#ifndef REALM_SYNC_CHANGESET_HPP
#define REALM_SYNC_CHANGESET_HPP

#include <realm/sync/instructions.hpp>
#include <realm/util/optional.hpp>

#include <type_traits>

namespace realm {
namespace sync {

using InternStrings = std::vector<StringBufferRange>;

struct BadChangesetError : Exception {
    BadChangesetError(const std::string& msg)
        : Exception(ErrorCodes::BadChangeset, util::format("%1. Please contact support.", msg))
    {
    }
};

struct Changeset {
    struct Range;
    using timestamp_type = uint_fast64_t;
    using file_ident_type = uint_fast64_t;
    using version_type = uint_fast64_t; // FIXME: Get from `History`.

    InternString intern_string(StringData);              // Slow!
    InternString find_string(StringData) const noexcept; // Slow!
    StringData string_data() const noexcept;

    std::string& string_buffer() noexcept;
    const std::string& string_buffer() const noexcept;
    const InternStrings& interned_strings() const noexcept;
    InternStrings& interned_strings() noexcept;

    StringBufferRange get_intern_string(InternString) const noexcept;
    util::Optional<StringBufferRange> try_get_intern_string(InternString) const noexcept;
    util::Optional<StringData> try_get_string(StringBufferRange) const noexcept;
    util::Optional<StringData> try_get_string(InternString) const noexcept;
    StringData get_string(StringBufferRange) const noexcept;
    StringData get_string(InternString) const noexcept;
    StringBufferRange append_string(StringData);

    PrimaryKey get_key(const Instruction::PrimaryKey& value) const noexcept;
    std::ostream& print_value(std::ostream& os, const Instruction::Payload& value) const noexcept;
    std::ostream& print_path(std::ostream& os, const Instruction::Path& value) const noexcept;
    std::ostream& print_path(std::ostream& os, InternString table, const Instruction::PrimaryKey& pk,
                             util::Optional<InternString> field = util::none,
                             const Instruction::Path* path = nullptr) const;

    /// Mark the changeset as "dirty" (i.e. modified by the merge algorithm).
    void set_dirty(bool dirty = true) noexcept;

    /// Whether or not the changeset is "dirty" (i.e. has been modified by the
    /// merge algorithm).
    bool is_dirty() const noexcept;

    // Interface to imitate std::vector:
    template <bool is_const>
    struct IteratorImpl;
    using iterator = IteratorImpl<false>;
    using const_iterator = IteratorImpl<true>;
    iterator begin() noexcept;
    iterator end() noexcept;
    const_iterator begin() const noexcept;
    const_iterator end() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
    bool empty() const noexcept;

    /// Size of the Changeset, not counting tombstones.
    ///
    /// FIXME: This is an O(n) operation.
    size_t size() const noexcept;

    void clear() noexcept;

    //@{
    /// Insert instructions, invalidating all iterators.
    iterator insert(const_iterator pos, Instruction);
    template <class InputIt>
    iterator insert(const_iterator pos, InputIt begin, InputIt end);
    //@}

    /// Erase an instruction, invalidating all iterators.
    iterator erase(const_iterator);

    /// Insert an instruction at the end, invalidating all iterators.
    void push_back(const Instruction&);

    //@{
    /// Insert instructions at \a position without invalidating other
    /// iterators.
    ///
    /// Only iterators created before any call to `insert_stable()` may be
    /// considered stable across calls to `insert_stable()`. In addition,
    /// "iterator stability" has a very specific meaning here: Other copies of
    /// \a position in the program will point to the newly inserted elements
    /// after calling `insert_stable()`, rather than point to the value at the
    /// position prior to insertion. This is different from, say, a tree
    /// structure, where iterator stability signifies the property that
    /// iterators keep pointing to the same element after insertion before or
    /// after that position.
    ///
    /// For the purpose of supporting `ChangesetIndex`, and the OT merge
    /// algorithm, these semantics are acceptable, since prepended instructions
    /// can never create new object or table references.
    iterator insert_stable(const_iterator position, Instruction);
    template <class InputIt>
    iterator insert_stable(const_iterator position, InputIt begin, InputIt end);
    //@}

