/*

    xml.js

    a simple XML DOM, encoder and parser for morphic.js

    written by Jens Mönig
    jens@moenig.org

    Copyright (C) 2015 by Jens Mönig

    This file is part of Snap!.

    Snap! is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as
    published by the Free Software Foundation, either version 3 of
    the License, or (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.


    prerequisites:
    --------------
    needs morphic.js


    hierarchy
    ---------
    the following tree lists all constructors hierarchically,
    indentation indicating inheritance. Refer to this list to get a
    contextual overview:

        Node*
            XML_Element
        ReadStream

    * defined in morphic.js


    toc
    ---
    the following list shows the order in which all constructors are
    defined. Use this list to locate code in this document:

        ReadStream
        XML_Element


    credits
    -------
    Nathan Dinsmore contributed to the design and implemented a first
    working version of a complete XMLSerializer. I have taken much of the
    overall design and many of the functions and methods in this file from
    Nathan's fine original prototype. Recently Nathan has once again
    worked his magic on the parser and optimized it by an order of
    magnitude.

*/

/*global modules, detect, Node, isNil*/

// Global stuff ////////////////////////////////////////////////////////

modules.xml = '2015-June-25';

// Declarations

var ReadStream;
var XML_Element;

// ReadStream ////////////////////////////////////////////////////////////

// I am a sequential reading interface to an Array or String

// ReadStream instance creation:

function ReadStream(arrayOrString) {
    this.contents = arrayOrString || '';
    this.index = 0;
}

// ReadStream constants:

ReadStream.prototype.nonSpace = /\S|$/g;
ReadStream.prototype.nonWord = /[\s\>\/\=]|$/g;

// ReadStream accessing:

ReadStream.prototype.next = function (count) {
    var element, start;
    if (count === undefined) {
        element = this.contents[this.index];
        this.index += 1;
        return element;
    }
    start = this.index;
    this.index += count;
    return this.contents.slice(start, this.index);
};

ReadStream.prototype.peek = function () {
    return this.contents[this.index];
};

ReadStream.prototype.skip = function (count) {
    this.index += count || 1;
};

ReadStream.prototype.atEnd = function () {
    return this.index > (this.contents.length - 1);
};

// ReadStream accessing String contents:

ReadStream.prototype.upTo = function (str) {
    var i = this.contents.indexOf(str, this.index);
    return i === -1 ? '' : this.contents.slice(this.index, this.index = i);
};

ReadStream.prototype.peekUpTo = function (str) {
    var i = this.contents.indexOf(str, this.index);
    return i === -1 ? '' : this.contents.slice(this.index, i);
};

ReadStream.prototype.skipSpace = function () {
    this.nonSpace.lastIndex = this.index;
    var result = this.nonSpace.exec(this.contents);
    if (result) this.index = result.index;
};

ReadStream.prototype.word = function () {
    this.nonWord.lastIndex = this.index;
    var result = this.nonWord.exec(this.contents);
    return result ? this.contents.slice(this.index, this.index = result.index) : '';
};

// XML_Element ///////////////////////////////////////////////////////////
/*
    I am a DOM-Node which can encode itself to as well as parse itself
    from a well-formed XML string. Note that there is no separate parser
    object, all the parsing can be done in a single object.
*/

// XML_Element inherits from Node:

XML_Element.prototype = Object.create(Node.prototype);
XML_Element.prototype.constructor = XML_Element;
XML_Element.uber = Node.prototype;

// XML_Element preferences settings:

XML_Element.prototype.indentation = '  ';

// XML_Element instance creation:

function XML_Element(tag, contents, parent) {
    this.init(tag, contents, parent);
}

XML_Element.prototype.init = function (tag, contents, parent) {
    // additional properties:
    this.tag = tag || 'unnamed';
    this.attributes = {};
    this.contents = contents || '';

    // initialize inherited properties:
    XML_Element.uber.init.call(this);

    // override inherited properties
    if (parent) parent.addChild(this);
};

// XML_Element DOM navigation: (aside from what's inherited from Node)

XML_Element.prototype.require = function (tagName) {
    // answer the first direct child with the specified tagName, or throw
    // an error if it doesn't exist
    var child = this.childNamed(tagName);
    if (!child) {
        throw new Error('Missing required element <' + tagName + '>!');
    }
    return child;
};

