#draw_map.py: draw a rectilinear world map and save it to output.png

#Consult https://tools.ietf.org/html/rfc7946 for a specification of several of the types used here

import shapefile        #https://pypi.org/project/pyshp/
from PIL import Image, ImageDraw

#downloaded/unzipped from https://www.naturalearthdata.com/downloads/110m-cultural-vectors/, "Admin 0 - Countries" -> "Download Countries"
SHAPEFILE_PATH = "res/ne_110m_admin_0_countries/ne_110m_admin_0_countries.shp"

def to_screen_coords(p):
    """convert from lat/long to pixel coordinates using a sensible projection."""
    #1:1 rectilinear projection sure is easy
    return (p[0] + 180, -p[1] + 90)

def render_poly(seq):
    """render an RFC7946 Polygon instance."""
    #polygons can have multiple independent boundaries (for example, if it's a donut shape), so for wireframe renderings you can think of it more like a collection of polygons
    for linear_ring in seq:
        for idx, p1 in enumerate(linear_ring[:-1]):
            p2 = linear_ring[idx+1]
            coords = (to_screen_coords(p1), to_screen_coords(p2))
            draw.line(coords, fill="black")

image = Image.new("RGB", (260, 180), "white")
draw = ImageDraw.Draw(image)

with shapefile.Reader(SHAPEFILE_PATH) as sf:
    for shape_rec in sf:
        #convert to RFC7946 GeoJSON format
        shape = shape_rec.__geo_interface__

        coords = shape["geometry"]["coordinates"]
        t = shape["geometry"]["type"]

        #handle all geometry types described at https://tools.ietf.org/html/rfc7946#section-3.1.1
        if t == "Point":
            raise NotImplemented #todo
        elif t == "MultiPoint":
            raise NotImplemented #todo
        elif t == "Polygon":
            render_poly(coords)
        elif t == "MultiPolygon":
            for poly in coords:
                render_poly(poly)
        elif t == "MultiLineString":
            raise Exception("I don't know what a MultiLineString even is, to be honest")
        else:
            raise Exception(f"Unknown geometry type {t}")

image.save("output.png")