function deserializer_create(buffer, dataview) {
    return {
        'offset': 0,
        'size': buffer.byteLength,
        'buffer': buffer,
        'view': dataview,
        'strview': new Uint8Array(buffer),
    };
}

function des_u8(d) {
    const value = d.view.getUint8(d.offset);
    d.offset += 1;
    return value;
}

function des_u16(d) {
    const value = d.view.getUint16(d.offset, true);
    d.offset += 2;
    return value;
}

function des_u32(d) {
    const value = d.view.getUint32(d.offset, true);
    d.offset += 4;
    return value;
}

function des_f32(d) {
    const value = d.view.getFloat32(d.offset, true);
    d.offset += 4;
    return value;
}

function des_f32array(d, count) {
    const result = [];

    for (let i = 0; i < count; ++i) {
        const item = d.view.getFloat32(d.offset, true);
        d.offset += 4;
        result.push(item);
    }

    return result;
}

function des_event(d) {
    const event = {};

    event.type = des_u8(d);
    event.user_id = des_u32(d);

    switch (event.type) {
        case EVENT.PREDRAW: {
            event.x = des_f32(d);
            event.y = des_f32(d);
            break;
        }

        case EVENT.SET_COLOR: {
            event.color = des_u32(d);
            break;
        }

        case EVENT.SET_WIDTH: {
            event.width = des_u16(d);
            break;
        }

        case EVENT.STROKE: {
            const stroke_id = des_u32(d);
            const point_count = des_u16(d);
            const width = des_u16(d);
            const color = des_u32(d);
            const coords = des_f32array(d, point_count * 2);

            event.stroke_id = stroke_id;
            event.points = [];

            for (let i = 0; i < point_count; ++i) {
                const x = coords[2 * i + 0];
                const y = coords[2 * i + 1];
                event.points.push({'x': x, 'y': y});
            }

            event.color = color;
            event.width = width;

            break;
        }

        case EVENT.IMAGE:
        case EVENT.IMAGE_MOVE: {
            event.image_id = des_u32(d);
            event.x = des_f32(d);
            event.y = des_f32(d);
            break;
        }

        case EVENT.UNDO:
        case EVENT.REDO: {
            break;
        }

        case EVENT.ERASER: {
            event.stroke_id = des_u32(d);
            break;
        }

        default: {
            console.error('fuck');
        }
    }

    return event;
}

function bitmap_bbox(event) {
    const bbox = {
        'xmin': event.x, 
        'xmax': event.x + event.bitmap.width, 
        'ymin': event.y, 
        'ymax': event.y + event.bitmap.height
    };

    return bbox;
}

function init_player_defaults(state, player_id, color = config.default_color, width = config.default_width) {
    state.players[player_id] = {
        'color': color,
        'width': width,
        'points': [],
    };
}

function handle_event(state, context, event) {
    if (config.debug_print) console.debug(`event type ${event.type} from user ${event.user_id}`);

    let need_draw = false;

    if (!(event.user_id in state.players)) {
        init_player_defaults(state, event.user_id);
    }

    switch (event.type) {
        case EVENT.PREDRAW: {
            geometry_add_point(state, context, event.user_id, {'x': event.x, 'y': event.y});
            need_draw = true;
            break;
        }

        case EVENT.SET_COLOR: {
            state.players[event.user_id].color = event.color;
            break;
        }

        case EVENT.SET_WIDTH: {
            state.players[event.user_id].width = event.width;
            break;
        }

        case EVENT.STROKE: {
            if (event.user_id != state.me) {
                geometry_clear_player(state, context, event.user_id);
                need_draw = true;
            }

            geometry_add_stroke(state, context, event);

            break;
        }

        case EVENT.UNDO: {
            need_draw = true;
            console.error('todo');
            // for (let i = state.events.length - 1; i >=0; --i) {
            //     const other_event = state.events[i];

            //     // Users can only undo their own, undeleted (not already undone) events
            //     if (other_event.user_id === event.user_id && !other_event.deleted) {
            //         if (other_event.type === EVENT.STROKE) {
            //             other_event.deleted = true;
            //             const stats = stroke_stats(other_event.points, state.cursor.width);
            //             redraw_region(stats.bbox);
            //             break;
            //         } else if (other_event.type === EVENT.IMAGE) {
            //             other_event.deleted = true;
            //             const item = document.querySelector(`img[data-image-id="${other_event.image_id}"]`);
            //             if (item) item.remove();
            //             break;
            //         } else if (other_event.type === EVENT.ERASER) {
            //             other_event.deleted = true;
            //             const erased = find_stroke_backwards(other_event.stroke_id);
            //             if (erased) {
            //                 erased.deleted = false;
            //                 const stats = stroke_stats(erased.points, state.cursor.width);
            //                 redraw_region(stats.bbox);
            //             }
            //             break;
            //         } else if (other_event.type === EVENT.IMAGE_MOVE) {
            //             const item = document.querySelector(`img[data-image-id="${other_event.image_id}"]`);
                        
