Start on ArraySortedMap in C++ (#721)

* Implement ArraySortedMap.remove
* Implement ArraySortedMap.insert
* Ensure ArraySortedMap.insert avoids copying on duplicates
* Port more ArraySortedMapTests

7 files changed, 783 insertions, 0 deletions

diff --git a/Firestore/core/CMakeLists.txt b/Firestore/core/CMakeLists.txt
index f143a71..2fc88c6 100644
--- a/Firestore/core/CMakeLists.txt
+++ b/Firestore/core/CMakeLists.txt
@@ -14,12 +14,14 @@
 
 add_subdirectory(src/firebase/firestore)
 add_subdirectory(src/firebase/firestore/core)
+add_subdirectory(src/firebase/firestore/immutable)
 add_subdirectory(src/firebase/firestore/model)
 add_subdirectory(src/firebase/firestore/remote)
 add_subdirectory(src/firebase/firestore/util)
 
 add_subdirectory(test/firebase/firestore)
 add_subdirectory(test/firebase/firestore/core)
+add_subdirectory(test/firebase/firestore/immutable)
 add_subdirectory(test/firebase/firestore/model)
 add_subdirectory(test/firebase/firestore/remote)
 add_subdirectory(test/firebase/firestore/util)
diff --git a/Firestore/core/src/firebase/firestore/immutable/CMakeLists.txt b/Firestore/core/src/firebase/firestore/immutable/CMakeLists.txt
new file mode 100644
index 0000000..e8a95cd
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/immutable/CMakeLists.txt
@@ -0,0 +1,21 @@
+# Copyright 2018 Google
+#
+# 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.
+
+cc_library(
+  firebase_firestore_immutable
+  SOURCES
+    array_sorted_map.cc
+    array_sorted_map.h
+    map_entry.h
+)
diff --git a/Firestore/core/src/firebase/firestore/immutable/array_sorted_map.cc b/Firestore/core/src/firebase/firestore/immutable/array_sorted_map.cc
new file mode 100644
index 0000000..48e7553
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/immutable/array_sorted_map.cc
@@ -0,0 +1,30 @@
+/*
+ * Copyright 2018 Google
+ *
+ * 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.
+ */
+
+#include "Firestore/core/src/firebase/firestore/immutable/array_sorted_map.h"
+
+namespace firebase {
+namespace firestore {
+namespace immutable {
+namespace impl {
+
+// Define external storage for constants:
+constexpr ArraySortedMapBase::size_type ArraySortedMapBase::kFixedSize;
+
+}  // namespace impl
+}  // namespace immutable
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/src/firebase/firestore/immutable/array_sorted_map.h b/Firestore/core/src/firebase/firestore/immutable/array_sorted_map.h
new file mode 100644
index 0000000..d0210a8
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/immutable/array_sorted_map.h
@@ -0,0 +1,318 @@
+/*
+ * Copyright 2018 Google
+ *
+ * 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 FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_IMMUTABLE_ARRAY_SORTED_MAP_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_IMMUTABLE_ARRAY_SORTED_MAP_H_
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <functional>
+#include <memory>
+#include <utility>
+
+#include "Firestore/core/src/firebase/firestore/immutable/map_entry.h"
+
+namespace firebase {
+namespace firestore {
+namespace immutable {
+
+namespace impl {
+
+/**
+ * A base class for implementing ArraySortedMap, containing types and constants
+ * that don't depend upon the template parameters to the main class.
+ *
+ * Note that this exists as a base class rather than as just a namespace in
+ * order to make it possible for users of ArraySortedMap to avoid needing to
+ * declare storage for each instantiation of the template.
+ */
+class ArraySortedMapBase {
+ public:
+  /**
+   * The type of size() methods on immutable collections. Note that this is not
+   * size_t specifically to save space in the TreeSortedMap implementation.
+   */
+  using size_type = uint32_t;
+
+  /**
+   * The maximum size of an ArraySortedMap.
+   *
+   * This is the size threshold where we use a tree backed sorted map instead of
+   * an array backed sorted map. This is a more or less arbitrary chosen value,
+   * that was chosen to be large enough to fit most of object kind of Firebase
+   * data, but small enough to not notice degradation in performance for
+   * inserting and lookups. Feel free to empirically determine this constant,
+   * but don't expect much gain in real world performance.
