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_s32(d) {
    const value = d.view.getInt32(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_align(d, to) {
    // TODO: non-stupid version of this
    while (d.offset % to != 0) {
        d.offset++;
    }
}

function des_f32array(d, count) {
    const result = new Float32Array(d.buffer, d.offset, count);
    d.offset += 4 * count;
    return result;
}

function des_u8array(d, count) {
    const result = new Uint8Array(d.buffer, d.offset, count);
    d.offset += count;
    return result;
}

function des_event(d, state = null) {
    const event = {};

    event.type = des_u32(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.USER_JOINED:
        case EVENT.LEAVE:
        case EVENT.CLEAR: {
            break;
        }

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

        case EVENT.MOVE_CANVAS: {
            event.offset_x = des_s32(d);
            event.offset_y = des_s32(d);
            event.zoom_level = des_s32(d);
            break;
        }

        case EVENT.ZOOM_CANVAS: {
            event.zoom_level = des_s32(d);
            event.zoom_cx = des_f32(d);
            event.zoom_cy = 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);

            event.coords = des_f32array(d, point_count * 2);
            event.press = des_u8array(d, point_count);

            des_align(d, 4);

            // TODO: remove, this is duplicate data 
            
            event.stroke_id = stroke_id;

            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': [],
        'online': false,
        'cursor': {'x': 0, 'y': 0},
    };
}

function handle_event(state, context, event, options = {}) {
    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.USER_JOINED: {
            state.players[event.user_id].online = true;
            draw_html(state);
            break;
        }

        case EVENT.PREDRAW: {
            geometry_add_point(state, context, event.user_id, {'x': event.x, 'y': event.y, 'pressure': 128}, false); // TODO: add pressure to predraw events
            need_draw = true;
            break;
        }

        case EVENT.CLEAR: {
            geometry_clear_player(state, context, event.user_id);
            break;
        }

        case EVENT.LEAVE: {
            if (event.user_id in state.players) {
                state.players[event.user_id].online = false;
                draw_html(state);
            }
            break;
        }

        case EVENT.MOVE_CURSOR: {
            if (event.user_id in state.players) {
                state.players[event.user_id].cursor.x = event.x;
                state.players[event.user_id].cursor.y = event.y;
                state.players[event.user_id].online = true;
            }
            
            // Should we syncronize this to RAF?
            draw_html(state);

            break;
        }

        case EVENT.MOVE_CANVAS: {
            // Double-check just in case
            // Non-triple equals in on purpose
            if (event.user_id == state.following_player) {
                state.canvas.offset.x = event.offset_x;
                state.canvas.offset.y = event.offset_y;

                const zoom_level = event.zoom_level;
                const dz = (zoom_level > 0 ? config.zoom_delta : -config.zoom_delta);
                const zoom = Math.pow(1.0 + dz, Math.abs(zoom_level))

                state.canvas.zoom_level = zoom_level;
                state.canvas.zoom = zoom;
                state.canvas.target_zoom = zoom;

                need_draw = true;
            }

            break;
        }

        case EVENT.ZOOM_CANVAS: {
            if (event.user_id == state.following_player) {
                const zoom_level = event.zoom_level;
                const zoom_center = {'x': event.zoom_cx, 'y': event.zoom_cy};
                const dz = (zoom_level > 0 ? config.zoom_delta : -config.zoom_delta);
                const zoom = Math.pow(1.0 + dz, Math.abs(zoom_level))

                state.canvas.zoom_level = zoom_level;
                state.canvas.target_zoom = zoom;
                state.canvas.zoom_screenp = canvas_to_screen(state, zoom_center);

                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: {
            const point_count = event.coords.length / 2;

            if (point_count === 0) {
                break;
            }

            let last_stroke = null;

            for (let i = state.events.length - 1; i >= 0; --i) {
                if (state.events[i].type === EVENT.STROKE) {
                    last_stroke = state.events[i];
                    break;
                }
            }

            const index_difference = state.events.length - (last_stroke === null ? 0 : last_stroke.index);
            wasm_ensure_by(state, index_difference, event.coords.length);
           
            const pressures = state.wasm.buffers['pressures'];
            const xs = state.wasm.buffers['xs'];
            const ys = state.wasm.buffers['ys'];
            
            event.coords_from = xs.tv.size;
            event.coords_to = xs.tv.size + point_count;

            for (let i = 0; i < index_difference - 1; ++i) {
                // Create empty records for all non-stroke events that happened since the last stroke
                tv_add(state.wasm.buffers['coords_from'].tv, xs.tv.size);
                state.wasm.buffers['coords_from'].used += 4; // 4 bytes, not 4 ints
            }

            // Create actual records for this stroke
            tv_add(state.wasm.buffers['coords_from'].tv, xs.tv.size + point_count);
            state.wasm.buffers['coords_from'].used += 4; // 4 bytes, not 4 ints

            for (let i = 0; i < event.coords.length; i += 2) {
                tv_add(xs.tv, event.coords[i + 0]);
                tv_add(ys.tv, event.coords[i + 1]);
            }

            state.wasm.buffers['xs'].used += point_count * 4;
            state.wasm.buffers['ys'].used += point_count * 4;

            tv_append(pressures.tv, event.press);
            state.wasm.buffers['pressures'].used += point_count;
            
            delete event.coords;
            delete event.press;

            // TODO: do not do this for my own strokes when we bake locally
            geometry_clear_player(state, context, event.user_id);
            need_draw = true;

            event.index = state.events.length;

            geometry_add_stroke(state, context, event, state.events.length, options.skip_bvh === true);

            state.stroke_count++;

            break;
        }

        case EVENT.UNDO: {
            geometry_add_dummy_stroke(context);

            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;
                        if (other_event.bvh_node) {
                            bvh_delete_stroke(state, other_event);
                        }
                        need_draw = true;
                        break;
                    } else if (other_event.type === EVENT.UNDO) {
                        // do not undo an undo, we are not Notepad
                    } else {
                        console.error('cant undo event type', other_event.type);
                        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;

                    geometry_add_dummy_stroke(context);
                    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_u32(d);
    let do_draw = false;

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

    switch (message_type) {
        case MESSAGE.JOIN:
        case MESSAGE.INIT: {
            console.time('init');

            state.online = true;
            state.server_lsn = des_u32(d);

            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);
                if (config.debug_print) console.debug('init in');
            }

            state.me = parseInt(localStorage.getItem('sessionId'));

            init_player_defaults(state, state.me);

            set_color_u32(state, color);

            document.querySelector('#stroke-width').value = width;
            fire_event(state, width_event(width));

            const event_count = des_u32(d);
            const user_count = des_u32(d);
            const total_points = des_u32(d);
    
            wasm_ensure_by(state, event_count, round_to_pow2(total_points * 2, 4096));

            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);
                const user_online = des_u8(d);

                init_player_defaults(state, user_id, user_color, user_width);
                state.players[user_id].online = user_online === 1;
            }

            des_align(d, 4);

            for (let i = 0; i < event_count; ++i) {
                const event = des_event(d, state);
                handle_event(state, context, event, {'skip_bvh': true});

                if (event.type !== EVENT.STROKE || event.coords_to - event.coords_from > 0) {
                    state.events.push(event);
                }
            }

            state.sn = event_count;

            bvh_construct(state);

            document.getElementById('debug-render-from').max = state.stroke_count;
            document.getElementById('debug-render-to').max = state.stroke_count;

            do_draw = true;

            send_ack(event_count);
            sync_queue(state);

            console.timeEnd('init');

            update_cursor(state);
            draw_html(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, state);
                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);
    }
}