// Copyright (c) 2016, the SDSL Project Authors.  All rights reserved.
// Please see the AUTHORS file for details.  Use of this source code is governed
// by a BSD license that can be found in the LICENSE file.
/*!\file int_vector_buffer.hpp
 * \brief int_vector_buffer.hpp contains the sdsl::int_vector_buffer class.
 * \author Maike Zwerger, Timo Beller and Simon Gog
 */
#ifndef INCLUDED_INT_VECTOR_BUFFER
#define INCLUDED_INT_VECTOR_BUFFER

#include <cassert>
#include <fstream>
#include <iterator>
#include <stdint.h>
#include <string>

#include <sdsl/int_vector.hpp>
#include <sdsl/ram_fs.hpp>
#include <sdsl/sfstream.hpp>
#include <sdsl/util.hpp>

namespace sdsl
{

template <uint8_t t_width = 0>
class int_vector_buffer
{
public:
    class iterator;

    typedef typename int_vector<t_width>::difference_type difference_type;
    typedef typename int_vector<t_width>::value_type value_type;

private:
    static_assert(t_width <= 64, "int_vector_buffer: width must be at most 64 bits.");
    sdsl::isfstream m_ifile;
    sdsl::osfstream m_ofile;
    std::string m_filename;
    int_vector<t_width> m_buffer;
    bool m_need_to_write = false;
    // length of int_vector header in bytes: 0 for plain, 8 for int_vector<t_width> (0 < t_width), 9 for int_vector<0>
    uint64_t m_offset = 0;
    uint64_t m_buffersize = 8; // in elements! m_buffersize*width() must be a multiple of 8!
    uint64_t m_size = 0;       // size of int_vector_buffer
    uint64_t m_begin = 0;      // number in elements

    //! Read block containing element at index idx.
    void read_block(const uint64_t idx)
    {
        m_begin = (idx / m_buffersize) * m_buffersize;
        if (m_begin >= m_size)
        {
            util::set_to_value(m_buffer, 0);
        }
        else
        {
            m_ifile.seekg(m_offset + (m_begin * width()) / 8);
            assert(m_ifile.good());
            m_ifile.read((char *)m_buffer.data(), (m_buffersize * width()) / 8);
            if ((uint64_t)m_ifile.gcount() < (m_buffersize * width()) / 8)
            {
                m_ifile.clear();
            }
            assert(m_ifile.good());
            for (uint64_t i = m_size - m_begin; i < m_buffersize; ++i)
            {
                m_buffer[i] = 0;
            }
        }
    }

    //! Write current block to file.
    void write_block()
    {
        if (m_need_to_write)
        {
            m_ofile.seekp(m_offset + (m_begin * width()) / 8);
            assert(m_ofile.good());
            if (m_begin + m_buffersize >= m_size)
            {
                // last block in file
                uint64_t wb = ((m_size - m_begin) * width() + 7) / 8;
                m_ofile.write((char *)m_buffer.data(), wb);
            }
            else
            {
                m_ofile.write((char *)m_buffer.data(), (m_buffersize * width()) / 8);
            }
            m_ofile.flush();
            assert(m_ofile.good());
            m_need_to_write = false;
        }
    }

    //! Read value from idx.
    uint64_t read(const uint64_t idx)
    {
        assert(is_open());
        assert(idx < m_size);
        if (idx < m_begin or m_begin + m_buffersize <= idx)
        {
            write_block();
            read_block(idx);
        }
        return m_buffer[idx - m_begin];
    }

    //! Write value to idx.
    void write(const uint64_t idx, const uint64_t value)
    {
        assert(is_open());
        // If idx is not in current block, write current block and load needed block
        if (idx < m_begin or m_begin + m_buffersize <= idx)
        {
            write_block();
            read_block(idx);
        }
        if (m_size <= idx)
        {
            m_size = idx + 1;
        }
        m_need_to_write = true;
        m_buffer[idx - m_begin] = value;
    }

public:
    //! Constructor.
    int_vector_buffer()
    {
        m_buffer = int_vector<t_width>();
    }

