Update source files

frontend/src/shared/utils/binaryDecoding.ts

@@ -0,0 +1,59 @@
+/**
+ * Binary decoding utilities for territory snapshot data from Rust backend.
+ *
+ * The TerritorySnapshot uses a sparse binary format to minimize data transfer:
+ * - Only claimed tiles (owner_id != 0) are transmitted
+ * - All other tiles default to unclaimed (owner_id = 0)
+ * - Binary format: [count:4][tile_changes...]
+ *   where each change is [index:4][owner:2] (6 bytes per claimed tile)
+ */
+
+export interface TileOwnership {
+  index: number;
+  owner_id: number;
+}
+
+/**
+ * Decode sparse binary territory snapshot from Rust backend.
+ *
+ * @param data Binary data array (serialized from Vec<u8> in Rust)
+ * @returns Array of claimed tiles with indices and owner IDs, or null if invalid
+ */
+export function decodeTerritorySnapshot(data: number[] | Uint8Array): TileOwnership[] | null {
+  // Convert to Uint8Array if needed for faster access
+  const bytes = data instanceof Uint8Array ? data : new Uint8Array(data);
+
+  if (bytes.length < 4) {
+    console.error("Invalid territory snapshot: not enough data for count");
+    return null;
+  }
+
+  // Use DataView for faster little-endian reads
+  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+
+  // Read count (4 bytes, little-endian u32)
+  const count = view.getUint32(0, true);
+
+  const expectedSize = 4 + count * 6;
+  if (bytes.length !== expectedSize) {
+    console.error(
+      `Invalid territory snapshot: expected ${expectedSize} bytes, got ${bytes.length}`
+    );
+    return null;
+  }
+
+  const tiles: TileOwnership[] = new Array(count);
+  for (let i = 0; i < count; i++) {
+    const offset = 4 + i * 6;
+
+    // Read index (4 bytes, little-endian u32)
+    const index = view.getUint32(offset, true);
+
+    // Read owner_id (2 bytes, little-endian u16)
+    const owner_id = view.getUint16(offset + 4, true);
+
+    tiles[i] = { index, owner_id };
+  }
+
+  return tiles;
+}