<?php
// Bencode.php
// Created: 2022-01-13
// Updated: 2023-07-21

namespace Index\Serialisation;

use RuntimeException;
use Index\IO\Stream;
use Index\IO\TempFileStream;

/**
 * Provides a Bencode serialiser.
 */
final class Bencode {
    public const DEFAULT_DEPTH = 512;

    public static function encode(mixed $input, int $depth = self::DEFAULT_DEPTH): string {
        if($depth < 1)
            throw new RuntimeException('Maximum depth reached, structure is too dense.');

        switch(gettype($input)) {
            case 'string':
                return sprintf('%d:%s', strlen($input), $input);

            case 'integer':
                return sprintf('i%de', $input);

            case 'array':
                if(array_is_list($input)) {
                    $output = 'l';
                    foreach($input as $item)
                        $output .= self::encode($item, $depth - 1);
                } else {
                    $output = 'd';
                    foreach($input as $key => $value) {
                        $output .= self::encode((string)$key, $depth - 1);
                        $output .= self::encode($value, $depth - 1);
                    }
                }

                return $output . 'e';

            case 'object':
                if($input instanceof IBencodeSerialisable)
                    return self::encode($input->bencodeSerialise(), $depth - 1);

                $input = get_object_vars($input);
                $output = 'd';

                foreach($input as $key => $value) {
                    $output .= self::encode((string)$key, $depth - 1);
                    $output .= self::encode($value, $depth - 1);
                }

                return $output . 'e';

            default:
                return '';
        }
    }

    public static function decode(Stream|string $input, int $depth = self::DEFAULT_DEPTH, bool $dictAsObject = false): mixed {
        if(!($input instanceof Stream)) {
            $input = TempFileStream::fromString($input);
            $input->seek(0);
        }

        if($depth < 1)
            throw new RuntimeException('Maximum depth reached, structure is too dense.');

        $char = $input->readChar();
        if($char === null)
            throw new RuntimeException('Unexpected end of stream in $input.');

        switch($char) {
            case 'i':
                $number = '';

                for(;;) {
                    $char = $input->readChar();
                    if($char === null)
                        throw new RuntimeException('Unexpected end of stream while parsing integer.');
                    if($char === 'e')
                        break;
                    if($char === '-' && $number !== '')
                        throw new RuntimeException('Unexpected - (minus) while parsing integer.');
                    if($char === '0' && $number === '-')
                        throw new RuntimeException('Negative integer zero.');
                    if($char === '0' && $number === '0')
                        throw new RuntimeException('Integer double zero.');
                    if(!ctype_digit($char))
                        throw new RuntimeException('Unexpected character while parsing integer.');
                    $number .= $char;
                }

                return (int)$number;

            case 'l':
                $list = [];

                for(;;) {
                    $char = $input->readChar();
                    if($char === null)
                        throw new RuntimeException('Unexpected end of stream while parsing list.');
                    if($char === 'e')
                        break;
                    $input->seek(-1, Stream::CURRENT);
                    $list[] = self::decode($input, $depth - 1, $dictAsObject);
                }

                return $list;

            case 'd':
                $dict = [];

                for(;;) {
                    $char = $input->readChar();
                    if($char === null)
                        throw new RuntimeException('Unexpected end of stream while parsing dictionary');
                    if($char === 'e')
                        break;
                    if(!ctype_digit($char))
                        throw new RuntimeException('Unexpected dictionary key type, expected a string.');
                    $input->seek(-1, Stream::CURRENT);
                    $dict[self::decode($input, $depth - 1, $dictAsObject)] = self::decode($input, $depth - 1, $dictAsObject);
                }

                if($dictAsObject)
                    $dict = (object)$dict;

                return $dict;

            default:
                if(!ctype_digit($char))
                    throw new RuntimeException('Unexpected character while parsing string.');

                $length = $char;

                for(;;) {
                    $char = $input->readChar();
                    if($char === null)
                        throw new RuntimeException('Unexpected end of character while parsing string length.');
                    if($char === ':')
                        break;
                    if($char === '0' && $length === '0')
                        throw new RuntimeException('Integer double zero while parsing string length.');
                    if(!ctype_digit($char))
                        throw new RuntimeException('Unexpected character while parsing string length.');

                    $length .= $char;
                }

                return $input->read((int)$length);
        }
    }
}