// Copyright 2009-present MongoDB, Inc.
//
// 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.

#pragma once

#include <memory>

#include <mongocxx/change_stream-fwd.hpp>
#include <mongocxx/client-fwd.hpp>
#include <mongocxx/collection-fwd.hpp>
#include <mongocxx/database-fwd.hpp>

#include <bsoncxx/document/view.hpp>
#include <bsoncxx/stdx/optional.hpp>

#include <mongocxx/config/prelude.hpp>

namespace mongocxx {
namespace v_noabi {

///
/// A MongoDB change stream.
///
class change_stream {
   public:
    /// A change stream iterator.
    class iterator;

    ///
    /// Move constructs a change_stream.
    ///
    MONGOCXX_ABI_EXPORT_CDECL() change_stream(change_stream&& other) noexcept;

    ///
    /// Move assigns a change_stream.
    ///
    MONGOCXX_ABI_EXPORT_CDECL(change_stream&) operator=(change_stream&& other) noexcept;

    ///
    /// Destroys a change_stream.
    ///
    MONGOCXX_ABI_EXPORT_CDECL() ~change_stream();

    ///
    /// A change_stream::iterator points to the beginning of any
    /// available notifications. Each call to begin() advances to the next
    /// available notification. The state of all iterators is tracked by the
    /// change_stream itself, so advancing one iterator advances all iterators.
    ///
    /// change_stream::begin() and increment operators may block if the current batch of documents
    /// is exhausted. They will not return until a notification is available, the max_await_time
    /// (from the options::change_stream) milliseconds have elapsed, or a server error is
    /// encountered.
    ///
    /// When change_stream.begin() == change_stream.end(), no notifications
    /// are available. Each call to change_stream.begin() checks again for
    /// newly-available notifications.
    ///
    /// @return
    ///   The change_stream::iterator
    /// @exception
    ///   Throws mongocxx::v_noabi::query_exception if the query failed.
    ///
    MONGOCXX_ABI_EXPORT_CDECL(iterator) begin() const;

    ///
    /// A change_stream::iterator indicating stream exhaustion, meaning that
    /// no notifications are available from the stream.
    ///
    /// @return
    ///   The change_stream::iterator indicating exhaustion
    ///
    MONGOCXX_ABI_EXPORT_CDECL(iterator) end() const;

    ///
    /// Returns a resume token for this change stream.
    ///
    /// If the change stream has not been iterated, and either resume_after or
    /// start_after was specified in the options to this change stream, the
    /// specified value will be returned by this method. If neither resume_after or
    /// start_after was set on the options for this change stream, and it has
    /// not been iterated, this method will return no token.
    ///
    /// Once this change stream has been iterated, this method will return the
    /// resume token of the most recently returned document in the stream, or a
    /// postBatchResumeToken if the current batch of documents has been exhausted.
    ///
    /// @see
    /// - https://www.mongodb.com/docs/manual/changeStreams/#resume-tokens
    ///
    /// The returned document::view is valid for the lifetime of the stream and
    /// its data may be updated if the change stream is iterated after this function.
    /// The value may be copied to extend its lifetime or preserve the
    /// current resume token.
    ///
    /// @return
    ///   The token.
    ///
    MONGOCXX_ABI_EXPORT_CDECL(bsoncxx::v_noabi::stdx::optional<bsoncxx::v_noabi::document::view>)
    get_resume_token() const;

   private:
    friend ::mongocxx::v_noabi::client;
    friend ::mongocxx::v_noabi::collection;
    friend ::mongocxx::v_noabi::database;

    friend ::mongocxx::v_noabi::change_stream::iterator;

    change_stream(void* change_stream_ptr);

    class impl;
    std::unique_ptr<impl> _impl;
};

///
/// A MongoDB change stream iterator.
///
class change_stream::iterator {
   public:
    // Support input-iterator (caveat of post-increment returning void)
    using difference_type = std::int64_t;
    using value_type = bsoncxx::v_noabi::document::view const;
    using pointer = std::add_pointer<value_type>::type;
    using reference = std::add_lvalue_reference<value_type>::type;
    using iterator_category = std::input_iterator_tag;

    ///
    /// Default-construct an iterator.
    /// Default-constucted iterators can be compared (all default-constructed
    /// iterators are ==), assigned, and copied.
    ///
    MONGOCXX_ABI_EXPORT_CDECL() iterator();

    ///
    /// Dereferences the view for the document currently being pointed to.
    ///
    /// The returned document::view is valid until the iterator is incremented. The value may be
    /// copied to extend its lifetime.
    ///
    MONGOCXX_ABI_EXPORT_CDECL(bsoncxx::v_noabi::document::view const&) operator*() const;

    ///
    /// Accesses a member of the dereferenced document currently being pointed to.
    ///
    /// The returned document::view is valid until the iterator is incremented. The value may be
    /// copied to extend its lifetime.
    ///
    MONGOCXX_ABI_EXPORT_CDECL(bsoncxx::v_noabi::document::view const*) operator->() const;

    ///
    /// Pre-increments the iterator to move to the next document.
    ///
    /// change_stream::begin() and increment operators may block if the current batch of documents
    /// is exhausted. They will not return until a notification is available, the max_await_time
    /// (from the options::change_stream) milliseconds have elapsed, or a server error is
    /// encountered.
    ///
    /// If no notification is available, callers may call change_stream::begin() to check for more
    /// notifications.
    ///
    /// @throws mongocxx::v_noabi::query_exception if the query failed
    ///
    MONGOCXX_ABI_EXPORT_CDECL(iterator&) operator++();

    ///
    /// Post-increments the iterator to move to the next document.
    ///
    /// change_stream::begin() and increment operators may block if the current batch of documents
    /// is exhausted. They will not return until a notification is available, the max_await_time
    /// (from the options::change_stream) milliseconds have elapsed, or a server error is
    /// encountered.
    ///
    /// If no notification is available, callers may call change_stream::begin() to check for more
    /// notifications.
    ///
    /// @throws mongocxx::v_noabi::query_exception if the query failed
    ///
    MONGOCXX_ABI_EXPORT_CDECL(void) operator++(int);

    ///
    /// @relates bsoncxx::v_noabi::change_stream::iterator
    ///
    /// Compare two iterators for (in)-equality.
    ///
    /// Iterators compare equal if they point to the same underlying change_stream or if both are
    /// exhausted.
    ///
    /// @{
    friend MONGOCXX_ABI_EXPORT_CDECL(bool) operator==(
        change_stream::iterator const&,
        change_stream::iterator const&) noexcept;

    friend MONGOCXX_ABI_EXPORT_CDECL(bool) operator!=(
        change_stream::iterator const&,
        change_stream::iterator const&) noexcept;
    /// @}
    ///

   private:
    friend ::mongocxx::v_noabi::change_stream;

    enum class iter_type { k_tracking, k_default_constructed, k_end };

    explicit iterator(iter_type type, change_stream const* change_stream);

    bool is_exhausted() const;

    // iter_type==k_default_constructed is equivalent to _change_stream==nullptr
    iter_type _type;
    change_stream const* _change_stream;
};

} // namespace v_noabi
} // namespace mongocxx

#include <mongocxx/config/postlude.hpp>

///
/// @file
/// Provides @ref mongocxx::v_noabi::change_stream.
///
