from calendar import timegm
from datetime import date
from types import SimpleNamespace

from django.http import HttpResponse
from django.utils.http import http_date
from django.views.decorators.cache import cache_page
from lxml import etree
from lxml.builder import ElementMaker


__all__ = ("Sitemap",)


S = ElementMaker(
    namespace="http://www.sitemaps.org/schemas/sitemap/0.9",
    nsmap={
        None: "http://www.sitemaps.org/schemas/sitemap/0.9",
        "xhtml": "http://www.w3.org/1999/xhtml",
    },
)
X = ElementMaker(
    namespace="http://www.w3.org/1999/xhtml",
    nsmap={"xhtml": "http://www.w3.org/1999/xhtml"},
)


class Sitemap:
    def __init__(self, *, build_absolute_uri):
        self.urls = []
        self.build_absolute_uri = build_absolute_uri
        self.lastmod = None
        self.all_urls_lastmod = True

    def add(self, loc, *, changefreq=None, lastmod=None, priority=None, alternates={}):
        children = [S.loc(self.build_absolute_uri(loc))]
        if changefreq is not None:
            children.append(S.changefreq(changefreq))
        if isinstance(lastmod, date):
            new = timegm(
                lastmod.utctimetuple()
                if hasattr(lastmod, "utctimetuple")
                else lastmod.timetuple()
            )
            self.lastmod = max(self.lastmod, new) if self.lastmod else new
            children.append(S.lastmod(lastmod.isoformat()))
        elif lastmod is not None:
            children.append(S.lastmod(lastmod))
        else:
            self.all_urls_lastmod = False
        if priority:
            children.append(S.priority(str(priority)))

        for code, url in alternates.items():
            children.append(
                X.link(
                    {
                        "rel": "alternate",
                        "hreflang": code,
                        "href": self.build_absolute_uri(url),
                    }
                )
            )

        self.urls.append(S.url(*children))

    def add_django_sitemap(self, sitemap):
        if callable(sitemap):
            sitemap = sitemap()

        for url in sitemap.get_urls(site=SimpleNamespace(domain="_"), protocol="_"):
            # Replace this with url["location"].removeprefix("_://_") when
            # supporting only Python 3.9 or better.
            loc = url["location"]
            if loc.startswith("_://_"):
                loc = loc[5:]
            self.add(
                loc,
                changefreq=url.get("changefreq"),
                lastmod=url.get("lastmod"),
                priority=url.get("priority"),
            )

    def serialize(self, *, pretty_print=False):
        return etree.tostring(
            S.urlset(*self.urls),
            encoding="UTF-8",
            pretty_print=pretty_print,
            xml_declaration=True,
        )

    def response(self, *, pretty_print=False):
        response = HttpResponse(
            self.serialize(pretty_print=pretty_print), content_type="application/xml"
        )
        response["X-Robot-Tag"] = "noindex, noodp, noarchive"
        if self.all_urls_lastmod and self.lastmod is not None:
            response["Last-Modified"] = http_date(self.lastmod)
        return response


def robots_txt(*, timeout=0, sitemaps=["/sitemap.xml"]):
    @cache_page(timeout)
    def view(request):
        lines = ["User-agent: *\n"]
        lines.extend(
            "Sitemap: %s\n" % request.build_absolute_uri(str(sitemap))
            for sitemap in sitemaps
        )
        return HttpResponse("".join(lines), content_type="text/plain")

    return view