<?php
namespace PHP81_BC;

use DateTime;
use DateTimeZone;
use DateTimeInterface;
use Exception;
use IntlDateFormatter;
use IntlGregorianCalendar;
use InvalidArgumentException;

/**
 * Locale-formatted strftime using IntlDateFormatter (PHP 8.1 compatible)
 * This provides a cross-platform alternative to strftime() for when it will be removed from PHP.
 * Note that output can be slightly different between libc sprintf and this function as it is using ICU.
 *
 * Usage:
 * use function \PHP81_BC\strftime;
 * echo strftime('%A %e %B %Y %X', new \DateTime('2021-09-28 00:00:00'), 'fr_FR');
 *
 * Original use:
 * \setlocale(LC_TIME, 'fr_FR.UTF-8');
 * echo \strftime('%A %e %B %Y %X', strtotime('2021-09-28 00:00:00'));
 *
 * @param  string $format Date format
 * @param  integer|string|DateTime $timestamp Timestamp
 * @return string
 * @author BohwaZ <https://bohwaz.net/>
 */
function strftime (string $format, $timestamp = null, ?string $locale = null) : string {
    if (!($timestamp instanceof DateTimeInterface)) {
        $timestamp = is_int($timestamp) ? '@' . $timestamp : (string) $timestamp;

        try {
            $timestamp = new DateTime($timestamp);
        } catch (Exception $e) {
            throw new InvalidArgumentException('$timestamp argument is neither a valid UNIX timestamp, a valid date-time string or a DateTime object.', 0, $e);
        }
    }

    $timestamp->setTimezone(new DateTimeZone(date_default_timezone_get()));

    if (empty($locale)) {
        // get current locale
        $locale = setlocale(LC_TIME, '0');
    }
    // remove trailing part not supported by ext-intl locale
    $locale = preg_replace('/[^\w-].*$/', '', $locale);

    $intl_formats = [
        '%a' => 'EEE',	// An abbreviated textual representation of the day	Sun through Sat
        '%A' => 'EEEE',	// A full textual representation of the day	Sunday through Saturday
        '%b' => 'MMM',	// Abbreviated month name, based on the locale	Jan through Dec
        '%B' => 'MMMM',	// Full month name, based on the locale	January through December
        '%h' => 'MMM',	// Abbreviated month name, based on the locale (an alias of %b)	Jan through Dec
    ];

    $intl_formatter = function (DateTimeInterface $timestamp, string $format) use ($intl_formats, $locale) {
        $tz = $timestamp->getTimezone();
        $date_type = IntlDateFormatter::FULL;
        $time_type = IntlDateFormatter::FULL;
        $pattern = '';

        switch ($format) {
            // %c = Preferred date and time stamp based on locale
            // Example: Tue Feb 5 00:45:10 2009 for February 5, 2009 at 12:45:10 AM
            case '%c':
                $date_type = IntlDateFormatter::LONG;
                $time_type = IntlDateFormatter::SHORT;
                break;

            // %x = Preferred date representation based on locale, without the time
            // Example: 02/05/09 for February 5, 2009
            case '%x':
                $date_type = IntlDateFormatter::SHORT;
                $time_type = IntlDateFormatter::NONE;
                break;

            // Localized time format
            case '%X':
                $date_type = IntlDateFormatter::NONE;
                $time_type = IntlDateFormatter::MEDIUM;
                break;

            default:
                $pattern = $intl_formats[$format];
        }

        // In October 1582, the Gregorian calendar replaced the Julian in much of Europe, and
        //  the 4th October was followed by the 15th October.
        // ICU (including IntlDateFormattter) interprets and formats dates based on this cutover.
        // Posix (including strftime) and timelib (including DateTimeImmutable) instead use
        //  a "proleptic Gregorian calendar" - they pretend the Gregorian calendar has existed forever.
        // This leads to the same instants in time, as expressed in Unix time, having different representations
        //  in formatted strings.
        // To adjust for this, a custom calendar can be supplied with a cutover date arbitrarily far in the past.
        $calendar = IntlGregorianCalendar::createInstance();
        $calendar->setGregorianChange(PHP_INT_MIN);

        return (new IntlDateFormatter($locale, $date_type, $time_type, $tz, $calendar, $pattern))->format($timestamp);
    };