    //! Constructor for int_vector_buffer.
    /*!\param filename   File that contains the data read from / written to.
     *  \param mode       Openmode:
     *                    std::ios::in opens an existing file (that must exist already),
     *                    std::ios::out creates a new file (that may exist already).
     *  \param buffersize Buffersize in bytes. This has to be a multiple of 8, if not the next multiple of 8 will be
     * taken \param int_width  The width of each integer. \param is_plain   If false (default) the file will be
     * interpreted as int_vector. If true the file will be interpreted as plain array with t_width bits per integer. In
     * second case (is_plain==true), t_width must be 8, 16, 32 or 64.
     */
    int_vector_buffer(const std::string filename,
                      std::ios::openmode mode = std::ios::in,
                      const uint64_t buffer_size = 1024 * 1024,
                      const uint8_t int_width = t_width,
                      bool const is_plain = false)
    {
        m_filename = filename;
        assert(!(mode & std::ios::app));
        mode &= ~std::ios::app;
        m_buffer.width(int_width);
        if (is_plain)
        {
            m_offset = 0;
            // is_plain is only allowed with width() in {8, 16, 32, 64}
            assert(8 == width() or 16 == width() or 32 == width() or 64 == width());
        }
        else
        {
            m_offset = 8; // TODO: make this dependent on header size of int_vector<t_width>
        }

        // Open file for IO
        m_ofile.open(m_filename, mode | std::ios::out | std::ios::binary);
        assert(m_ofile.good());
        m_ifile.open(m_filename, std::ios::in | std::ios::binary);
        assert(m_ifile.good());
        if (mode & std::ios::in)
        {
            uint64_t size = 0;
            if (is_plain)
            {
                m_ifile.seekg(0, std::ios_base::end);
                size = m_ifile.tellg() * 8;
            }
            else
            {
                uint8_t width = 0;
                int_vector<0>::read_header(size, width, m_ifile);
                m_buffer.width(width);
            }
            assert(m_ifile.good());
            m_size = size / width();
        }
        buffersize(buffer_size);
    }

    //! Move constructor.
    int_vector_buffer(int_vector_buffer && ivb) :
        m_filename(std::move(ivb.m_filename)),
        m_buffer(std::move(ivb.m_buffer)),
        m_need_to_write(ivb.m_need_to_write),
        m_offset(ivb.m_offset),
        m_buffersize(ivb.m_buffersize),
        m_size(ivb.m_size),
        m_begin(ivb.m_begin)
    {
        ivb.m_ifile.close();
        ivb.m_ofile.close();
        m_ifile.open(m_filename, std::ios::in | std::ios::binary);
        m_ofile.open(m_filename, std::ios::in | std::ios::out | std::ios::binary);
        assert(m_ifile.good());
        assert(m_ofile.good());
        // set ivb to default-constructor state
        ivb.m_filename = "";
        ivb.m_buffer = int_vector<t_width>();
        ivb.m_need_to_write = false;
        ivb.m_offset = 0;
        ivb.m_buffersize = 8;
        ivb.m_size = 0;
        ivb.m_begin = 0;
    }

    //! Destructor.
    ~int_vector_buffer()
    {
        close();
    }

    //! Move assignment operator.
    int_vector_buffer<t_width> & operator=(int_vector_buffer && ivb)
    {
        close();
        ivb.m_ifile.close();
        ivb.m_ofile.close();
        m_filename = ivb.m_filename;
        m_ifile.open(m_filename, std::ios::in | std::ios::binary);
        m_ofile.open(m_filename, std::ios::in | std::ios::out | std::ios::binary);
        assert(m_ifile.good());
        assert(m_ofile.good());
        // assign the values of ivb to this
        m_buffer = (int_vector<t_width> &&) ivb.m_buffer;
        m_need_to_write = ivb.m_need_to_write;
        m_offset = ivb.m_offset;
        m_buffersize = ivb.m_buffersize;
        m_size = ivb.m_size;
        m_begin = ivb.m_begin;
        // set ivb to default-constructor state
        ivb.m_filename = "";
        ivb.m_buffer = int_vector<t_width>();
        ivb.m_need_to_write = false;
        ivb.m_offset = 0;
        ivb.m_buffersize = 8;
        ivb.m_size = 0;
        ivb.m_begin = 0;
        return *this;
    }

