SQL Engine Support

package io.cdap.cdap.etl.api.engine.sql;

public interface SQLEngine {
    /**
     * Check if join operation is supported.
     */
    boolean canJoin(SQLJoinDefinition joinDefinition);
    
    /**
     * Execute join operation.
     */
    SQLDataset join(SQLJoinRequest joinRequest);
    
    /**
     * Check if transform operation is supported.
     */
    boolean canTransform(SQLTransformDefinition transformDefinition);
    
    /**
     * Execute transform operation.
     */
    SQLDataset transform(SQLTransformRequest transformRequest);
    
    /**
     * Check if dataset exists.
     */
    boolean exists(String datasetName);
    
    /**
     * Read data from dataset.
     */
    SQLDataset read(SQLReadRequest readRequest);
    
    /**
     * Write data to dataset.
     */
    SQLWriteResult write(SQLWriteRequest writeRequest);
    
    /**
     * Clean up dataset.
     */
    void cleanup(String datasetName);
}

package io.cdap.cdap.etl.api.engine.sql;

public interface BatchSQLEngine extends SQLEngine {
    // Inherits all SQLEngine capabilities for batch operations
    // Additional batch-specific optimizations may be added
}

public class SparkSQLEngine implements BatchSQLEngine {
    
    private final SparkSession sparkSession;
    private final Map<String, Dataset<Row>> registeredDatasets;
    
    public SparkSQLEngine(SparkSession sparkSession) {
        this.sparkSession = sparkSession;
        this.registeredDatasets = new HashMap<>();
    }
    
    @Override
    public boolean canJoin(SQLJoinDefinition joinDefinition) {
        // Check if all required datasets are available
        for (String datasetName : joinDefinition.getDatasetNames()) {
            if (!exists(datasetName)) {
                return false;
            }
        }
        
        // Check if join type is supported
        JoinType joinType = joinDefinition.getJoinType();
        return joinType == JoinType.INNER || 
               joinType == JoinType.LEFT_OUTER || 
               joinType == JoinType.RIGHT_OUTER || 
               joinType == JoinType.FULL_OUTER;
    }
    
    @Override
    public SQLDataset join(SQLJoinRequest joinRequest) {
        SQLJoinDefinition joinDef = joinRequest.getJoinDefinition();
        String outputDatasetName = joinRequest.getOutputDatasetName();
        
        // Build SQL join query
        StringBuilder query = new StringBuilder();
        query.append("SELECT ");
        
        // Add selected fields
        List<String> selectedFields = joinDef.getSelectedFields();
        if (selectedFields.isEmpty()) {
            query.append("*");
        } else {
            query.append(String.join(", ", selectedFields));
        }
        
        // Add FROM clause with main dataset
        String mainDataset = joinDef.getMainDataset();
        query.append(" FROM ").append(mainDataset);
        
        // Add join clauses
        for (JoinClause joinClause : joinDef.getJoinClauses()) {
            query.append(" ").append(joinClause.getJoinType().toString());
            query.append(" JOIN ").append(joinClause.getDatasetName());
            query.append(" ON ").append(joinClause.getOnCondition());
        }
        
        // Add WHERE clause if specified
        if (joinDef.getWhereCondition() != null) {
            query.append(" WHERE ").append(joinDef.getWhereCondition());
        }
        
        // Execute query
        Dataset<Row> resultDataset = sparkSession.sql(query.toString());
        
        // Register result dataset
        resultDataset.createOrReplaceTempView(outputDatasetName);
        registeredDatasets.put(outputDatasetName, resultDataset);
        
        return new SparkSQLDataset(outputDatasetName, resultDataset.schema(), resultDataset);
    }
    
    @Override
    public boolean canTransform(SQLTransformDefinition transformDefinition) {
        String inputDataset = transformDefinition.getInputDataset();
        String sqlQuery = transformDefinition.getSqlQuery();
        
        // Check if input dataset exists
        if (!exists(inputDataset)) {
            return false;
        }
        
        // Validate SQL query syntax
        try {
            sparkSession.sql("EXPLAIN " + sqlQuery);
            return true;
        } catch (Exception e) {
            return false;
        }
    }
    
    @Override
    public SQLDataset transform(SQLTransformRequest transformRequest) {
        SQLTransformDefinition transformDef = transformRequest.getTransformDefinition();
        String outputDatasetName = transformRequest.getOutputDatasetName();
        String sqlQuery = transformDef.getSqlQuery();
        
        // Execute transformation query
        Dataset<Row> resultDataset = sparkSession.sql(sqlQuery);
        
