#!/usr/bin/python3

import os
import urllib.request

from html.parser import HTMLParser

COMMON_PREFIX = "http://viewfinderpanoramas.org/"
COMMON_SUFFIX = ".zip"

def fetch_new_map():
    fetch_to_file(COMMON_PREFIX + "Coverage%20map%20viewfinderpanoramas_org3.htm",
                  "coverage-dem3.html")
    fetch_to_file(COMMON_PREFIX + "Coverage%20map%20viewfinderpanoramas_org1.htm",
                  "coverage-dem1.html")

def fetch_to_file(url, fname):
    if os.path.exists(fname):
        return
    req = urllib.request.urlopen(url)
    assert req.getcode() == 200, req.read()
    with open(fname, "w") as f:
        f.write(req.read().decode("utf-8"))

fetch_new_map()

class CoverageDEM3MapParser(HTMLParser):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.coords_to_link = {}
        self.image_scale = 0

    @staticmethod
    def _get_attr(attrs, attrname):
        return next(val for key, val in attrs if key == attrname)

    def handle_starttag(self, tag, attrs):
        if tag == "area":
            coordattr = self._get_attr(attrs, "coords")
            coords = tuple(int(c) for c in coordattr.split(", "))
            assert len(coords) == 4, "Unexpected tag: %s, %s" % (tag, attrs)

            link = self._get_attr(attrs, "href")
            assert link.startswith(COMMON_PREFIX)
            link = link[len(COMMON_PREFIX):]
            assert link.endswith(COMMON_SUFFIX)
            link = link[:-len(COMMON_SUFFIX)]

            self.coords_to_link[coords] = link
        if tag == "img":
            width = int(self._get_attr(attrs, "width"))
            height = int(self._get_attr(attrs, "height"))
            assert width == 2 * height
            self.image_scale = width / 360

def populate_links(fname, lats_to_link):
    parser = CoverageDEM3MapParser()
    with open(fname) as f:
        parser.feed(f.read())

    scale = parser.image_scale
    for coords in parser.coords_to_link:
        xmin, ymin, xmax, ymax = coords
        for x in range(int(xmin / scale), int(xmax / scale)):
            for y in range(int(ymin / scale) + 1, int(ymax / scale) + 1):
                lats_to_link[90 - y, x - 180] = parser.coords_to_link[coords]

def self_test_dem3(lats_to_link):
    lat = 44
    while lat <= 47:
        lng = 0
        while lng <= 5:
            assert "L31" in lats_to_link[lat, lng]
            lng += 1
        lat += 1

def self_test_dem1(lats_to_link):
    assert "TATRA" in lats_to_link[49, 19]
    for lat, lng in lats_to_link:
        assert -90 <= lat <= 89
        assert -180 <= lng <= 179, lng

def write_db(dest, lats_to_link):
    with open(dest, "w") as f:
        for lat in range(-90, 90):
            for lng in range(-180, 180):
                if (lat, lng) in lats_to_link:
                    print("%d %d %s" % (lat, lng,
                                        lats_to_link.get((lat, lng))),
                          file=f)

lats_to_link = {}
populate_links("coverage-dem3.html", lats_to_link)
self_test_dem3(lats_to_link)
populate_links("coverage-dem1.html", lats_to_link)
self_test_dem1(lats_to_link)

write_db("tiles.dat", lats_to_link)