/*
 * 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.
 */
package org.apache.drill.exec.planner.sql;

import org.apache.calcite.sql.SqlIdentifier;
import com.google.common.base.Joiner;
import com.google.common.base.Strings;
import com.google.common.collect.Lists;
import org.apache.calcite.schema.SchemaPlus;
import org.apache.drill.common.config.DrillConfig;
import org.apache.drill.common.exceptions.UserException;
import org.apache.drill.exec.ExecConstants;
import org.apache.drill.exec.store.AbstractSchema;
import org.apache.drill.exec.store.dfs.WorkspaceSchemaFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class SchemaUtilities {
  private static final Logger logger = LoggerFactory.getLogger(SchemaUtilities.class);
  public static final Joiner SCHEMA_PATH_JOINER = Joiner.on(".").skipNulls();

  /**
   * Search and return schema with given schemaPath. First search in schema tree starting from defaultSchema,
   * if not found search starting from rootSchema. Root schema tree is derived from the defaultSchema reference.
   *
   * @param defaultSchema Reference to the default schema in complete schema tree.
   * @param schemaPath Schema path to search.
   * @return SchemaPlus object from default or root schema, or null if not found.
   */
  public static SchemaPlus findSchema(final SchemaPlus defaultSchema, final List<String> schemaPath) {
    if (schemaPath.size() == 0) {
      return defaultSchema;
    }
    SchemaPlus schema = searchSchemaTree(defaultSchema, schemaPath);
    SchemaPlus rootSchema;
    if (schema == null && (rootSchema = rootSchema(defaultSchema)) != defaultSchema) {
      schema = searchSchemaTree(rootSchema, schemaPath);
    }
    return schema;
  }

  /**
   * Same utility as {@link #findSchema(SchemaPlus, List)} except the search schema path given here is complete path
   * instead of list. Use "." separator to divided the schema into nested schema names.
   * @param defaultSchema default schema
   * @param schemaPath current schema path
   * @return found schema path
   */
  public static SchemaPlus findSchema(final SchemaPlus defaultSchema, final String schemaPath) {
    final List<String> schemaPathAsList = getSchemaPathAsList(schemaPath);
    return findSchema(defaultSchema, schemaPathAsList);
  }

  /**
   * Utility function to get the commonPrefix schema between two supplied schemas.
   *
   * Eg: if the defaultSchema: dfs and the schemaPath is dfs.tmp.`cicks.json`
   *     then this function returns dfs if (caseSensitive is not true
   *     otherwise it returns empty string.
   *
   * @param defaultSchema default schema
   * @param schemaPath current schema path
   * @param isCaseSensitive true if caseSensitive comparision is required.
   * @return common prefix schemaPath
   */
  public static String getPrefixSchemaPath(final String defaultSchema,
                                           final String schemaPath,
                                           final boolean isCaseSensitive) {
    if (!isCaseSensitive) {
      return Strings.commonPrefix(defaultSchema.toLowerCase(), schemaPath.toLowerCase());
    }
    else {
      return Strings.commonPrefix(defaultSchema, schemaPath);
    }
  }

  /** Utility method to search for schema path starting from the given <i>schema</i> reference */
  public static SchemaPlus searchSchemaTree(SchemaPlus schema, final List<String> schemaPath) {
    for (String schemaName : schemaPath) {

      // schemas in Drill are case insensitive and stored in lower case
      schema = schema.getSubSchema(schemaName.toLowerCase());
      if (schema == null) {
        return null;
      }
    }
    return schema;
  }

  /**
   * @param schema current schema
   * @return true if the given <i>schema</i> is root schema. False otherwise.
   */
  public static boolean isRootSchema(SchemaPlus schema) {
    return schema == null || schema.getParentSchema() == null;
  }

  /**
   * Unwrap given <i>SchemaPlus</i> instance as Drill schema instance (<i>AbstractSchema</i>). Once unwrapped, return
   * default schema from <i>AbstractSchema</i>. If the given schema is not an instance of <i>AbstractSchema</i> a
   * {@link UserException} is thrown.
   */
  public static AbstractSchema unwrapAsDrillSchemaInstance(SchemaPlus schemaPlus)  {
    try {
      return (AbstractSchema) schemaPlus.unwrap(AbstractSchema.class).getDefaultSchema();
    } catch (ClassCastException e) {
      throw UserException.validationError(e)
          .message("Schema [%s] is not a Drill schema.", getSchemaPath(schemaPlus))
          .build(logger);
    }
  }

