// 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 csa_alphabet_strategy.hpp
 * \brief csa_alphabet_strategy.hpp includes different strategy classes for representing an alphabet of a CSA.
 * \author Simon Gog
 */

#ifndef INCLUDED_CSA_ALPHABET_STRATEGY
#define INCLUDED_CSA_ALPHABET_STRATEGY

// TODO: Strategy with 1-to-1 mapping and C_array type as template parameter
//       This can be also used for a integer based CSA.

/* A alphabet strategy provides the following features:
 *   * Member `sigma` which contains the size (=number of unique symbols) of the alphabet.
 *   * Container `char2comp` which maps a symbol to a number [0..sigma-1]. The alphabetic
 *     order is preserved.
 *   * Container `comp2char` which is the inverse mapping of char2comp.
 *   * Container `C` contains the cumulative counts of occurrences. C[i] is the cumulative
 *     count of occurrences of symbols `comp2char[0]` to `comp2char[i-1]` in the text.
 *     C is of size `sigma+1`.
 *   * Typedefs for the four above members:
 *       * char2comp_type
 *       * comp2char_type
 *       * C_type
 *       * sigma_type
 *   * Constructor. Takes a int_vector_buffer<8> for byte-alphabets
 *     and int_vector_buffer<0> for integer-alphabets.
 *
 *    \par Note
 *   sigma_type has to be large enough to represent the alphabet size 2*sigma,
 *   since there is code which will perform a binary search on array `C`.
 */

#include <string>

#include <sdsl/config.hpp>
#include <sdsl/int_vector.hpp>
#include <sdsl/rank_support.hpp>
#include <sdsl/sd_vector.hpp>
#include <sdsl/sdsl_concepts.hpp>
#include <sdsl/select_support.hpp>

namespace sdsl
{

// forward declarations

class byte_alphabet;

template <class bit_vector_type = bit_vector,
          class rank_support_type = rank_support_scan<>,
          class select_support_type = select_support_scan<>,
          class C_array_type = int_vector<>>
class succinct_byte_alphabet;

template <class bit_vector_type = sd_vector<>,
          class rank_support_type = typename bit_vector_type::rank_1_type,
          class select_support_type = typename bit_vector_type::select_1_type,
          class C_array_type = int_vector<>>
class int_alphabet;

template <uint8_t int_width>
constexpr const char * key_text()
{
    return conf::KEY_TEXT_INT;
}

template <uint8_t int_width>
constexpr const char * key_bwt()
{
    return conf::KEY_BWT_INT;
}

template <>
inline constexpr const char * key_text<8>()
{
    return conf::KEY_TEXT;
}

template <>
inline constexpr const char * key_bwt<8>()
{
    return conf::KEY_BWT;
}

template <class t_alphabet_strategy>
struct alphabet_trait
{
    typedef byte_alphabet type;
};

template <>
struct alphabet_trait<int_alphabet_tag>
{
    typedef int_alphabet<> type;
};

// see
// http://stackoverflow.com/questions/13514587/c-check-for-nested-typedef-of-a-template-parameter-to-get-its-scalar-base-type
// for the next three functions

template <class t_wt, class t_enable = void>
struct wt_alphabet_trait
{
    typedef t_enable type;
};

template <class t_wt>
struct wt_alphabet_trait<t_wt, typename enable_if_type<typename t_wt::alphabet_category>::type>
{
    using type = typename alphabet_trait<typename t_wt::alphabet_category>::type;
};