+   */
+  // TODO(wilhuff): actually use this for switching implementations.
+  static constexpr size_type kFixedSize = 25;
+};
+
+/**
+ * A bounded-size array that allocates its contents directly in itself. This
+ * saves a heap allocation when compared with std::vector (though std::vector
+ * can resize itself while FixedArray cannot).
+ *
+ * Unlike std::array, FixedArray keeps track of its size and grows up to the
+ * fixed_size limit. Inserting more elements than fixed_size will trigger an
+ * assertion failure.
+ *
+ * ArraySortedMap does not actually contain its array: it contains a shared_ptr
+ * to a FixedArray.
+ *
+ * @tparam T The type of an element in the array.
+ * @tparam fixed_size the fixed size to use in creating the FixedArray.
+ */
+template <typename T, ArraySortedMapBase::size_type fixed_size>
+class FixedArray {
+ public:
+  using size_type = ArraySortedMapBase::size_type;
+  using array_type = std::array<T, fixed_size>;
+  using iterator = typename array_type::iterator;
+  using const_iterator = typename array_type::const_iterator;
+
+  FixedArray() {
+  }
+
+  template <typename SourceIterator>
+  FixedArray(SourceIterator src_begin, SourceIterator src_end) {
+    append(src_begin, src_end);
+  }
+
+  /**
+   * Appends to this array, copying from the given src_begin up to but not
+   * including the src_end.
+   */
+  template <typename SourceIterator>
+  void append(SourceIterator src_begin, SourceIterator src_end) {
+    size_type appending = static_cast<size_type>(src_end - src_begin);
+    size_type new_size = size_ + appending;
+    assert(new_size <= fixed_size);
+
+    std::copy(src_begin, src_end, end());
+    size_ = new_size;
+  }
+
+  /**
+   * Appends a single value to the array.
+   */
+  void append(T&& value) {
+    size_type new_size = size_ + 1;
+    assert(new_size <= fixed_size);
+
+    *end() = std::move(value);
+    size_ = new_size;
+  }
+
+  const_iterator begin() const {
+    return contents_.begin();
+  }
+
+  const_iterator end() const {
+    return begin() + size_;
+  }
+
+  size_type size() const {
+    return size_;
+  }
+
+ private:
+  iterator begin() {
+    return contents_.begin();
+  }
+
+  iterator end() {
+    return begin() + size_;
+  }
+
+  array_type contents_;
+  size_type size_ = 0;
+};
+
+}  // namespace impl
+
+/**
+ * ArraySortedMap is a value type containing a map. It is immutable, but has
+ * methods to efficiently create new maps that are mutations of it.
+ */
+template <typename K, typename V, typename C = std::less<K>>
+class ArraySortedMap : public impl::ArraySortedMapBase {
+ public:
+  using key_comparator_type = KeyComparator<K, V, C>;
+
+  /**
+   * The type of the entries stored in the map.
+   */
+  using value_type = std::pair<K, V>;
+
+  /**
+   * The type of the fixed-size array containing entries of value_type.
+   */
+  using array_type = impl::FixedArray<value_type, kFixedSize>;
+  using const_iterator = typename array_type::const_iterator;
+
+  using array_pointer = std::shared_ptr<const array_type>;
+
+  /**
+   * Creates an empty ArraySortedMap.
+   */
+  explicit ArraySortedMap(const C& comparator = C())
+      : array_(EmptyArray()), key_comparator_(comparator) {
+  }
+
+  /**
+   * Creates an ArraySortedMap containing the given entries.
+   */
+  ArraySortedMap(std::initializer_list<value_type> entries,
+                 const C& comparator = C())
+      : array_(std::make_shared<array_type>(entries.begin(), entries.end())),
+        key_comparator_(comparator) {
+  }
+
+  /**
+   * Creates a new map identical to this one, but with a key-value pair added or
+   * updated.
+   *
+   * @param key The key to insert/update.
+   * @param value The value to associate with the key.
+   * @return A new dictionary with the added/updated value.
+   */
+  ArraySortedMap insert(const K& key, const V& value) const {
+    const_iterator current_end = end();
+    const_iterator pos = LowerBound(key);
+    bool replacing_entry = false;
+
+    if (pos != current_end) {
+      // LowerBound found an entry where pos->first >= pair.first. Reversing the
+      // argument order here tests pair.first < pos->first.
