Start on ArraySortedMap in C++ (#721)

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

4 files changed, 431 insertions, 0 deletions

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_