/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#include "mongo/platform/basic.h"

#include "mongo/db/pipeline/document_source_out_replace_coll.h"

#include "mongo/rpc/get_status_from_command_result.h"

namespace mongo {

static AtomicWord<unsigned> aggOutCounter;

DocumentSourceOutReplaceColl::~DocumentSourceOutReplaceColl() {
    DESTRUCTOR_GUARD(
        // Make sure we drop the temp collection if anything goes wrong. Errors are ignored
        // here because nothing can be done about them. Additionally, if this fails and the
        // collection is left behind, it will be cleaned up next time the server is started.
        if (_tempNs.size()) {
            auto cleanupClient =
                pExpCtx->opCtx->getServiceContext()->makeClient("$out_replace_coll_cleanup");
            AlternativeClientRegion acr(cleanupClient);
            // Create a new operation context so that any interrputs on the current operation will
            // not affect the dropCollection operation below.
            auto cleanupOpCtx = cc().makeOperationContext();

            OutStageWriteBlock writeBlock(cleanupOpCtx.get());

            // Reset the operation context back to original once dropCollection is done.
            ON_BLOCK_EXIT(
                [this] { pExpCtx->mongoProcessInterface->setOperationContext(pExpCtx->opCtx); });

            pExpCtx->mongoProcessInterface->setOperationContext(cleanupOpCtx.get());
            pExpCtx->mongoProcessInterface->directClient()->dropCollection(_tempNs.ns());
        });
}

void DocumentSourceOutReplaceColl::initializeWriteNs() {
    OutStageWriteBlock writeBlock(pExpCtx->opCtx);

    DBClientBase* conn = pExpCtx->mongoProcessInterface->directClient();

    const auto& outputNs = getOutputNs();
    _tempNs = NamespaceString(str::stream() << outputNs.db() << ".tmp.agg_out."
                                            << aggOutCounter.addAndFetch(1));

    // Save the original collection options and index specs so we can check they didn't change
    // during computation.
    _originalOutOptions = pExpCtx->mongoProcessInterface->getCollectionOptions(outputNs);
    _originalIndexes = conn->getIndexSpecs(outputNs.ns());

    // Check if it's capped to make sure we have a chance of succeeding before we do all the work.
    // If the collection becomes capped during processing, the collection options will have changed,
    // and the $out will fail.
    uassert(17152,
            str::stream() << "namespace '" << outputNs.ns()
                          << "' is capped so it can't be used for $out",
            _originalOutOptions["capped"].eoo());

    // We will write all results into a temporary collection, then rename the temporary
    // collection to be the target collection once we are done.
    _tempNs = NamespaceString(str::stream() << outputNs.db() << ".tmp.agg_out."
                                            << aggOutCounter.addAndFetch(1));

    // Create temp collection, copying options from the existing output collection if any.
    {
        BSONObjBuilder cmd;
        cmd << "create" << _tempNs.coll();
        cmd << "temp" << true;
        cmd.appendElementsUnique(_originalOutOptions);

        BSONObj info;
        uassert(16994,
                str::stream() << "failed to create temporary $out collection '" << _tempNs.ns()
                              << "': "
                              << getStatusFromCommandResult(info).reason(),
                conn->runCommand(outputNs.db().toString(), cmd.done(), info));
    }

    if (_originalIndexes.empty()) {
        return;
    }

    // Copy the indexes of the output collection to the temp collection.
    std::vector<BSONObj> tempNsIndexes;
    for (const auto& indexSpec : _originalIndexes) {
        // Replace the spec's 'ns' field value, which is the original collection, with the temp
        // collection.
        tempNsIndexes.push_back(indexSpec.addField(BSON("ns" << _tempNs.ns()).firstElement()));
    }
    try {
        conn->createIndexes(_tempNs.ns(), tempNsIndexes);
    } catch (DBException& ex) {
        ex.addContext("Copying indexes for $out failed");
        throw;
    }
};

void DocumentSourceOutReplaceColl::finalize() {
    OutStageWriteBlock writeBlock(pExpCtx->opCtx);

    const auto& outputNs = getOutputNs();
    auto renameCommandObj =
        BSON("renameCollection" << _tempNs.ns() << "to" << outputNs.ns() << "dropTarget" << true);

    pExpCtx->mongoProcessInterface->renameIfOptionsAndIndexesHaveNotChanged(
        pExpCtx->opCtx, renameCommandObj, outputNs, _originalOutOptions, _originalIndexes);

    // The rename succeeded, so the temp collection no longer exists.
    _tempNs = {};
};

}  // namespace mongo