Container 2020 day 2

#pragma once
#include <algorithm>
#include <numeric>
#include <cassert>
#include <stdexcept>
namespace API
{
    template<typename T>
    class Container
    {
    public:
        using pointer = T*;
        using const_pointer = const T*;
        using iterator = T*; //aliases for generic code
        using const_iterator = const T*;
        using value_type = T;
        using size_type = size_t;
        using reference = T&;
        using const_reference = const T&;

        friend void swap(Container& a, Container& b) noexcept;

        Container() = default;
        explicit Container(size_type count) : _data(new T[count]), _count(count), _capacity(count){
            std::fill(begin(), end(), T());
        };

        explicit Container(const Container& that) : _data(new T[that._capacity]), _count(that._count), _capacity(that._capacity)  {
            std::copy(begin(), end(), _data);
        }

        Container(Container&& that) noexcept {
            _count = that._count;
            _capacity = that._capacity;
            _data = that._data;
            that._data = nullptr;
            that._count = 0;
            that._capacity = 0;
        }

        Container& operator=(Container&& that) noexcept {
            swap(that);
            return *this;
        }

        void swap(Container& that) noexcept {
            using std::swap;
            swap(_data, that._data);
            swap(_count, that._count);
            swap(_capacity, that._capacity);
        }

        Container& operator=(const Container& that) { // copy assignment
            delete[] _data;
            _data = new T[that._capacity]; //overwrites an existing pointer
            _count = that._count;
            _capacity = that._capacity;
            std::copy(that.begin(), that.end(), _data);
            return *this;
        }

        ~Container() {
            //TODO: maybe have to call destructors or T (~T)
            delete[] _data;
        }

        void reserve(size_type newCapacity) {
            if (newCapacity <= _capacity) { return;  } //never decrease the allocation
            pointer newBuffer = new T[newCapacity];
            std::move(begin(), end(), newBuffer);
            delete[] _data; //TODO: potentially need to deconstruct objects
            _data = newBuffer;
            _capacity = newCapacity;
        }

        void push_back(const T& value) {
            if (_capacity == 0) {
                reserve(2);
            }
            else if (_count == _capacity) {
                reserve(2 * _capacity);
            }
            _data[_count] = value;
            _count++;
        }

        reference at(size_type index) {
            if (index >= size()) {
                throw std::out_of_range("Container at() index is out of range!");
            }
            return _data[index];
        }
        const_reference at(size_type index) const {
            if (index >= size()) {
                throw std::out_of_range("Container at() index is out of range!");
            }
            return _data[index];
        }

        reference operator[](size_type index) noexcept{
            assert(index < size() && "Container operator[] index is out of range!");
            return _data[index];
        }
        const_reference operator[](size_type index) const noexcept {
            assert(index < size() && "Container operator[] index is out of range!");
            return _data[index];
        }

        reference front() noexcept {
            assert(!empty() && "front() on empty container is UB");
            return _data[0];
        }
        const_reference front() const noexcept {
            assert(!empty() && "front() on empty container is UB");
            return _data[0];
        }

        const_reference back() const noexcept {
            assert(!empty() && "back() on empty container is UB");
            return _data[size() - 1];
        }
        reference back() noexcept {
            assert(!empty() && "back() on empty container is UB");
            return _data[size() - 1];
        }

        [[nodiscard]] constexpr bool empty() const noexcept {
            return size() == 0;
        }

        size_type size() const noexcept {
            return _count;
        }

        //TODO: make free functions of these
        const_iterator begin() const noexcept { return _data; }
        const_iterator cbegin() const noexcept { return _data; }
        iterator begin() noexcept { return _data; }

        const_iterator end() const noexcept { return _data + _count; }
        const_iterator cend() const noexcept { return _data + _count; }
        iterator end() noexcept { return _data + _count; }

    private:
        T* _data = nullptr;
        size_type _count = 0;
        size_type _capacity = 0;
    };

    template<typename T>
    void swap(Container<T>& a, Container<T>& b) noexcept {
        a.swap(b);
        /*std::swap(a._capacity, b._capacity);
        std::swap(a._count, b._count);
        std::swap(a._data, b._data);*/
    }

    template<typename T>
    bool operator==(const Container<T>& lhs, const Container<T>& rhs) noexcept {
        if (std::size(lhs) != std::size(rhs)) { return false; }
        return std::equal(std::begin(lhs), std::end(lhs), std::begin(rhs));
    }
    template<typename T>
    bool operator<(const Container<T>& lhs, const Container<T>& rhs) noexcept {
        return std::lexicographical_compare(lhs.begin(), lhs.end(),
            rhs.begin(), rhs.end());
    }

    template<typename T>
    bool operator!=(const Container<T>& lhs, const Container<T>& rhs) noexcept {
        return not(lhs == rhs);
    }
    template<typename T>
    bool operator>(const Container<T>& lhs, const Container<T>& rhs) noexcept {
        return rhs < lhs;
    }
    template<typename T>
    bool operator<=(const Container<T>& lhs, const Container<T>& rhs) noexcept {
        !(lhs > rhs);
    }
    template<typename T>
    bool operator>=(const Container<T>& lhs, const Container<T>& rhs) noexcept {
        !(lhs < rhs);
    }
}