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/* Copyright (c) The m-m-m Team, Licensed under the Apache License, Version 2.0
 * http://www.apache.org/licenses/LICENSE-2.0 */
package io.github.mmm.base.temporal;

import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.OffsetDateTime;
import java.time.OffsetTime;
import java.time.YearMonth;
import java.time.ZonedDateTime;
import java.time.temporal.Temporal;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import io.github.mmm.base.lang.FromStringParser;

/**
 * Parser that can detect {@link String}s representing a {@link Temporal} value via {@link #parse(String)} but returns
 * {@code null} if not a {@link Temporal} instead of throwing an exception.
 *
 * @see #parse(String)
 * @since 1.0.0
 */
public final class TemporalParser implements FromStringParser {

  private static final Pattern TEMPORAL_PATTERN = Pattern.compile(
      "([0-9]{4}-[0-1][0-9]-[0-3][0-9])?T?([0-2][0-9]:[0-5][0-9]:[0-5][0-9](.[0-9]{1,9})?(Z|[+][0-9]{2}:[0-9]{2}(\\[[^\\]]+\\])?)?)?");

  private static final Pattern YEAR_MONTH_PATTERN = Pattern.compile("[0-9]{4}-[0-1][0-9]");

  private static final TemporalParser INSTANCE = new TemporalParser();

  private TemporalParser() {

  }

  /**
   * @param value the {@link Object#toString() default string representation} of a (potential) {@link Temporal} value.
   *        This can be {@link Instant}, {@link LocalDate}, {@link LocalTime}, {@link LocalDateTime},
   *        {@link OffsetTime}, {@link OffsetDateTime}, {@link ZonedDateTime}, or {@link YearMonth}. Please note that
   *        {@link java.time.chrono.ChronoLocalDate} such as {@link java.time.chrono.HijrahDate},
   *        {@link java.time.chrono.JapaneseDate}, {@link java.time.chrono.MinguoDate}, or
   *        {@link java.time.chrono.ThaiBuddhistDate} are not supported. Also {@link java.time.Year} is not supported as
   *        it can easily be confused with a regular integer and can also be detected easily with just two lines of
   *        code.
   * @return the given {@code value} parsed as {@link Temporal} or {@code null} if not any of the supported
   *         {@link Temporal} types.
   */
  @Override
  public Temporal parse(String value) {

    if (value == null) {
      return null;
    }
    int length = value.length();
    if (length < 5) {
      return null;
    }
    if ((length == 7) && YEAR_MONTH_PATTERN.matcher(value).matches()) {
      return YearMonth.parse(value);
    }
    Matcher matcher = TEMPORAL_PATTERN.matcher(value);
    if (matcher.matches()) {
      String date = matcher.group(1);
      String time = matcher.group(2);
      if (time == null) {
        if (date == null) {
          return null;
        }
        return LocalDate.parse(value);
      } else if (date == null) {
        String tz = matcher.group(4);
        if (tz == null) {
          return LocalTime.parse(value);
        } else {
          return OffsetTime.parse(value);
        }
      } else {
        String tz = matcher.group(4);
        if (tz == null) {
          return LocalDateTime.parse(value);
        } else if (tz.equals("Z")) {
          return Instant.parse(value);
        } else if (tz.startsWith("+")) {
          if (tz.length() == 6) {
            return OffsetDateTime.parse(value);
          } else {
            return ZonedDateTime.parse(value);
          }
        } else {
          // ...
        }
      }
    }
    return null;
  }

  /**
   * @return the singleton instance of this {@link FromStringParser} for {@link Temporal}.
   */
  public static TemporalParser get() {

    return INSTANCE;
  }

}