    /// Erase instruction at \a position without invalidating other iterators.
    /// If erasing the object would invalidate other iterators, it is turned
    /// into a tombstone instead, and subsequent derefencing of the iterator
    /// will return `nullptr`. An iterator pointing to a tombstone remains valid
    /// and can be incremented.
    ///
    /// Only iterators created before any call to `insert_stable()` may be
    /// considered stable across calls to `erase_stable()`. If other copies of
    /// \a position exist in the program, they will either point to the
    /// subsequent element if that element was previously inserted with
    /// `insert_stable()`, or otherwise it will be turned into a tombstone.
    iterator erase_stable(const_iterator position);

#if REALM_DEBUG
    struct Reflector;
    struct Printer;
    void verify() const;
    void print(std::ostream&) const;
    void print() const; // prints to std::err
#endif

    /// The version that this changeset produced. Note: This may not be the
    /// version produced by this changeset on the client on which this changeset
    /// originated, but may for instance be the version produced on the server
    /// after receiving and re-sending this changeset to another client.
    ///
    /// FIXME: The explanation above is confusing. The truth is that if this
    /// changeset was received by a client from the server, then \a version is
    /// the version that was produced on the server by this changeset.
    ///
    /// FIXME: This property, as well as \a last_integrated_remote_version, \a
    /// origin_timestamp, and \a origin_file_ident should probably be removed
    /// from this class, as they are not a logical part of a changeset, and also
    /// are difficult to document without knowing more about what context the
    /// changeset object occurs. Also, functions such as
    /// InstructionApplier::apply() that a changeset as argument, but do not
    /// care about those properties.
    version_type version = 0;

    /// On clients, the last integrated server version. On the server, this is
    /// the last integrated client version.
    ///
    /// FIXME: The explanation above is confusing. The truth is that if this
    /// changeset was received by a client from the server, then \a
    /// last_integrated_remote_version is the last client version that was
    /// integrated by the server at the server version referencened by \a
    /// version.
    version_type last_integrated_remote_version = 0;

    /// Timestamp at origin when the original untransformed changeset was
    /// produced.
    timestamp_type origin_timestamp = 0;

    /// The identifier of the file in the context of which the original
    /// untransformed changeset was produced.
    file_ident_type origin_file_ident = 0;

    /// Must be set before passing this Changeset to Transformer::transform_remote_changesets
    /// to the index of this changeset within the received changesets.
    ///
    /// In FLX sync the server may send multiple idempotent changesets with the same server version
    /// when bootstrapping data. Internal data structures within the OT Transformer require the
    /// input changesets to be sortable in the order that they were received. If the version number
    /// is not increasing, this will be used to determine the correct sort order.
    ///
    /// FIXME: This is a hack that we need to figure out a better way of fixing. This can maybe
    /// be part of refactoring the ChangesetIndex
    size_t transform_sequence = 0;

    /// If the changeset was compacted during download, the size of the original
    /// changeset. Only applies to changesets sent by the server.
    std::size_t original_changeset_size = 0;

    /// Compare for exact equality, including that interned strings have the
    /// same integer values, and there is the same number of interned strings,
    /// same topology of tombstones, etc.
    bool operator==(const Changeset& that) const noexcept;
    bool operator!=(const Changeset& that) const noexcept;

private:
    std::vector<Instruction> m_instructions;
    std::string m_string_buffer;
    InternStrings m_strings;
    bool m_is_dirty = false;

    iterator const_iterator_to_iterator(const_iterator);
};

std::ostream& operator<<(std::ostream&, const Changeset& changeset);

/// An iterator type that hides the implementation details of the support for
/// iterator stability.
///
/// A `Changeset::iterator` is composed of an
/// `std::vector<InstructionContainer>::iterator` and a `size_t` representing
/// the index into the current `InstructionContainer`. If that container is
/// empty, and the position is zero, the iterator is pointing to a tombstone.
template <bool is_const>
struct Changeset::IteratorImpl {
    using list_type = std::vector<Instruction>;
    using inner_iterator_type = std::conditional_t<is_const, list_type::const_iterator, list_type::iterator>;

