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diff --git a/cmds/idmap2/include/idmap2/ResourceMapping.h b/cmds/idmap2/include/idmap2/ResourceMapping.h
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+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef IDMAP2_INCLUDE_IDMAP2_RESOURCEMAPPING_H_
+#define IDMAP2_INCLUDE_IDMAP2_RESOURCEMAPPING_H_
+
+#include <map>
+#include <memory>
+#include <utility>
+
+#include "androidfw/ApkAssets.h"
+#include "idmap2/Policies.h"
+#include "idmap2/ResourceUtils.h"
+#include "idmap2/Result.h"
+#include "idmap2/XmlParser.h"
+
+using android::idmap2::utils::OverlayManifestInfo;
+
+namespace android::idmap2 {
+
+struct TargetValue {
+  typedef uint8_t DataType;
+  typedef uint32_t DataValue;
+  DataType data_type;
+  DataValue data_value;
+};
+
+using TargetResourceMap = std::map<ResourceId, TargetValue>;
+using OverlayResourceMap = std::map<ResourceId, ResourceId>;
+
+class ResourceMapping {
+ public:
+  // Creates a ResourceMapping using the target and overlay APKs. Setting enforce_overlayable to
+  // `false` disables all overlayable and policy enforcement: this is intended for backwards
+  // compatibility pre-Q and unit tests.
+  static Result<ResourceMapping> FromApkAssets(const ApkAssets& target_apk_assets,
+                                               const ApkAssets& overlay_apk_assets,
+                                               const OverlayManifestInfo& overlay_info,
+                                               const PolicyBitmask& fulfilled_policies,
+                                               bool enforce_overlayable);
+
+  // Retrieves the mapping of target resource id to overlay value.
+  inline TargetResourceMap GetTargetToOverlayMap() const {
+    return target_map_;
+  }
+
+  // Retrieves the mapping of overlay resource id to target resource id. This allows a reference to
+  // an overlay resource to appear as a reference to its corresponding target resource at runtime.
+  OverlayResourceMap GetOverlayToTargetMap() const;
+
+  // Retrieves the build-time package id of the target package.
+  inline uint32_t GetTargetPackageId() const {
+    return target_package_id_;
+  }
+
+  // Retrieves the build-time package id of the overlay package.
+  inline uint32_t GetOverlayPackageId() const {
+    return overlay_package_id_;
+  }
+
+  // Retrieves the offset that was added to the index of inline string overlay values so the indices
+  // do not collide with the indices of the overlay resource table string pool.
+  inline uint32_t GetStringPoolOffset() const {
+    return string_pool_offset_;
+  }
+
+  // Retrieves the raw string pool data from the xml referenced in android:resourcesMap.
+  inline const std::pair<const uint8_t*, uint32_t> GetStringPoolData() const {
+    return std::make_pair(string_pool_data_.get(), string_pool_data_length_);
+  }
+
+ private:
+  ResourceMapping() = default;
+
+  // Apps a mapping of target resource id to the type and value of the data that overlays the
+  // target resource. The data_type is the runtime format of the data value (see
+  // Res_value::dataType). If rewrite_overlay_reference is `true` then references to an overlay
+  // resource should appear as a reference to its corresponding target resource at runtime.
+  Result<Unit> AddMapping(ResourceId target_resource, TargetValue::DataType data_type,
+                          TargetValue::DataValue data_value, bool rewrite_overlay_reference);
+
+  // Removes the overlay value mapping for the target resource.
+  void RemoveMapping(ResourceId target_resource);
+
+  // Parses the mapping of target resources to overlay resources to generate a ResourceMapping.
+  static Result<ResourceMapping> CreateResourceMapping(const AssetManager2* target_am,
+                                                       const LoadedPackage* target_package,
+                                                       const LoadedPackage* overlay_package,
+                                                       size_t string_pool_offset,
+                                                       const XmlParser& overlay_parser);
+
+  // Generates a ResourceMapping that maps target resources to overlay resources by name. To overlay
+  // a target resource, a resource must exist in the overlay with the same type and entry name as
+  // the target resource.
+  static Result<ResourceMapping> CreateResourceMappingLegacy(const AssetManager2* target_am,
+                                                             const AssetManager2* overlay_am,
+                                                             const LoadedPackage* target_package,
+                                                             const LoadedPackage* overlay_package);
+
+  // Removes resources that do not pass policy or overlayable checks of the target package.
+  void FilterOverlayableResources(const AssetManager2* target_am,
+                                  const LoadedPackage* target_package,
+                                  const LoadedPackage* overlay_package,
+                                  const OverlayManifestInfo& overlay_info,
+                                  const PolicyBitmask& fulfilled_policies);
+
+  TargetResourceMap target_map_;
+  std::multimap<ResourceId, ResourceId> overlay_map_;
+
+  uint32_t target_package_id_ = 0;
+  uint32_t overlay_package_id_ = 0;
+  uint32_t string_pool_offset_ = 0;
+  uint32_t string_pool_data_length_ = 0;
+  std::unique_ptr<uint8_t[]> string_pool_data_ = nullptr;
+};
+
+}  // namespace android::idmap2
+
+#endif  // IDMAP2_INCLUDE_IDMAP2_RESOURCEMAPPING_H_