<?php

namespace App\Services;

use Generator;

/** Read the accepted original one feature at a time, without changing its bytes. */
final class RetainedGeoJsonCollection
{
    public function __construct(private readonly string $path) {}

    /** @return array{type:mixed,feature_count:int,first_properties:array<string,mixed>,exceededTransferLimit:mixed} */
    public function manifest(): array
    {
        $features = $this->features();
        $count = 0;
        $first = [];
        foreach ($features as $feature) {
            if ($count === 0) {
                $first = $feature['properties'] ?? [];
            }
            $count++;
        }
        $metadata = $features->getReturn();

        return ['type' => $metadata['type'] ?? null, 'feature_count' => $count, 'first_properties' => $first,
            'exceededTransferLimit' => $metadata['exceededTransferLimit'] ?? false];
    }

    /** @return Generator<int,array<string,mixed>,mixed,array<string,mixed>> */
    public function features(): Generator
    {
        $stream = fopen($this->path, 'rb');
        abort_unless(is_resource($stream), 422, 'Exemplar privado indisponível.');
        $buffer = '';
        $position = 0;
        $peek = static function () use ($stream, &$buffer, &$position): ?string {
            if ($position === strlen($buffer)) {
                $buffer = fread($stream, 65536);
                $position = 0;
            }

            return $buffer !== '' ? $buffer[$position] : null;
        };
        $take = static function () use ($peek, &$position): ?string {
            $char = $peek();
            if ($char !== null) {
                $position++;
            }

            return $char;
        };
        $white = static function () use ($peek, $take): void {
            while (($c = $peek()) !== null && str_contains(" \t\r\n", $c)) {
                $take();
            }
        };
        $expect = static function (string $expected) use ($white, $take): void {
            $white();
            abort_unless($take() === $expected, 422, 'Estrutura JSON do exemplar inválida.');
        };
        $value = static function () use ($white, $peek, $take, &$buffer, &$position): string {
            $white();
            $first = $peek();
            abort_unless($first !== null, 422, 'Exemplar JSON truncado.');
            $structured = in_array($first, ['{', '[', '"'], true);
            $result = $structured ? $take() : '';
            $depth = $first === '"' ? 0 : 1;
            $quoted = $first === '"';
            $delimiters = $first === '{' ? '{}"' : ($first === '[' ? '[]"' : '"');
            while (true) {
                abort_unless($peek() !== null, 422, 'Exemplar JSON truncado.');
                // Search whole numeric/coordinate spans in C; never loop through every byte in PHP.
                $span = strcspn($buffer, $structured ? ($quoted ? '"\\' : $delimiters) : ",]} \t\r\n", $position);
                $result .= substr($buffer, $position, $span);
                $position += $span;
                abort_if(strlen($result) > 4 * 1024 * 1024, 422, 'Elemento JSON excede o limite seguro de leitura.');
                if ($position === strlen($buffer)) {
                    continue;
                }
                if (! $structured) {
                    break;
                }
                $c = $take();
                $result .= $c;
                if ($quoted) {
                    if ($c === '\\') {
                        $escaped = $take();
                        abort_unless($escaped !== null, 422, 'Exemplar JSON truncado.');
                        $result .= $escaped;
                    } elseif ($c === '"') {
                        $quoted = false;
                    }
                } elseif ($c === '"') {
                    $quoted = true;
                } elseif ($c === $first) {
                    $depth++;
                } else {
                    $depth--;
                }
                if (! $quoted && $depth === 0) {
                    break;
                }
            }
            abort_unless($result !== '', 422, 'Valor JSON ausente.');

            return $result;
        };
        $decode = static function (string $bytes): mixed {
            try {
                return json_decode($bytes, true, 512, JSON_THROW_ON_ERROR);
            } catch (\JsonException) {
                abort(422, 'JSON do exemplar inválido.');
            }
        };
        try {
            $expect('{');
            $metadata = [];
            $keys = [];
            $index = 0;
            $hadFeatures = false;
            $white();
            abort_if($peek() === '}', 422, 'Exemplar sem coleção de elementos.');
            while (true) {
                $key = $decode($value());
                abort_unless(is_string($key) && ! isset($keys[$key]), 422, 'Chave JSON inválida ou repetida.');
                $keys[$key] = true;
                $expect(':');
                if ($key === 'features') {
                    $hadFeatures = true;
                    $expect('[');
                    $white();
                    if ($peek() !== ']') {
                        while (true) {
                            $feature = $decode($value());
                            abort_unless(is_array($feature) && ($feature['type'] ?? null) === 'Feature', 422, 'Elemento geográfico inválido.');
                            yield $index++ => $feature;
                            unset($feature);
                            $white();
                            if ($peek() === ']') {
                                break;
                            }$expect(',');
                        }
                    }
                    $expect(']');
                } else {
                    $metadata[$key] = $decode($value());
                }
                $white();
                if ($peek() === '}') {
                    break;
                }$expect(',');
            }
            $expect('}');
            $white();
            abort_unless($peek() === null && $hadFeatures,422,'Exemplar incompleto ou com conteúdo adicional.');

            return $metadata;
        } finally {
            fclose($stream);
        }
    }
}