    // reference_type is a pointer because we have no way to create a reference
    // to a tombstone instruction. Alternatively, it could have been
    // `util::Optional<Instruction&>`, but that runs into other issues.
    using reference_type = std::conditional_t<is_const, const Instruction*, Instruction*>;

    using pointer_type = std::conditional_t<is_const, const Instruction*, Instruction*>;
    using difference_type = std::ptrdiff_t;

    IteratorImpl()
        : m_pos(0)
    {
    }
    template <bool is_const_ = is_const>
    IteratorImpl(const IteratorImpl<false>& other, std::enable_if_t<is_const_>* = nullptr)
        : m_inner(other.m_inner)
        , m_pos(other.m_pos)
    {
    }
    IteratorImpl(inner_iterator_type inner, size_t pos = 0)
        : m_inner(inner)
        , m_pos(pos)
    {
    }

    inline IteratorImpl& operator++()
    {
        ++m_pos;
        if (m_pos >= m_inner->size()) {
            ++m_inner;
            m_pos = 0;
        }
        return *this;
    }

    IteratorImpl operator++(int)
    {
        auto copy = *this;
        ++(*this);
        return copy;
    }

    IteratorImpl& operator--()
    {
        if (m_pos == 0) {
            --m_inner;
            m_pos = m_inner->size();
            if (m_pos != 0)
                --m_pos;
        }
        else {
            --m_pos;
        }
        return *this;
    }

    IteratorImpl operator--(int)
    {
        auto copy = *this;
        --(*this);
        return copy;
    }

    reference_type operator*() const
    {
        if (m_inner->size()) {
            return &m_inner->at(m_pos);
        }
        // It was a tombstone.
        return nullptr;
    }

    pointer_type operator->() const
    {
        if (m_inner->size()) {
            return &m_inner->at(m_pos);
        }
        // It was a tombstone.
        return nullptr;
    }

    bool operator==(const IteratorImpl& other) const
    {
        return m_inner == other.m_inner && m_pos == other.m_pos;
    }

    bool operator!=(const IteratorImpl& other) const
    {
        return !(*this == other);
    }

    bool operator<(const IteratorImpl& other) const
    {
        if (m_inner == other.m_inner)
            return m_pos < other.m_pos;
        return m_inner < other.m_inner;
    }

    bool operator<=(const IteratorImpl& other) const
    {
        if (m_inner == other.m_inner)
            return m_pos <= other.m_pos;
        return m_inner < other.m_inner;
    }

    bool operator>(const IteratorImpl& other) const
    {
        if (m_inner == other.m_inner)
            return m_pos > other.m_pos;
        return m_inner > other.m_inner;
    }

    bool operator>=(const IteratorImpl& other) const
    {
        if (m_inner == other.m_inner)
            return m_pos >= other.m_pos;
        return m_inner > other.m_inner;
    }

    inner_iterator_type m_inner;
    size_t m_pos;
};

struct Changeset::Range {
    iterator begin;
    iterator end;
};

#if REALM_DEBUG
struct Changeset::Reflector {
    struct Tracer {
        virtual void name(StringData) = 0;
        virtual void path(StringData, InternString table, const Instruction::PrimaryKey& object_key,
                          util::Optional<InternString> field, const Instruction::Path* path) = 0;
        virtual void field(StringData, InternString) = 0;
        virtual void field(StringData, Instruction::Payload::Type) = 0;
        virtual void field(StringData, Instruction::AddColumn::CollectionType) = 0;
        virtual void field(StringData, const Instruction::PrimaryKey&) = 0;
        virtual void field(StringData, const Instruction::Payload&) = 0;
        virtual void field(StringData, const Instruction::Path&) = 0;
        virtual void field(StringData, uint32_t) = 0;
        virtual void set_changeset(const Changeset*) = 0;
        virtual void after_each() {}
        virtual void before_each() {}
    };