    //! Returns the width of the integers which are accessed via the [] operator.
    uint8_t width() const
    {
        return m_buffer.width();
    }

    //! Returns the number of elements currently stored.
    uint64_t size() const
    {
        return m_size;
    }

    //! Returns the filename.
    std::string filename() const
    {
        return m_filename;
    }

    //! Returns the buffersize in bytes
    uint64_t buffersize() const
    {
        assert(m_buffersize * width() % 8 == 0);
        return (m_buffersize * width()) / 8;
    }

    //! Set the buffersize in bytes
    void buffersize(uint64_t buffersize)
    {
        if (0ULL == buffersize)
            buffersize = 8;
        write_block();
        if (0 == (buffersize * 8) % width())
        {
            m_buffersize =
                buffersize * 8 / width(); // m_buffersize might not be multiple of 8, but m_buffersize*width() is.
        }
        else
        {
            uint64_t element_buffersize =
                (buffersize * 8) / width() + 1; // one more element than fits into given buffersize in byte
            m_buffersize = element_buffersize + 7 - (element_buffersize + 7) % 8; // take next multiple of 8
        }
        m_buffer = int_vector<t_width>(m_buffersize, 0, width());
        if (0 != m_buffersize)
            read_block(0);
    }

    //! Returns whether state of underlying streams are good
    bool good()
    {
        return m_ifile.good() and m_ofile.good();
    }

    //! Returns whether underlying streams are currently associated to a file
    bool is_open()
    {
        return m_ifile.is_open() and m_ofile.is_open();
        ;
    }

    //! Delete all content and set size to 0
    void reset()
    {
        // reset file
        assert(m_ifile.good());
        assert(m_ofile.good());
        m_ifile.close();
        m_ofile.close();
        m_ofile.open(m_filename, std::ios::out | std::ios::binary);
        assert(m_ofile.good());
        m_ifile.open(m_filename, std::ios::in | std::ios::binary);
        assert(m_ifile.good());
        assert(m_ofile.good());
        // reset member variables
        m_need_to_write = false;
        m_size = 0;
        // reset buffer
        read_block(0);
    }

    // Forward declaration
    class reference;

    //! [] operator
    /*!\param i Index the i-th integer of length width().
     *  \return A reference to the i-th integer of length width().
     */
    reference operator[](uint64_t idx)
    {
        return reference(this, idx);
    }

    //! Appends the given element value to the end of the int_vector_buffer
    void push_back(const uint64_t value)
    {
        write(m_size, value);
    }

    //! Close the int_vector_buffer.
    /*! It is not possible to read from / write into the int_vector_buffer after calling this method
     *  \param remove_file If true, the underlying file will be removed on closing.
     */
    void close(bool remove_file = false)
    {
        if (is_open())
        {
            if (!remove_file)
            {
                write_block();
                if (0 < m_offset)
                { // in case of int_vector, write header and trailing zeros
                    uint64_t size = m_size * width();
                    m_ofile.seekp(0, std::ios::beg);
                    int_vector<t_width>::write_header(size, width(), m_ofile);
                    assert(m_ofile.good());
                    uint64_t wb = (size + 7) / 8;
                    if (wb % 8)
                    {
                        m_ofile.seekp(m_offset + wb);
                        assert(m_ofile.good());
                        m_ofile.write("\0\0\0\0\0\0\0\0", 8 - wb % 8);
                        assert(m_ofile.good());
                    }
                }
            }
            m_ifile.close();
            assert(m_ifile.good());
            m_ofile.close();
            assert(m_ofile.good());
            if (remove_file)
            {
                sdsl::remove(m_filename);
            }
        }
    }

    iterator begin()
    {
        return iterator(*this, 0);
    }

    iterator end()
    {
        return iterator(*this, size());
    }

    class reference
    {
        friend class int_vector_buffer<t_width>;

    private:
        int_vector_buffer<t_width> * const m_int_vector_buffer = nullptr;
        uint64_t m_idx = 0;

        reference()
        {}

        reference(int_vector_buffer<t_width> * _int_vector_buffer, uint64_t _idx) :
            m_int_vector_buffer(_int_vector_buffer),
            m_idx(_idx)
        {}

    public:
        //! Conversion to int for read operations
        operator uint64_t() const
        {
            return m_int_vector_buffer->read(m_idx);
        }

