/*
 * 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.spark.sql

import java.util

import scala.jdk.CollectionConverters._

import org.apache.spark.annotation.Stable
import org.apache.spark.api.java.JavaRDD
import org.apache.spark.rdd.RDD
import org.apache.spark.sql.catalyst.encoders.AgnosticEncoders.StringEncoder
import org.apache.spark.sql.catalyst.util.{CaseInsensitiveMap, SparkCharVarcharUtils}
import org.apache.spark.sql.errors.DataTypeErrors
import org.apache.spark.sql.types.StructType

/**
 * Interface used to load a [[Dataset]] from external storage systems (e.g. file systems,
 * key-value stores, etc). Use `SparkSession.read` to access this.
 *
 * @since 1.4.0
 */
@Stable
abstract class DataFrameReader {

  /**
   * Specifies the input data source format.
   *
   * @since 1.4.0
   */
  def format(source: String): this.type = {
    this.source = source
    this
  }

  /**
   * Specifies the input schema. Some data sources (e.g. JSON) can infer the input schema
   * automatically from data. By specifying the schema here, the underlying data source can skip
   * the schema inference step, and thus speed up data loading.
   *
   * @since 1.4.0
   */
  def schema(schema: StructType): this.type = {
    if (schema != null) {
      val replaced = SparkCharVarcharUtils.failIfHasCharVarchar(schema).asInstanceOf[StructType]
      this.userSpecifiedSchema = Option(replaced)
      validateSingleVariantColumn()
    }
    this
  }

  /**
   * Specifies the schema by using the input DDL-formatted string. Some data sources (e.g. JSON)
   * can infer the input schema automatically from data. By specifying the schema here, the
   * underlying data source can skip the schema inference step, and thus speed up data loading.
   *
   * {{{
   *   spark.read.schema("a INT, b STRING, c DOUBLE").csv("test.csv")
   * }}}
   *
   * @since 2.3.0
   */
  def schema(schemaString: String): this.type = schema(StructType.fromDDL(schemaString))

  /**
   * Adds an input option for the underlying data source.
   *
   * All options are maintained in a case-insensitive way in terms of key names. If a new option
   * has the same key case-insensitively, it will override the existing option.
   *
   * @since 1.4.0
   */
  def option(key: String, value: String): this.type = {
    this.extraOptions = this.extraOptions + (key -> value)
    validateSingleVariantColumn()
    this
  }

  /**
   * Adds an input option for the underlying data source.
   *
   * All options are maintained in a case-insensitive way in terms of key names. If a new option
   * has the same key case-insensitively, it will override the existing option.
   *
   * @since 2.0.0
   */
  def option(key: String, value: Boolean): this.type = option(key, value.toString)

  /**
   * Adds an input option for the underlying data source.
   *
   * All options are maintained in a case-insensitive way in terms of key names. If a new option
   * has the same key case-insensitively, it will override the existing option.
   *
   * @since 2.0.0
   */
  def option(key: String, value: Long): this.type = option(key, value.toString)

  /**
   * Adds an input option for the underlying data source.
   *
   * All options are maintained in a case-insensitive way in terms of key names. If a new option
   * has the same key case-insensitively, it will override the existing option.
   *
   * @since 2.0.0
   */
  def option(key: String, value: Double): this.type = option(key, value.toString)

  /**
   * (Scala-specific) Adds input options for the underlying data source.
   *
   * All options are maintained in a case-insensitive way in terms of key names. If a new option
   * has the same key case-insensitively, it will override the existing option.
   *
   * @since 1.4.0
   */
  def options(options: scala.collection.Map[String, String]): this.type = {
    this.extraOptions ++= options
    validateSingleVariantColumn()
    this
  }

  /**
   * Adds input options for the underlying data source.
   *
   * All options are maintained in a case-insensitive way in terms of key names. If a new option
   * has the same key case-insensitively, it will override the existing option.
   *
   * @since 1.4.0
   */
  def options(opts: util.Map[String, String]): this.type = options(opts.asScala)

  /**
   * Loads input in as a `DataFrame`, for data sources that don't require a path (e.g. external
   * key-value stores).
   *
   * @since 1.4.0
   */
  def load(): DataFrame

  /**
   * Loads input in as a `DataFrame`, for data sources that require a path (e.g. data backed by a
   * local or distributed file system).
   *
   * @since 1.4.0
   */
  def load(path: String): DataFrame

  /**
   * Loads input in as a `DataFrame`, for data sources that support multiple paths. Only works if
   * the source is a HadoopFsRelationProvider.
   *
   * @since 1.6.0
   */
  @scala.annotation.varargs
  def load(paths: String*): DataFrame