+      replacing_entry = !key_comparator_(key, *pos);
+      if (replacing_entry && value == pos->second) {
+        return *this;
+      }
+    }
+
+    // Copy the segment before the found position. If not found, this is
+    // everything.
+    auto copy = std::make_shared<array_type>(begin(), pos);
+
+    // Copy the value to be inserted.
+    copy->append(value_type(key, value));
+
+    if (replacing_entry) {
+      // Skip the thing at pos because it compares the same as the pair above.
+      copy->append(pos + 1, current_end);
+    } else {
+      copy->append(pos, current_end);
+    }
+    return wrap(copy);
+  }
+
+  /**
+   * Creates a new map identical to this one, but with a key removed from it.
+   *
+   * @param key The key to remove.
+   * @return A new dictionary without that value.
+   */
+  ArraySortedMap erase(const K& key) const {
+    const_iterator current_end = end();
+    const_iterator pos = find(key);
+    if (pos == current_end) {
+      return *this;
+    } else if (size() <= 1) {
+      // If the key was found and it's the last entry, removing it would make
+      // the result empty.
+      return wrap(EmptyArray());
+    } else {
+      auto copy = std::make_shared<array_type>(begin(), pos);
+      copy->append(pos + 1, current_end);
+      return wrap(copy);
+    }
+  }
+
+  /**
+   * Finds a value in the map.
+   *
+   * @param key The key to look up.
+   * @return An iterator pointing to the entry containing the key, or end() if
+   *     not found.
+   */
+  const_iterator find(const K& key) const {
+    const_iterator not_found = end();
+    const_iterator lower_bound = LowerBound(key);
+    if (lower_bound != not_found && !key_comparator_(key, *lower_bound)) {
+      return lower_bound;
+    } else {
+      return not_found;
+    }
+  }
+
+  // TODO(wilhuff): indexof
+
+  /** Returns true if the map contains no elements. */
+  bool empty() const {
+    return size() == 0;
+  }
+
+  /** Returns the number of items in this map. */
+  size_type size() const {
+    return array_->size();
+  }
+
+  /**
+   * Returns an iterator pointing to the first entry in the map. If there are
+   * no entries in the map, begin() == end().
+   */
+  const_iterator begin() const {
+    return array_->begin();
+  }
+
+  /**
+   * Returns an iterator pointing past the last entry in the map.
+   */
+  const_iterator end() const {
+    return array_->end();
+  }
+
+ private:
+  static array_pointer EmptyArray() {
+    static const array_pointer kEmptyArray =
+        std::make_shared<const array_type>();
+    return kEmptyArray;
+  }
+
+  ArraySortedMap(const array_pointer& array,
+                 const key_comparator_type& key_comparator) noexcept
+      : array_(array), key_comparator_(key_comparator) {
+  }
+
+  ArraySortedMap wrap(const array_pointer& array) const noexcept {
+    return ArraySortedMap(array, key_comparator_);
+  }
+
+  const_iterator LowerBound(const K& key) const {
+    return std::lower_bound(begin(), end(), key, key_comparator_);
+  }
+
+  array_pointer array_;
+  key_comparator_type key_comparator_;
+};
+
+}  // namespace immutable
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_IMMUTABLE_ARRAY_SORTED_MAP_H_
diff --git a/Firestore/core/src/firebase/firestore/immutable/map_entry.h b/Firestore/core/src/firebase/firestore/immutable/map_entry.h
new file mode 100644
index 0000000..2130b5b
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/immutable/map_entry.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2018 Google
+ *
+ * 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 FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_IMMUTABLE_MAP_ENTRY_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_IMMUTABLE_MAP_ENTRY_H_
+
+#include <functional>
+#include <utility>
+
+namespace firebase {
+namespace firestore {
+namespace immutable {
+
+/**
+ * Compares two keys out of a map entry.
+ *
+ * @tparam K The type of the first value in the pair.
+ * @tparam V The type of the second value in the pair.