//! A simple space greedy representation for byte alphabets.
/*!
 *  \par Space consumption:
 *       At least: 2.5 kB
 *       Details:  char2comp + comp2char take  2*256 + 2*8 bytes
 *                 m_C                   takes       257*8 bytes
 *                 m_sigma               takes           2 bytes
 */
class byte_alphabet
{
  public:
    typedef int_vector<>::size_type size_type;
    typedef int_vector<8> char2comp_type;
    typedef int_vector<8> comp2char_type;
    typedef int_vector<64> C_type;
    typedef uint16_t sigma_type;
    typedef uint8_t char_type;
    typedef uint8_t comp_char_type;
    typedef std::string string_type;
    enum
    {
        int_width = 8
    };

    typedef byte_alphabet_tag alphabet_category;

    const char2comp_type & char2comp;
    const comp2char_type & comp2char;
    const C_type & C;
    const sigma_type & sigma;

  private:
    char2comp_type m_char2comp; // Mapping from a character into the compact alphabet.
    comp2char_type m_comp2char; // Inverse mapping of m_char2comp.
    C_type m_C;                 // Cumulative counts for the compact alphabet [0..sigma].
    sigma_type m_sigma;         // Effective size of the alphabet.
  public:
    //! Default constructor
    byte_alphabet()
      : char2comp(m_char2comp)
      , comp2char(m_comp2char)
      , C(m_C)
      , sigma(m_sigma)
      , m_sigma(0)
    {}

    //! Construct from a byte-stream
    /*!
     *  \param text_buf Byte stream.
     *  \param len      Length of the byte stream.
     */
    byte_alphabet(int_vector_buffer<8> & text_buf, int_vector_size_type len)
      : char2comp(m_char2comp)
      , comp2char(m_comp2char)
      , C(m_C)
      , sigma(m_sigma)
    {
        m_sigma = 0;
        if (0 == len or 0 == text_buf.size()) return;
        assert(len <= text_buf.size());
        // initialize vectors
        m_C = int_vector<64>(257, 0);
        m_char2comp = int_vector<8>(256, 0);
        m_comp2char = int_vector<8>(256, 0);
        // count occurrences of each symbol
        for (size_type i = 0; i < len; ++i) { ++m_C[text_buf[i]]; }
        assert(1 == m_C[0]); // null-byte should occur exactly once
        m_sigma = 0;
        for (int i = 0; i < 256; ++i)
            if (m_C[i])
            {
                m_char2comp[i] = m_sigma;
                m_comp2char[sigma] = i;
                m_C[m_sigma] = m_C[i];
                ++m_sigma;
            }
        m_comp2char.resize(m_sigma);
        m_C.resize(m_sigma + 1);
        for (int i = (int)m_sigma; i > 0; --i) m_C[i] = m_C[i - 1];
        m_C[0] = 0;
        for (int i = 1; i <= (int)m_sigma; ++i) m_C[i] += m_C[i - 1];
        assert(C[sigma] == len);
    }

    byte_alphabet(const byte_alphabet & bas)
      : char2comp(m_char2comp)
      , comp2char(m_comp2char)
      , C(m_C)
      , sigma(m_sigma)
      , m_char2comp(bas.m_char2comp)
      , m_comp2char(bas.m_comp2char)
      , m_C(bas.m_C)
      , m_sigma(bas.m_sigma)
    {}

    byte_alphabet(byte_alphabet && bas)
      : char2comp(m_char2comp)
      , comp2char(m_comp2char)
      , C(m_C)
      , sigma(m_sigma)
      , m_char2comp(std::move(bas.m_char2comp))
      , m_comp2char(std::move(bas.m_comp2char))
      , m_C(std::move(bas.m_C))
      , m_sigma(bas.m_sigma)
    {}

    byte_alphabet & operator=(const byte_alphabet & bas)
    {
        if (this != &bas)
        {
            byte_alphabet tmp(bas);
            *this = std::move(tmp);
        }
        return *this;
    }

    byte_alphabet & operator=(byte_alphabet && bas)
    {
        if (this != &bas)
        {
            m_char2comp = std::move(bas.m_char2comp);
            m_comp2char = std::move(bas.m_comp2char);
            m_C = std::move(bas.m_C);
            m_sigma = std::move(bas.m_sigma);
        }
        return *this;
    }

    size_type serialize(std::ostream & out, structure_tree_node * v, std::string name = "") const
    {
        structure_tree_node * child = structure_tree::add_child(v, name, util::class_name(*this));
        size_type written_bytes = 0;
        written_bytes += m_char2comp.serialize(out, child, "m_char2comp");
        written_bytes += m_comp2char.serialize(out, child, "m_comp2char");
        written_bytes += m_C.serialize(out, child, "m_C");
        written_bytes += write_member(m_sigma, out, child, "m_sigma");
        structure_tree::add_size(child, written_bytes);
        return written_bytes;
    }

    void load(std::istream & in)
    {
        m_char2comp.load(in);
        m_comp2char.load(in);
        m_C.load(in);
        read_member(m_sigma, in);
    }