  /**
   * Construct a `DataFrame` representing the database table accessible via JDBC URL url named
   * table and connection properties.
   *
   * You can find the JDBC-specific option and parameter documentation for reading tables via JDBC
   * in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-jdbc.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @since 1.4.0
   */
  def jdbc(url: String, table: String, properties: util.Properties): DataFrame = {
    assertNoSpecifiedSchema("jdbc")
    // properties should override settings in extraOptions.
    this.extraOptions ++= properties.asScala
    // explicit url and dbtable should override all
    this.extraOptions ++= Seq("url" -> url, "dbtable" -> table)
    format("jdbc").load()
  }

  // scalastyle:off line.size.limit
  /**
   * Construct a `DataFrame` representing the database table accessible via JDBC URL url named
   * table. Partitions of the table will be retrieved in parallel based on the parameters passed
   * to this function.
   *
   * Don't create too many partitions in parallel on a large cluster; otherwise Spark might crash
   * your external database systems.
   *
   * You can find the JDBC-specific option and parameter documentation for reading tables via JDBC
   * in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-jdbc.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @param table
   *   Name of the table in the external database.
   * @param columnName
   *   Alias of `partitionColumn` option. Refer to `partitionColumn` in <a
   *   href="https://spark.apache.org/docs/latest/sql-data-sources-jdbc.html#data-source-option">
   *   Data Source Option</a> in the version you use.
   * @param connectionProperties
   *   JDBC database connection arguments, a list of arbitrary string tag/value. Normally at least
   *   a "user" and "password" property should be included. "fetchsize" can be used to control the
   *   number of rows per fetch and "queryTimeout" can be used to wait for a Statement object to
   *   execute to the given number of seconds.
   * @since 1.4.0
   */
  // scalastyle:on line.size.limit
  def jdbc(
      url: String,
      table: String,
      columnName: String,
      lowerBound: Long,
      upperBound: Long,
      numPartitions: Int,
      connectionProperties: util.Properties): DataFrame = {
    // columnName, lowerBound, upperBound and numPartitions override settings in extraOptions.
    this.extraOptions ++= Map(
      "partitionColumn" -> columnName,
      "lowerBound" -> lowerBound.toString,
      "upperBound" -> upperBound.toString,
      "numPartitions" -> numPartitions.toString)
    jdbc(url, table, connectionProperties)
  }

  /**
   * Construct a `DataFrame` representing the database table accessible via JDBC URL url named
   * table using connection properties. The `predicates` parameter gives a list expressions
   * suitable for inclusion in WHERE clauses; each one defines one partition of the `DataFrame`.
   *
   * Don't create too many partitions in parallel on a large cluster; otherwise Spark might crash
   * your external database systems.
   *
   * You can find the JDBC-specific option and parameter documentation for reading tables via JDBC
   * in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-jdbc.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @param table
   *   Name of the table in the external database.
   * @param predicates
   *   Condition in the where clause for each partition.
   * @param connectionProperties
   *   JDBC database connection arguments, a list of arbitrary string tag/value. Normally at least
   *   a "user" and "password" property should be included. "fetchsize" can be used to control the
   *   number of rows per fetch.
   * @since 1.4.0
   */
  def jdbc(
      url: String,
      table: String,
      predicates: Array[String],
      connectionProperties: util.Properties): DataFrame

  /**
   * Loads a JSON file and returns the results as a `DataFrame`.
   *
   * See the documentation on the overloaded `json()` method with varargs for more details.
   *
   * @since 1.4.0
   */
  def json(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    json(Seq(path): _*)
  }

  /**
   * Loads JSON files and returns the results as a `DataFrame`.
   *
   * <a href="http://jsonlines.org/">JSON Lines</a> (newline-delimited JSON) is supported by
   * default. For JSON (one record per file), set the `multiLine` option to true.
   *
   * This function goes through the input once to determine the input schema. If you know the
   * schema in advance, use the version that specifies the schema to avoid the extra scan.
   *
   * You can find the JSON-specific options for reading JSON files in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-json.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @since 2.0.0
   */
  @scala.annotation.varargs
  def json(paths: String*): DataFrame = {
    validateJsonSchema()
    format("json").load(paths: _*)
  }

  /**
   * Loads a `Dataset[String]` storing JSON objects (<a href="http://jsonlines.org/">JSON Lines
   * text format or newline-delimited JSON</a>) and returns the result as a `DataFrame`.
   *
   * Unless the schema is specified using `schema` function, this function goes through the input
   * once to determine the input schema.
   *
   * @param jsonDataset
   *   input Dataset with one JSON object per record
   * @since 2.2.0
   */
  def json(jsonDataset: Dataset[String]): DataFrame

