<?php
/**
 * Geoplot — geotemporal hash
 *
 * PHP port of generate_geotemporal_hash() from extractGeoFrame.py
 * by Wizardry and Steamworks.
 *
 * The hash interleaves, MSB→LSB, one bit each of the 32-bit quantized
 * latitude, longitude and UTC timestamp, then base32-encodes (RFC 4648)
 * the 96-bit stream, padded to 100 bits → 20 characters.
 *
 * (c) Wizardry and Steamworks 2026
 * SPDX-License-Identifier: MIT
 */

if (!defined('DOKU_INC')) die();

class Geoplot_Geohash {

    const LAT_MIN  = -90.0;
    const LAT_MAX  =  90.0;
    const LON_MIN  = -180.0;
    const LON_MAX  =  180.0;
    const TIME_MIN = 946684800;    // 2000-01-01T00:00:00Z
    const TIME_MAX = 4102444800;   // 2100-01-01T00:00:00Z
    const TIME_RANGE = 3155760000; // 100 * 365.25 * 86400

    const ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';

    private static function clamp($v, $lo, $hi) {
        return $v < $lo ? $lo : ($v > $hi ? $hi : $v);
    }

    /**
     * @param float $lat   Decimal degrees, [-90, 90]
     * @param float $lon   Decimal degrees, [-180, 180]
     * @param int   $ts    Unix UTC timestamp
     * @return string      20-character base32 geotemporal hash
     */
    public static function generate($lat, $lon, $ts) {
        $lat = self::clamp((float)$lat, self::LAT_MIN, self::LAT_MAX);
        $lon = self::clamp((float)$lon, self::LON_MIN, self::LON_MAX);
        $ts  = self::clamp((int)$ts,   self::TIME_MIN, self::TIME_MAX);

        $norm_lat  = ($lat - self::LAT_MIN) / (self::LAT_MAX - self::LAT_MIN);
        $norm_lon  = ($lon - self::LON_MIN) / (self::LON_MAX - self::LON_MIN);
        $norm_time = ($ts  - self::TIME_MIN) / self::TIME_RANGE;

        $MAX = 4294967295; // 2^32 - 1

        $int_lat  = (int) floor($norm_lat  * $MAX);
        $int_lon  = (int) floor($norm_lon  * $MAX);
        $int_time = (int) floor($norm_time * $MAX);

        // Interleave MSB→LSB: lat_i, lon_i, time_i
        $bits = '';
        for ($i = 31; $i >= 0; $i--) {
            $bits .= (($int_lat  >> $i) & 1) ? '1' : '0';
            $bits .= (($int_lon  >> $i) & 1) ? '1' : '0';
            $bits .= (($int_time >> $i) & 1) ? '1' : '0';
        }

        // Pad to multiple of 5, base32-encode
        $rem = strlen($bits) % 5;
        if ($rem !== 0) {
            $bits .= str_repeat('0', 5 - $rem);
        }

        $out = '';
        $len = strlen($bits);
        for ($i = 0; $i < $len; $i += 5) {
            $out .= self::ALPHABET[bindec(substr($bits, $i, 5))];
        }
        return $out;
    }

    /**
     * Longest common prefix of an array of strings.
     */
    public static function longestCommonPrefix(array $strings) {
        if (empty($strings)) return '';
        $prefix = array_shift($strings);
        foreach ($strings as $s) {
            $n = min(strlen($prefix), strlen($s));
            $i = 0;
            while ($i < $n && $prefix[$i] === $s[$i]) $i++;
            $prefix = substr($prefix, 0, $i);
            if ($prefix === '') break;
        }
        return $prefix;
    }
}