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  /*
   * This file is available under and governed by the GNU General Public
   * License version 2 only, as published by the Free Software Foundation.
   * However, the following notice accompanied the original version of this
   * file:
   *
   * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   *  * Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
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   *    this list of conditions and the following disclaimer in the documentation
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  package java.time.chrono;
  
  import static java.time.temporal.ChronoField.ERA;
  import static java.time.temporal.ChronoUnit.ERAS;
  
  import java.time.DateTimeException;
  import java.time.temporal.UnsupportedTemporalTypeException;
  import java.time.format.DateTimeFormatterBuilder;
  import java.time.format.TextStyle;
  import java.time.temporal.ChronoField;
  import java.time.temporal.Temporal;
  import java.time.temporal.TemporalAccessor;
  import java.time.temporal.TemporalAdjuster;
  import java.time.temporal.TemporalField;
  import java.time.temporal.TemporalQueries;
  import java.time.temporal.TemporalQuery;
  import java.time.temporal.ValueRange;
  import java.util.Locale;
  
  /**
   * An era of the time-line.
   * <p>
   * Most calendar systems have a single epoch dividing the time-line into two eras.
   * However, some calendar systems, have multiple eras, such as one for the reign
   * of each leader.
   * In all cases, the era is conceptually the largest division of the time-line.
   * Each chronology defines the Era's that are known Eras and a
   * {@link Chronology#eras Chronology.eras} to get the valid eras.
   * <p>
   * For example, the Thai Buddhist calendar system divides time into two eras,
   * before and after a single date. By contrast, the Japanese calendar system
   * has one era for the reign of each Emperor.
   * <p>
   * Instances of {@code Era} may be compared using the {@code ==} operator.
   *
   * @implSpec
   * This interface must be implemented with care to ensure other classes operate correctly.
   * All implementations must be singletons - final, immutable and thread-safe.
   * It is recommended to use an enum whenever possible.
   *
   * @since 1.8
   */
  public interface Era extends TemporalAccessor, TemporalAdjuster {
  
      /**
       * Gets the numeric value associated with the era as defined by the chronology.
       * Each chronology defines the predefined Eras and methods to list the Eras
       * of the chronology.
       * <p>
       * All fields, including eras, have an associated numeric value.
       * The meaning of the numeric value for era is determined by the chronology
       * according to these principles:
       * <ul>
       * <li>The era in use at the epoch 1970-01-01 (ISO) has the value 1.
       * <li>Later eras have sequentially higher values.
       * <li>Earlier eras have sequentially lower values, which may be negative.
       * </ul>
       *
       * @return the numeric era value
       */
      int getValue();
  
      //-----------------------------------------------------------------------
      /**
       * Checks if the specified field is supported.
       * <p>
       * This checks if this era can be queried for the specified field.
       * If false, then calling the {@link #range(TemporalField) range} and
       * {@link #get(TemporalField) get} methods will throw an exception.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@code ERA} field returns true.
       * All other {@code ChronoField} instances will return false.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
       * passing {@code this} as the argument.
       * Whether the field is supported is determined by the field.
       *
       * @param field  the field to check, null returns false
       * @return true if the field is supported on this era, false if not
       */
      @Override
      default boolean isSupported(TemporalField field) {
          if (field instanceof ChronoField) {
              return field == ERA;
          }
          return field != null && field.isSupportedBy(this);
      }
  
      /**
       * Gets the range of valid values for the specified field.
       * <p>
       * The range object expresses the minimum and maximum valid values for a field.
       * This era is used to enhance the accuracy of the returned range.
       * If it is not possible to return the range, because the field is not supported
       * or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@code ERA} field returns the range.
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
       * passing {@code this} as the argument.
       * Whether the range can be obtained is determined by the field.
       * <p>
       * The default implementation must return a range for {@code ERA} from
       * zero to one, suitable for two era calendar systems such as ISO.
       *
       * @param field  the field to query the range for, not null
       * @return the range of valid values for the field, not null
       * @throws DateTimeException if the range for the field cannot be obtained
       * @throws UnsupportedTemporalTypeException if the unit is not supported
       */
      @Override  // override for Javadoc
      default ValueRange range(TemporalField field) {
          return TemporalAccessor.super.range(field);
      }
  
