2018  Antonio Ospite <ao2@ao2.it>
# SPDX-License-Identifier: WTFPL
#
# Using a formula from:
# https://math.stackexchange.com/questions/12166/numbers-of-circles-around-a-circle

from math import pi, sin, cos, degrees
import svgwrite


def calc_inner_circle_radius(outer_circles_radius, number_of_circles):
    if outer_circles_radius <= 0:
        raise ValueError("Radius of outer circles cannot be zero")

    if number_of_circles < 3:
        raise ValueError("Number of outer circles cannot be smaller than 3")

    # Ratio between the inner circle and the outer circles
    ratio = sin(pi / number_of_circles) / (1 - sin(pi / number_of_circles))

    inner_circle_radius = outer_circles_radius / ratio

    return inner_circle_radius


def write_svg(filename, inner_circle_radius, outer_circles_radius,
              number_of_circles, unit=""):
    border = 10

    width = height = (inner_circle_radius + outer_circles_radius + border) * 2

    svg = svgwrite.Drawing(filename, profile='full',
                           size=(str(width) + unit, str(height) + unit),
                           viewBox=('0 0 %g %g') % (width, height))

    cx_inner = cy_inner = width / 2

    inner_circle = svgwrite.shapes.Circle(center=(cx_inner, cy_inner),
                                          r=inner_circle_radius,
                                          fill='none',
                                          stroke='black',
                                          stroke_width=0.5)
    svg.add(inner_circle)

    # Add a group for the first outer circle for extra flexibility.
    outer_circle_group = svgwrite.container.Group()
    svg.add(outer_circle_group)

    cx_outer = cx_inner + sin(0) * (inner_circle_radius +
                                    outer_circles_radius)
    cy_outer = cy_inner + cos(0) * (inner_circle_radius +
                                    outer_circles_radius)
    outer_circle = svgwrite.shapes.Circle(center=(cx_outer, cy_outer),
                                          r=outer_circles_radius,
                                          fill='none',
                                          stroke='black',
                                          stroke_width=0.5)
    outer_circle_group.add(outer_circle)

    # Clone the group for the other outer circles to make it easier to keep
    # visual symmetry by editing just the first group added above.
    for i in range(1, number_of_circles):
        theta = i * 2 * pi / number_of_circles
        outer_circle_clone = svgwrite.container.Use(outer_circle_group,
                                                    insert=(0, 0),
                                                    transform="rotate(%f, %f, %f)" %
                                                    (degrees(theta),
                                                     cx_inner,
                                                     cy_inner))
        svg.add(outer_circle_clone)

    svg.save()


def main():
    outer_circles_radius = 2.5
    number_of_circles = 22

    inner_circle_radius = calc_inner_circle_radius(outer_circles_radius, number_of_circles)

    write_svg("circle-surrounded-by-circles.svg", inner_circle_radius,
              outer_circles_radius, number_of_circles, unit="mm")


if __name__ == "__main__":
    main()