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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:

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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.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.

 *

 * 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:

     * <p><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><p>

     *

     * @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 for 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 for 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.getName());

        }

        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 == TemporalQuery.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)

}