        //! Assignment operator for write operations
        reference & operator=(uint64_t const & val)
        {
            m_int_vector_buffer->write(m_idx, val);
            return *this;
        }

        //! Assignment operator
        reference & operator=(reference const & x)
        {
            return *this = (uint64_t)(x);
        };

        reference(reference const &) = default;

        //! Prefix increment of the proxy object
        reference & operator++()
        {
            uint64_t x = m_int_vector_buffer->read(m_idx);
            m_int_vector_buffer->write(m_idx, x + 1);
            return *this;
        }

        //! Postfix increment of the proxy object
        uint64_t operator++(int)
        {
            uint64_t val = (uint64_t) * this;
            ++(*this);
            return val;
        }

        //! Prefix decrement of the proxy object
        reference & operator--()
        {
            uint64_t x = m_int_vector_buffer->read(m_idx);
            m_int_vector_buffer->write(m_idx, x - 1);
            return *this;
        }

        //! Postfix decrement of the proxy object
        uint64_t operator--(int)
        {
            uint64_t val = (uint64_t) * this;
            --(*this);
            return val;
        }

        //! Add assign from the proxy object
        reference & operator+=(const uint64_t x)
        {
            uint64_t w = m_int_vector_buffer->read(m_idx);
            m_int_vector_buffer->write(m_idx, w + x);
            return *this;
        }

        //! Subtract assign from the proxy object
        reference & operator-=(const uint64_t x)
        {
            uint64_t w = m_int_vector_buffer->read(m_idx);
            m_int_vector_buffer->write(m_idx, w - x);
            return *this;
        }

        bool operator==(reference const & x) const
        {
            return (uint64_t) * this == (uint64_t)x;
        }

        bool operator<(reference const & x) const
        {
            return (uint64_t) * this < (uint64_t)x;
        }
    };

    class iterator
    {
    private:
        int_vector_buffer<t_width> & m_ivb;
        uint64_t m_idx = 0;

    public:
        using iterator_category = std::random_access_iterator_tag;
        using value_type = sdsl::int_vector_buffer<t_width>::value_type;
        using difference_type = sdsl::int_vector_buffer<t_width>::difference_type;
        using pointer = value_type *;
        using reference = sdsl::int_vector_buffer<t_width>::reference;

        iterator() = delete;
        iterator(int_vector_buffer<t_width> & ivb, uint64_t idx = 0) : m_ivb(ivb), m_idx(idx)
        {}

        iterator & operator++()
        {
            ++m_idx;
            return *this;
        }

        iterator operator++(int)
        {
            iterator it = *this;
            ++(*this);
            return it;
        }

        iterator & operator--()
        {
            --m_idx;
            return *this;
        }

        iterator operator--(int)
        {
            iterator it = *this;
            --(*this);
            return it;
        }

        reference operator*() const
        {
            return m_ivb[m_idx];
        }

        iterator & operator+=(difference_type i)
        {
            if (i < 0)
                return *this -= (-i);
            m_idx += i;
            return *this;
        }

        iterator & operator-=(difference_type i)
        {
            if (i < 0)
                return *this += (-i);
            m_idx -= i;
            return *this;
        }

        iterator operator+(difference_type i) const
        {
            iterator it = *this;
            return it += i;
        }

        iterator operator-(difference_type i) const
        {
            iterator it = *this;
            return it -= i;
        }

        bool operator==(iterator const & it) const
        {
            return &m_ivb == &(it.m_ivb) and m_idx == it.m_idx;
        }

        bool operator!=(iterator const & it) const
        {
            return !(*this == it);
        }
        inline difference_type operator-(iterator const & it)
        {
            return (m_idx - it.m_idx);
        }
    };
};

} // namespace sdsl

#endif // include guard