    //! Equality operator.
    bool operator==(byte_alphabet const & other) const noexcept
    {
        return (m_char2comp == other.m_char2comp) && (m_comp2char == other.m_comp2char) && (m_C == other.m_C) &&
               (m_sigma == other.m_sigma);
    }

    //! Inequality operator.
    bool operator!=(byte_alphabet const & other) const noexcept { return !(*this == other); }

    template <typename archive_t>
    void CEREAL_SAVE_FUNCTION_NAME(archive_t & ar) const
    {
        ar(CEREAL_NVP(m_char2comp));
        ar(CEREAL_NVP(m_comp2char));
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }

    template <typename archive_t>
    void CEREAL_LOAD_FUNCTION_NAME(archive_t & ar)
    {
        ar(CEREAL_NVP(m_char2comp));
        ar(CEREAL_NVP(m_comp2char));
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }
};

//! A space-efficient representation for byte alphabets.
/*!
 *  The mapping `char2comp` and its inverse `comp2char` is realized internally
 *  by a bitvector of size 256 bits and a rank and a select structure. The rank
 *  structure is used to calculate `char2comp`; the select structure is used to
 *  calculate `comp2char`. Array `C` is represented by a bit-compressed
 *  `int_vector` and `sigma` by a uint16_t.
 *  The types to represent `char2comp`, `comp2char`, and `C` can be specified
 *  by template parameters.
 */
template <class bit_vector_type, class rank_support_type, class select_support_type, class C_array_type>
class succinct_byte_alphabet
{
  public:
    class char2comp_wrapper;
    class comp2char_wrapper;
    friend class char2comp_wrapper;
    friend class comp2char_wrapper;

    typedef int_vector<>::size_type size_type;
    typedef char2comp_wrapper char2comp_type;
    typedef comp2char_wrapper comp2char_type;
    typedef C_array_type C_type;
    typedef uint16_t sigma_type;
    typedef uint8_t char_type;
    typedef uint8_t comp_char_type;
    typedef std::string string_type;
    typedef byte_alphabet_tag alphabet_category;
    enum
    {
        int_width = 8
    };

    //! Helper class for the char2comp mapping
    class char2comp_wrapper
    {
      private:
        const succinct_byte_alphabet * m_strat;

      public:
        char2comp_wrapper(const succinct_byte_alphabet * strat)
          : m_strat(strat)
        {}
        comp_char_type operator[](char_type c) const
        {
            if (c >= m_strat->m_char.size() or !m_strat->m_char[c]) return (comp_char_type)0;
            return (comp_char_type)m_strat->m_char_rank((size_type)c);
        }
    };

    //! Helper class for the comp2char mapping
    class comp2char_wrapper
    {
      private:
        const succinct_byte_alphabet * m_strat;

      public:
        comp2char_wrapper(const succinct_byte_alphabet * strat)
          : m_strat(strat)
        {}
        char_type operator[](comp_char_type c) const { return (char_type)m_strat->m_char_select(((size_type)c) + 1); }
    };

    const char2comp_type char2comp;
    const comp2char_type comp2char;
    const C_type & C;
    const sigma_type & sigma;

  private:
    bit_vector_type m_char;            // `m_char[i]` indicates if character with code i is present or not
    rank_support_type m_char_rank;     // rank data structure for `m_char` to answer char2comp
    select_support_type m_char_select; // select data structure for `m_char` to answer comp2char
    C_type m_C;                        // cumulative counts for the compact alphabet [0..sigma]
    sigma_type m_sigma;                // effective size of the alphabet

  public:
    //! Default constructor
    succinct_byte_alphabet()
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
      , m_sigma(0)
    {}

