/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

/*
 * Modified by ScyllaDB
 * Copyright (C) 2017 ScyllaDB
 */

/*
 * This file is part of Scylla.
 *
 * Scylla is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Scylla 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
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
 */

// Since Scylla 2.0, we use system tables whose schemas were introduced in
// Cassandra 3. If Scylla boots to find a data directory with system tables
// with older schemas - produced by pre-2.0 Scylla or by pre-3.0 Cassandra,
// we need to migrate these old tables to the new format.
//
// We provide here a function, db::legacy_schema_migrator::migrate(),
// for a one-time migration from old to new system tables. The function
// reads old system tables, write them back in the new format, and finally
// delete the old system tables. Scylla's main should call this function and
// wait for the returned future, before starting to serve the database.

#include <boost/iterator/filter_iterator.hpp>
#include <seastar/core/future-util.hh>
#include <seastar/util/log.hh>
#include <map>
#include <unordered_set>
#include <chrono>

#include "database.hh"
#include "legacy_schema_migrator.hh"
#include "system_keyspace.hh"
#include "schema_tables.hh"
#include "schema_builder.hh"
#include "json.hh"
#include "cql3/query_processor.hh"
#include "cql3/untyped_result_set.hh"
#include "cql3/util.hh"
#include "utils/joinpoint.hh"
#include "types/user.hh"

static seastar::logger mlogger("legacy_schema_migrator");

namespace db {
namespace legacy_schema_migrator {

// local data carriers

class migrator {
public:
    static const std::unordered_set<sstring> legacy_schema_tables;

    migrator(sharded<service::storage_proxy>& sp, sharded<database>& db, cql3::query_processor& qp)
                    : _sp(sp), _db(db), _qp(qp) {
    }
    migrator(migrator&&) = default;

    typedef db_clock::time_point time_point;

    // TODO: we dont't support triggers.
    // this is a placeholder.
    struct trigger {
        time_point timestamp;
        sstring name;
        std::unordered_map<sstring, sstring> options;
    };

    struct table {
        time_point timestamp;
        schema_ptr metadata;
        std::vector<trigger> triggers;
    };

    struct type {
        time_point timestamp;
        user_type metadata;
    };

    struct function {
        time_point timestamp;
        sstring ks_name;
        sstring fn_name;
        std::vector<sstring> arg_names;
        std::vector<sstring> arg_types;
        sstring return_type;
        bool called_on_null_input;
        sstring language;
        sstring body;
    };

    struct aggregate {
        time_point timestamp;
        sstring ks_name;
        sstring fn_name;
        std::vector<sstring> arg_names;
        std::vector<sstring> arg_types;
        sstring return_type;
        sstring final_func;
        sstring initcond;
        sstring state_func;
        sstring state_type;
    };

    struct keyspace {
        time_point timestamp;
        sstring name;
        bool durable_writes;
        std::map<sstring, sstring> replication_params;

        std::vector<table> tables;
        std::vector<type> types;
        std::vector<function> functions;
        std::vector<aggregate> aggregates;
    };

    class unsupported_feature : public std::runtime_error {
    public:
        using runtime_error::runtime_error;
    };

    static sstring fmt_query(const char* fmt, const char* table) {
        return sprint(fmt, db::system_keyspace::NAME, table);
    }

    typedef ::shared_ptr<cql3::untyped_result_set> result_set_type;
    typedef const cql3::untyped_result_set::row row_type;

    future<> read_table(keyspace& dst, sstring cf_name, time_point timestamp) {
        auto fmt = "SELECT * FROM %s.%s WHERE keyspace_name = ? AND columnfamily_name = ?";
        auto tq = fmt_query(fmt, db::system_keyspace::legacy::COLUMNFAMILIES);
        auto cq = fmt_query(fmt, db::system_keyspace::legacy::COLUMNS);
        auto zq = fmt_query(fmt, db::system_keyspace::legacy::TRIGGERS);

        typedef std::tuple<future<result_set_type>, future<result_set_type>, future<result_set_type>, future<db::schema_tables::legacy::schema_mutations>> result_tuple;

