// Copyright 2017 The NXT Authors
//
// 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 COMMON_SERIALQUEUE_H_
#define COMMON_SERIALQUEUE_H_

#include "common/Assert.h"
#include "common/Serial.h"

#include <cstdint>
#include <vector>

template<typename T>
class SerialQueue {
    private:
        using SerialPair = std::pair<Serial, std::vector<T>>;
        using Storage = std::vector<SerialPair>;
        using StorageIterator = typename Storage::iterator;
        using ConstStorageIterator = typename Storage::const_iterator;

    public:
        class Iterator {
            public:
                Iterator(StorageIterator start);
                Iterator& operator++();

                bool operator==(const Iterator& other) const;
                bool operator!=(const Iterator& other) const;
                T& operator*() const;

            private:
                StorageIterator storageIterator;
                // Special case the serialIterator when it should be equal to storageIterator.begin()
                // otherwise we could ask storageIterator.begin() when storageIterator is storage.end()
                // which is invalid. storageIterator.begin() is tagged with a nullptr.
                T* serialIterator;
        };

        class ConstIterator {
            public:
                ConstIterator(ConstStorageIterator start);
                ConstIterator& operator++();

                bool operator==(const ConstIterator& other) const;
                bool operator!=(const ConstIterator& other) const;
                const T& operator*() const;

            private:
                ConstStorageIterator storageIterator;
                const T* serialIterator;
        };

        class BeginEnd {
            public:
                BeginEnd(StorageIterator start, StorageIterator end);

                Iterator begin() const;
                Iterator end() const;

            private:
                StorageIterator startIt;
                StorageIterator endIt;
        };

        class ConstBeginEnd {
            public:
                ConstBeginEnd(ConstStorageIterator start, ConstStorageIterator end);

                ConstIterator begin() const;
                ConstIterator end() const;

            private:
                ConstStorageIterator startIt;
                ConstStorageIterator endIt;
        };

        // The serial must be given in (not strictly) increasing order.
        void Enqueue(const T& value, Serial serial);
        void Enqueue(T&& value, Serial serial);
        void Enqueue(const std::vector<T>& values, Serial serial);
        void Enqueue(std::vector<T>&& values, Serial serial);

        bool Empty() const;

        // The UpTo variants of Iterate and Clear affect all values associated to a serial
        // that is smaller OR EQUAL to the given serial. Iterating is done like so:
        //     for (const T& value : queue.IterateAll()) { stuff(T); }
        ConstBeginEnd IterateAll() const;
        ConstBeginEnd IterateUpTo(Serial serial) const;
        BeginEnd IterateAll();
        BeginEnd IterateUpTo(Serial serial);

        void Clear();
        void ClearUpTo(Serial serial);

        Serial FirstSerial() const;

    private:
        // Returns the first StorageIterator that a serial bigger than serial.
        ConstStorageIterator FindUpTo(Serial serial) const;
        StorageIterator FindUpTo(Serial serial);
        Storage storage;
};

// SerialQueue

template<typename T>
void SerialQueue<T>::Enqueue(const T& value, Serial serial) {
    NXT_ASSERT(Empty() || storage.back().first <= serial);

    if (Empty() || storage.back().first < serial) {
        storage.emplace_back(SerialPair(serial, {}));
    }
    storage.back().second.emplace_back(value);
}

template<typename T>
void SerialQueue<T>::Enqueue(T&& value, Serial serial) {
    NXT_ASSERT(Empty() || storage.back().first <= serial);

    if (Empty() || storage.back().first < serial) {
        storage.emplace_back(SerialPair(serial, {}));
    }
    storage.back().second.emplace_back(value);
}

template<typename T>
void SerialQueue<T>::Enqueue(const std::vector<T>& values, Serial serial) {
    NXT_ASSERT(values.size() > 0);
    NXT_ASSERT(Empty() || storage.back().first <= serial);
    storage.emplace_back(SerialPair(serial, {values}));
}

template<typename T>
void SerialQueue<T>::Enqueue(std::vector<T>&& values, Serial serial) {
    NXT_ASSERT(values.size() > 0);
    NXT_ASSERT(Empty() || storage.back().first <= serial);
    storage.emplace_back(SerialPair(serial, {values}));
}

template<typename T>
bool SerialQueue<T>::Empty() const {
    return storage.empty();
}

template<typename T>
typename SerialQueue<T>::ConstBeginEnd SerialQueue<T>::IterateAll() const {
    return {storage.begin(), storage.end()};
}

template<typename T>
typename SerialQueue<T>::ConstBeginEnd SerialQueue<T>::IterateUpTo(Serial serial) const {
    return {storage.begin(), FindUpTo(serial)};
}

template<typename T>
typename SerialQueue<T>::BeginEnd SerialQueue<T>::IterateAll() {
    return {storage.begin(), storage.end()};
}

