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Java idiomatic client for Google Cloud BigQuery.
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/*
 * Copyright 2016 Google LLC
 *
 * 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 com.google.cloud.bigquery;

import com.google.api.services.bigquery.model.UserDefinedFunctionResource;
import com.google.common.base.Function;
import com.google.common.base.MoreObjects;
import java.io.Serializable;
import java.util.Objects;

/**
 * Google BigQuery User Defined Function. BigQuery supports user-defined functions (UDFs) written in
 * JavaScript. A UDF is similar to the "Map" function in a MapReduce: it takes a single row as input
 * and produces zero or more rows as output. The output can potentially have a different schema than
 * the input.
 *
 * @see User-Defined Functions
 *     
 */
public abstract class UserDefinedFunction implements Serializable {

  static final Function FROM_PB_FUNCTION =
      new Function() {
        @Override
        public UserDefinedFunction apply(UserDefinedFunctionResource userDefinedFunctionPb) {
          return UserDefinedFunction.fromPb(userDefinedFunctionPb);
        }
      };
  static final Function TO_PB_FUNCTION =
      new Function() {
        @Override
        public UserDefinedFunctionResource apply(UserDefinedFunction userDefinedFunction) {
          return userDefinedFunction.toPb();
        }
      };

  private static final long serialVersionUID = 8704260561787440287L;

  /**
   * Type of user-defined function. User defined functions can be provided inline as code blobs
   * ({@link #INLINE}) or as a Google Cloud Storage URI ({@link #FROM_URI}).
   */
  public enum Type {
    INLINE,
    FROM_URI
  }

  private final Type type;
  private final String content;

  UserDefinedFunction(Type type, String content) {
    this.type = type;
    this.content = content;
  }

  /** Returns the type of user defined function. */
  public Type getType() {
    return type;
  }

  /**
   * If {@link #getType()} is {@link Type#INLINE} this method returns a code blob. If {@link
   * #getType()} is {@link Type#FROM_URI} the method returns a Google Cloud Storage URI (e.g.
   * gs://bucket/path).
   */
  public String getContent() {
    return content;
  }

  /** A Google Cloud BigQuery user-defined function, as a code blob. */
  static final class InlineFunction extends UserDefinedFunction {

    private static final long serialVersionUID = 1083672109192091686L;

    InlineFunction(String inlineCode) {
      super(Type.INLINE, inlineCode);
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this).add("inlineCode", getContent()).toString();
    }

    @Override
    public com.google.api.services.bigquery.model.UserDefinedFunctionResource toPb() {
      return new com.google.api.services.bigquery.model.UserDefinedFunctionResource()
          .setInlineCode(getContent());
    }
  }

  /** A Google Cloud BigQuery user-defined function, as an URI to Google Cloud Storage. */
  static final class UriFunction extends UserDefinedFunction {

    private static final long serialVersionUID = 4660331691852223839L;

    UriFunction(String functionUri) {
      super(Type.FROM_URI, functionUri);
    }

    @Override
    public String toString() {
      return MoreObjects.toStringHelper(this).add("functionUri", getContent()).toString();
    }

    @Override
    public com.google.api.services.bigquery.model.UserDefinedFunctionResource toPb() {
      return new com.google.api.services.bigquery.model.UserDefinedFunctionResource()
          .setResourceUri(getContent());
    }
  }

  @Override
  public int hashCode() {
    return Objects.hash(type, content);
  }

  @Override
  public boolean equals(Object obj) {
    return obj instanceof UserDefinedFunction
        && Objects.equals(toPb(), ((UserDefinedFunction) obj).toPb());
  }

  public abstract com.google.api.services.bigquery.model.UserDefinedFunctionResource toPb();

  /** Creates a Google Cloud BigQuery user-defined function given a code blob. */
  public static UserDefinedFunction inline(String functionDefinition) {
    return new InlineFunction(functionDefinition);
  }

  /**
   * Creates a Google Cloud BigQuery user-defined function given a Google Cloud Storage URI (e.g.
   * gs://bucket/path).
   */
  public static UserDefinedFunction fromUri(String functionDefinition) {
    return new UriFunction(functionDefinition);
  }

  static UserDefinedFunction fromPb(
      com.google.api.services.bigquery.model.UserDefinedFunctionResource pb) {
    if (pb.getInlineCode() != null) {
      return new InlineFunction(pb.getInlineCode());
    }
    if (pb.getResourceUri() != null) {
      return new UriFunction(pb.getResourceUri());
    }
    throw new IllegalArgumentException("Invalid user-defined function");
  }
}