  /** Utility method to get the schema path for given schema instance. */
  public static String getSchemaPath(SchemaPlus schema) {
    return SCHEMA_PATH_JOINER.join(getSchemaPathAsList(schema));
  }

  /** Utility method to get the schema path for given list of schema path. */
  public static String getSchemaPath(List<String> schemaPath) {
    return SCHEMA_PATH_JOINER.join(schemaPath);
  }

  /** Utility method to get the list with schema path components for given schema path string. */
  public static List<String> getSchemaPathAsList(String schemaPath) {
    return Arrays.asList(schemaPath.split("\\."));
  }

  /** Utility method to get the schema path as list for given schema instance. */
  public static List<String> getSchemaPathAsList(SchemaPlus schema) {
    if (isRootSchema(schema)) {
      return Collections.emptyList();
    }

    List<String> path = Lists.newArrayListWithCapacity(5);
    while(schema != null) {
      final String name = schema.getName();
      if (!Strings.isNullOrEmpty(name)) {
        path.add(schema.getName());
      }
      schema = schema.getParentSchema();
    }

    return Lists.reverse(path);
  }

  /** Utility method to throw {@link UserException} with context information */
  public static void throwSchemaNotFoundException(final SchemaPlus defaultSchema, final String givenSchemaPath) {
    throw UserException.validationError()
        .message("Schema [%s] is not valid with respect to either root schema or current default schema.",
            givenSchemaPath)
        .addContext("Current default schema: ",
            isRootSchema(defaultSchema) ? "No default schema selected" : getSchemaPath(defaultSchema))
        .build(logger);
  }

  /** Utility method to throw {@link UserException} with context information */
  public static void throwSchemaNotFoundException(final SchemaPlus defaultSchema, final List<String> givenSchemaPath) {
    throw UserException.validationError()
            .message("Schema [%s] is not valid with respect to either root schema or current default schema.",
                    givenSchemaPath)
            .addContext("Current default schema: ",
                    isRootSchema(defaultSchema) ? "No default schema selected" : getSchemaPath(defaultSchema))
            .build(logger);
  }

  /**
   * Given reference to default schema in schema tree, search for schema with given <i>schemaPath</i>. Once a schema is
   * found resolve it into a mutable <i>AbstractDrillSchema</i> instance. A {@link UserException} is throws when:
   *   <li>No schema for given <i>schemaPath</i> is found.</li>
   *   <li>Schema found for given <i>schemaPath</i> is a root schema.</li>
   *   <li>Resolved schema is not a mutable schema.</li>
   *
   * @param defaultSchema default schema
   * @param schemaPath current schema path
   * @return mutable schema, exception otherwise
   */
  public static AbstractSchema resolveToMutableDrillSchema(final SchemaPlus defaultSchema, List<String> schemaPath) {
    return resolveToDrillSchemaInternal(defaultSchema, schemaPath, true);
  }

  /**
   * Given reference to default schema in schema tree, search for schema with given <i>schemaPath</i>. Once a schema is
   * found resolve it into a mutable <i>AbstractDrillSchema</i> instance. A {@link UserException} is throws when:
   *   <li>No schema for given <i>schemaPath</i> is found.</li>
   *   <li>Schema found for given <i>schemaPath</i> is a root schema.</li>
   *
   * @param defaultSchema
   * @param schemaPath
   * @return schema, if found. Otherwise, throws an {@link UserException}
   */
  public static AbstractSchema resolveToDrillSchema(final SchemaPlus defaultSchema, List<String> schemaPath) {
    return resolveToDrillSchemaInternal(defaultSchema, schemaPath, false);
  }

  private static AbstractSchema resolveToDrillSchemaInternal (SchemaPlus defaultSchema, List<String> schemaPath,
                                                              boolean checkMutable) {
    final SchemaPlus schema = findSchema(defaultSchema, schemaPath);

    if (schema == null) {
      throwSchemaNotFoundException(defaultSchema, SCHEMA_PATH_JOINER.join(schemaPath));
    }

    if (checkMutable && isRootSchema(schema)) {
      throw UserException.validationError()
          .message("Root schema is immutable. Drill does not allow creating or deleting tables or views in the root schema. " +
              "Select a schema using 'USE schema' command.")
          .build(logger);
    }