    //! Construct from a byte-stream
    /*!
     *  \param text_buf Byte stream.
     *  \param len      Length of the byte stream.
     */
    succinct_byte_alphabet(int_vector_buffer<8> & text_buf, int_vector_size_type len)
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
    {
        m_sigma = 0;
        if (0 == len or 0 == text_buf.size()) return;
        assert(len <= text_buf.size());
        // initialize vectors
        int_vector<64> D(257, 0);
        bit_vector tmp_char(256, 0);
        // count occurrences of each symbol
        for (size_type i = 0; i < len; ++i) { ++D[text_buf[i]]; }
        assert(1 == D[0]); // null-byte should occur exactly once
        m_sigma = 0;
        for (int i = 0; i < 256; ++i)
            if (D[i])
            {
                tmp_char[i] = 1;   // mark occurring character
                D[m_sigma] = D[i]; // compactify m_C
                ++m_sigma;
            }
        // resize to sigma+1, since CSAs also need the sum of all elements
        m_C = C_type(m_sigma + 1, 0, bits::hi(len) + 1);

        for (int i = (int)m_sigma; i > 0; --i) m_C[i] = D[i - 1];
        m_C[0] = 0;
        for (int i = 1; i <= (int)m_sigma; ++i) m_C[i] = m_C[i] + m_C[i - 1];
        assert(m_C[sigma] == len);
        m_char = tmp_char;
        util::init_support(m_char_rank, &m_char);
        util::init_support(m_char_select, &m_char);
    }

    //! Copy constructor
    succinct_byte_alphabet(const succinct_byte_alphabet & strat)
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
      , m_char(strat.m_char)
      , m_char_rank(strat.m_char_rank)
      , m_char_select(strat.m_char_select)
      , m_C(strat.m_C)
      , m_sigma(strat.m_sigma)
    {
        m_char_rank.set_vector(&m_char);
        m_char_select.set_vector(&m_char);
    }

    //! Move constructor
    succinct_byte_alphabet(succinct_byte_alphabet && strat)
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
      , m_char(std::move(strat.m_char))
      , m_char_rank(std::move(strat.m_char_rank))
      , m_char_select(std::move(strat.m_char_select))
      , m_C(std::move(strat.m_C))
      , m_sigma(std::move(strat.m_sigma))
    {
        m_char_rank.set_vector(&m_char);
        m_char_select.set_vector(&m_char);
    }

    succinct_byte_alphabet & operator=(const succinct_byte_alphabet & strat)
    {
        if (this != &strat)
        {
            succinct_byte_alphabet tmp(strat);
            *this = std::move(tmp);
        }
        return *this;
    }

    succinct_byte_alphabet & operator=(succinct_byte_alphabet && strat)
    {
        if (this != &strat)
        {
            m_char = std::move(strat.m_char);
            m_char_rank = std::move(strat.m_char_rank);
            m_char_rank.set_vector(&m_char);
            m_char_select = std::move(strat.m_char_select);
            m_char_select.set_vector(&m_char);
            m_C = std::move(strat.m_C);
            m_sigma = std::move(strat.m_sigma);
        }
        return *this;
    }

    //! Serialize method
    size_type serialize(std::ostream & out, structure_tree_node * v = nullptr, std::string name = "") const
    {
        structure_tree_node * child = structure_tree::add_child(v, name, util::class_name(*this));
        size_type written_bytes = 0;
        written_bytes += m_char.serialize(out, child, "m_char");
        written_bytes += m_char_rank.serialize(out, child, "m_char_rank");
        written_bytes += m_char_select.serialize(out, child, "m_char_select");
        written_bytes += m_C.serialize(out, child, "m_C");
        written_bytes += write_member(m_sigma, out, child, "m_sigma");
        structure_tree::add_size(child, written_bytes);
        return written_bytes;
    }