        return when_all(_qp.execute_internal(tq, { dst.name, cf_name }),
                        _qp.execute_internal(cq, { dst.name, cf_name }),
                        _qp.execute_internal(zq, { dst.name, cf_name }),
                        db::schema_tables::legacy::read_table_mutations(_sp, dst.name, cf_name, db::system_keyspace::legacy::column_families()))
                    .then([this, &dst, cf_name, timestamp](result_tuple&& t) {

            result_set_type tables = std::get<0>(t).get0();
            result_set_type columns = std::get<1>(t).get0();
            result_set_type triggers = std::get<2>(t).get0();
            db::schema_tables::legacy::schema_mutations sm = std::get<3>(t).get0();

            row_type& td = tables->one();

            auto ks_name = td.get_as<sstring>("keyspace_name");
            auto cf_name = td.get_as<sstring>("columnfamily_name");
            auto id = td.get_or("cf_id", generate_legacy_id(ks_name, cf_name));

            schema_builder builder(dst.name, cf_name, id);

            builder.with_version(sm.digest());

            cf_type cf = sstring_to_cf_type(td.get_or("type", sstring("standard")));
            if (cf == cf_type::super) {
                fail(unimplemented::cause::SUPER);
            }

            auto comparator = td.get_as<sstring>("comparator");
            bool is_compound = cell_comparator::check_compound(comparator);
            builder.set_is_compound(is_compound);
            cell_comparator::read_collections(builder, comparator);

            bool filter_sparse = false;

            data_type default_validator = {};
            if (td.has("default_validator")) {
                default_validator = db::schema_tables::parse_type(td.get_as<sstring>("default_validator"));
                if (default_validator->is_counter()) {
                    builder.set_is_counter(true);
                }
                builder.set_default_validation_class(default_validator);
            }

            /*
             * Determine whether or not the table is *really* dense
             * We cannot trust is_dense value of true (see CASSANDRA-11502, that fixed the issue for 2.2 only, and not retroactively),
             * but we can trust is_dense value of false.
             */
            auto is_dense = td.get_opt<bool>("is_dense");
            if (!is_dense || *is_dense) {
                is_dense = [&] {
                    /*
                     * As said above, this method is only here because we need to deal with thrift upgrades.
                     * Once a CF has been "upgraded", i.e. we've rebuilt and save its CQL3 metadata at least once,
                     * then we'll have saved the "is_dense" value and will be good to go.
                     *
                     * But non-upgraded thrift CF (and pre-7744 CF) will have no value for "is_dense", so we need
                     * to infer that information without relying on it in that case. And for the most part this is
                     * easy, a CF that has at least one REGULAR definition is not dense. But the subtlety is that not
                     * having a REGULAR definition may not mean dense because of CQL3 definitions that have only the
                     * PRIMARY KEY defined.
                     *
                     * So we need to recognize those special case CQL3 table with only a primary key. If we have some
                     * clustering columns, we're fine as said above. So the only problem is that we cannot decide for
                     * sure if a CF without REGULAR columns nor CLUSTERING_COLUMN definition is meant to be dense, or if it
                     * has been created in CQL3 by say:
                     *    CREATE TABLE test (k int PRIMARY KEY)
                     * in which case it should not be dense. However, we can limit our margin of error by assuming we are
                     * in the latter case only if the comparator is exactly CompositeType(UTF8Type).
                     */
                    std::optional<column_id> max_cl_idx;
                    const cql3::untyped_result_set::row * regular = nullptr;
                    for (auto& row : *columns) {
                        auto kind_str = row.get_as<sstring>("type");
                        if (kind_str == "compact_value") {
                            continue;
                        }

                        auto kind = db::schema_tables::deserialize_kind(kind_str);

                        if (kind == column_kind::regular_column) {
                            if (regular != nullptr) {
                                return false;
                            }
                            regular = &row;
                            continue;
                        }
                        if (kind == column_kind::clustering_key) {
                            max_cl_idx = std::max(column_id(row.get_or("component_index", 0)), max_cl_idx.value_or(column_id()));
                        }
                    }

                    auto is_cql3_only_pk_comparator = [](const sstring& comparator) {
                        if (!cell_comparator::check_compound(comparator)) {
                            return false;
                        }
                        // CMH. We don't have composites, nor a parser for it. This is a simple way of c
                        // checking the same.
                        auto comma = comparator.find(',');
                        if (comma != sstring::npos) {
                            return false;
                        }
                        auto off = comparator.find('(');
                        auto end = comparator.find(')');