        // Register result dataset
        resultDataset.createOrReplaceTempView(outputDatasetName);
        registeredDatasets.put(outputDatasetName, resultDataset);
        
        return new SparkSQLDataset(outputDatasetName, resultDataset.schema(), resultDataset);
    }
    
    @Override
    public boolean exists(String datasetName) {
        return registeredDatasets.containsKey(datasetName) ||
               sparkSession.catalog().tableExists(datasetName);
    }
    
    @Override
    public SQLDataset read(SQLReadRequest readRequest) {
        String datasetName = readRequest.getDatasetName();
        
        if (registeredDatasets.containsKey(datasetName)) {
            Dataset<Row> dataset = registeredDatasets.get(datasetName);
            return new SparkSQLDataset(datasetName, dataset.schema(), dataset);
        }
        
        // Try reading as table
        try {
            Dataset<Row> dataset = sparkSession.table(datasetName);
            return new SparkSQLDataset(datasetName, dataset.schema(), dataset);
        } catch (Exception e) {
            throw new SQLEngineException("Failed to read dataset: " + datasetName, e);
        }
    }
    
    @Override
    public SQLWriteResult write(SQLWriteRequest writeRequest) {
        String datasetName = writeRequest.getDatasetName();
        SQLDataset sqlDataset = writeRequest.getDataset();
        
        if (sqlDataset instanceof SparkSQLDataset) {
            SparkSQLDataset sparkDataset = (SparkSQLDataset) sqlDataset;
            Dataset<Row> dataset = sparkDataset.getSparkDataset();
            
            // Write dataset based on format
            WriteMode writeMode = writeRequest.getWriteMode();
            switch (writeMode) {
                case OVERWRITE:
                    dataset.write().mode("overwrite").saveAsTable(datasetName);
                    break;
                case APPEND:
                    dataset.write().mode("append").saveAsTable(datasetName);
                    break;
                case ERROR_IF_EXISTS:
                    dataset.write().mode("errorifexists").saveAsTable(datasetName);
                    break;
                default:
                    throw new SQLEngineException("Unsupported write mode: " + writeMode);
            }
            
            return new SQLWriteResult(datasetName, dataset.count());
        }
        
        throw new SQLEngineException("Unsupported dataset type: " + 
                                   sqlDataset.getClass().getName());
    }
    
    @Override
    public void cleanup(String datasetName) {
        registeredDatasets.remove(datasetName);
        
        try {
            sparkSession.catalog().dropTempView(datasetName);
        } catch (Exception e) {
            // Ignore cleanup errors
        }
    }
}

package io.cdap.cdap.etl.api.engine.sql;

public interface SQLEngineInput {
    /**
     * Get input dataset name.
     */
    String getDatasetName();
    
    /**
     * Get input schema.
     */
    Schema getSchema();
}

package io.cdap.cdap.etl.api.engine.sql;

public interface SQLEngineOutput {
    /**
     * Get output dataset name.
     */
    String getDatasetName();
    
    /**
     * Get output schema.
     */
    Schema getSchema();
}

package io.cdap.cdap.etl.api.engine.sql;

public interface StandardSQLCapabilities {
    /**
     * Check if SELECT operations are supported.
     */
    boolean supportsSelect();
    
    /**
     * Check if JOIN operations are supported.
     */
    boolean supportsJoin();
    
    /**
     * Check if GROUP BY operations are supported.
     */
    boolean supportsGroupBy();
    
    /**
     * Check if window functions are supported.
     */
    boolean supportsWindowFunctions();
    
    /**
     * Check if subqueries are supported.
     */
    boolean supportsSubqueries();
}

package io.cdap.cdap.etl.api.engine.sql.capability;

public interface PullCapability {
    /**
     * Check if source can be pulled into SQL engine.
     */
    boolean canPull(String sourceType);
    
    /**
     * Pull data from external source.
     */
    SQLDataset pull(PullRequest pullRequest);
}

package io.cdap.cdap.etl.api.engine.sql.capability;

public interface PushCapability {
    /**
     * Check if data can be pushed to sink.
     */
    boolean canPush(String sinkType);
    
    /**
     * Push data to external sink.
     */
    PushResult push(PushRequest pushRequest);
}

package io.cdap.cdap.etl.api.engine.sql.capability;

public class DefaultPullCapability implements PullCapability {
    @Override
    public boolean canPull(String sourceType) {
        // Default implementation - check supported source types
        return Arrays.asList("jdbc", "file", "kafka").contains(sourceType.toLowerCase());
    }
    