+ * @tparam C The comparator for use for values of type K
+ */
+template <typename K, typename V, typename C = std::less<K>>
+struct KeyComparator {
+  typedef std::pair<K, V> pair_type;
+
+  explicit KeyComparator(const C& comparator = C())
+      : key_comparator_(comparator) {
+  }
+
+  bool operator()(const K& lhs, const pair_type& rhs) const noexcept {
+    return key_comparator_(lhs, rhs.first);
+  }
+
+  bool operator()(const pair_type& lhs, const K& rhs) const noexcept {
+    return key_comparator_(lhs.first, rhs);
+  }
+
+  bool operator()(const pair_type& lhs, const pair_type& rhs) const noexcept {
+    return key_comparator_(lhs.first, rhs.first);
+  }
+
+ private:
+  C key_comparator_;
+};
+
+}  // namespace immutable
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_IMMUTABLE_MAP_ENTRY_H_
diff --git a/Firestore/core/test/firebase/firestore/immutable/CMakeLists.txt b/Firestore/core/test/firebase/firestore/immutable/CMakeLists.txt
new file mode 100644
index 0000000..e7b0b6e
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/immutable/CMakeLists.txt
@@ -0,0 +1,22 @@
+# Copyright 2018 Google
+#
+# 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.
+
+cc_test(
+  firebase_firestore_immutable_test
+  SOURCES
+    array_sorted_map_test.cc
+  DEPENDS
+    firebase_firestore_immutable
+    firebase_firestore_util
+)
diff --git a/Firestore/core/test/firebase/firestore/immutable/array_sorted_map_test.cc b/Firestore/core/test/firebase/firestore/immutable/array_sorted_map_test.cc
new file mode 100644
index 0000000..4dc6a4b
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/immutable/array_sorted_map_test.cc
@@ -0,0 +1,328 @@
+/*
+ * Copyright 2018 Google
+ *
+ * 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.
+ */
+
+#include "Firestore/core/src/firebase/firestore/immutable/array_sorted_map.h"
+
+#include <numeric>
+#include <random>
+
+#include "Firestore/core/src/firebase/firestore/util/secure_random.h"
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace immutable {
+
+typedef ArraySortedMap<int, int> IntMap;
+constexpr IntMap::size_type kFixedSize = IntMap::kFixedSize;
+
+template <typename K, typename V>
+testing::AssertionResult NotFound(const ArraySortedMap<K, V>& set,
+                                  const K& key) {
+  auto found = set.find(key);
+  if (found == set.end()) {
+    return testing::AssertionSuccess();
+  } else {
+    return testing::AssertionFailure()
+           << "Should not have found (" << found->first << ", " << found->second
+           << ") @ " << found;
+  }
+}
+
+template <typename K, typename V>
+testing::AssertionResult Found(const ArraySortedMap<K, V>& map,
+                               const K& key,
+                               const V& expected) {
+  auto found = map.find(key);
+  if (found == map.end()) {
+    return testing::AssertionFailure() << "Did not find key " << key;
+  }
+  if (found->second == expected) {
+    return testing::AssertionSuccess();
+  } else {
+    return testing::AssertionFailure() << "Found entry was (" << found->first
+                                       << ", " << found->second << ")";
+  }
+}
+
+/**
+ * Creates a vector containing a sequence of integers from the given starting
+ * element up to, but not including, the given end element, with values
+ * incremented by the given step.
+ *
+ * If step is negative the sequence is in descending order (but still starting
+ * at start and ending before end).
+ */
+std::vector<int> Sequence(int start, int end, int step = 1) {
+  std::vector<int> result;
+  if (step > 0) {
+    for (int i = start; i < end; i += step) {
+      result.push_back(i);
+    }
+  } else {
+    for (int i = start; i > end; i += step) {
+      result.push_back(i);
+    }
+  }
+  return result;
+}
+
+/**
+ * Creates a vector containing a sequence of integers with the given number of
+ * elements, from zero up to, but not including the given value.
+ */
+std::vector<int> Sequence(int num_elements) {
+  return Sequence(0, num_elements);
+}
+
+/**
+ * Creates a copy of the given vector with contents shuffled randomly.
+ */
+std::vector<int> Shuffled(const std::vector<int>& values) {
+  std::vector<int> result(values);
+  util::SecureRandom rng;
+  std::shuffle(result.begin(), result.end(), rng);
+  return result;
+}
+
+/**
+ * Creates a copy of the given vector with contents sorted.