    //! Load method
    void load(std::istream & in)
    {
        m_char.load(in);
        m_char_rank.load(in);
        m_char_rank.set_vector(&m_char);
        m_char_select.load(in);
        m_char_select.set_vector(&m_char);
        m_C.load(in);
        read_member(m_sigma, in);
    }

    //! Equality operator.
    bool operator==(succinct_byte_alphabet const & other) const noexcept
    {
        return (m_char == other.m_char) && (m_char_rank == other.m_char_rank) &&
               (m_char_select == other.m_char_select) && (m_C == other.m_C) && (m_sigma == other.m_sigma);
    }

    //! Inequality operator.
    bool operator!=(succinct_byte_alphabet const & other) const noexcept { return !(*this == other); }

    template <typename archive_t>
    void CEREAL_SAVE_FUNCTION_NAME(archive_t & ar) const
    {
        ar(CEREAL_NVP(m_char));
        ar(CEREAL_NVP(m_char_rank));
        ar(CEREAL_NVP(m_char_select));
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }

    template <typename archive_t>
    void CEREAL_LOAD_FUNCTION_NAME(archive_t & ar)
    {
        ar(CEREAL_NVP(m_char));
        ar(CEREAL_NVP(m_char_rank));
        m_char_rank.set_vector(&m_char);
        ar(CEREAL_NVP(m_char_select));
        m_char_select.set_vector(&m_char);
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }
};

template <typename bit_vector_type, typename size_type>
void init_char_bitvector(bit_vector_type & char_bv, const std::map<size_type, size_type> & D)
{
    // note: the alphabet has at least size 1, so the following is safe:
    auto largest_symbol = (--D.end())->first;
    bit_vector tmp_char(largest_symbol + 1, 0);
    for (const auto & x : D) { tmp_char[x.first] = 1; }
    char_bv = tmp_char;
}

template <typename t_hi_bit_vector, typename t_select_1, typename t_select_0, typename size_type>
void init_char_bitvector(sd_vector<t_hi_bit_vector, t_select_1, t_select_0> & char_bv,
                         const std::map<size_type, size_type> & D)
{
    auto largest_symbol = (--D.end())->first;
    sd_vector_builder builder(largest_symbol + 1, D.size());
    for (const auto & x : D) { builder.set(x.first); }
    char_bv = std::move(sd_vector<t_hi_bit_vector, t_select_1, t_select_0>(builder));
}

/*!\brief Provides an alphabet mapping that implements an identity map (i.e. each character is mapped to its rank).
 * \details This mapping is faster for FM indices and should always be used for ranges containing all characters of the
 *          underlying alphabet type. Indices based on a text not containing all characters of its alphabet type will
 *          have a much higher memory footprint using this alphabet mapping.
 */
class plain_byte_alphabet
{
  public:
    //! Helper class for the char2comp and comp2char mapping.
    class mapping_wrapper;

    typedef int_vector<>::size_type size_type;
    typedef mapping_wrapper char2comp_type;
    typedef mapping_wrapper comp2char_type;
    typedef int_vector<64> C_type;
    typedef uint16_t sigma_type;
    typedef uint8_t char_type;
    typedef uint8_t comp_char_type;
    typedef std::string string_type;
    typedef byte_alphabet_tag alphabet_category;
    enum
    {
        int_width = 8
    };

    //! Helper class for the char2comp and comp2char mapping.
    class mapping_wrapper
    {
      public:
        //! Default constructor.
        mapping_wrapper() = default;

        //! Random access operator.
        constexpr char_type operator[](char_type const c) const noexcept { return c; }
    };

    const char2comp_type char2comp{};
    const comp2char_type comp2char{};
    const C_type & C;
    const sigma_type & sigma;

  private:
    C_type m_C;         // Cumulative counts for the compact alphabet [0..sigma].
    sigma_type m_sigma; // Effective size of the alphabet.

  public:
    //! Default constructor.
    plain_byte_alphabet()
      : C(m_C)
      , sigma(m_sigma)
      , m_sigma(0)
    {}

