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+/* Copyright (c) 2015, 2017 The Linux Foundation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ *       copyright notice, this list of conditions and the following
+ *       disclaimer in the documentation and/or other materials provided
+ *       with the distribution.
+ *     * Neither the name of The Linux Foundation, nor the names of its
+ *       contributors may be used to endorse or promote products derived
+ *       from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
+ * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+#ifndef __LOC_UNORDERDED_SETMAP_H__
+#define __LOC_UNORDERDED_SETMAP_H__
+
+#include <algorithm>
+#include <unordered_set>
+#include <unordered_map>
+
+using std::unordered_set;
+using std::unordered_map;
+
+namespace loc_util {
+
+// Trim from *fromSet* any elements that also exist in *rVals*.
+// The optional *goneVals*, if not null, will be populated with removed elements.
+template <typename T>
+inline static void trimSet(unordered_set<T>& fromSet, const unordered_set<T>& rVals,
+                           unordered_set<T>* goneVals) {
+    for (auto val : rVals) {
+        if (fromSet.erase(val) > 0 && nullptr != goneVals) {
+            goneVals->insert(val);
+        }
+    }
+}
+
+// this method is destructive to the input unordered_sets.
+// the return set is the interset extracted out from the two input sets, *s1* and *s2*.
+// *s1* and *s2* will be left with the intersect removed from them.
+template <typename T>
+static unordered_set<T> removeAndReturnInterset(unordered_set<T>& s1, unordered_set<T>& s2) {
+    unordered_set<T> common(0);
+    for (auto b = s2.begin(); b != s2.end(); b++) {
+        auto a = find(s1.begin(), s1.end(), *b);
+        if (a != s1.end()) {
+            // this is a common item of both l1 and l2, remove from both
+            // but after we add to common
+            common.insert(*a);
+            s1.erase(a);
+            s2.erase(b);
+        }
+    }
+    return common;
+}
+
+template <typename KEY, typename VAL>
+class LocUnorderedSetMap {
+    unordered_map<KEY, unordered_set<VAL>> mMap;
+
+
+    // Trim the VALs pointed to by *iter*, with everything that also exist in *rVals*.
+    // If the set becomes empty, remove the map entry. *goneVals*, if not null, records
+    // the trimmed VALs.
+    bool trimOrRemove(typename unordered_map<KEY, unordered_set<VAL>>::iterator iter,
+                      const unordered_set<VAL>& rVals, unordered_set<VAL>* goneVals) {
+        trimSet<VAL>(iter->second, rVals, goneVals);
+        bool removeEntry = (iter->second.empty());
+        if (removeEntry) {
+            mMap.erase(iter);
+        }
+        return removeEntry;
+    }
+
+public:
+    inline LocUnorderedSetMap() {}
+    inline LocUnorderedSetMap(size_t size) : mMap(size) {}
+
+    inline bool empty() { return mMap.empty(); }
+
+    // This gets the raw pointer to the VALs pointed to by *key*
+    // If the entry is not in the map, nullptr will be returned.
+    inline unordered_set<VAL>* getValSetPtr(const KEY& key) {
+        auto entry = mMap.find(key);
+        return (entry != mMap.end()) ? &(entry->second) : nullptr;
+    }
+
+    //  This gets a copy of VALs pointed to by *key*
+    // If the entry is not in the map, an empty set will be returned.
+    inline unordered_set<VAL> getValSet(const KEY& key) {
+        auto entry = mMap.find(key);
+        return (entry != mMap.end()) ? entry->second : unordered_set<VAL>(0);
+    }
+
+    // This gets all the KEYs from the map
+    inline unordered_set<KEY> getKeys() {
+        unordered_set<KEY> keys(0);
+        for (auto entry : mMap) {
+            keys.insert(entry.first);
+        }
+        return keys;
+    }
+
+    inline bool remove(const KEY& key) {
+        return mMap.erase(key) > 0;
+    }
+
+    // This looks into all the entries keyed by *keys*. Remove any VALs from the entries
+    // that also exist in *rVals*. If the entry is left with an empty set, the entry will
+    // be removed. The optional parameters *goneKeys* and *goneVals* will record the KEYs
+    // (or entries) and the collapsed VALs removed from the map, respectively.
+    inline void trimOrRemove(unordered_set<KEY>&& keys, const unordered_set<VAL>& rVals,
+                             unordered_set<KEY>* goneKeys, unordered_set<VAL>* goneVals) {
+        trimOrRemove(keys, rVals, goneKeys, goneVals);
+    }
+    inline void trimOrRemove(unordered_set<KEY>& keys, const unordered_set<VAL>& rVals,
+                             unordered_set<KEY>* goneKeys, unordered_set<VAL>* goneVals) {
+        for (auto key : keys) {
+            auto iter = mMap.find(key);
+            if (iter != mMap.end() && trimOrRemove(iter, rVals, goneVals) && nullptr != goneKeys) {
+                goneKeys->insert(iter->first);
+            }
+        }
+    }
+
+    // This adds all VALs from *newVals* to the map entry keyed by *key*. Or if it
+    // doesn't exist yet, add the set to the map.
+    bool add(const KEY& key, const unordered_set<VAL>& newVals) {
+        bool newEntryAdded = false;
+        if (!newVals.empty()) {
+            auto iter = mMap.find(key);
+            if (iter != mMap.end()) {
+                iter->second.insert(newVals.begin(), newVals.end());
+            } else {
+                mMap[key] = newVals;
+                newEntryAdded = true;
+            }
+        }
+        return newEntryAdded;
+    }
+
+    // This adds to each of entries in the map keyed by *keys* with the VALs in the
+    // *enwVals*. If there new entries added (new key in *keys*), *newKeys*, if not
+    // null, would be populated with those keys.
+    inline void add(const unordered_set<KEY>& keys, const unordered_set<VAL>&& newVals,
+                    unordered_set<KEY>* newKeys) {
+        add(keys, newVals, newKeys);
+    }
+    inline void add(const unordered_set<KEY>& keys, const unordered_set<VAL>& newVals,
+                    unordered_set<KEY>* newKeys) {
+        for (auto key : keys) {
+            if (add(key, newVals) && nullptr != newKeys) {
+                newKeys->insert(key);
+            }
+        }
+    }
+
+    // This puts *newVals* into the map keyed by *key*, and returns the VALs that are
+    // in effect removed from the keyed VAL set in the map entry.
+    // This call would also remove those same VALs from *newVals*.
+    inline unordered_set<VAL> update(const KEY& key, unordered_set<VAL>& newVals) {
+        unordered_set<VAL> goneVals(0);
+
+        if (newVals.empty()) {
+            mMap.erase(key);
+        } else {
+            auto curVals = mMap[key];
+            mMap[key] = newVals;
+            goneVals = removeAndReturnInterset(curVals, newVals);
+        }
+        return goneVals;
+    }
+};
+
+} // namespace loc_util
+
+#endif // #ifndef __LOC_UNORDERDED_SETMAP_H__