    final AbstractSchema drillSchema = unwrapAsDrillSchemaInstance(schema);
    if (checkMutable && !drillSchema.isMutable()) {
      throw UserException.validationError()
          .message("Unable to create or drop objects. Schema [%s] is immutable.", getSchemaPath(schema))
          .build(logger);
    }

    return drillSchema;
  }

  /**
   * Looks in schema tree for default temporary workspace instance.
   *
   * @param defaultSchema default schema
   * @param config drill config
   * @return default temporary workspace, null if workspace was not found
   */
  public static AbstractSchema getTemporaryWorkspace(SchemaPlus defaultSchema, DrillConfig config) {
    String temporarySchema = config.getString(ExecConstants.DEFAULT_TEMPORARY_WORKSPACE);
    List<String> temporarySchemaPath = Lists.newArrayList(temporarySchema);
    SchemaPlus schema = findSchema(defaultSchema, temporarySchemaPath);
    return schema == null ? null : unwrapAsDrillSchemaInstance(schema);
  }

  /**
   * Checks that passed schema path is the same as temporary workspace path.
   * Check is case-sensitive.
   *
   * @param schemaPath schema path
   * @param config drill config
   * @return true is schema path corresponds to temporary workspace, false otherwise
   */
  public static boolean isTemporaryWorkspace(String schemaPath, DrillConfig config) {
    return schemaPath.equals(config.getString(ExecConstants.DEFAULT_TEMPORARY_WORKSPACE));
  }

  /**
   * Makes sure that passed workspace exists, is default temporary workspace, mutable and file-based
   * (instance of {@link WorkspaceSchemaFactory.WorkspaceSchema}).
   *
   * @param schema drill schema
   * @param config drill config
   * @return mutable & file-based workspace instance, otherwise throws validation error
   */
  public static WorkspaceSchemaFactory.WorkspaceSchema resolveToValidTemporaryWorkspace(AbstractSchema schema,
                                                                                        DrillConfig config) {
    if (schema == null) {
      throw UserException.validationError()
          .message("Default temporary workspace is not found")
          .build(logger);
    }

    if (!isTemporaryWorkspace(schema.getFullSchemaName(), config)) {
      throw UserException
          .validationError()
          .message(String.format("Temporary tables are not allowed to be created / dropped " +
                  "outside of default temporary workspace [%s].",
              config.getString(ExecConstants.DEFAULT_TEMPORARY_WORKSPACE)))
          .build(logger);
    }

    if (!schema.isMutable()) {
      throw UserException.validationError()
          .message("Unable to create or drop temporary table. Schema [%s] is immutable.", schema.getFullSchemaName())
          .build(logger);
    }

    if (schema instanceof WorkspaceSchemaFactory.WorkspaceSchema) {
      return (WorkspaceSchemaFactory.WorkspaceSchema) schema;
    } else {
      throw UserException.validationError()
          .message("Temporary workspace [%s] must be file-based, instance of " +
              "WorkspaceSchemaFactory.WorkspaceSchema", schema)
          .build(logger);
    }
  }

  /**
   * If table schema is not indicated in sql call, returns temporary workspace.
   * If schema is indicated, resolves to mutable table schema.
   *
   * @param tableSchema table schema
   * @param defaultSchema default schema
   * @param config drill config
   * @return resolved schema
   */
  public static AbstractSchema resolveToTemporarySchema(List<String> tableSchema, SchemaPlus defaultSchema, DrillConfig config) {
    if (tableSchema.size() == 0) {
      return SchemaUtilities.getTemporaryWorkspace(defaultSchema, config);
    } else {
      return SchemaUtilities.resolveToMutableDrillSchema(defaultSchema, tableSchema);
    }
  }

  /**
   * Finds root of given schema.
   * @param schema current schema
   * @return root schema
   */
  public static SchemaPlus rootSchema(SchemaPlus schema) {
    while (!isRootSchema(schema)) {
      schema = schema.getParentSchema();
    }
    return schema;
  }

  /**
   * Returns schema path which corresponds to the specified table identifier.
   * If table identifier contains only table name, empty list will be returned.
   *
   * @param tableIdentifier table identifier
   * @return schema path which corresponds to the specified table identifier
   */
  public static List<String> getSchemaPath(SqlIdentifier tableIdentifier) {
    return tableIdentifier.isSimple()
        ? Collections.emptyList()
        : tableIdentifier.names.subList(0, tableIdentifier.names.size() - 1);
  }
}
