//
// ========================================================================
// Copyright (c) 1995-2020 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under
// the terms of the Eclipse Public License 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0
//
// This Source Code may also be made available under the following
// Secondary Licenses when the conditions for such availability set
// forth in the Eclipse Public License, v. 2.0 are satisfied:
// the Apache License v2.0 which is available at
// https://www.apache.org/licenses/LICENSE-2.0
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//

package org.eclipse.jetty.util;

import java.time.Instant;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

Date Format Cache.
Computes String representations of Dates and caches
the results so that subsequent requests within the same second
will be fast.
Only format strings that contain either "ss".  Sub second formatting is
not handled.
The timezone of the date may be included as an ID with the "zzz"
format string or as an offset with the "ZZZ" format string.
If consecutive calls are frequently very different, then this
may be a little slower than a normal DateFormat.
/**
 * Date Format Cache.
 * Computes String representations of Dates and caches
 * the results so that subsequent requests within the same second
 * will be fast.
 *
 * Only format strings that contain either "ss".  Sub second formatting is
 * not handled.
 *
 * The timezone of the date may be included as an ID with the "zzz"
 * format string or as an offset with the "ZZZ" format string.
 *
 * If consecutive calls are frequently very different, then this
 * may be a little slower than a normal DateFormat.
 */
public class DateCache
{
    public static final String DEFAULT_FORMAT = "EEE MMM dd HH:mm:ss zzz yyyy";

    private final String _formatString;
    private final String _tzFormatString;
    private final DateTimeFormatter _tzFormat;
    private final Locale _locale;
    private final ZoneId _zoneId;

    private volatile Tick _tick;

    public static class Tick
    {
        final long _seconds;
        final String _string;

        public Tick(long seconds, String string)
        {
            _seconds = seconds;
            _string = string;
        }
    }

    
Constructor.
Make a DateCache that will use a default format. The default format
generates the same results as Date.toString().
/**
     * Constructor.
     * Make a DateCache that will use a default format. The default format
     * generates the same results as Date.toString().
     */
    public DateCache()
    {
        this(DEFAULT_FORMAT);
    }

    
Constructor.
Make a DateCache that will use the given format
Params:
format – the format to use/**
     * Constructor.
     * Make a DateCache that will use the given format
     *
     * @param format the format to use
     */
    public DateCache(String format)
    {
        this(format, null, TimeZone.getDefault());
    }

    public DateCache(String format, Locale l)
    {
        this(format, l, TimeZone.getDefault());
    }

    public DateCache(String format, Locale l, String tz)
    {
        this(format, l, TimeZone.getTimeZone(tz));
    }

    public DateCache(String format, Locale l, TimeZone tz)
    {
        _formatString = format;
        _locale = l;

        int zIndex = _formatString.indexOf("ZZZ");
        if (zIndex >= 0)
        {
            final String ss1 = _formatString.substring(0, zIndex);
            final String ss2 = _formatString.substring(zIndex + 3);
            int tzOffset = tz.getRawOffset();

            StringBuilder sb = new StringBuilder(_formatString.length() + 10);
            sb.append(ss1);
            sb.append("'");
            if (tzOffset >= 0)
                sb.append('+');
            else
            {
                tzOffset = -tzOffset;
                sb.append('-');
            }

            int raw = tzOffset / (1000 * 60);             // Convert to seconds
            int hr = raw / 60;
            int min = raw % 60;

            if (hr < 10)
                sb.append('0');
            sb.append(hr);
            if (min < 10)
                sb.append('0');
            sb.append(min);
            sb.append('\'');

            sb.append(ss2);
            _tzFormatString = sb.toString();
        }
        else
            _tzFormatString = _formatString;

        if (_locale != null)
        {
            _tzFormat = DateTimeFormatter.ofPattern(_tzFormatString, _locale);
        }
        else
        {
            _tzFormat = DateTimeFormatter.ofPattern(_tzFormatString);
        }
        _zoneId = tz.toZoneId();
        _tzFormat.withZone(_zoneId);
        _tick = null;
    }

    public TimeZone getTimeZone()
    {
        return TimeZone.getTimeZone(_zoneId);
    }

    
Format a date according to our stored formatter.
Params:
inDate – the Date
Returns:
Formatted date/**
     * Format a date according to our stored formatter.
     *
     * @param inDate the Date
     * @return Formatted date
     */
    public String format(Date inDate)
    {
        long seconds = inDate.getTime() / 1000;

        Tick tick = _tick;

        // Is this the cached time
        if (tick == null || seconds != tick._seconds)
        {
            return ZonedDateTime.ofInstant(inDate.toInstant(), _zoneId).format(_tzFormat);
        }

        return tick._string;
    }

    
Format a date according to our stored formatter.
If it happens to be in the same second as the last formatNow
call, then the format is reused.
Params:
inDate – the date in milliseconds since unix epoch
Returns:
Formatted date/**
     * Format a date according to our stored formatter.
     * If it happens to be in the same second as the last formatNow
     * call, then the format is reused.
     *
     * @param inDate the date in milliseconds since unix epoch
     * @return Formatted date
     */
    public String format(long inDate)
    {
        long seconds = inDate / 1000;

        Tick tick = _tick;

        // Is this the cached time
        if (tick == null || seconds != tick._seconds)
        {
            // It's a cache miss
            return ZonedDateTime.ofInstant(Instant.ofEpochMilli(inDate), _zoneId).format(_tzFormat);
        }

        return tick._string;
    }

    
Format a date according to our stored formatter.
The passed time is expected to be close to the current time, so it is
compared to the last value passed and if it is within the same second,
the format is reused.  Otherwise a new cached format is created.
Params:
now – the milliseconds since unix epoch
Returns:
Formatted date/**
     * Format a date according to our stored formatter.
     * The passed time is expected to be close to the current time, so it is
     * compared to the last value passed and if it is within the same second,
     * the format is reused.  Otherwise a new cached format is created.
     *
     * @param now the milliseconds since unix epoch
     * @return Formatted date
     */
    public String formatNow(long now)
    {
        long seconds = now / 1000;

        Tick tick = _tick;

        // Is this the cached time
        if (tick != null && tick._seconds == seconds)
            return tick._string;
        return formatTick(now)._string;
    }

    public String now()
    {
        return formatNow(System.currentTimeMillis());
    }

    public Tick tick()
    {
        return formatTick(System.currentTimeMillis());
    }

    protected Tick formatTick(long now)
    {
        long seconds = now / 1000;

        Tick tick = _tick;
        // recheck the tick, to save multiple formats
        if (tick == null || tick._seconds != seconds)
        {
            String s = ZonedDateTime.ofInstant(Instant.ofEpochMilli(now), _zoneId).format(_tzFormat);
            _tick = new Tick(seconds, s);
            tick = _tick;
        }
        return tick;
    }

    public String getFormatString()
    {
        return _formatString;
    }
}