                        return comparator.compare(off, end - off, utf8_type->name()) == 0;
                    };

                    if (max_cl_idx) {
                        auto n = std::count(comparator.begin(), comparator.end(), ','); // num comp - 1
                        return *max_cl_idx == n;
                    }

                    if (regular) {
                        return false;
                    }

                    return !is_cql3_only_pk_comparator(comparator);

                }();

                // now, if switched to sparse, remove redundant compact_value column and the last clustering column,
                // directly copying CASSANDRA-11502 logic. See CASSANDRA-11315.

                filter_sparse = !*is_dense;
            }
            builder.set_is_dense(*is_dense);

            auto is_cql = !*is_dense && is_compound;
            auto is_static_compact = !*is_dense && !is_compound;

            // org.apache.cassandra.schema.LegacySchemaMigrator#isEmptyCompactValueColumn
            auto is_empty_compact_value = [](const cql3::untyped_result_set::row& column_row) {
                auto kind_str = column_row.get_as<sstring>("type");
                // Cassandra only checks for "compact_value", but Scylla generates "regular" instead (#2586)
                return (kind_str == "compact_value" || kind_str == "regular")
                       && column_row.get_as<sstring>("column_name").empty();
            };

            for (auto& row : *columns) {
                auto kind_str = row.get_as<sstring>("type");
                auto kind = db::schema_tables::deserialize_kind(kind_str);
                auto component_index = kind > column_kind::clustering_key ? 0 : column_id(row.get_or("component_index", 0));
                auto name = row.get_or<sstring>("column_name", sstring());
                auto validator = db::schema_tables::parse_type(row.get_as<sstring>("validator"));

                if (is_empty_compact_value(row)) {
                    continue;
                }

                if (filter_sparse) {
                    if (kind_str == "compact_value") {
                        continue;
                    }
                    if (kind == column_kind::clustering_key) {
                        if (cf == cf_type::super && component_index != 0) {
                            continue;
                        }
                        if (cf != cf_type::super && !is_compound) {
                            continue;
                        }
                    }
                }

                std::optional<index_metadata_kind> index_kind;
                sstring index_name;
                index_options_map options;
                if (row.has("index_type")) {
                    index_kind = schema_tables::deserialize_index_kind(row.get_as<sstring>("index_type"));
                }
                if (row.has("index_name")) {
                    index_name = row.get_as<sstring>("index_name");
                }
                if (row.has("index_options")) {
                    options = json::to_map(row.get_as<sstring>("index_options"), index_options_map());
                    sstring type;
                    auto i = options.find("index_keys");
                    if (i != options.end()) {
                        options.erase(i);
                        type = "KEYS";
                    }
                    i = options.find("index_keys_and_values");
                    if (i != options.end()) {
                        options.erase(i);
                        type = "KEYS_AND_VALUES";
                    }
                    if (type.empty()) {
                        if (validator->is_collection() && validator->is_multi_cell()) {
                            type = "FULL";
                        } else {
                            type = "VALUES";
                        }
                    }
                    auto column = cql3::util::maybe_quote(name);
                    options["target"] = validator->is_collection()
                                    ? type + "(" + column + ")"
                                    : column;
                }
                if (index_kind) {
                    // Origin assumes index_name is always set, so let's do the same
                    builder.with_index(index_metadata(index_name, options, *index_kind, index_metadata::is_local_index::no));
                }

                data_type column_name_type = [&] {
                    if (is_static_compact && kind == column_kind::regular_column) {
                        return db::schema_tables::parse_type(comparator);
                    }
                    return utf8_type;
                }();
                auto column_name = [&] {
                    try {
                        return column_name_type->from_string(name);
                    } catch (marshal_exception&) {
                        // #2597: Scylla < 2.0 writes names in serialized form, try to recover
                        column_name_type->validate(to_bytes_view(name), cql_serialization_format::latest());
                        return to_bytes(name);
                    }
                }();
                builder.with_column(std::move(column_name), std::move(validator), kind, component_index);
            }