    @Override
    public SQLDataset pull(PullRequest pullRequest) {
        // Default pull implementation
        throw new UnsupportedOperationException("Pull not implemented");
    }
}

package io.cdap.cdap.etl.api.engine.sql.capability;

public class DefaultPushCapability implements PushCapability {
    @Override
    public boolean canPush(String sinkType) {
        // Default implementation - check supported sink types
        return Arrays.asList("jdbc", "file", "elasticsearch").contains(sinkType.toLowerCase());
    }
    
    @Override
    public PushResult push(PushRequest pushRequest) {
        // Default push implementation
        throw new UnsupportedOperationException("Push not implemented");
    }
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public interface SQLDataset {
    /**
     * Get dataset name.
     */
    String getDatasetName();
    
    /**
     * Get dataset schema.
     */
    Schema getSchema();
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public interface SQLDatasetConsumer extends SQLDataset {
    /**
     * Consume data from the dataset.
     */
    Iterator<StructuredRecord> consume();
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public interface SQLDatasetProducer extends SQLDataset {
    /**
     * Produce data to the dataset.
     */
    void produce(Iterator<StructuredRecord> records);
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public interface SQLPullDataset extends SQLDatasetConsumer {
    /**
     * Pull data from external source.
     */
    void pull();
    
    /**
     * Get pull statistics.
     */
    PullStatistics getPullStatistics();
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public interface SQLPushDataset extends SQLDatasetProducer {
    /**
     * Push data to external sink.
     */
    void push();
    
    /**
     * Get push statistics.
     */
    PushStatistics getPushStatistics();
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public class SQLDatasetDescription {
    /**
     * Create dataset description.
     */
    public SQLDatasetDescription(String name, Schema schema, Map<String, String> properties) {}
    
    /**
     * Get dataset name.
     */
    public String getName() {}
    
    /**
     * Get dataset schema.
     */
    public Schema getSchema() {}
    
    /**
     * Get dataset properties.
     */
    public Map<String, String> getProperties() {}
}

package io.cdap.cdap.etl.api.engine.sql.dataset;

public interface RecordCollection extends Iterable<StructuredRecord> {
    /**
     * Get collection size.
     */
    long size();
    
    /**
     * Check if collection is empty.
     */
    boolean isEmpty();
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLJoinRequest {
    /**
     * Create join request.
     */
    public SQLJoinRequest(SQLJoinDefinition joinDefinition, String outputDatasetName) {}
    
    /**
     * Get join definition.
     */
    public SQLJoinDefinition getJoinDefinition() {}
    
    /**
     * Get output dataset name.
     */
    public String getOutputDatasetName() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLJoinDefinition {
    /**
     * Get participating datasets.
     */
    public List<String> getDatasetNames() {}
    
    /**
     * Get join type.
     */
    public JoinType getJoinType() {}
    
    /**
     * Get selected fields.
     */
    public List<String> getSelectedFields() {}
    
    /**
     * Get join conditions.
     */
    public List<JoinClause> getJoinClauses() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLTransformRequest {
    /**
     * Create transform request.
     */
    public SQLTransformRequest(SQLTransformDefinition transformDefinition, String outputDatasetName) {}
    
    /**
     * Get transform definition.
     */
    public SQLTransformDefinition getTransformDefinition() {}
    
    /**
     * Get output dataset name.
     */
    public String getOutputDatasetName() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLTransformDefinition {
    /**
     * Create transform definition.
     */
    public SQLTransformDefinition(String inputDataset, String sqlQuery) {}
    
    /**
     * Get input dataset name.
     */
    public String getInputDataset() {}
    
    /**
     * Get SQL query for transformation.
     */
    public String getSqlQuery() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLReadRequest {
    /**
     * Create read request.
     */
    public SQLReadRequest(String datasetName) {}
    
    /**
     * Get dataset name to read.
     */
    public String getDatasetName() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLWriteRequest {
    /**
     * Create write request.
     */
    public SQLWriteRequest(String datasetName, SQLDataset dataset, WriteMode writeMode) {}
    
    /**
     * Get target dataset name.
     */
    public String getDatasetName() {}
    
    /**
     * Get source dataset.
     */
    public SQLDataset getDataset() {}
    
    /**
     * Get write mode.
     */
    public WriteMode getWriteMode() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLPullRequest {
    /**
     * Create pull request.
     */
    public SQLPullRequest(String sourceType, Map<String, String> sourceProperties) {}
    
    /**
     * Get source type.
     */
    public String getSourceType() {}
    
    /**
     * Get source properties.
     */
    public Map<String, String> getSourceProperties() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLPushRequest {
    /**
     * Create push request.
     */
    public SQLPushRequest(SQLDataset dataset, String sinkType, 
                         Map<String, String> sinkProperties) {}
    