            //             const ix = state.images[other_event.image_id].x -= other_event.x;
            //             const iy = state.images[other_event.image_id].y -= other_event.y;

            //             item.style.transform = `translate(${ix}px, ${iy}px)`;

            //             break;
            //         }
            //     }
            // }

            break;
        }

        case EVENT.IMAGE: {
            try {
                (async () => {
                    const url = config.image_url + event.image_id;
                    const r = await fetch(config.image_url + event.image_id);
                    const blob = await r.blob();
                    const bitmap = await createImageBitmap(blob);
                    const p = {'x': event.x, 'y': event.y};

                    event.width = bitmap.width;
                    event.height = bitmap.height;

                    add_image(context, event.image_id, bitmap, p);

                    // God knows when this will actually complete (it loads the image from the server)
                    // so do not set need_draw. Instead just schedule the draw ourselves when done
                    schedule_draw(state, context);
                })();
            } catch (e) {
                console.log('Could not load image bitmap:', e);
            }

            break;
        }

        case EVENT.IMAGE_MOVE: {
            // Already moved due to local prediction
            if (event.user_id !== state.me) {
                const image_id = event.image_id;
                const image_event = find_image(state, image_id);

                if (image_event) {
                    // if (config.debug_print) console.debug('move image', image_id, 'to', image_event.x, image_event.y);
                    image_event.x = event.x;
                    image_event.y = event.y;
                    move_image(context, image_event);
                    need_draw = true;
                }
            }

            break;
        }

        case EVENT.ERASER: {
            need_draw = true;
            console.error('todo');
            // if (event.deleted) {
            //     break;
            // }

            // for (const other_event of state.events) {
            //     if (other_event.type === EVENT.STROKE && other_event.stroke_id === event.stroke_id) {
            //         // Might already be deleted because of local prediction
            //         if (!other_event.deleted) {
            //             other_event.deleted = true;
            //             const stats = stroke_stats(other_event.points, state.cursor.width);
            //             redraw_region(stats.bbox);
            //         }
            //         break;
            //     }
            // }
            break;
        }

        default: { 
            console.error('fuck');
        }
    }

    return need_draw;
}

async function handle_message(state, context, d) {
    const message_type = des_u8(d);
    let do_draw = false;

    // if (config.debug_print) console.debug(message_type);

    switch (message_type) {
        case MESSAGE.JOIN:
        case MESSAGE.INIT: {
            state.server_lsn = des_u32(d);
            state.online = true;

            if (state.server_lsn > state.lsn) {
                // Server knows something that we don't
                state.lsn = state.server_lsn;
            }

            let color = config.default_color;
            let width = config.default_width;

            if (message_type === MESSAGE.JOIN) {
                localStorage.setItem('sessionId', des_u32(d));
                if (config.debug_print) console.debug('join in');
            } else {
                color = des_u32(d);
                width = des_u16(d);
                state.me = parseInt(localStorage.getItem('sessionId'));
                if (config.debug_print) console.debug('init in');
            }

            init_player_defaults(state, state.me);

            const color_code = color_from_u32(color).substring(1);

            switch_color(state, document.querySelector(`.color[data-color="${color_code}"]`));
            document.querySelector('#stroke-width').value = width;
            fire_event(state, width_event(width));

            const event_count = des_u32(d);
            const user_count = des_u32(d);

            if (config.debug_print) console.debug(`${event_count} events in init`);
            
            state.events.length = 0;

            for (let i = 0; i < user_count; ++i) {
                const user_id = des_u32(d);
                const user_color = des_u32(d);
                const user_width = des_u16(d);

                init_player_defaults(state, user_id, user_color, user_width);
            }

            for (let i = 0; i < event_count; ++i) {
                const event = des_event(d);
                handle_event(state, context, event);
                state.events.push(event);
            }

            do_draw = true;

            send_ack(event_count);
            sync_queue(state);

            break;
        }

        case MESSAGE.FIRE: {
            const event = des_event(d);
            const need_draw = handle_event(state, context, event);

            do_draw = do_draw || need_draw;

            break;
        }

        case MESSAGE.ACK: {
            const lsn = des_u32(d);

            if (config.debug_print) console.debug(`ack ${lsn} in`);
            
            if (lsn > state.server_lsn) {
                // ACKs may arrive out of order
                state.server_lsn = lsn;
            }
            
            break;
        }

        case MESSAGE.SYN: {
            const sn = des_u32(d);
            const count = des_u32(d);

            const we_expect = sn - state.sn;
            const first = count - we_expect;

            if (config.debug_print) console.debug(`syn ${sn} in`);

            for (let i = 0; i < count; ++i) {
                const event = des_event(d);
                if (i >= first) {
                    const need_draw = handle_event(state, context, event);
                    do_draw = do_draw || need_draw;
                    state.events.push(event);
                }
            }

            state.sn = sn;

            send_ack(sn); // await?

            break;
        }

        default: {
            console.error('fuck');
            return;
        }
    }

    if (do_draw) {
        schedule_draw(state, context);
    }
}