      /**
       * Gets the value of the specified field from this era as an {@code int}.
       * <p>
       * This queries this era for the value of the specified field.
       * The returned value will always be within the valid range of values for the field.
       * If it is not possible to return the value, because the field is not supported
       * or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@code ERA} field returns the value of the era.
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
       * passing {@code this} as the argument. Whether the value can be obtained,
       * and what the value represents, is determined by the field.
       *
       * @param field  the field to get, not null
       * @return the value for the field
       * @throws DateTimeException if a value for the field cannot be obtained or
       *         the value is outside the range of valid values for the field
       * @throws UnsupportedTemporalTypeException if the field is not supported or
       *         the range of values exceeds an {@code int}
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override  // override for Javadoc and performance
      default int get(TemporalField field) {
          if (field == ERA) {
              return getValue();
          }
          return TemporalAccessor.super.get(field);
      }
  
      /**
       * Gets the value of the specified field from this era as a {@code long}.
       * <p>
       * This queries this era for the value of the specified field.
       * If it is not possible to return the value, because the field is not supported
       * or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@code ERA} field returns the value of the era.
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
       * passing {@code this} as the argument. Whether the value can be obtained,
       * and what the value represents, is determined by the field.
       *
       * @param field  the field to get, not null
       * @return the value for the field
       * @throws DateTimeException if a value for the field cannot be obtained
       * @throws UnsupportedTemporalTypeException if the field is not supported
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      default long getLong(TemporalField field) {
          if (field == ERA) {
              return getValue();
          } else if (field instanceof ChronoField) {
              throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
          }
          return field.getFrom(this);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Queries this era using the specified query.
       * <p>
       * This queries this era using the specified query strategy object.
       * The {@code TemporalQuery} object defines the logic to be used to
       * obtain the result. Read the documentation of the query to understand
       * what the result of this method will be.
       * <p>
       * The result of this method is obtained by invoking the
       * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
       * specified query passing {@code this} as the argument.
       *
       * @param <R> the type of the result
       * @param query  the query to invoke, not null
       * @return the query result, null may be returned (defined by the query)
       * @throws DateTimeException if unable to query (defined by the query)
       * @throws ArithmeticException if numeric overflow occurs (defined by the query)
       */
      @SuppressWarnings("unchecked")
      @Override
      default <R> R query(TemporalQuery<R> query) {
          if (query == TemporalQueries.precision()) {
              return (R) ERAS;
          }
          return TemporalAccessor.super.query(query);
      }
  
      /**
       * Adjusts the specified temporal object to have the same era as this object.
       * <p>
       * This returns a temporal object of the same observable type as the input
       * with the era changed to be the same as this.
       * <p>
       * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
       * passing {@link ChronoField#ERA} as the field.
       * <p>
       * In most cases, it is clearer to reverse the calling pattern by using
       * {@link Temporal#with(TemporalAdjuster)}:
       * <pre>
       *   // these two lines are equivalent, but the second approach is recommended
       *   temporal = thisEra.adjustInto(temporal);
       *   temporal = temporal.with(thisEra);
       * </pre>
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param temporal  the target object to be adjusted, not null
       * @return the adjusted object, not null
       * @throws DateTimeException if unable to make the adjustment
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      default Temporal adjustInto(Temporal temporal) {
          return temporal.with(ERA, getValue());
      }
  
      //-----------------------------------------------------------------------
      /**
       * Gets the textual representation of this era.
       * <p>
       * This returns the textual name used to identify the era,
       * suitable for presentation to the user.
       * The parameters control the style of the returned text and the locale.
       * <p>
       * If no textual mapping is found then the {@link #getValue() numeric value} is returned.
       * <p>
       * This default implementation is suitable for all implementations.
       *
       * @param style  the style of the text required, not null
       * @param locale  the locale to use, not null
       * @return the text value of the era, not null
       */
      default String getDisplayName(TextStyle style, Locale locale) {
          return new DateTimeFormatterBuilder().appendText(ERA, style).toFormatter(locale).format(this);
      }
  
      // NOTE: methods to convert year-of-era/proleptic-year cannot be here as they may depend on month/day (Japanese)
  }
  