template<typename T>
typename SerialQueue<T>::BeginEnd SerialQueue<T>::IterateUpTo(Serial serial) {
    return {storage.begin(), FindUpTo(serial)};
}

template<typename T>
void SerialQueue<T>::Clear() {
    storage.clear();
}

template<typename T>
void SerialQueue<T>::ClearUpTo(Serial serial) {
    storage.erase(storage.begin(), FindUpTo(serial));
}

template<typename T>
Serial SerialQueue<T>::FirstSerial() const {
    NXT_ASSERT(!Empty());
    return storage.front().first;
}

template<typename T>
typename SerialQueue<T>::ConstStorageIterator SerialQueue<T>::FindUpTo(Serial serial) const {
    auto it = storage.begin();
    while (it != storage.end() && it->first <= serial) {
        it ++;
    }
    return it;
}

template<typename T>
typename SerialQueue<T>::StorageIterator SerialQueue<T>::FindUpTo(Serial serial) {
    auto it = storage.begin();
    while (it != storage.end() && it->first <= serial) {
        it ++;
    }
    return it;
}

// SerialQueue::BeginEnd

template<typename T>
SerialQueue<T>::BeginEnd::BeginEnd(typename SerialQueue<T>::StorageIterator start, typename SerialQueue<T>::StorageIterator end)
    : startIt(start), endIt(end) {
}

template<typename T>
typename SerialQueue<T>::Iterator SerialQueue<T>::BeginEnd::begin() const {
    return {startIt};
}

template<typename T>
typename SerialQueue<T>::Iterator SerialQueue<T>::BeginEnd::end() const {
    return {endIt};
}

// SerialQueue::Iterator

template<typename T>
SerialQueue<T>::Iterator::Iterator(typename SerialQueue<T>::StorageIterator start)
    : storageIterator(start), serialIterator(nullptr) {
}

template<typename T>
typename SerialQueue<T>::Iterator& SerialQueue<T>::Iterator::operator++() {
    T* vectorData = storageIterator->second.data();

    if (serialIterator == nullptr) {
        serialIterator = vectorData + 1;
    } else {
        serialIterator ++;
    }

    if (serialIterator >= vectorData + storageIterator->second.size()) {
        serialIterator = nullptr;
        storageIterator ++;
    }

    return *this;
}

template<typename T>
bool SerialQueue<T>::Iterator::operator==(const typename SerialQueue<T>::Iterator& other) const {
    return other.storageIterator == storageIterator && other.serialIterator == serialIterator;
}

template<typename T>
bool SerialQueue<T>::Iterator::operator!=(const typename SerialQueue<T>::Iterator& other) const {
    return !(*this == other);
}

template<typename T>
T& SerialQueue<T>::Iterator::operator*() const {
    if (serialIterator == nullptr) {
        return *storageIterator->second.begin();
    }
    return *serialIterator;
}

// SerialQueue::ConstBeginEnd

template<typename T>
SerialQueue<T>::ConstBeginEnd::ConstBeginEnd(typename SerialQueue<T>::ConstStorageIterator start, typename SerialQueue<T>::ConstStorageIterator end)
    : startIt(start), endIt(end) {
}

template<typename T>
typename SerialQueue<T>::ConstIterator SerialQueue<T>::ConstBeginEnd::begin() const {
    return {startIt};
}

template<typename T>
typename SerialQueue<T>::ConstIterator SerialQueue<T>::ConstBeginEnd::end() const {
    return {endIt};
}

// SerialQueue::ConstIterator

template<typename T>
SerialQueue<T>::ConstIterator::ConstIterator(typename SerialQueue<T>::ConstStorageIterator start)
    : storageIterator(start), serialIterator(nullptr) {
}

template<typename T>
typename SerialQueue<T>::ConstIterator& SerialQueue<T>::ConstIterator::operator++() {
    const T* vectorData = storageIterator->second.data();

    if (serialIterator == nullptr) {
        serialIterator = vectorData + 1;
    } else {
        serialIterator ++;
    }

    if (serialIterator >= vectorData + storageIterator->second.size()) {
        serialIterator = nullptr;
        storageIterator ++;
    }

    return *this;
}

template<typename T>
bool SerialQueue<T>::ConstIterator::operator==(const typename SerialQueue<T>::ConstIterator& other) const {
    return other.storageIterator == storageIterator && other.serialIterator == serialIterator;
}

template<typename T>
bool SerialQueue<T>::ConstIterator::operator!=(const typename SerialQueue<T>::ConstIterator& other) const {
    return !(*this == other);
}

template<typename T>
const T& SerialQueue<T>::ConstIterator::operator*() const {
    if (serialIterator == nullptr) {
        return *storageIterator->second.begin();
    }
    return *serialIterator;
}

#endif // COMMON_SERIALQUEUE_H_