<?php

namespace App\Services;

/**
 * Class PolylineEncoder
 *
 * Encodes a list of latitude/longitude coordinates into an encoded polyline string.
 *
 * This implementation is compatible with Google's Polyline Algorithm Format:
 * https://developers.google.com/maps/documentation/utilities/polylinealgorithm
 *
 * Example input:
 * [
 *   [lat, lng],
 *   [lat, lng]
 * ]
 *
 * or if `$lng_lat_format = true`:
 * [
 *   [lng, lat],
 *   [lng, lat]
 * ]
 *
 * @package App\Services
 */
class PolylineEncoder
{
    /**
     * Encode an array of coordinates into a polyline string.
     *
     * Each coordinate is encoded as a delta from the previous point,
     * scaled by the given precision factor.
     *
     * @param array $coords Array of coordinate pairs:
     *                      - default: [lat, lng]
     *                      - if $lng_lat_format = true: [lng, lat]
     * @param int $precision Number of decimal places to preserve (default: 6)
     * @param bool $lng_lat_format If true, input is treated as [lng, lat] instead of [lat, lng]
     *
     * @return string Encoded polyline string
     */
    public function encodePolyline(array $coords, int $precision = 6, bool $lng_lat_format = false): string
    {
        $factor = 10 ** $precision;
        $output = '';
        $prevLat = 0;
        $prevLng = 0;

        foreach ($coords as [$a, $b]) {
            [$lat, $lng] = $lng_lat_format ? [$b, $a] : [$a, $b];

            $output .= $this->encodeValue((int)round($lat * $factor) - $prevLat);
            $output .= $this->encodeValue((int)round($lng * $factor) - $prevLng);

            $prevLat = (int)round($lat * $factor);
            $prevLng = (int)round($lng * $factor);
        }

        return $output;
    }

    /**
     * Encodes a single integer value using Google's polyline encoding algorithm.
     *
     * Steps:
     * - Left shift the value
     * - Invert bits if negative
     * - Split into 5-bit chunks
     * - Convert to ASCII characters
     *
     * @param int $value Signed integer delta to encode
     *
     * @return string Encoded character sequence
     */
    public function encodeValue(int $value): string
    {
        $value = $value < 0 ? ~($value << 1) : ($value << 1);
        $result = '';

        while ($value >= 0x20) {
            $result .= chr((0x20 | ($value & 0x1f)) + 63);
            $value >>= 5;
        }

        return $result . chr($value + 63);
    }
}