Iterate lexicographic ordering implementation

src/stores/SpaceStore.tsx

@@ -34,12 +34,7 @@ import {setHasDiff} from "../utils/sets";
 import {ISpaceSummaryEvent, ISpaceSummaryRoom} from "../components/structures/SpaceRoomDirectory";
 import RoomViewStore from "./RoomViewStore";
 import { arrayHasOrderChange } from "../utils/arrays";
-import {
-    ALPHABET_END,
-    ALPHABET_START,
-    averageBetweenStrings,
-    midPointsBetweenStrings,
-} from "../utils/stringOrderField";
+import { reorderLexicographically } from "../utils/stringOrderField";
 
 interface IState {}
 
@@ -645,64 +640,18 @@ export class SpaceStoreClass extends AsyncStoreWithClient<IState> {
     }
 
     public moveRootSpace(fromIndex: number, toIndex: number): void {
-        if (
-            fromIndex < 0 || toIndex < 0 ||
-            fromIndex > this.rootSpaces.length || toIndex > this.rootSpaces.length ||
-            fromIndex === toIndex
-        ) {
-            return;
-        }
-        const space = this.rootSpaces[fromIndex];
-        const orders = this.rootSpaces.map(this.getSpaceTagOrdering);
+        const currentOrders = this.rootSpaces.map(this.getSpaceTagOrdering);
+        const changes = reorderLexicographically(currentOrders, fromIndex, toIndex);
 
-        let prevOrder: string;
-        let nextOrder: string;
+        changes.forEach(({ index, order }) => {
+            this.setRootSpaceOrder(this.rootSpaces[index], order);
+        });
 
-        if (toIndex > fromIndex) {
-            // moving down
-            prevOrder = orders[toIndex];
-            nextOrder = orders[toIndex + 1];
+        if (changes.length) {
+            this.notifyIfOrderChanged();
         } else {
-            // accounts for downwards displacement of existing inhabitant of this index
-            prevOrder = toIndex > 0 ? orders[toIndex - 1] : String.fromCharCode(ALPHABET_START).repeat(5); // TODO
-            nextOrder = orders[toIndex];
+            // TODO
         }
-        console.log("@@ start", {fromIndex, toIndex, orders, prevOrder, nextOrder});
-
-        if (prevOrder === undefined) {
-            // to be able to move to this toIndex we will first need to insert a bunch of orders for earlier elements
-            const firstUndefinedIndex = orders.indexOf(undefined);
-            const numUndefined = orders.length - firstUndefinedIndex;
-            const lastOrder = orders[firstUndefinedIndex - 1] ?? String.fromCharCode(ALPHABET_START); // TODO
-            nextOrder = String.fromCharCode(ALPHABET_END).repeat(lastOrder.length + 1);
-            const newOrders = midPointsBetweenStrings(lastOrder, nextOrder, numUndefined);
-
-            if (newOrders.length === numUndefined) {
-                console.log("@@ precalc", {firstUndefinedIndex, numUndefined, lastOrder, newOrders});
-                for (let i = firstUndefinedIndex, j = 0; i <= toIndex; i++, j++) {
-                    if (i === toIndex && toIndex < fromIndex) continue;
-                    if (i === fromIndex) continue;
-                    const newOrder = newOrders[j];
-                    console.log("@@ preset", {i, j, newOrder});
-                    this.setRootSpaceOrder(this.rootSpaces[i], newOrder);
-                }
-
-                prevOrder = newOrders[newOrders.length - 1];
-            } else {
-                prevOrder = nextOrder; // rebuild
-            }
-        }
-
-        if (prevOrder !== nextOrder) {
-            const order = averageBetweenStrings(prevOrder, nextOrder ?? String.fromCharCode(ALPHABET_END).repeat(prevOrder.length + 1));
-            console.log("@@ set", {prevOrder, nextOrder, order});
-            this.setRootSpaceOrder(space, order);
-        } else {
-            // TODO REBUILD
-        }
-
-        this.notifyIfOrderChanged();
-        console.log("@@ done", this.rootSpaces.map(this.getSpaceTagOrdering));
     }
 }
 

src/utils/arrays.ts

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {percentageOf, percentageWithin} from "./numbers";
+import { percentageOf, percentageWithin } from "./numbers";
 
 /**
  * Quickly resample an array to have less/more data points. If an input which is larger
@@ -223,6 +223,21 @@ export function arrayMerge<T>(...a: T[][]): T[] {
     }, new Set<T>()));
 }
 