    /*! Construct from a byte-stream.
     *  \param text_buf Byte stream.
     *  \param len      Length of the byte stream.
     */
    plain_byte_alphabet(int_vector_buffer<8> & text_buf, int_vector_size_type len)
      : C(m_C)
      , sigma(m_sigma)
    {
        m_sigma = 0;
        if (0 == len || 0 == text_buf.size()) return;

        assert(len <= text_buf.size());

        // initialize vectors
        m_C = int_vector<64>(257, 0);
        // count occurrences of each symbol
        for (size_type i = 0; i < len; ++i) ++m_C[text_buf[i]];

        assert(1 == m_C[0]); // null-byte should occur exactly once

        m_sigma = 255;
        for (int i = 0; i < 256; ++i)
        {
            if (m_C[i])
            {
                m_sigma = i + 1;
                // m_C[m_sigma]	= m_C[i];
                // ++m_sigma;
            }
        }
        // m_C.resize(m_sigma + 1);
        for (int i = (int)256; i > 0; --i) m_C[i] = m_C[i - 1];
        m_C[0] = 0;
        for (int i = 1; i <= (int)256; ++i) m_C[i] += m_C[i - 1];

        assert(C[sigma] == len);
    }

    //! Copy constructor.
    plain_byte_alphabet(plain_byte_alphabet const & strat)
      : C(m_C)
      , sigma(m_sigma)
      , m_C(strat.m_C)
      , m_sigma(strat.m_sigma)
    {}

    //! Move constructor.
    plain_byte_alphabet(plain_byte_alphabet && strat) noexcept
      : C(m_C)
      , sigma(m_sigma)
      , m_C(std::move(strat.m_C))
      , m_sigma(strat.m_sigma)
    {}

    //! Copy assignment.
    plain_byte_alphabet & operator=(plain_byte_alphabet const & strat)
    {
        if (this != &strat)
        {
            plain_byte_alphabet tmp(strat);
            *this = std::move(tmp);
        }
        return *this;
    }

    //! Move assignment.
    plain_byte_alphabet & operator=(plain_byte_alphabet && strat) noexcept
    {
        if (this != &strat)
        {
            m_C = std::move(strat.m_C);
            m_sigma = strat.m_sigma;
        }
        return *this;
    }

    //!\cond
    size_type serialize(std::ostream & out, structure_tree_node * v, std::string const & name = "") const
    {
        structure_tree_node * child = structure_tree::add_child(v, name, util::class_name(*this));
        size_type written_bytes = 0;
        written_bytes += m_C.serialize(out, child, "m_C");
        written_bytes += write_member(m_sigma, out, child, "m_sigma");
        structure_tree::add_size(child, written_bytes);
        return written_bytes;
    }

    void load(std::istream & in)
    {
        m_C.load(in);
        read_member(m_sigma, in);
    }

    template <typename archive_t>
    void CEREAL_SAVE_FUNCTION_NAME(archive_t & ar) const
    {
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }

    template <typename archive_t>
    void CEREAL_LOAD_FUNCTION_NAME(archive_t & ar)
    {
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }

    bool operator==(plain_byte_alphabet const & other) const noexcept
    {
        return (m_C == other.m_C) && (m_sigma == other.m_sigma);
    }

    bool operator!=(plain_byte_alphabet const & other) const noexcept { return !(*this == other); }
    //!\endcond
};

//! A space-efficient representation for byte alphabets.
/*!
 *  The mapping `char2comp` and its inverse `comp2char` is realized internally
 *  by a bitvector of size sigma bits and a rank and a select structure, if the
 *  alphabet contains not all symbols in the range [0..sigma-1]. If it contains
 *  all symbols, i.e. the alphabet is continuous, then we map the symbols
 *  directly and no extra space is used.
 *
 *  The types to represent `char2comp`, `comp2char`, and `C` can be specified
 *  by template parameters.
 */
template <class bit_vector_type, class rank_support_type, class select_support_type, class C_array_type>
class int_alphabet
{
  public:
    class char2comp_wrapper;
    class comp2char_wrapper;
    friend class char2comp_wrapper;
    friend class comp2char_wrapper;