    // Same order as https://www.php.net/manual/en/function.strftime.php
    $translation_table = [
        // Day
        '%a' => $intl_formatter,
        '%A' => $intl_formatter,
        '%d' => 'd',
        '%e' => function ($timestamp) {
            return sprintf('% 2u', $timestamp->format('j'));
        },
        '%j' => function ($timestamp) {
            // Day number in year, 001 to 366
            return sprintf('%03d', $timestamp->format('z')+1);
        },
        '%u' => 'N',
        '%w' => 'w',

        // Week
        '%U' => function ($timestamp) {
            // Number of weeks between date and first Sunday of year
            $day = new DateTime(sprintf('%d-01 Sunday', $timestamp->format('Y')));
            return sprintf('%02u', 1 + ($timestamp->format('z') - $day->format('z')) / 7);
        },
        '%V' => 'W',
        '%W' => function ($timestamp) {
            // Number of weeks between date and first Monday of year
            $day = new DateTime(sprintf('%d-01 Monday', $timestamp->format('Y')));
            return sprintf('%02u', 1 + ($timestamp->format('z') - $day->format('z')) / 7);
        },

        // Month
        '%b' => $intl_formatter,
        '%B' => $intl_formatter,
        '%h' => $intl_formatter,
        '%m' => 'm',

        // Year
        '%C' => function ($timestamp) {
            // Century (-1): 19 for 20th century
            return floor($timestamp->format('Y') / 100);
        },
        '%g' => function ($timestamp) {
            return substr($timestamp->format('o'), -2);
        },
        '%G' => 'o',
        '%y' => 'y',
        '%Y' => 'Y',

        // Time
        '%H' => 'H',
        '%k' => function ($timestamp) {
            return sprintf('% 2u', $timestamp->format('G'));
        },
        '%I' => 'h',
        '%l' => function ($timestamp) {
            return sprintf('% 2u', $timestamp->format('g'));
        },
        '%M' => 'i',
        '%p' => 'A', // AM PM (this is reversed on purpose!)
        '%P' => 'a', // am pm
        '%r' => 'h:i:s A', // %I:%M:%S %p
        '%R' => 'H:i', // %H:%M
        '%S' => 's',
        '%T' => 'H:i:s', // %H:%M:%S
        '%X' => $intl_formatter, // Preferred time representation based on locale, without the date

        // Timezone
        '%z' => 'O',
        '%Z' => 'T',

        // Time and Date Stamps
        '%c' => $intl_formatter,
        '%D' => 'm/d/Y',
        '%F' => 'Y-m-d',
        '%s' => 'U',
        '%x' => $intl_formatter,
    ];

    $out = preg_replace_callback('/(?<!%)%([_#-]?)([a-zA-Z])/', function ($match) use ($translation_table, $timestamp) {
        $prefix = $match[1];
        $char = $match[2];
        $pattern = '%'.$char;
        if ($pattern === '%n') {
            return "\n";
        } elseif ($pattern === '%t') {
            return "\t";
        }

        if (!isset($translation_table[$pattern])) {
            throw new InvalidArgumentException(sprintf('Format "%s" is unknown in time format', $pattern));
        }

        $replace = $translation_table[$pattern];

        if (is_string($replace)) {
            $result = $timestamp->format($replace);
        } else {
            $result = $replace($timestamp, $pattern);
        }

        switch ($prefix) {
            case '_':
                // replace leading zeros with spaces but keep last char if also zero
                return preg_replace('/\G0(?=.)/', ' ', $result);
            case '#':
            case '-':
                // remove leading zeros but keep last char if also zero
                return preg_replace('/^0+(?=.)/', '', $result);
        }

        return $result;
    }, $format);

    $out = str_replace('%%', '%', $out);
    return $out;
}