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package com.pippsford.stencil.apply;

import java.math.BigDecimal;

import com.pippsford.common.TypeSafeMap;
import com.pippsford.stencil.value.Data;

/**
 * This value processor provides additional fields to assist in processing of collections with the [with] directive.
 *
 * @author Simon Greatrix on 08/01/2021.
 */
public class AugmentedIndex implements ValueProcessor {

  /** Instance of the processor. */
  public static final AugmentedIndex INSTANCE = new AugmentedIndex();


  private AugmentedIndex() {
    // do nothing
  }


  /**
   * Adds index related fields to the current values. The current values are expected to include "index" and "size". The fields added are:
   *
   * 
   *   isFirst
   *   Boolean. True if the index is zero.
   *
   *   isLast
   *   Boolean. True if the index is equal to one less than the size.
   *
   *   isOdd
   *   Boolean. True if the index is odd.
   *
   *   isEven
   *   Boolean. True if the index is even.
   *
   *   index1
   *   Integer. A 1-based index as an alternative to the standard 0-based index.
   * 
   *
   * The following additional fields are added if a page size is passed in.
   *
   * 
   *   isFirstOnPage
   *   Boolean. True if this is the first entry on a page.
   *
   *   isLastOnPage
   *   Boolean. True if this is the last entry on a page, or if this is the last entry overall.
   *
   *   pageRow
   *   Integer. The row on the current page (one based)
   *
   *   pageNumber
   *   Integer. The current page number (one based)
   *
   *   pageCount
   *   Integer. The number of pages.
   * 
   *
   * Note: a prefix may be specified to prevent the added fields masking another field.
   *
   * Example:
   * 
   *   [apply AugmentedIndex($,20)]
   *   Prefix all the fields with '$' and use a page size of 20.
   *
   *   [apply AugmentedIndex(,pageSize)]
   *   Use the standard field names and get the page size from the current values.
   *
   *   [apply AugmentedIndex]
   *   Use the standard field named and do not enable paging.
   * 
   *
   * @param valueProvider the value provider.
   * @param arguments     two arguments: prefix (which may be an empty string), and a page size.
   */
  @Override
  public Object apply(Data valueProvider, Parameter[] arguments) {
    Integer index = TypeSafeMap.asInt(valueProvider.get("index"));
    Integer size = TypeSafeMap.asInt(valueProvider.get("size"));

    if (index == null) {
      throw new IllegalArgumentException("No 'index' property in provided data");
    }
    if (size == null) {
      throw new IllegalArgumentException("No 'size' property in provided data");
    }

    String prefix = arguments.length > 0 ? arguments[0].asString() : "";
    Integer pageSize = null;
    if (arguments.length > 1) {
      Parameter paramSize = arguments[1];
      if (paramSize.isNumber()) {
        BigDecimal bigSize = paramSize.asNumber();
        try {
          pageSize = bigSize.intValueExact();
        } catch (ArithmeticException e) {
          throw new IllegalArgumentException("Page size specified as '" + bigSize + "' but could not translate to a sensible size.");
        }
      } else {
        throw new IllegalArgumentException("Page size specified as '" + arguments[1] + "' but could not translate to actual size.");
      }
    }

    valueProvider.put(prefix + "isFirst", index == 0);
    valueProvider.put(prefix + "isLast", index == size - 1);
    valueProvider.put(prefix + "index1", index + 1);
    valueProvider.put(prefix + "isEven", (index & 1) == 0);
    valueProvider.put(prefix + "isOdd", (index & 1) == 1);

    if (pageSize != null) {
      valueProvider.put(prefix + "isFirstOnPage", (index % pageSize) == 0);
      valueProvider.put(prefix + "isLastOnPage", (index % pageSize) == (pageSize - 1) || (index == size - 1));
      valueProvider.put(prefix + "pageRow", 1 + (index % pageSize));
      valueProvider.put(prefix + "pageNumber", 1 + (index / pageSize));
      valueProvider.put(prefix + "pageCount", (size / pageSize) + (((size % pageSize) != 0) ? 1 : 0));
    }

    return null;
  }

}