    /**
     * Get dataset to push.
     */
    public SQLDataset getDataset() {}
    
    /**
     * Get sink type.
     */
    public String getSinkType() {}
    
    /**
     * Get sink properties.
     */
    public Map<String, String> getSinkProperties() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLReadResult {
    /**
     * Create read result.
     */
    public SQLReadResult(SQLDataset dataset, long recordCount) {}
    
    /**
     * Get result dataset.
     */
    public SQLDataset getDataset() {}
    
    /**
     * Get number of records read.
     */
    public long getRecordCount() {}
}

package io.cdap.cdap.etl.api.engine.sql.request;

public class SQLWriteResult {
    /**
     * Create write result.
     */
    public SQLWriteResult(String datasetName, long recordCount) {}
    
    /**
     * Get dataset name written to.
     */
    public String getDatasetName() {}
    
    /**
     * Get number of records written.
     */
    public long getRecordCount() {}
}

package io.cdap.cdap.etl.api.engine.sql;

public class SQLEngineException extends Exception {
    /**
     * Create SQL engine exception.
     */
    public SQLEngineException(String message) {}
    
    /**
     * Create SQL engine exception with cause.
     */
    public SQLEngineException(String message, Throwable cause) {}
}

public class QueryOptimizer {
    
    public static SQLTransformDefinition optimizeQuery(SQLTransformDefinition originalDef,
                                                      Map<String, Statistics> datasetStats) {
        String originalQuery = originalDef.getSqlQuery();
        
        // Parse and analyze query
        QueryAnalysis analysis = analyzeQuery(originalQuery);
        
        // Apply optimizations based on statistics
        StringBuilder optimizedQuery = new StringBuilder();
        
        // Add query hints for join optimization
        if (analysis.hasJoins()) {
            optimizedQuery.append("/* + USE_HASH_JOIN */ ");
        }
        
        // Optimize WHERE clauses - push down predicates
        optimizedQuery.append(pushDownPredicates(originalQuery, analysis));
        
        // Add partitioning hints
        if (analysis.hasGroupBy()) {
            optimizedQuery.append(" /* + PARTITION_BY(")
                         .append(String.join(", ", analysis.getGroupByFields()))
                         .append(") */");
        }
        
        return new SQLTransformDefinition(originalDef.getInputDataset(), 
                                        optimizedQuery.toString());
    }
    
    private static String pushDownPredicates(String query, QueryAnalysis analysis) {
        // Implementation to push WHERE clauses closer to data sources
        // This is a simplified example - real implementation would use SQL parser
        
        if (analysis.hasSelectivePredicates()) {
            // Rewrite query to apply filters early
            return rewriteWithEarlyFilters(query, analysis.getSelectivePredicates());
        }
        
        return query;
    }
}

public class HybridSQLEngine implements BatchSQLEngine {
    
    private final BatchSQLEngine primaryEngine;
    private final BatchSQLEngine fallbackEngine;
    
    public HybridSQLEngine(BatchSQLEngine primaryEngine, BatchSQLEngine fallbackEngine) {
        this.primaryEngine = primaryEngine;
        this.fallbackEngine = fallbackEngine;
    }
    
    @Override
    public boolean canTransform(SQLTransformDefinition transformDefinition) {
        return primaryEngine.canTransform(transformDefinition) || 
               fallbackEngine.canTransform(transformDefinition);
    }
    
    @Override
    public SQLDataset transform(SQLTransformRequest transformRequest) {
        // Try primary engine first
        if (primaryEngine.canTransform(transformRequest.getTransformDefinition())) {
            try {
                return primaryEngine.transform(transformRequest);
            } catch (Exception e) {
                // Log warning and fall back
                logWarning("Primary engine failed, falling back", e);
            }
        }
        
        // Use fallback engine
        if (fallbackEngine.canTransform(transformRequest.getTransformDefinition())) {
            return fallbackEngine.transform(transformRequest);
        }
        
        throw new SQLEngineException("No suitable engine found for transformation");
    }
    
    @Override
    public SQLDataset join(SQLJoinRequest joinRequest) {
        // Similar hybrid approach for joins
        if (primaryEngine.canJoin(joinRequest.getJoinDefinition())) {
            try {
                return primaryEngine.join(joinRequest);
            } catch (Exception e) {
                logWarning("Primary engine join failed, falling back", e);
            }
        }
        
        if (fallbackEngine.canJoin(joinRequest.getJoinDefinition())) {
            return fallbackEngine.join(joinRequest);
        }
        
        throw new SQLEngineException("No suitable engine found for join");
    }
}