            if (is_static_compact) {
                builder.set_regular_column_name_type(db::schema_tables::parse_type(comparator));
            }

            if (td.has("read_repair_chance")) {
                builder.set_read_repair_chance(td.get_as<double>("read_repair_chance"));
            }
            if (td.has("local_read_repair_chance")) {
                builder.set_dc_local_read_repair_chance(td.get_as<double>("local_read_repair_chance"));
            }
            if (td.has("gc_grace_seconds")) {
                builder.set_gc_grace_seconds(td.get_as<int32_t>("gc_grace_seconds"));
            }
            if (td.has("min_compaction_threshold")) {
                builder.set_min_compaction_threshold(td.get_as<int32_t>("min_compaction_threshold"));
            }
            if (td.has("max_compaction_threshold")) {
                builder.set_max_compaction_threshold(td.get_as<int32_t>("max_compaction_threshold"));
            }
            if (td.has("comment")) {
                builder.set_comment(td.get_as<sstring>("comment"));
            }
            if (td.has("memtable_flush_period_in_ms")) {
                builder.set_memtable_flush_period(td.get_as<int32_t>("memtable_flush_period_in_ms"));
            }
            if (td.has("caching")) {
                builder.set_caching_options(caching_options::from_sstring(td.get_as<sstring>("caching")));
            }
            if (td.has("default_time_to_live")) {
                builder.set_default_time_to_live(gc_clock::duration(td.get_as<int32_t>("default_time_to_live")));
            }
            if (td.has("speculative_retry")) {
                builder.set_speculative_retry(td.get_as<sstring>("speculative_retry"));
            }
            if (td.has("compaction_strategy_class")) {
                auto strategy = td.get_as<sstring>("compaction_strategy_class");
                try {
                    builder.set_compaction_strategy(sstables::compaction_strategy::type(strategy));
                } catch (const exceptions::configuration_exception& e) {
                    // If compaction strategy class isn't supported, fallback to size tiered.
                    mlogger.warn("Falling back to size-tiered compaction strategy after the problem: {}", e.what());
                    builder.set_compaction_strategy(sstables::compaction_strategy_type::size_tiered);
                }
            }
            if (td.has("compaction_strategy_options")) {
                builder.set_compaction_strategy_options(json::to_map(td.get_as<sstring>("compaction_strategy_options")));
            }
            auto comp_param = td.get_as<sstring>("compression_parameters");
            compression_parameters cp(json::to_map(comp_param));
            builder.set_compressor_params(cp);

            if (td.has("min_index_interval")) {
                builder.set_min_index_interval(td.get_as<int32_t>("min_index_interval"));
            } else if (td.has("index_interval")) { // compatibility
                builder.set_min_index_interval(td.get_as<int32_t>("index_interval"));
            }
            if (td.has("max_index_interval")) {
                builder.set_max_index_interval(td.get_as<int32_t>("max_index_interval"));
            }
            if (td.has("bloom_filter_fp_chance")) {
                builder.set_bloom_filter_fp_chance(td.get_as<double>("bloom_filter_fp_chance"));
            } else {
                builder.set_bloom_filter_fp_chance(builder.get_bloom_filter_fp_chance());
            }
            if (td.has("dropped_columns")) {
                auto map = td.get_map<sstring, int64_t>("dropped_columns");
                for (auto&& e : map) {
                    builder.without_column(e.first, api::timestamp_type(e.second));
                };
            }

