<?php

namespace PSX\Schema\Transformer;

use PSX\Schema\Exception\TransformerException;
use PSX\Schema\Parser\TypeSchema\BCLayer;
use PSX\Schema\TransformerInterface;

/**
 * Transform an existing JSON Schema to a valid TypeSchema
 *
 * @author  Christoph Kappestein <christoph.kappestein@gmail.com>
 * @license http://www.apache.org/licenses/LICENSE-2.0
 * @link    http://phpsx.org
 */
class JsonSchema implements TransformerInterface
{
    public function transform(string $schema): string
    {
        $data = \json_decode($schema);
        if (!$data instanceof \stdClass) {
            throw new TransformerException('Provided schema must be an object');
        }

        $keywords = [];
        $definitions = new \stdClass();
        foreach ($data as $key => $value) {
            if ($key === 'definitions' || $key === '$defs') {
                $definitions = $value;
            } else {
                $keywords[$key] = $value;
            }
        }

        $defs = [];
        if ($definitions instanceof \stdClass) {
            foreach ($definitions as $name => $type) {
                if ($type instanceof \stdClass) {
                    $defs[$name] = $this->convertSchema($type, $defs);
                }
            }
        }

        $root = null;
        if (!empty($keywords)) {
            $result = $this->convertSchema((object) $keywords, $defs);
            if (!isset($result->{'$ref'})) {
                throw new TransformerException('The root schema must be an object');
            }

            $root = $result->{'$ref'};
        }

        $result = new \stdClass();
        $result->definitions = $defs;
        if ($root !== null) {
            $result->{'$ref'} = $root;
        }

        return \json_encode($result, JSON_PRETTY_PRINT);
    }

    private function convertSchema(\stdClass $schema, array &$definitions)
    {
        $schema = BCLayer::transform($schema);

        $result = [];
        if (isset($schema->description)) {
            $result['description'] = $schema->description;
        }

        $type = $schema->type ?? null;
        if ($type === 'object') {
            $title = $schema->title ?? 'Inline' . substr(md5(json_encode($schema)), 0, 8);

            if (isset($schema->properties) && $schema->properties instanceof \stdClass) {
                $rawRequired = [];
                if (isset($schema->required) && is_array($schema->required)) {
                    $rawRequired = $schema->required;
                }

                $required = [];
                $properties = [];
                foreach ($schema->properties as $name => $value) {
                    $properties[$name] = $this->convertSchema($value, $definitions);

                    if (in_array($name, $rawRequired)) {
                        $required[] = $name;
                    }
                }

                $result['type'] = 'object';
                $result['properties'] = $properties;

                if (!empty($required)) {
                    $result['required'] = $required;
                }
            } elseif (isset($schema->additionalProperties) && $schema->additionalProperties instanceof \stdClass) {
                $result['type'] = 'object';
                $result['additionalProperties'] = $this->convertSchema($schema->additionalProperties, $definitions);
            } else {
                throw new TransformerException('Could not assign object type to either a struct or map');
            }

            $definitions[$title] = $result;

            return (object) [
                '$ref' => $title,
            ];
        } elseif ($type === 'array') {
            $result['type'] = 'array';

            if (isset($schema->items) && $schema->items instanceof \stdClass) {
                $result['items'] = $this->convertSchema($schema->items, $definitions);
            } else {
                throw new TransformerException('Array must contain an items property');
            }
        } elseif ($type === 'string') {
            $result['type'] = 'string';
            $result = $this->copyKeywords($schema, $result, ['maxLength', 'minLength', 'pattern']);
        } elseif ($type === 'boolean') {
            $result['type'] = 'boolean';
        } elseif ($type === 'number' || $type === 'integer') {
            $result['type'] = $type;
            $result = $this->copyKeywords($schema, $result, ['multipleOf', 'maximum', 'exclusiveMaximum', 'minimum', 'exclusiveMinimum']);
        } elseif (isset($schema->oneOf) && is_array($schema->oneOf)) {
            $list = [];
            foreach ($schema->oneOf as $subSchema) {
                $list[] = $this->convertSchema($subSchema, $definitions);
            }

            $result['oneOf'] = $list;
        } elseif (isset($schema->allOf) && is_array($schema->allOf)) {
            $list = [];
            foreach ($schema->allOf as $subSchema) {
                $list[] = $this->convertSchema($subSchema, $definitions);
            }

            $result['allOf'] = $list;
        } elseif (isset($schema->{'$ref'})) {
            $ref = $schema->{'$ref'};
            $ref = str_replace('#/definitions/', '', $ref);
            $ref = str_replace('#/$defs/', '', $ref);

            $result['$ref'] = $ref;
        } else {
            $result['type'] = 'any';
        }

        return (object) $result;
    }

    private function copyKeywords(\stdClass $schema, array $result, array $allowedKeywords)
    {
        foreach ($allowedKeywords as $keyword) {
            if (isset($schema->{$keyword})) {
                $result[$keyword] = $schema->{$keyword};
            }
        }

        return $result;
    }
}
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