    Reflector(Tracer& tracer, const Changeset& changeset)
        : m_tracer(tracer)
        , m_changeset(changeset)
    {
        tracer.set_changeset(&changeset);
    }

    void visit_all() const;

private:
    Tracer& m_tracer;
    const Changeset& m_changeset;

    void table_instr(const Instruction::TableInstruction&) const;
    void object_instr(const Instruction::ObjectInstruction&) const;
    void path_instr(const Instruction::PathInstruction&) const;

    friend struct Instruction;
#define REALM_DEFINE_REFLECTOR_VISITOR(X) void operator()(const Instruction::X&) const;
    REALM_FOR_EACH_INSTRUCTION_TYPE(REALM_DEFINE_REFLECTOR_VISITOR)
#undef REALM_DEFINE_REFLECTOR_VISITOR
};

struct Changeset::Printer : Changeset::Reflector::Tracer {
    explicit Printer(std::ostream& os)
        : m_out(os)
    {
    }

    // ChangesetReflector::Tracer interface:
    void name(StringData) final;
    void path(StringData, InternString table, const Instruction::PrimaryKey&, util::Optional<InternString> field,
              const Instruction::Path* path) final;
    void field(StringData, InternString) final;
    void field(StringData, Instruction::Payload::Type) final;
    void field(StringData, Instruction::AddColumn::CollectionType) final;
    void field(StringData, const Instruction::PrimaryKey&) final;
    void field(StringData, const Instruction::Payload&) final;
    void field(StringData, const Instruction::Path&) final;
    void field(StringData, uint32_t) final;
    void set_changeset(const Changeset* changeset) final
    {
        m_changeset = changeset;
    }
    void after_each() final;

private:
    std::ostream& m_out;
    bool m_first = true;
    const Changeset* m_changeset = nullptr;
    void pad_or_ellipsis(StringData, int width) const;
    void print_field(StringData name, std::string value);

    std::string primary_key_to_string(const Instruction::PrimaryKey&);
};
#endif // REALM_DEBUG


/// Implementation:

inline Changeset::iterator Changeset::begin() noexcept
{
    return m_instructions.begin();
}

inline Changeset::iterator Changeset::end() noexcept
{
    return m_instructions.end();
}

inline Changeset::const_iterator Changeset::begin() const noexcept
{
    return m_instructions.begin();
}

inline Changeset::const_iterator Changeset::end() const noexcept
{
    return m_instructions.end();
}

inline Changeset::const_iterator Changeset::cbegin() const noexcept
{
    return m_instructions.cbegin();
}

inline Changeset::const_iterator Changeset::cend() const noexcept
{
    return m_instructions.end();
}

inline bool Changeset::empty() const noexcept
{
    return size() == 0;
}

inline size_t Changeset::size() const noexcept
{
    size_t sum = 0;
    for (auto& x : m_instructions)
        sum += x.size();
    return sum;
}

inline void Changeset::clear() noexcept
{
    m_instructions.clear();
}

inline util::Optional<StringBufferRange> Changeset::try_get_intern_string(InternString string) const noexcept
{
    if (string.value >= m_strings.size())
        return util::none;
    return m_strings[string.value];
}

inline StringBufferRange Changeset::get_intern_string(InternString string) const noexcept
{
    REALM_ASSERT(string.value < m_strings.size());
    return m_strings[string.value];
}

inline InternStrings& Changeset::interned_strings() noexcept
{
    return m_strings;
}

inline const InternStrings& Changeset::interned_strings() const noexcept
{
    return m_strings;
}

inline auto Changeset::string_buffer() noexcept -> std::string&
{
    return m_string_buffer;
}

inline auto Changeset::string_buffer() const noexcept -> const std::string&
{
    return m_string_buffer;
}

inline util::Optional<StringData> Changeset::try_get_string(StringBufferRange range) const noexcept
{
    if (range.offset > m_string_buffer.size())
        return util::none;
    if (range.offset + range.size > m_string_buffer.size())
        return util::none;
    return StringData{m_string_buffer.data() + range.offset, range.size};
}

