<?php
declare(strict_types=1);

namespace MyPrayerJournal;

/**
 * The different distance formats supported
 */
enum DistanceFormat
{
    case LessThanXMinutes;
    case XMinutes;
    case AboutXHours;
    case XHours;
    case XDays;
    case AboutXWeeks;
    case XWeeks;
    case AboutXMonths;
    case XMonths;
    case AboutXYears;
    case XYears;
    case OverXYears;
    case AlmostXYears;

    /**
     * Return the formatting string for the given format and number
     * 
     * @param DistanceFormat $it The distance format
     * @param bool $singular If true, returns the singular version; if false (default), returns the plural version
     * @return string The format string
     */
    public static function format(DistanceFormat $it, bool $singular = false): string
    {
        return match ($it) {
            DistanceFormat::LessThanXMinutes => $singular ? 'less than a minute' : 'less than %i minutes',
            DistanceFormat::XMinutes         => $singular ? 'a minute'           : '%i minutes',
            DistanceFormat::AboutXHours      => $singular ? 'about an hour'      : 'about %i hours',
            DistanceFormat::XHours           => $singular ? 'an hour'            : '%i hours',
            DistanceFormat::XDays            => $singular ? 'a day'              : '%i days',
            DistanceFormat::AboutXWeeks      => $singular ? 'about a week'       : 'about %i weeks',
            DistanceFormat::XWeeks           => $singular ? 'a week'             : '%i weeks',
            DistanceFormat::AboutXMonths     => $singular ? 'about a month'      : 'about %i months',
            DistanceFormat::XMonths          => $singular ? 'a month'            : '%i months',
            DistanceFormat::AboutXYears      => $singular ? 'about a year'       : 'about %i years',
            DistanceFormat::XYears           => $singular ? 'a year'             : '%i years',
            DistanceFormat::OverXYears       => $singular ? 'over a year'        : 'over %i years',
            DistanceFormat::AlmostXYears     => $singular ? 'almost a year'      : 'almost %i years',
        };
    }
}

class Dates
{
    /** Minutes in a day */
    private const A_DAY =  1_440;

    /** Minutes in two days(-ish) */
    private const ALMOST_2_DAYS = 2_520;
    
    /** Minutes in a month */
    private const A_MONTH = 43_200;
    
    /** Minutes in two months */
    private const TWO_MONTHS = 86_400;

    /**
     * Get a UTC-referenced current date/time
     * 
     * @return \DateTimeImmutable The current date/time with UTC reference
     */
    public static function now(): \DateTimeImmutable
    {
        return new \DateTimeImmutable(timezone: new \DateTimeZone('Etc/UTC'));
    }

    /**
     * Format the distance between two instants in approximate English terms
     * 
     * @param \DateTimeInterface $startOn The starting date/time for the comparison
     * @param \DateTimeInterface $endOn THe ending date/time for the comparison
     * @return string The formatted interval
     */
    public static function formatDistance(\DateTimeInterface $startOn, \DateTimeInterface $endOn): string
    {
        $diff    = $startOn->diff($endOn);
        $minutes =
            $diff->i + ($diff->h * 60) + ($diff->d * 60 * 24) + ($diff->m * 60 * 24 * 30) + ($diff->y * 60 * 24 * 365);
        $months = round($minutes / self::A_MONTH);
        $years  = $months / 12;
        [ $format, $number ] = match (true) {
            $minutes < 1                   => [ DistanceFormat::LessThanXMinutes, 1 ],
            $minutes < 45                  => [ DistanceFormat::XMinutes, $minutes ],
            $minutes < 90                  => [ DistanceFormat::AboutXHours, 1 ],
            $minutes < self::A_DAY         => [ DistanceFormat::AboutXHours, round($minutes / 60) ],
            $minutes < self::ALMOST_2_DAYS => [ DistanceFormat::XDays, 1 ],
            $minutes < self::A_MONTH       => [ DistanceFormat::XDays, round($minutes / self::A_DAY) ],
            $minutes < self::TWO_MONTHS    => [ DistanceFormat::AboutXMonths, round($minutes / self::A_MONTH) ],
            $months      < 12              => [ DistanceFormat::XMonths, round($minutes / self::A_MONTH) ],
            $months % 12 < 3               => [ DistanceFormat::AboutXYears, $years ],
            $months % 12 < 9               => [ DistanceFormat::OverXYears, $years ],
            default                        => [ DistanceFormat::AlmostXYears, $years + 1 ],
        };

        $relativeWords = sprintf(DistanceFormat::format($format, $number == 1), $number);
        return $startOn > $endOn ? "$relativeWords ago" : "in $relativeWords";
    }
}