Separate out into files

packages/core/src/runtime/history-ledger.ts

@@ -0,0 +1,51 @@
+import { shallowRef } from "vue";
+import type { NativeTransaction, NativeViewEntry } from "../types";
+
+export class NativeHistoryLedger {
+  readonly keys = shallowRef<string[]>([]);
+
+  get length() {
+    return this.keys.value.length;
+  }
+
+  get previousKey() {
+    return this.keys.value.at(-2);
+  }
+
+  initialize(key: string) {
+    this.keys.value = [key];
+  }
+
+  contains(key: string) {
+    return this.keys.value.includes(key);
+  }
+
+  indexOf(key: string) {
+    return this.keys.value.lastIndexOf(key);
+  }
+
+  accept(target: NativeViewEntry, transaction: NativeTransaction | null) {
+    const history = this.keys.value;
+    if (!history.length) return this.initialize(target.key);
+
+    if (
+      transaction?.kind === "pop" ||
+      transaction?.kind === "dismiss" ||
+      transaction?.replace
+    ) {
+      const targetIndex = history.lastIndexOf(target.key);
+      this.keys.value =
+        targetIndex >= 0
+          ? history.slice(0, targetIndex + 1)
+          : [...history.slice(0, -1), target.key];
+      return;
+    }
+
+    const existingIndex = history.lastIndexOf(target.key);
+    this.keys.value = transaction
+      ? [...history, target.key]
+      : existingIndex >= 0
+        ? history.slice(0, existingIndex + 1)
+        : [...history, target.key];
+  }
+}