  /**
   * Loads a `JavaRDD[String]` storing JSON objects (<a href="http://jsonlines.org/">JSON Lines
   * text format or newline-delimited JSON</a>) and returns the result as a `DataFrame`.
   *
   * Unless the schema is specified using `schema` function, this function goes through the input
   * once to determine the input schema.
   *
   * @note
   *   this method is not supported in Spark Connect.
   * @param jsonRDD
   *   input RDD with one JSON object per record
   * @since 1.4.0
   */
  @deprecated("Use json(Dataset[String]) instead.", "2.2.0")
  def json(jsonRDD: JavaRDD[String]): DataFrame

  /**
   * Loads an `RDD[String]` storing JSON objects (<a href="http://jsonlines.org/">JSON Lines text
   * format or newline-delimited JSON</a>) and returns the result as a `DataFrame`.
   *
   * Unless the schema is specified using `schema` function, this function goes through the input
   * once to determine the input schema.
   *
   * @note
   *   this method is not supported in Spark Connect.
   * @param jsonRDD
   *   input RDD with one JSON object per record
   * @since 1.4.0
   */
  @deprecated("Use json(Dataset[String]) instead.", "2.2.0")
  def json(jsonRDD: RDD[String]): DataFrame

  /**
   * Loads a CSV file and returns the result as a `DataFrame`. See the documentation on the other
   * overloaded `csv()` method for more details.
   *
   * @since 2.0.0
   */
  def csv(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    csv(Seq(path): _*)
  }

  /**
   * Loads an `Dataset[String]` storing CSV rows and returns the result as a `DataFrame`.
   *
   * If the schema is not specified using `schema` function and `inferSchema` option is enabled,
   * this function goes through the input once to determine the input schema.
   *
   * If the schema is not specified using `schema` function and `inferSchema` option is disabled,
   * it determines the columns as string types and it reads only the first line to determine the
   * names and the number of fields.
   *
   * If the enforceSchema is set to `false`, only the CSV header in the first line is checked to
   * conform specified or inferred schema.
   *
   * @note
   *   if `header` option is set to `true` when calling this API, all lines same with the header
   *   will be removed if exists.
   *
   * @param csvDataset
   *   input Dataset with one CSV row per record
   * @since 2.2.0
   */
  def csv(csvDataset: Dataset[String]): DataFrame

  /**
   * Loads CSV files and returns the result as a `DataFrame`.
   *
   * This function will go through the input once to determine the input schema if `inferSchema`
   * is enabled. To avoid going through the entire data once, disable `inferSchema` option or
   * specify the schema explicitly using `schema`.
   *
   * You can find the CSV-specific options for reading CSV files in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-csv.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @since 2.0.0
   */
  @scala.annotation.varargs
  def csv(paths: String*): DataFrame = format("csv").load(paths: _*)

  /**
   * Loads a XML file and returns the result as a `DataFrame`. See the documentation on the other
   * overloaded `xml()` method for more details.
   *
   * @since 4.0.0
   */
  def xml(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    xml(Seq(path): _*)
  }

  /**
   * Loads XML files and returns the result as a `DataFrame`.
   *
   * This function will go through the input once to determine the input schema if `inferSchema`
   * is enabled. To avoid going through the entire data once, disable `inferSchema` option or
   * specify the schema explicitly using `schema`.
   *
   * You can find the XML-specific options for reading XML files in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-xml.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @since 4.0.0
   */
  @scala.annotation.varargs
  def xml(paths: String*): DataFrame = {
    validateXmlSchema()
    format("xml").load(paths: _*)
  }

  /**
   * Loads an `Dataset[String]` storing XML object and returns the result as a `DataFrame`.
   *
   * If the schema is not specified using `schema` function and `inferSchema` option is enabled,
   * this function goes through the input once to determine the input schema.
   *
   * @param xmlDataset
   *   input Dataset with one XML object per record
   * @since 4.0.0
   */
  def xml(xmlDataset: Dataset[String]): DataFrame

  /**
   * Loads a Parquet file, returning the result as a `DataFrame`. See the documentation on the
   * other overloaded `parquet()` method for more details.
   *
   * @since 2.0.0
   */
  def parquet(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    parquet(Seq(path): _*)
  }

  /**
   * Loads a Parquet file, returning the result as a `DataFrame`.
   *
   * Parquet-specific option(s) for reading Parquet files can be found in <a href=
   * "https://spark.apache.org/docs/latest/sql-data-sources-parquet.html#data-source-option"> Data
   * Source Option</a> in the version you use.
   *
   * @since 1.4.0
   */
  @scala.annotation.varargs
  def parquet(paths: String*): DataFrame = format("parquet").load(paths: _*)