+ */
+std::vector<int> Sorted(const std::vector<int>& values) {
+  std::vector<int> result(values);
+  std::sort(result.begin(), result.end());
+  return result;
+}
+
+/**
+ * Creates a vector of pairs where each pair has the same first and second
+ * corresponding to an element in the given vector.
+ */
+std::vector<std::pair<int, int>> Pairs(const std::vector<int>& values) {
+  std::vector<std::pair<int, int>> result;
+  for (auto&& value : values) {
+    result.emplace_back(value, value);
+  }
+  return result;
+}
+
+/**
+ * Creates an ArraySortedMap by inserting a pair for each value in the vector.
+ * Each pair will have the same key and value.
+ */
+IntMap ToMap(const std::vector<int>& values) {
+  IntMap result;
+  for (auto&& value : values) {
+    result = result.insert(value, value);
+  }
+  return result;
+}
+
+/**
+ * Appends the contents of the given container to a new vector.
+ */
+template <typename Container>
+std::vector<typename Container::value_type> Append(const Container& container) {
+  std::vector<typename Container::value_type> result;
+  result.insert(result.begin(), container.begin(), container.end());
+  return result;
+}
+
+// TODO(wilhuff): ReverseTraversal
+
+#define ASSERT_SEQ_EQ(x, y) ASSERT_EQ((x), Append(y));
+#define EXPECT_SEQ_EQ(x, y) EXPECT_EQ((x), Append(y));
+
+TEST(ArraySortedMap, SearchForSpecificKey) {
+  IntMap map{{1, 3}, {2, 4}};
+
+  ASSERT_TRUE(Found(map, 1, 3));
+  ASSERT_TRUE(Found(map, 2, 4));
+  ASSERT_TRUE(NotFound(map, 3));
+}
+
+TEST(ArraySortedMap, RemoveKeyValuePair) {
+  IntMap map{{1, 3}, {2, 4}};
+
+  IntMap new_map = map.erase(1);
+  ASSERT_TRUE(Found(new_map, 2, 4));
+  ASSERT_TRUE(NotFound(new_map, 1));
+
+  // Make sure the original one is not mutated
+  ASSERT_TRUE(Found(map, 1, 3));
+  ASSERT_TRUE(Found(map, 2, 4));
+}
+
+TEST(ArraySortedMap, MoreRemovals) {
+  IntMap map = IntMap()
+                   .insert(1, 1)
+                   .insert(50, 50)
+                   .insert(3, 3)
+                   .insert(4, 4)
+                   .insert(7, 7)
+                   .insert(9, 9)
+                   .insert(1, 20)
+                   .insert(18, 18)
+                   .insert(3, 2)
+                   .insert(4, 71)
+                   .insert(7, 42)
+                   .insert(9, 88);
+
+  ASSERT_TRUE(Found(map, 7, 42));
+  ASSERT_TRUE(Found(map, 3, 2));
+  ASSERT_TRUE(Found(map, 1, 20));
+
+  IntMap s1 = map.erase(7);
+  IntMap s2 = map.erase(3);
+  IntMap s3 = map.erase(1);
+
+  ASSERT_TRUE(NotFound(s1, 7));
+  ASSERT_TRUE(Found(s1, 3, 2));
+  ASSERT_TRUE(Found(s1, 1, 20));
+
+  ASSERT_TRUE(Found(s2, 7, 42));
+  ASSERT_TRUE(NotFound(s2, 3));
+  ASSERT_TRUE(Found(s2, 1, 20));
+
+  ASSERT_TRUE(Found(s3, 7, 42));
+  ASSERT_TRUE(Found(s3, 3, 2));
+  ASSERT_TRUE(NotFound(s3, 1));
+}
+
+TEST(ArraySortedMap, RemovesMiddle) {
+  IntMap map{{1, 1}, {2, 2}, {3, 3}};
+  ASSERT_TRUE(Found(map, 1, 1));
+  ASSERT_TRUE(Found(map, 2, 2));
+  ASSERT_TRUE(Found(map, 3, 3));
+
+  IntMap s1 = map.erase(2);
+  ASSERT_TRUE(Found(s1, 1, 1));
