<?php declare (strict_types=1);

namespace Sabre\Xml;

use XMLReader;

/**
 * The Reader class expands upon PHP's built-in XMLReader.
 *
 * The intended usage, is to assign certain XML elements to PHP classes. These
 * need to be registered using the $elementMap public property.
 *
 * After this is done, a single call to parse() will parse the entire document,
 * and delegate sub-sections of the document to element classes.
 *
 * @copyright Copyright (C) 2009-2015 fruux GmbH (https://fruux.com/).
 * @author Evert Pot (http://evertpot.com/)
 * @license http://sabre.io/license/ Modified BSD License
 */
class Reader extends XMLReader {

    use ContextStackTrait;

    /**
     * Returns the current nodename in clark-notation.
     *
     * For example: "{http://www.w3.org/2005/Atom}feed".
     * Or if no namespace is defined: "{}feed".
     *
     * This method returns null if we're not currently on an element.
     *
     * @return string|null
     */
    function getClark() {

        if (! $this->localName) {
            return null;
        }

        return '{' . $this->namespaceURI . '}' . $this->localName;

    }

    /**
     * Reads the entire document.
     *
     * This function returns an array with the following three elements:
     *    * name - The root element name.
     *    * value - The value for the root element.
     *    * attributes - An array of attributes.
     *
     * This function will also disable the standard libxml error handler (which
     * usually just results in PHP errors), and throw exceptions instead.
     */
    function parse() : array {

        $previousEntityState = libxml_disable_entity_loader(true);
        $previousSetting = libxml_use_internal_errors(true);

        try {

            while ($this->nodeType !== self::ELEMENT) {
                if (!$this->read()) {
                    $errors = libxml_get_errors();
                    libxml_clear_errors();
                    if ($errors) {
                        throw new LibXMLException($errors);
                    }
                }
            }
            $result = $this->parseCurrentElement();

            // last line of defense in case errors did occur above
            $errors = libxml_get_errors();
            libxml_clear_errors();
            if ($errors) {
                throw new LibXMLException($errors);
            }

        } finally {
            libxml_use_internal_errors($previousSetting);
            libxml_disable_entity_loader($previousEntityState);
        }

        return $result;
    }



    /**
     * parseGetElements parses everything in the current sub-tree,
     * and returns a an array of elements.
     *
     * Each element has a 'name', 'value' and 'attributes' key.
     *
     * If the the element didn't contain sub-elements, an empty array is always
     * returned. If there was any text inside the element, it will be
     * discarded.
     *
     * If the $elementMap argument is specified, the existing elementMap will
     * be overridden while parsing the tree, and restored after this process.
     */
    function parseGetElements(array $elementMap = null) : array {

        $result = $this->parseInnerTree($elementMap);
        if (!is_array($result)) {
            return [];
        }
        return $result;

    }

    /**
     * Parses all elements below the current element.
     *
     * This method will return a string if this was a text-node, or an array if
     * there were sub-elements.
     *
     * If there's both text and sub-elements, the text will be discarded.
     *
     * If the $elementMap argument is specified, the existing elementMap will
     * be overridden while parsing the tree, and restored after this process.
     *
     * @return array|string
     */
    function parseInnerTree(array $elementMap = null) {

        $text = null;
        $elements = [];

        if ($this->nodeType === self::ELEMENT && $this->isEmptyElement) {
            // Easy!
            $this->next();
            return null;
        }

        if (!is_null($elementMap)) {
            $this->pushContext();
            $this->elementMap = $elementMap;
        }

        try {

            if (!$this->read()) {
                $errors = libxml_get_errors();
                libxml_clear_errors();
                if ($errors) {
                    throw new LibXMLException($errors);
                }
                throw new ParseException('This should never happen (famous last words)');
            }

            while (true) {

                if (!$this->isValid()) {

                    $errors = libxml_get_errors();

                    if ($errors) {
                        libxml_clear_errors();
                        throw new LibXMLException($errors);
                    }
                }

                switch ($this->nodeType) {
                    case self::ELEMENT :
                        $elements[] = $this->parseCurrentElement();
                        break;
                    case self::TEXT :
                    case self::CDATA :
                        $text .= $this->value;
                        $this->read();
                        break;
                    case self::END_ELEMENT :
                        // Ensuring we are moving the cursor after the end element.
                        $this->read();
                        break 2;
                    case self::NONE :
                        throw new ParseException('We hit the end of the document prematurely. This likely means that some parser "eats" too many elements. Do not attempt to continue parsing.');
                    default :
                        // Advance to the next element
                        $this->read();
                        break;
                }

            }

        } finally {

            if (!is_null($elementMap)) {
                $this->popContext();
            }

        }
        return ($elements ? $elements : $text);

    }

    /**
     * Reads all text below the current element, and returns this as a string.
     */
    function readText() : string {

        $result = '';
        $previousDepth = $this->depth;

        while ($this->read() && $this->depth != $previousDepth) {
            if (in_array($this->nodeType, [XMLReader::TEXT, XMLReader::CDATA, XMLReader::WHITESPACE])) {
                $result .= $this->value;
            }
        }
        return $result;

    }

    /**
     * Parses the current XML element.
     *
     * This method returns arn array with 3 properties:
     *   * name - A clark-notation XML element name.
     *   * value - The parsed value.
     *   * attributes - A key-value list of attributes.
     */
    function parseCurrentElement() : array {

        $name = $this->getClark();

        $attributes = [];

        if ($this->hasAttributes) {
            $attributes = $this->parseAttributes();
        }

        $value = call_user_func(
            $this->getDeserializerForElementName($name),
            $this
        );

        return [
            'name'       => $name,
            'value'      => $value,
            'attributes' => $attributes,
        ];
    }


    /**
     * Grabs all the attributes from the current element, and returns them as a
     * key-value array.
     *
     * If the attributes are part of the same namespace, they will simply be
     * short keys. If they are defined on a different namespace, the attribute
     * name will be retured in clark-notation.
     */
    function parseAttributes() : array {

        $attributes = [];

        while ($this->moveToNextAttribute()) {
            if ($this->namespaceURI) {

                // Ignoring 'xmlns', it doesn't make any sense.
                if ($this->namespaceURI === 'http://www.w3.org/2000/xmlns/') {
                    continue;
                }

                $name = $this->getClark();
                $attributes[$name] = $this->value;

            } else {
                $attributes[$this->localName] = $this->value;
            }
        }
        $this->moveToElement();

        return $attributes;

    }

    /**
     * Returns the function that should be used to parse the element identified
     * by it's clark-notation name.
     */
    function getDeserializerForElementName(string $name) : callable {

        if (!array_key_exists($name, $this->elementMap)) {
            if (substr($name, 0, 2) == '{}' && array_key_exists(substr($name, 2), $this->elementMap)) {
                $name = substr($name, 2);
            } else {
                return ['Sabre\\Xml\\Element\\Base', 'xmlDeserialize'];
            }
        }

        $deserializer = $this->elementMap[$name];
        if (is_subclass_of($deserializer, 'Sabre\\Xml\\XmlDeserializable')) {
            return [$deserializer, 'xmlDeserialize'];
        }

        if (is_callable($deserializer)) {
            return $deserializer;
        }

        $type = gettype($deserializer);
        if ($type === 'string') {
            $type .= ' (' . $deserializer . ')';
        } elseif ($type === 'object') {
            $type .= ' (' . get_class($deserializer) . ')';
        }
        throw new \LogicException('Could not use this type as a deserializer: ' . $type . ' for element: ' . $name);

    }

}