    typedef int_vector<>::size_type size_type;
    typedef char2comp_wrapper char2comp_type;
    typedef comp2char_wrapper comp2char_type;
    typedef C_array_type C_type;
    typedef uint64_t sigma_type;
    typedef uint64_t char_type;
    typedef uint64_t comp_char_type;
    typedef std::vector<char_type> string_type;
    typedef int_alphabet_tag alphabet_category;
    enum
    {
        int_width = 0
    };

    //! Helper class for the char2comp mapping
    class char2comp_wrapper
    {
      private:
        const int_alphabet * m_strat;

      public:
        char2comp_wrapper(const int_alphabet * strat)
          : m_strat(strat)
        {}
        comp_char_type operator[](char_type c) const
        {
            if (m_strat->m_char.size() > 0)
            { // if alphabet is not continuous
                if (c >= m_strat->m_char.size() or !m_strat->m_char[c]) return (comp_char_type)0;
                return (comp_char_type)m_strat->m_char_rank((size_type)c);
            }
            else
            { // direct map if it is continuous
                if (c >= m_strat->m_sigma) return 0;
                return (comp_char_type)c;
            }
            return 0;
        }
    };

    //! Helper class for the comp2char mapping
    class comp2char_wrapper
    {
      private:
        const int_alphabet * m_strat;

      public:
        comp2char_wrapper(const int_alphabet * strat)
          : m_strat(strat)
        {}
        char_type operator[](comp_char_type c) const
        {
            if (m_strat->m_char.size() > 0)
            { // if alphabet is not continuous
                return (char_type)m_strat->m_char_select(((size_type)c) + 1);
            }
            else
            { // direct map if it is continuous
                return (char_type)c;
            }
        }
    };

    const char2comp_type char2comp;
    const comp2char_type comp2char;
    const C_type & C;
    const sigma_type & sigma;

  private:
    bit_vector_type m_char;            // `m_char[i]` indicates if character with code i is present or not
    rank_support_type m_char_rank;     // rank data structure for `m_char` to answer char2comp
    select_support_type m_char_select; // select data structure for `m_char` to answer comp2char
    C_type m_C;                        // cumulative counts for the compact alphabet [0..sigma]
    sigma_type m_sigma;                // effective size of the alphabet

    //! Check if the alphabet is continuous.
    bool is_continuous_alphabet(std::map<size_type, size_type> & D)
    {
        if (D.size() == 0)
        { // an empty alphabet is continuous
            return true;
        }
        else
        {
            //            max key      + 1  ==  size of map
            return ((--D.end())->first + 1) == D.size();
        }
    }

  public:
    //! Default constructor
    int_alphabet()
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
      , m_sigma(0)
    {}

    //! Construct from a byte-stream
    /*!
     *  \param text_buf Byte stream.
     *  \param len      Length of the byte stream.
     */
    int_alphabet(int_vector_buffer<0> & text_buf, int_vector_size_type len)
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
    {
        m_sigma = 0;
        if (0 == len or 0 == text_buf.size()) return;
        assert(len <= text_buf.size());
        // initialize vectors
        std::map<size_type, size_type> D;
        // count occurrences of each symbol
        for (size_type i = 0; i < len; ++i) { D[text_buf[i]]++; }
        m_sigma = D.size();
        if (is_continuous_alphabet(D))
        {
            // do not initialize m_char, m_char_rank and m_char_select since we can map directly
        }
        else
        {
            init_char_bitvector(m_char, D);
        }
        assert(D.find(0) != D.end() and 1 == D[0]); // null-byte should occur exactly once

        // resize to sigma+1, since CSAs also need the sum of all elements
        m_C = C_type(m_sigma + 1, 0, bits::hi(len) + 1);
        size_type sum = 0, idx = 0;
        for (std::map<size_type, size_type>::const_iterator it = D.begin(), end = D.end(); it != end; ++it)
        {
            m_C[idx++] = sum;
            sum += it->second;
        }
        m_C[idx] = sum; // insert sum of all elements
    }

