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   * Licensed to the Apache Software Foundation (ASF) under one
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   * 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
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  package org.apache.cassandra.cql3.statements.schema;
  
  import java.util.Collection;
  import java.util.List;
  import java.util.function.Predicate;
  import java.util.stream.Stream;
  
  import org.apache.cassandra.audit.AuditLogContext;
  import org.apache.cassandra.audit.AuditLogEntryType;
  import org.apache.cassandra.auth.FunctionResource;
  import org.apache.cassandra.auth.Permission;
  import org.apache.cassandra.cql3.CQL3Type;
  import org.apache.cassandra.cql3.CQLStatement;
  import org.apache.cassandra.cql3.functions.FunctionName;
  import org.apache.cassandra.cql3.functions.UDFunction;
  import org.apache.cassandra.cql3.functions.UserFunction;
  import org.apache.cassandra.db.marshal.AbstractType;
  import org.apache.cassandra.schema.*;
  import org.apache.cassandra.schema.Keyspaces.KeyspacesDiff;
  import org.apache.cassandra.service.ClientState;
  import org.apache.cassandra.tcm.ClusterMetadata;
  import org.apache.cassandra.transport.Event.SchemaChange;
  import org.apache.cassandra.transport.Event.SchemaChange.Change;
  
  import static java.lang.String.format;
  import static java.lang.String.join;
  import static java.util.stream.Collectors.joining;
  import static java.util.stream.Collectors.toList;
  
  import static com.google.common.collect.Iterables.transform;
  
  public final class DropFunctionStatement extends AlterSchemaStatement
  {
      private final String functionName;
      private final Collection<CQL3Type.Raw> arguments;
      private final boolean argumentsSpeficied;
      private final boolean ifExists;
  
      public DropFunctionStatement(String keyspaceName,
                                   String functionName,
                                   Collection<CQL3Type.Raw> arguments,
                                   boolean argumentsSpeficied,
                                   boolean ifExists)
      {
          super(keyspaceName);
          this.functionName = functionName;
          this.arguments = arguments;
          this.argumentsSpeficied = argumentsSpeficied;
          this.ifExists = ifExists;
      }
  
      @Override
      public Keyspaces apply(ClusterMetadata metadata)
      {
          String name =
              argumentsSpeficied
            ? format("%s.%s(%s)", keyspaceName, functionName, join(", ", transform(arguments, CQL3Type.Raw::toString)))
            : format("%s.%s", keyspaceName, functionName);
  
          Keyspaces schema = metadata.schema.getKeyspaces();
          KeyspaceMetadata keyspace = schema.getNullable(keyspaceName);
          if (null == keyspace)
          {
              if (ifExists)
                  return schema;
  
              throw ire("Function '%s' doesn't exist", name);
          }
  
          Collection<UserFunction> functions = keyspace.userFunctions.get(new FunctionName(keyspaceName, functionName));
          if (functions.size() > 1 && !argumentsSpeficied)
          {
              throw ire("'DROP FUNCTION %s' matches multiple function definitions; " +
                        "specify the argument types by issuing a statement like " +
                        "'DROP FUNCTION %s (type, type, ...)'. You can use cqlsh " +
                        "'DESCRIBE FUNCTION %s' command to find all overloads",
                        functionName, functionName, functionName);
          }
  
          arguments.stream()
                   .filter(raw -> !raw.isImplicitlyFrozen() && raw.isFrozen())
                   .findFirst()
                   .ifPresent(t -> { throw ire("Argument '%s' cannot be frozen; remove frozen<> modifier from '%s'", t, t); });
  
          List<AbstractType<?>> argumentTypes = prepareArgumentTypes(keyspace.types);
  
          Predicate<UserFunction> filter = UserFunctions.Filter.UDF;
          if (argumentsSpeficied)
              filter = filter.and(f -> f.typesMatch(argumentTypes));
  
          UserFunction function = functions.stream().filter(filter).findAny().orElse(null);
          if (null == function)
          {
              if (ifExists)
                  return schema;
  
              throw ire("Function '%s' doesn't exist", name);
          }
  
          String dependentAggregates =
              keyspace.userFunctions
                      .aggregatesUsingFunction(function)
                      .map(a -> a.name().toString())
                      .collect(joining(", "));
  
          if (!dependentAggregates.isEmpty())
              throw ire("Function '%s' is still referenced by aggregates %s", name, dependentAggregates);
  
          String dependentTables = keyspace.tablesUsingFunction(function)
                                           .map(table -> table.name)
                                           .collect(joining(", "));
  
          if (!dependentTables.isEmpty())
              throw ire("Function '%s' is still referenced by column masks in tables %s", name, dependentTables);
  
          return schema.withAddedOrUpdated(keyspace.withSwapped(keyspace.userFunctions.without(function)));
      }
  
      SchemaChange schemaChangeEvent(KeyspacesDiff diff)
      {
          UserFunctions dropped = diff.altered.get(0).udfs.dropped;
          assert dropped.size() == 1;
          return SchemaChange.forFunction(Change.DROPPED, (UDFunction) dropped.iterator().next());
      }
  
      public void authorize(ClientState client)
      {
          KeyspaceMetadata keyspace = Schema.instance.getKeyspaceMetadata(keyspaceName);
          if (null == keyspace)
              return;
  
          Stream<UserFunction> functions = keyspace.userFunctions.get(new FunctionName(keyspaceName, functionName)).stream();
          if (argumentsSpeficied)
              functions = functions.filter(f -> f.typesMatch(prepareArgumentTypes(keyspace.types)));
  
          functions.forEach(f -> client.ensurePermission(Permission.DROP, FunctionResource.function(f)));
      }
  
      @Override
      public AuditLogContext getAuditLogContext()
      {
          return new AuditLogContext(AuditLogEntryType.DROP_FUNCTION, keyspaceName, functionName);
      }
  
      public String toString()
      {
          return String.format("%s (%s, %s)", getClass().getSimpleName(), keyspaceName, functionName);
      }
  
      private List<AbstractType<?>> prepareArgumentTypes(Types types)
      {
          return arguments.stream()
                          .map(t -> t.prepare(keyspaceName, types))
                          .map(t -> t.getType().udfType())
                          .collect(toList());
      }
  
      public static final class Raw extends CQLStatement.Raw
      {
          private final FunctionName name;
          private final List<CQL3Type.Raw> arguments;
          private final boolean argumentsSpecified;
          private final boolean ifExists;
  
          public Raw(FunctionName name,
                     List<CQL3Type.Raw> arguments,
                     boolean argumentsSpecified,
                     boolean ifExists)
          {
              this.name = name;
              this.arguments = arguments;
              this.argumentsSpecified = argumentsSpecified;
              this.ifExists = ifExists;
          }
  
          public DropFunctionStatement prepare(ClientState state)
          {
              String keyspaceName = name.hasKeyspace() ? name.keyspace : state.getKeyspace();
              return new DropFunctionStatement(keyspaceName, name.name, arguments, argumentsSpecified, ifExists);
          }
      }
  }
  