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Trino - Prometheus connector
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/*
 * 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.
 */
package io.trino.plugin.prometheus;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.inject.Inject;
import io.trino.spi.TrinoException;
import io.trino.spi.connector.ColumnHandle;
import io.trino.spi.connector.ColumnMetadata;
import io.trino.spi.connector.ConnectorMetadata;
import io.trino.spi.connector.ConnectorSession;
import io.trino.spi.connector.ConnectorTableHandle;
import io.trino.spi.connector.ConnectorTableMetadata;
import io.trino.spi.connector.ConnectorTableVersion;
import io.trino.spi.connector.Constraint;
import io.trino.spi.connector.ConstraintApplicationResult;
import io.trino.spi.connector.RelationColumnsMetadata;
import io.trino.spi.connector.SchemaTableName;
import io.trino.spi.connector.SchemaTablePrefix;
import io.trino.spi.connector.TableNotFoundException;

import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.UnaryOperator;

import static com.google.common.collect.ImmutableList.toImmutableList;
import static io.trino.spi.StandardErrorCode.NOT_SUPPORTED;
import static io.trino.spi.connector.RelationColumnsMetadata.forTable;
import static java.util.Objects.requireNonNull;

public class PrometheusMetadata
        implements ConnectorMetadata
{
    private final PrometheusClient prometheusClient;

    @Inject
    public PrometheusMetadata(PrometheusClient prometheusClient)
    {
        this.prometheusClient = requireNonNull(prometheusClient, "prometheusClient is null");
    }

    @Override
    public List listSchemaNames(ConnectorSession session)
    {
        return listSchemaNames();
    }

    private static List listSchemaNames()
    {
        return ImmutableList.copyOf(ImmutableSet.of("default"));
    }

    @Override
    public PrometheusTableHandle getTableHandle(ConnectorSession session, SchemaTableName tableName, Optional startVersion, Optional endVersion)
    {
        if (startVersion.isPresent() || endVersion.isPresent()) {
            throw new TrinoException(NOT_SUPPORTED, "This connector does not support versioned tables");
        }

        if (!listSchemaNames(session).contains(tableName.getSchemaName())) {
            return null;
        }

        if (prometheusClient.getTable(tableName.getSchemaName(), tableName.getTableName()) == null) {
            return null;
        }

        return new PrometheusTableHandle(tableName.getSchemaName(), tableName.getTableName(), Optional.empty());
    }

    @Override
    public ConnectorTableMetadata getTableMetadata(ConnectorSession session, ConnectorTableHandle table)
    {
        return getTableMetadata(((PrometheusTableHandle) table).toSchemaTableName());
    }

    @Override
    public List listTables(ConnectorSession session, Optional optionalSchemaName)
    {
        Set schemaNames = optionalSchemaName.map(ImmutableSet::of)
                .orElseGet(() -> ImmutableSet.copyOf(ImmutableSet.of("default")));

        return schemaNames.stream()
                .flatMap(schemaName ->
                        prometheusClient.getTableNames(schemaName).stream().map(tableName -> new SchemaTableName(schemaName, tableName)))
                .collect(toImmutableList());
    }

    @Override
    public Map getColumnHandles(ConnectorSession session, ConnectorTableHandle tableHandle)
    {
        PrometheusTableHandle prometheusTableHandle = (PrometheusTableHandle) tableHandle;

        PrometheusTable table = prometheusClient.getTable(prometheusTableHandle.schemaName(), prometheusTableHandle.tableName());
        if (table == null) {
            throw new TableNotFoundException(prometheusTableHandle.toSchemaTableName());
        }

        ImmutableMap.Builder columnHandles = ImmutableMap.builder();
        int index = 0;
        for (ColumnMetadata column : table.columnsMetadata()) {
            columnHandles.put(column.getName(), new PrometheusColumnHandle(column.getName(), column.getType(), index));
            index++;
        }
        return columnHandles.buildOrThrow();
    }

    @Override
    public Iterator streamRelationColumns(ConnectorSession session, Optional schemaName, UnaryOperator> relationFilter)
    {
        Map relationColumns = new HashMap<>();

        SchemaTablePrefix prefix = schemaName.map(SchemaTablePrefix::new)
                .orElseGet(SchemaTablePrefix::new);
        for (SchemaTableName tableName : listTables(session, prefix)) {
            ConnectorTableMetadata tableMetadata = getTableMetadata(tableName);
            // table can disappear during listing operation
            if (tableMetadata != null) {
                relationColumns.put(tableName, forTable(tableName, tableMetadata.getColumns()));
            }
        }

        return relationFilter.apply(relationColumns.keySet()).stream()
                .map(relationColumns::get)
                .iterator();
    }

    private ConnectorTableMetadata getTableMetadata(SchemaTableName tableName)
    {
        if (!listSchemaNames().contains(tableName.getSchemaName())) {
            return null;
        }

        PrometheusTable table = prometheusClient.getTable(tableName.getSchemaName(), tableName.getTableName());
        if (table == null) {
            return null;
        }

        return new ConnectorTableMetadata(tableName, table.columnsMetadata());
    }

    private List listTables(ConnectorSession session, SchemaTablePrefix prefix)
    {
        if (prefix.getTable().isEmpty()) {
            return listTables(session, prefix.getSchema());
        }
        return ImmutableList.of(prefix.toSchemaTableName());
    }

    @Override
    public ColumnMetadata getColumnMetadata(ConnectorSession session, ConnectorTableHandle tableHandle, ColumnHandle columnHandle)
    {
        return ((PrometheusColumnHandle) columnHandle).columnMetadata();
    }

    @Override
    public Optional> applyFilter(ConnectorSession session, ConnectorTableHandle handle, Constraint constraint)
    {
        PrometheusTableHandle tableHandle = ((PrometheusTableHandle) handle)
                .withPredicate(constraint.getSummary());
        return Optional.of(new ConstraintApplicationResult<>(tableHandle, constraint.getSummary(), constraint.getExpression(), false));
    }
}