    //! Copy constructor
    int_alphabet(const int_alphabet & strat)
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
      , m_char(strat.m_char)
      , m_char_rank(strat.m_char_rank)
      , m_char_select(strat.m_char_select)
      , m_C(strat.m_C)
      , m_sigma(strat.m_sigma)
    {
        m_char_rank.set_vector(&m_char);
        m_char_select.set_vector(&m_char);
    }

    //! Copy constructor
    int_alphabet(int_alphabet && strat)
      : char2comp(this)
      , comp2char(this)
      , C(m_C)
      , sigma(m_sigma)
      , m_char(std::move(strat.m_char))
      , m_char_rank(std::move(strat.m_char_rank))
      , m_char_select(std::move(strat.m_char_select))
      , m_C(std::move(strat.m_C))
      , m_sigma(std::move(strat.m_sigma))
    {
        m_char_rank.set_vector(&m_char);
        m_char_select.set_vector(&m_char);
    }

    int_alphabet & operator=(const int_alphabet & strat)
    {
        if (this != &strat)
        {
            int_alphabet tmp(strat);
            *this = std::move(tmp);
        }
        return *this;
    }

    int_alphabet & operator=(int_alphabet && strat)
    {
        if (this != &strat)
        {
            m_char = std::move(strat.m_char);
            m_char_rank = std::move(strat.m_char_rank);
            m_char_rank.set_vector(&m_char);
            m_char_select = std::move(strat.m_char_select);
            m_char_select.set_vector(&m_char);
            m_C = std::move(strat.m_C);
            m_sigma = std::move(strat.m_sigma);
        }
        return *this;
    }

    //! Serialize method
    size_type serialize(std::ostream & out, structure_tree_node * v = nullptr, std::string name = "") const
    {
        structure_tree_node * child = structure_tree::add_child(v, name, util::class_name(*this));
        size_type written_bytes = 0;
        written_bytes += m_char.serialize(out, child, "m_char");
        written_bytes += m_char_rank.serialize(out, child, "m_char_rank");
        written_bytes += m_char_select.serialize(out, child, "m_char_select");
        written_bytes += m_C.serialize(out, child, "m_C");
        written_bytes += write_member(m_sigma, out, child, "m_sigma");
        structure_tree::add_size(child, written_bytes);
        return written_bytes;
    }

    //! Load method
    void load(std::istream & in)
    {
        m_char.load(in);
        m_char_rank.load(in);
        m_char_rank.set_vector(&m_char);
        m_char_select.load(in);
        m_char_select.set_vector(&m_char);
        m_C.load(in);
        read_member(m_sigma, in);
    }

    //! Equality operator.
    bool operator==(int_alphabet const & other) const noexcept
    {
        return (m_char == other.m_char) && (m_char_rank == other.m_char_rank) &&
               (m_char_select == other.m_char_select) && (m_C == other.m_C) && (m_sigma == other.m_sigma);
    }

    //! Inequality operator.
    bool operator!=(int_alphabet const & other) const noexcept { return !(*this == other); }

    template <typename archive_t>
    void CEREAL_SAVE_FUNCTION_NAME(archive_t & ar) const
    {
        ar(CEREAL_NVP(m_char));
        ar(CEREAL_NVP(m_char_rank));
        ar(CEREAL_NVP(m_char_select));
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }

    template <typename archive_t>
    void CEREAL_LOAD_FUNCTION_NAME(archive_t & ar)
    {
        ar(CEREAL_NVP(m_char));
        ar(CEREAL_NVP(m_char_rank));
        m_char_rank.set_vector(&m_char);
        ar(CEREAL_NVP(m_char_select));
        m_char_select.set_vector(&m_char);
        ar(CEREAL_NVP(m_C));
        ar(CEREAL_NVP(m_sigma));
    }
};

} // end namespace sdsl

#endif
