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/*
 * Copyright 2024 Datastrato Pvt Ltd.
 * This software is licensed under the Apache License version 2.
 */

package com.datastrato.gravitino.rel.indexes;

import com.datastrato.gravitino.annotation.Evolving;

/**
 * The Index interface defines methods for implementing table index columns. Currently, settings for
 * PRIMARY_KEY and UNIQUE_KEY are provided.
 */
@Evolving
public interface Index {

  /** @return The type of the index. eg: PRIMARY_KEY and UNIQUE_KEY. */
  IndexType type();

  /** @return The name of the index. */
  String name();

  /**
   * @return The field name under the table contained in the index. it is the column names, could be
   *     "a.b.c" for nested column, but normally it could only be "a".
   */
  String[][] fieldNames();

  /**
   * The enum IndexType defines the type of the index. Currently, PRIMARY_KEY and UNIQUE_KEY are
   * supported.
   */
  enum IndexType {
    /**
     * PRIMARY KEY index in a relational database is a field or a combination of fields that
     * uniquely identifies each record in a table. It serves as a unique identifier for each row,
     * ensuring that no two rows have the same key. The PRIMARY KEY is used to establish
     * relationships between tables and enforce the entity integrity of a database. Additionally, it
     * helps in indexing and organizing the data for efficient retrieval and maintenance.
     */
    PRIMARY_KEY,
    /**
     * UNIQUE KEY in a relational database is a field or a combination of fields that ensures each
     * record in a table has a distinct value or combination of values. Unlike a primary key, a
     * UNIQUE KEY allows for the presence of null values, but it still enforces the constraint that
     * no two records can have the same unique key value(s). UNIQUE KEYs are used to maintain data
     * integrity by preventing duplicate entries in specific columns, and they can be applied to
     * columns that are not designated as the primary key. The uniqueness constraint imposed by
     * UNIQUE KEY helps in avoiding redundancy and ensuring data accuracy in the database.
     */
    UNIQUE_KEY,
  }
}