+/**
+ * Moves a single element from fromIndex to toIndex.
+ * @param list the list from which to construct the new list.
+ * @param fromIndex the index of the element to move.
+ * @param toIndex the index of where to put the element.
+ * @returns A new array with the requested value moved.
+ */
+export function reorder<T>(list: T[], fromIndex: number, toIndex: number): T[] {
+    const result = Array.from(list);
+    const [removed] = result.splice(fromIndex, 1);
+    result.splice(toIndex, 0, removed);
+
+    return result;
+}
+
 /**
  * Helper functions to perform LINQ-like queries on arrays.
  */

src/utils/stringOrderField.ts

@@ -14,6 +14,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { reorder } from "./arrays";
+
 export const ALPHABET_START = 0x20;
 export const ALPHABET_END = 0x7E;
 export const ALPHABET = new Array(1 + ALPHABET_END - ALPHABET_START)
@@ -54,3 +56,80 @@ export const midPointsBetweenStrings = (a: string, b: string, count: number, alp
     }
     return Array(count).fill(undefined).map((_, i) => baseToString(aBase + step + (i * step), alphabet));
 };
+
+interface IEntry {
+    index: number;
+    order: string;
+}
+
+export const reorderLexicographically = (
+    orders: Array<string | undefined>,
+    fromIndex: number,
+    toIndex: number,
+): IEntry[] => {
+    if (
+        fromIndex < 0 || toIndex < 0 ||
+        fromIndex > orders.length || toIndex > orders.length ||
+        fromIndex === toIndex
+    ) {
+        return [];
+    }
+
+    const ordersWithIndices: IEntry[] = orders.map((order, index) => ({ index, order }));
+    const newOrder = reorder(ordersWithIndices, fromIndex, toIndex);
+
+    const isMoveTowardsRight = toIndex > fromIndex;
+    const orderToLeftUndefined = newOrder[toIndex - 1]?.order === undefined;
+
+    let leftBoundIdx = toIndex;
+    let rightBoundIdx = toIndex;
+
+    const canDisplaceLeft = isMoveTowardsRight || orderToLeftUndefined || true; // TODO
+    if (canDisplaceLeft) {
+        const nextBase = newOrder[toIndex + 1]?.order !== undefined
+            ? stringToBase(newOrder[toIndex + 1].order)
+            : Number.MAX_VALUE;
+        for (let i = toIndex - 1, j = 0; i >= 0; i--, j++) {
+            if (newOrder[i]?.order !== undefined && nextBase - stringToBase(newOrder[i].order) > j) break;
+            leftBoundIdx = i;
+        }
+    }
+
+    const canDisplaceRight = !orderToLeftUndefined;
+    // TODO check if there is enough space on the right hand side at all,
+    // I guess find the last set order and then compare it to prevBase + $requiredGap
+    if (canDisplaceRight) {
+        const prevBase = newOrder[toIndex - 1]?.order !== undefined
+            ? stringToBase(newOrder[toIndex - 1]?.order)
+            : Number.MIN_VALUE;
+        for (let i = toIndex + 1, j = 0; i < newOrder.length; i++, j++) {
+            if (newOrder[i]?.order === undefined || stringToBase(newOrder[i].order) - prevBase > j) break; // TODO verify
+            rightBoundIdx = i;
+        }
+    }
+
+    const leftDiff = toIndex - leftBoundIdx;
+    const rightDiff = rightBoundIdx - toIndex;
+
+    if (orderToLeftUndefined || leftDiff < rightDiff) {
+        rightBoundIdx = toIndex;
+    } else {
+        leftBoundIdx = toIndex;
+    }
+
+    const prevOrder = newOrder[leftBoundIdx - 1]?.order
+        ?? String.fromCharCode(ALPHABET_START).repeat(5); // TODO
+    const nextOrder = newOrder[rightBoundIdx + 1]?.order
+        ?? String.fromCharCode(ALPHABET_END).repeat(prevOrder.length + 1); // TODO
+
+    const changes = midPointsBetweenStrings(prevOrder, nextOrder, 1 + rightBoundIdx - leftBoundIdx);
+    // TODO If we exceed maxLen then reorder EVERYTHING
+
+    console.log("@@ test", { prevOrder, nextOrder, changes, leftBoundIdx, rightBoundIdx, orders, fromIndex, toIndex, newOrder, orderToLeftUndefined });
+
+    return changes.map((order, i) => {
+        const index = newOrder[leftBoundIdx + i].index;
+
+        return { index, order };
+    });
+};