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Core functionality for GeoPackage implementations
There is a newer version: 6.6.7
package mil.nga.geopackage.db;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.TimeZone;

import mil.nga.geopackage.GeoPackageException;

/**
 * Date converter between database date formats and date objects
 * 
 * @author osbornb
 * @since 1.3.0
 */
public class DateConverter {

	/**
	 * Date format
	 */
	public static final String DATE_FORMAT = "yyyy-MM-dd";

	/**
	 * Non standard Date format
	 */
	public static final String DATE_FORMAT2 = "yyyy/MM/dd";

	/**
	 * Date Time format
	 */
	public static final String DATETIME_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'";

	/**
	 * Date Time format w/o milliseconds for parsing string dates
	 */
	public static final String DATETIME_FORMAT2 = "yyyy-MM-dd'T'HH:mm:ss'Z'";

	/**
	 * Date Time format w/o seconds for parsing string dates
	 */
	public static final String DATETIME_FORMAT3 = "yyyy-MM-dd'T'HH:mm'Z'";

	/**
	 * SQLite date function
	 * 
	 * @since 3.3.0
	 */
	public static final String FUNCTION_DATE = "date";

	/**
	 * SQLite time function
	 * 
	 * @since 3.3.0
	 */
	public static final String FUNCTION_TIME = "time";

	/**
	 * SQLite datetime function
	 * 
	 * @since 3.3.0
	 */
	public static final String FUNCTION_DATETIME = "datetime";

	/**
	 * SQLite julianday function
	 * 
	 * @since 3.3.0
	 */
	public static final String FUNCTION_JULIANDAY = "julianday";

	/**
	 * SQLite strftime function
	 * 
	 * @since 3.3.0
	 */
	public static final String FUNCTION_STRFTIME = "strftime";

	/**
	 * Get a date converter for the data type
	 * 
	 * @param type
	 *            data type
	 * @return date converter
	 */
	public static DateConverter converter(GeoPackageDataType type) {

		DateConverter converter = null;

		switch (type) {
		case DATE:
			converter = dateConverter();
			break;
		case DATETIME:
			converter = dateTimeConverter();
			break;
		default:
			throw new GeoPackageException("Not a date data type: " + type);
		}

		return converter;
	}

	/**
	 * Get a date converter
	 * 
	 * @return date converter
	 */
	public static DateConverter dateConverter() {
		return new DateConverter(DATE_FORMAT, DATE_FORMAT2);
	}

	/**
	 * Get a date time converter
	 * 
	 * @return date converter
	 */
	public static DateConverter dateTimeConverter() {
		return new DateConverter(DATETIME_FORMAT, DATETIME_FORMAT2,
				DATETIME_FORMAT3);
	}

	/**
	 * Get a date converter for the provided formats
	 * 
	 * @param formats
	 *            formats
	 * @return date converter
	 */
	public static DateConverter dateConverter(String... formats) {
		return new DateConverter(formats);

	}

	/**
	 * Simple date formatters
	 */
	private final List formatters = new ArrayList<>();

	/**
	 * Is parsing a date value from a string always expected
	 */
	private boolean expected = true;

	/**
	 * Constructor
	 * 
	 * @param formats
	 *            date formats
	 * @since 6.2.0
	 */
	public DateConverter(String... formats) {
		for (String format : formats) {
			addFormat(format);
		}
	}

	/**
	 * Add date format
	 * 
	 * @param format
	 *            date format
	 * @since 6.2.0
	 */
	public void addFormat(String format) {
		SimpleDateFormat sdf = new SimpleDateFormat(format);
		sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
		formatters.add(sdf);
	}

	/**
	 * Is a parsed date value always expected
	 * 
	 * @return true if always expected
	 * @since 6.2.0
	 */
	public boolean isExpected() {
		return expected;
	}

	/**
	 * Set if a parsed date value is always expected
	 * 
	 * @param expected
	 *            true if always expected
	 * @since 6.2.0
	 */
	public void setExpected(boolean expected) {
		this.expected = expected;
	}

	/**
	 * Get the formatted string date value of the date
	 * 
	 * @param date
	 *            date
	 * @return formatted string date
	 */
	public String stringValue(Date date) {
		String value = null;
		if (date != null) {
			SimpleDateFormat sdf = formatters.get(0);
			synchronized (sdf) {
				value = sdf.format(date);
			}
		}
		return value;
	}

	/**
	 * Get the date value of the formatted string date
	 * 
	 * @param date
	 *            formatted string date
	 * @return date
	 */
	public Date dateValue(String date) {
		Date value = null;
		if (date != null) {

			// Try each simple date formatter in order
			ParseException exception = null;
			for (SimpleDateFormat sdf : formatters) {
				try {
					synchronized (sdf) {
						value = sdf.parse(date);
					}
					break;
				} catch (ParseException e) {
					if (exception == null) {
						exception = e;
					}
				}
			}

			// If no value could be parsed when expected
			if (value == null && expected) {
				throw new GeoPackageException(
						"Failed to parse date string: " + date, exception);
			}

		}
		return value;
	}

	/**
	 * Determine if the date/time string value is a SQLite function
	 * 
	 * @param value
	 *            date/time string value
	 * @return true if a function, false if the value should be parsed
	 * @since 3.3.0
	 */
	public static boolean isFunction(String value) {
		boolean function = false;
		if (value != null) {
			value = value.trim().toLowerCase();
			function = value.startsWith(FUNCTION_DATE)
					|| value.startsWith(FUNCTION_TIME)
					|| value.startsWith(FUNCTION_DATETIME)
					|| value.startsWith(FUNCTION_JULIANDAY)
					|| value.startsWith(FUNCTION_STRFTIME);
		}
		return function;
	}

}