inline util::Optional<StringData> Changeset::try_get_string(InternString str) const noexcept
{
    if (auto range = try_get_intern_string(str)) {
        return try_get_string(*range);
    }
    return util::none;
}

inline StringData Changeset::get_string(StringBufferRange range) const noexcept
{
    auto string = try_get_string(range);
    REALM_ASSERT(string);
    return *string;
}

inline StringData Changeset::get_string(InternString string) const noexcept
{
    return get_string(get_intern_string(string));
}

inline StringData Changeset::string_data() const noexcept
{
    return StringData{m_string_buffer.data(), m_string_buffer.size()};
}

inline StringBufferRange Changeset::append_string(StringData string)
{
    // We expect more strings. Only do this at the beginning because until C++20, reserve
    // will shrink_to_fit if the request is less than the current capacity.
    constexpr size_t small_string_buffer_size = 1024;
    if (m_string_buffer.capacity() < small_string_buffer_size) {
        m_string_buffer.reserve(small_string_buffer_size);
    }
    size_t offset = m_string_buffer.size();
    m_string_buffer.append(string.data(), string.size());
    return StringBufferRange{uint32_t(offset), uint32_t(string.size())};
}

inline bool Changeset::is_dirty() const noexcept
{
    return m_is_dirty;
}

inline void Changeset::set_dirty(bool dirty) noexcept
{
    m_is_dirty = dirty;
}

inline Changeset::iterator Changeset::insert(const_iterator pos, Instruction instr)
{
    Instruction* p = &instr;
    return insert(pos, p, p + 1);
}

template <class InputIt>
inline Changeset::iterator Changeset::insert(const_iterator pos, InputIt begin, InputIt end)
{
    if (pos.m_pos == 0)
        return m_instructions.insert(pos.m_inner, begin, end);
    return insert_stable(pos, begin, end);
}

inline Changeset::iterator Changeset::erase(const_iterator pos)
{
    if (pos.m_inner->size() <= 1)
        return m_instructions.erase(pos.m_inner);
    return erase_stable(pos);
}

inline Changeset::iterator Changeset::insert_stable(const_iterator pos, Instruction instr)
{
    Instruction* p = &instr;
    return insert_stable(pos, p, p + 1);
}

template <class InputIt>
inline Changeset::iterator Changeset::insert_stable(const_iterator cpos, InputIt begin, InputIt end)
{
    iterator pos = const_iterator_to_iterator(cpos);
    size_t i = 0;
    for (auto it = begin; it != end; ++it, ++i) {
        pos.m_inner->insert(pos.m_pos + i, *it);
    }
    return pos;
}

inline Changeset::iterator Changeset::erase_stable(const_iterator cpos)
{
    auto pos = const_iterator_to_iterator(cpos);
    auto begin = m_instructions.begin();
    auto end = m_instructions.end();
    REALM_ASSERT(pos.m_inner >= begin);
    REALM_ASSERT(pos.m_inner < end);
    pos.m_inner->erase(pos.m_pos);
    if (pos.m_pos >= pos.m_inner->size()) {
        do {
            ++pos.m_inner;
        } while (pos.m_inner != end && pos.m_inner->is_empty());
        pos.m_pos = 0;
    }
    return pos;
}

inline void Changeset::push_back(const Instruction& instr)
{
    m_instructions.emplace_back(instr);
}

inline auto Changeset::const_iterator_to_iterator(const_iterator cpos) -> iterator
{
    size_t offset = cpos.m_inner - m_instructions.cbegin();
    return iterator{m_instructions.begin() + offset, cpos.m_pos};
}

inline bool Changeset::operator!=(const Changeset& that) const noexcept
{
    return !(*this == that);
}

} // namespace sync
} // namespace realm

namespace std {

template <bool is_const>
struct iterator_traits<realm::sync::Changeset::IteratorImpl<is_const>> {
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::bidirectional_iterator_tag;
};

} // namespace std

#endif // REALM_SYNC_CHANGESET_HPP