// Copyright 2023 PingCAP, 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.

#include <Columns/ColumnString.h>
#include <Columns/ColumnsNumber.h>
#include <Columns/IColumn.h>
#include <Columns/VirtualColumnUtils.h>
#include <DataStreams/OneBlockInputStream.h>
#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypesNumber.h>
#include <Databases/IDatabase.h>
#include <Interpreters/Context.h>
#include <Parsers/queryToString.h>
#include <Storages/ColumnDefault.h>
#include <Storages/System/StorageSystemColumns.h>


namespace DB
{
namespace ErrorCodes
{
extern const int TABLE_IS_DROPPED;
} // namespace ErrorCodes

StorageSystemColumns::StorageSystemColumns(const std::string & name_)
    : name(name_)
{
    setColumns(ColumnsDescription({
        {"database", std::make_shared<DataTypeString>()},
        {"table", std::make_shared<DataTypeString>()},
        {"name", std::make_shared<DataTypeString>()},
        {"type", std::make_shared<DataTypeString>()},
        {"default_kind", std::make_shared<DataTypeString>()},
        {"default_expression", std::make_shared<DataTypeString>()},
        {"data_compressed_bytes", std::make_shared<DataTypeUInt64>()},
        {"data_uncompressed_bytes", std::make_shared<DataTypeUInt64>()},
        {"marks_bytes", std::make_shared<DataTypeUInt64>()},
    }));
}


BlockInputStreams StorageSystemColumns::read(
    const Names & column_names,
    const SelectQueryInfo & query_info,
    const Context & context,
    QueryProcessingStage::Enum & processed_stage,
    const size_t /*max_block_size*/,
    const unsigned /*num_streams*/)
{
    check(column_names);
    processed_stage = QueryProcessingStage::FetchColumns;

    Block block_to_filter;

    std::map<std::pair<std::string, std::string>, StoragePtr> storages;

    {
        Databases databases = context.getDatabases();

        /// Add `database` column.
        MutableColumnPtr database_column_mut = ColumnString::create();
        for (const auto & database : databases)
            database_column_mut->insert(database.first);
        block_to_filter.insert(
            ColumnWithTypeAndName(std::move(database_column_mut), std::make_shared<DataTypeString>(), "database"));

        /// Filter block with `database` column.
        VirtualColumnUtils::filterBlockWithQuery(query_info.query, block_to_filter, context);

        if (!block_to_filter.rows())
            return BlockInputStreams();

        ColumnPtr database_column = block_to_filter.getByName("database").column;
        size_t rows = database_column->size();

        /// Add `table` column.
        MutableColumnPtr table_column_mut = ColumnString::create();
        IColumn::Offsets offsets(rows);
        for (size_t i = 0; i < rows; ++i)
        {
            const std::string database_name = (*database_column)[i].get<std::string>();
            const DatabasePtr database = databases.at(database_name);
            offsets[i] = i ? offsets[i - 1] : 0;

            for (auto iterator = database->getIterator(context); iterator->isValid(); iterator->next())
            {
                const String & table_name = iterator->name();
                storages.emplace(
                    std::piecewise_construct,
                    std::forward_as_tuple(database_name, table_name),
                    std::forward_as_tuple(iterator->table()));
                table_column_mut->insert(table_name);
                offsets[i] += 1;
            }
        }

        for (size_t i = 0; i < block_to_filter.columns(); ++i)
        {
            ColumnPtr & column = block_to_filter.safeGetByPosition(i).column;
            column = column->replicate(offsets);
        }

        block_to_filter.insert(
            ColumnWithTypeAndName(std::move(table_column_mut), std::make_shared<DataTypeString>(), "table"));
    }

    /// Filter block with `database` and `table` columns.
    VirtualColumnUtils::filterBlockWithQuery(query_info.query, block_to_filter, context);

    if (!block_to_filter.rows())
        return BlockInputStreams();

    ColumnPtr filtered_database_column = block_to_filter.getByName("database").column;
    ColumnPtr filtered_table_column = block_to_filter.getByName("table").column;

    /// We compose the result.
    MutableColumns res_columns = getSampleBlock().cloneEmptyColumns();

    size_t rows = filtered_database_column->size();
    for (size_t i = 0; i < rows; ++i)
    {
        const std::string database_name = (*filtered_database_column)[i].get<std::string>();
        const std::string table_name = (*filtered_table_column)[i].get<std::string>();

        NamesAndTypesList columns;
        ColumnDefaults column_defaults;

        {
            StoragePtr storage = storages.at(std::make_pair(database_name, table_name));
            TableStructureLockHolder table_lock;

            try
            {
                table_lock = storage->lockStructureForShare(context.getCurrentQueryId());
            }
            catch (const Exception & e)
            {
                /** There are case when IStorage::drop was called,
                  *  but we still own the object.
                  * Then table will throw exception at attempt to lock it.
                  * Just skip the table.
                  */
                if (e.code() == ErrorCodes::TABLE_IS_DROPPED)
                    continue;
                else
                    throw;
            }

            columns = storage->getColumns().getAll();
            column_defaults = storage->getColumns().defaults;
        }

        for (const auto & column : columns)
        {
            size_t i = 0;

            res_columns[i++]->insert(database_name);
            res_columns[i++]->insert(table_name);
            res_columns[i++]->insert(column.name);
            res_columns[i++]->insert(column.type->getName());

            {
                const auto it = column_defaults.find(column.name);
                if (it == std::end(column_defaults))
                {
                    res_columns[i++]->insertDefault();
                    res_columns[i++]->insertDefault();
                }
                else
                {
                    res_columns[i++]->insert(toString(it->second.kind));
                    res_columns[i++]->insert(queryToString(it->second.expression));
                }
            }

            {
                res_columns[i++]->insertDefault();
                res_columns[i++]->insertDefault();
                res_columns[i++]->insertDefault();
            }
        }
    }

    return BlockInputStreams(
        1,
        std::make_shared<OneBlockInputStream>(getSampleBlock().cloneWithColumns(std::move(res_columns))));
}

} // namespace DB