  /**
   * Loads an ORC file and returns the result as a `DataFrame`.
   *
   * @param path
   *   input path
   * @since 1.5.0
   */
  def orc(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    orc(Seq(path): _*)
  }

  /**
   * Loads ORC files and returns the result as a `DataFrame`.
   *
   * ORC-specific option(s) for reading ORC files can be found in <a href=
   * "https://spark.apache.org/docs/latest/sql-data-sources-orc.html#data-source-option"> Data
   * Source Option</a> in the version you use.
   *
   * @param paths
   *   input paths
   * @since 2.0.0
   */
  @scala.annotation.varargs
  def orc(paths: String*): DataFrame = format("orc").load(paths: _*)

  /**
   * Returns the specified table/view as a `DataFrame`. If it's a table, it must support batch
   * reading and the returned DataFrame is the batch scan query plan of this table. If it's a
   * view, the returned DataFrame is simply the query plan of the view, which can either be a
   * batch or streaming query plan.
   *
   * @param tableName
   *   is either a qualified or unqualified name that designates a table or view. If a database is
   *   specified, it identifies the table/view from the database. Otherwise, it first attempts to
   *   find a temporary view with the given name and then match the table/view from the current
   *   database. Note that, the global temporary view database is also valid here.
   * @since 1.4.0
   */
  def table(tableName: String): DataFrame

  /**
   * Loads text files and returns a `DataFrame` whose schema starts with a string column named
   * "value", and followed by partitioned columns if there are any. See the documentation on the
   * other overloaded `text()` method for more details.
   *
   * @since 2.0.0
   */
  def text(path: String): DataFrame = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    text(Seq(path): _*)
  }

  /**
   * Loads text files and returns a `DataFrame` whose schema starts with a string column named
   * "value", and followed by partitioned columns if there are any. The text files must be encoded
   * as UTF-8.
   *
   * By default, each line in the text files is a new row in the resulting DataFrame. For example:
   * {{{
   *   // Scala:
   *   spark.read.text("/path/to/spark/README.md")
   *
   *   // Java:
   *   spark.read().text("/path/to/spark/README.md")
   * }}}
   *
   * You can find the text-specific options for reading text files in <a
   * href="https://spark.apache.org/docs/latest/sql-data-sources-text.html#data-source-option">
   * Data Source Option</a> in the version you use.
   *
   * @param paths
   *   input paths
   * @since 1.6.0
   */
  @scala.annotation.varargs
  def text(paths: String*): DataFrame = format("text").load(paths: _*)

  /**
   * Loads text files and returns a [[Dataset]] of String. See the documentation on the other
   * overloaded `textFile()` method for more details.
   * @since 2.0.0
   */
  def textFile(path: String): Dataset[String] = {
    // This method ensures that calls that explicit need single argument works, see SPARK-16009
    textFile(Seq(path): _*)
  }

  /**
   * Loads text files and returns a [[Dataset]] of String. The underlying schema of the Dataset
   * contains a single string column named "value". The text files must be encoded as UTF-8.
   *
   * If the directory structure of the text files contains partitioning information, those are
   * ignored in the resulting Dataset. To include partitioning information as columns, use `text`.
   *
   * By default, each line in the text files is a new row in the resulting DataFrame. For example:
   * {{{
   *   // Scala:
   *   spark.read.textFile("/path/to/spark/README.md")
   *
   *   // Java:
   *   spark.read().textFile("/path/to/spark/README.md")
   * }}}
   *
   * You can set the text-specific options as specified in `DataFrameReader.text`.
   *
   * @param paths
   *   input path
   * @since 2.0.0
   */
  @scala.annotation.varargs
  def textFile(paths: String*): Dataset[String] = {
    assertNoSpecifiedSchema("textFile")
    text(paths: _*).select("value").as(StringEncoder)
  }

  /**
   * A convenient function for schema validation in APIs.
   */
  protected def assertNoSpecifiedSchema(operation: String): Unit = {
    if (userSpecifiedSchema.nonEmpty) {
      throw DataTypeErrors.userSpecifiedSchemaUnsupportedError(operation)
    }
  }

  /**
   * Ensure that the `singleVariantColumn` option cannot be used if there is also a user specified
   * schema.
   */
  protected def validateSingleVariantColumn(): Unit = ()

  protected def validateJsonSchema(): Unit = ()

  protected def validateXmlSchema(): Unit = ()

  ///////////////////////////////////////////////////////////////////////////////////////
  // Builder pattern config options
  ///////////////////////////////////////////////////////////////////////////////////////

  protected var source: String = _

  protected var userSpecifiedSchema: Option[StructType] = None

  protected var extraOptions: CaseInsensitiveMap[String] = CaseInsensitiveMap[String](Map.empty)
}