            // ignore version. we're transient
            if (!triggers->empty()) {
                throw unsupported_feature("triggers");
            }

            dst.tables.emplace_back(table{timestamp, builder.build() });
        });
    }

    future<> read_tables(keyspace& dst) {
        auto query = fmt_query("SELECT columnfamily_name, writeTime(type) AS timestamp FROM %s.%s WHERE keyspace_name = ?",
                        db::system_keyspace::legacy::COLUMNFAMILIES);
        return _qp.execute_internal(query, {dst.name}).then([this, &dst](result_set_type result) {
            return parallel_for_each(*result, [this, &dst](row_type& row) {
                return read_table(dst, row.get_as<sstring>("columnfamily_name"), row.get_as<time_point>("timestamp"));
            }).finally([result] {});
        });
    }

    future<time_point> read_type_timestamp(keyspace& dst, sstring type_name) {
        // TODO: Unfortunately there is not a single REGULAR column in system.schema_usertypes, so annoyingly we cannot
        // use the writeTime() CQL function, and must resort to a lower level.
        // Origin digs up the actual cells of target partition and gets timestamp from there.
        // We should do the same, but g-dam thats messy. Lets give back dung value for now.
        return make_ready_future<time_point>(dst.timestamp);
    }

    future<> read_types(keyspace& dst) {
        auto query = fmt_query("SELECT * FROM %s.%s WHERE keyspace_name = ?", db::system_keyspace::legacy::USERTYPES);
        return _qp.execute_internal(query, {dst.name}).then([this, &dst](result_set_type result) {
            return parallel_for_each(*result, [this, &dst](row_type& row) {
                auto name = row.get_blob("type_name");
                auto columns = row.get_list<bytes>("field_names");
                auto types = row.get_list<sstring>("field_types");
                std::vector<data_type> field_types;
                for (auto&& value : types) {
                    field_types.emplace_back(db::schema_tables::parse_type(value));
                }
                auto ut = user_type_impl::get_instance(dst.name, name, columns, field_types, false);
                return read_type_timestamp(dst, value_cast<sstring>(utf8_type->deserialize(name))).then([ut = std::move(ut), &dst](time_point timestamp) {
                    dst.types.emplace_back(type{timestamp, ut});
                });
            }).finally([result] {});
        });
    }

    future<> read_functions(keyspace& dst) {
        auto query = fmt_query("SELECT * FROM %s.%s WHERE keyspace_name = ?", db::system_keyspace::legacy::FUNCTIONS);
        return _qp.execute_internal(query, {dst.name}).then([this, &dst](result_set_type result) {
            if (!result->empty()) {
                throw unsupported_feature("functions");
            }
        });
    }

    future<> read_aggregates(keyspace& dst) {
        auto query = fmt_query("SELECT * FROM %s.%s WHERE keyspace_name = ?", db::system_keyspace::legacy::AGGREGATES);
        return _qp.execute_internal(query, {dst.name}).then([this, &dst](result_set_type result) {
            if (!result->empty()) {
                throw unsupported_feature("aggregates");
            }
        });
    }

    future<keyspace> read_keyspace(sstring ks_name, bool durable_writes, sstring strategy_class, sstring strategy_options, time_point timestamp) {
        auto map = json::to_map(strategy_options);
        map.emplace("class", std::move(strategy_class));
        auto ks = ::make_lw_shared<keyspace>(keyspace{timestamp, std::move(ks_name), durable_writes, std::move(map) });

        return read_tables(*ks).then([this, ks] {
            //Collection<Type> types = readTypes(keyspaceName);
            return read_types(*ks);
        }).then([this, ks] {
            return read_functions(*ks);
        }).then([this, ks] {
            return read_aggregates(*ks);
        }).then([this, ks] {
            return make_ready_future<keyspace>(std::move(*ks));
        });
    }

    future<> read_all_keyspaces() {
        static auto ks_filter = [](row_type& row) {
            auto ks_name = row.get_as<sstring>("keyspace_name");
            return ks_name != db::system_keyspace::NAME && ks_name != db::schema_tables::v3::NAME;
        };

        auto query = fmt_query("SELECT keyspace_name, durable_writes, strategy_options, strategy_class, writeTime(durable_writes) AS timestamp FROM %s.%s",
                        db::system_keyspace::legacy::KEYSPACES);