+  ASSERT_TRUE(NotFound(s1, 2));
+  ASSERT_TRUE(Found(s1, 3, 3));
+}
+
+TEST(ArraySortedMap, Increasing) {
+  auto total = static_cast<int>(kFixedSize);
+  IntMap map;
+
+  for (int i = 0; i < total; i++) {
+    map = map.insert(i, i);
+  }
+  ASSERT_EQ(kFixedSize, map.size());
+
+  for (int i = 0; i < total; i++) {
+    map = map.erase(i);
+  }
+  ASSERT_EQ(0u, map.size());
+}
+
+TEST(ArraySortedMap, Override) {
+  IntMap map = IntMap().insert(10, 10).insert(10, 8);
+
+  ASSERT_TRUE(Found(map, 10, 8));
+  ASSERT_FALSE(Found(map, 10, 10));
+}
+
+TEST(ArraySortedMap, ChecksSize) {
+  std::vector<int> to_insert = Sequence(kFixedSize);
+  IntMap map = ToMap(to_insert);
+
+  // Replacing an existing entry should not hit increase size
+  map = map.insert(5, 10);
+
+  int next = kFixedSize;
+  ASSERT_DEATH_IF_SUPPORTED(map.insert(next, next), "new_size <= fixed_size");
+}
+
+TEST(ArraySortedMap, Empty) {
+  IntMap map = IntMap().insert(10, 10).erase(10);
+  EXPECT_TRUE(map.empty());
+  EXPECT_EQ(0u, map.size());
+  EXPECT_TRUE(NotFound(map, 1));
+  EXPECT_TRUE(NotFound(map, 10));
+}
+
+TEST(ArraySortedMap, EmptyGet) {
+  IntMap map;
+  EXPECT_TRUE(NotFound(map, 10));
+}
+
+TEST(ArraySortedMap, EmptySize) {
+  IntMap map;
+  EXPECT_TRUE(map.empty());
+  EXPECT_EQ(0u, map.size());
+}
+
+TEST(ArraySortedMap, EmptyRemoval) {
+  IntMap map;
+  IntMap new_map = map.erase(1);
+  EXPECT_TRUE(new_map.empty());
+  EXPECT_EQ(0u, new_map.size());
+  EXPECT_TRUE(NotFound(new_map, 1));
+}
+
+TEST(ArraySortedMap, InsertionAndRemovalOfMaxItems) {
+  auto expected_size = kFixedSize;
+  int n = static_cast<int>(expected_size);
+  std::vector<int> to_insert = Shuffled(Sequence(n));
+  std::vector<int> to_remove = Shuffled(to_insert);
+
+  // Add them to the map
+  IntMap map = ToMap(to_insert);
+  ASSERT_EQ(expected_size, map.size())
+      << "Check if all N objects are in the map";
+
+  // check the order is correct
+  ASSERT_SEQ_EQ(Pairs(Sorted(to_insert)), map);
+
+  for (int i : to_remove) {
+    map = map.erase(i);
+  }
+  ASSERT_EQ(0u, map.size()) << "Check we removed all of the items";
+}
+
+TEST(ArraySortedMap, BalanceProblem) {
+  std::vector<int> to_insert{1, 7, 8, 5, 2, 6, 4, 0, 3};
+
+  IntMap map = ToMap(to_insert);
+  ASSERT_SEQ_EQ(Pairs(Sorted(to_insert)), map);
+}
+
+// TODO(wilhuff): PredecessorKey
+
+// TODO(wilhuff): Iterators
+
+// TODO(wilhuff): IndexOf
+
+TEST(ArraySortedMap, AvoidsCopying) {
+  IntMap map = IntMap().insert(10, 20);
+  auto found = map.find(10);
+  ASSERT_NE(found, map.end());
+  EXPECT_EQ(20, found->second);
+
+  // Verify that inserting something with equal keys and values just returns
+  // the same underlying array.
+  IntMap duped = map.insert(10, 20);
+  auto duped_found = duped.find(10);
+
+  // If everything worked correctly, the backing array should not have been
+  // copied and the pointer to the entry with 10 as key should be the same.
+  EXPECT_EQ(found, duped_found);
+}
+
+}  // namespace immutable
+}  // namespace firestore
+}  // namespace firebase