using Invercargill;
using Invercargill.DataStructures;
using Astralis;

namespace Statum {

    /**
     * Base class for pre-rendered Statum pages.
     *
     * A page is a static, precompressed document served at its route. Build-time
     * composition (templates/fragments, `pstm-res` rewriting) aside, it is just a
     * precompressed resource — so a generated subclass (emitted by
     * `statum-mkpstm`) provides the precompressed byte arrays and the
     * encoding/ETag accessors, and this base does lean `Accept-Encoding`
     * negotiation, `ETag`/`If-None-Match` handling and serving.
     *
     * No slots are resolved: pages are loaded by browser navigations, which carry
     * no `X-Statum-Slot` headers, so the page endpoint stays as fast as possible.
     */
    public abstract class StatumPage : Object, Endpoint {

        /** Content type of the served page (normally `text/html`). */
        public abstract string content_type { get; }

        /** Best supported encoding from the encodings this page carries. */
        public abstract string get_best_encoding(Set<string> supported);

        /** The bytes for `encoding`. */
        public abstract unowned uint8[] get_encoding(string encoding);

        /** The ETag for `encoding`. */
        public abstract string get_etag_for(string encoding);

        public async HttpResult handle_request(HttpContext http_context, RouteContext route_context) throws GLib.Error {
            var best = get_best_encoding(parse_accept_encoding(http_context));
            var etag = get_etag_for(best);

            if (etag_matches(http_context, etag)) {
                return new HttpEmptyResult(StatusCode.NOT_MODIFIED);
            }

            var result = new HttpDataResult(Wrap.byte_array(get_encoding(best)));
            result.set_header("Content-Type", content_type);
            result.set_header("Content-Encoding", best);
            result.set_header("ETag", etag);
            return result;
        }

        private static Set<string> parse_accept_encoding(HttpContext http_context) {
            var supported = new HashSet<string>();
            foreach (var header in http_context.request.headers.get_or_empty("Accept-Encoding")) {
                foreach (var token in header.split(",")) {
                    var encoding = token.strip();
                    if (encoding.length > 0) {
                        supported.add(encoding);
                    }
                }
            }
            return supported;
        }

        private static bool etag_matches(HttpContext http_context, string etag) {
            foreach (var header in http_context.request.headers.get_or_empty("If-None-Match")) {
                if (header.contains(etag)) {
                    return true;
                }
            }
            return false;
        }
    }
}