        return _qp.execute_internal(query).then([this](result_set_type result) {
            auto i = boost::make_filter_iterator(ks_filter, result->begin(), result->end());
            auto e = boost::make_filter_iterator(ks_filter, result->end(), result->end());
            return parallel_for_each(i, e, [this](row_type& row) {
                return read_keyspace(row.get_as<sstring>("keyspace_name")
                                , row.get_as<bool>("durable_writes")
                                , row.get_as<sstring>("strategy_class")
                                , row.get_as<sstring>("strategy_options")
                                , row.get_as<db_clock::time_point>("timestamp")
                                ).then([this](keyspace ks) {
                    _keyspaces.emplace_back(std::move(ks));
                   });
            }).finally([result] {});
        });
    }

    future<> drop_legacy_tables() {
        mlogger.info("Dropping legacy schema tables");
        return parallel_for_each(legacy_schema_tables, [this](const sstring& cfname) {
            return do_with(utils::make_joinpoint([] { return db_clock::now();}),[this, cfname](auto& tsf) {
                auto with_snapshot = !_keyspaces.empty();
                return _db.invoke_on_all([&tsf, cfname, with_snapshot](database& db) {
                    return db.drop_column_family(db::system_keyspace::NAME, cfname, [&tsf] { return tsf.value(); }, with_snapshot);
                });
            });
        });
    }

    future<> store_keyspaces_in_new_schema_tables() {
        mlogger.info("Moving {} keyspaces from legacy schema tables to the new schema keyspace ({})",
                        _keyspaces.size(), db::schema_tables::v3::NAME);

        std::vector<mutation> mutations;

        for (auto& ks : _keyspaces) {
            auto ksm = ::make_lw_shared<keyspace_metadata>(ks.name
                            , ks.replication_params["class"] // TODO, make ksm like c3?
                            , ks.replication_params
                            , ks.durable_writes);

            // we want separate time stamps for tables/types, so cannot bulk them into the ksm.
            for (auto&& m : db::schema_tables::make_create_keyspace_mutations(ksm, ks.timestamp.time_since_epoch().count(), false)) {
                mutations.emplace_back(std::move(m));
            }
            for (auto& t : ks.tables) {
                db::schema_tables::add_table_or_view_to_schema_mutation(t.metadata, t.timestamp.time_since_epoch().count(), true, mutations);
            }
            for (auto& t : ks.types) {
                db::schema_tables::add_type_to_schema_mutation(t.metadata, t.timestamp.time_since_epoch().count(), mutations);
            }
        }
        return _qp.proxy().mutate_locally(std::move(mutations));
    }

    future<> flush_schemas() {
        return _qp.proxy().get_db().invoke_on_all([this] (database& db) {
            return parallel_for_each(db::schema_tables::all_table_names(schema_features::full()), [this, &db](const sstring& cf_name) {
                auto& cf = db.find_column_family(db::schema_tables::NAME, cf_name);
                return cf.flush();
            });
        });
    }

    future<> migrate() {
        return read_all_keyspaces().then([this]() {
            // write metadata to the new schema tables
            return store_keyspaces_in_new_schema_tables()
                                                .then(std::bind(&migrator::flush_schemas, this))
                                                .then(std::bind(&migrator::drop_legacy_tables, this))
                                                .then([] { mlogger.info("Completed migration of legacy schema tables"); });
        });
    }

    sharded<service::storage_proxy>& _sp;
    sharded<database>& _db;
    cql3::query_processor& _qp;
    std::vector<keyspace> _keyspaces;
};

const std::unordered_set<sstring> migrator::legacy_schema_tables = {
                db::system_keyspace::legacy::KEYSPACES,
                db::system_keyspace::legacy::COLUMNFAMILIES,
                db::system_keyspace::legacy::COLUMNS,
                db::system_keyspace::legacy::TRIGGERS,
                db::system_keyspace::legacy::USERTYPES,
                db::system_keyspace::legacy::FUNCTIONS,
                db::system_keyspace::legacy::AGGREGATES,
};

}
}

future<>
db::legacy_schema_migrator::migrate(sharded<service::storage_proxy>& sp, sharded<database>& db, cql3::query_processor& qp) {
    return do_with(migrator(sp, db, qp), std::bind(&migrator::migrate, std::placeholders::_1));
}