XML_Element.prototype.childNamed = function (tagName) {
    // answer the first direct child with the specified tagName, or null
    return detect(
        this.children,
        function (child) {return child.tag === tagName; }
    );
};

XML_Element.prototype.childrenNamed = function (tagName) {
    // answer all direct children with the specified tagName
    return this.children.filter(
        function (child) {return child.tag === tagName; }
    );
};

XML_Element.prototype.parentNamed = function (tagName) {
    // including myself
    if (this.tag === tagName) {
        return this;
    }
    if (!this.parent) {
        return null;
    }
    return this.parent.parentNamed(tagName);
};

// XML_Element output:

XML_Element.prototype.toString = function (isFormatted, indentationLevel) {
    var result = '',
        indent = '',
        level = indentationLevel || 0,
        key,
        i;

    // spaces for indentation, if any
    if (isFormatted) {
        for (i = 0; i < level; i += 1) {
            indent += this.indentation;
        }
        result += indent;
    }

    // opening tag
    result += ('<' + this.tag);

    // attributes, if any
    for (key in this.attributes) {
        if (Object.prototype.hasOwnProperty.call(this.attributes, key)
                && this.attributes[key]) {
            result += ' ' + key + '="' + this.attributes[key] + '"';
        }
    }

    // contents, subnodes, and closing tag
    if (!this.contents.length && !this.children.length) {
        result += '/>';
    } else {
        result += '>';
        result += this.contents;
        this.children.forEach(function (element) {
            if (isFormatted) {
                result += '\n';
            }
            result += element.toString(isFormatted, level + 1);
        });
        if (isFormatted && this.children.length) {
            result += ('\n' + indent);
        }
        result += '</' + this.tag + '>';
    }
    return result;
};

XML_Element.prototype.escape = function (string, ignoreQuotes) {
    var src = isNil(string) ? '' : string.toString(),
        result = '',
        i,
        ch;
    for (i = 0; i < src.length; i += 1) {
        ch = src[i];
        switch (ch) {
        case '\'':
            result += '&apos;';
            break;
        case '\"':
            result += ignoreQuotes ? ch : '&quot;';
            break;
        case '<':
            result += '&lt;';
            break;
        case '>':
            result += '&gt;';
            break;
        case '&':
            result += '&amp;';
            break;
        case '\n': // escape CR b/c of export to URL feature
            result += '&#xD;';
            break;
        case '~': // escape tilde b/c it's overloaded in serializer.store()
            result += '&#126;';
            break;
        default:
            result += ch;
        }
    }
    return result;
};

XML_Element.prototype.unescape = function (string) {
    return string.replace(/&(amp|apos|quot|lt|gt|#xD|#126);/g, function(_, name) {
        switch (name) {
            case 'amp': return '&';
            case 'apos': return '\'';
            case 'quot': return '"';
            case 'lt': return '<';
            case 'gt': return '>';
            case '#xD': return '\n';
            case '#126': return '~';
            default: console.warn('unreachable');
        }
    });
};

// XML_Element parsing:

XML_Element.prototype.parseString = function (string) {
    var stream = new ReadStream(string);
    stream.upTo('<');
    stream.skip();
    this.parseStream(stream);
};

XML_Element.prototype.parseStream = function (stream) {
    var key, value, ch, child;

    // tag:
    this.tag = stream.word();
    stream.skipSpace();

    // attributes:
    ch = stream.peek();
    while (ch !== '>' && ch !== '/') {
        key = stream.word();
        stream.skipSpace();
        if (stream.next() !== '=') {
            throw new Error('Expected "=" after attribute name');
        }
        stream.skipSpace();
        ch = stream.next();
        if (ch !== '"' && ch !== "'") {
            throw new Error('Expected single- or double-quoted attribute value');
        }
        value = stream.upTo(ch);
        stream.skip(1);
        stream.skipSpace();
        this.attributes[key] = this.unescape(value);
        ch = stream.peek();
    }

    // empty tag:
    if (ch === '/') {
        stream.skip();
        if (stream.next() !== '>') {
            throw new Error('Expected ">" after "/" in empty tag');
        }
        return;
    }
    if (stream.next() !== '>') {
        throw new Error('Expected ">" after tag name and attributes');
    }

    // contents and children
    while (!stream.atEnd()) {
        ch = stream.next();
        if (ch === '<') {
            if (stream.peek() === '/') { // closing tag
                stream.skip();
                if (stream.word() !== this.tag) {
                    throw new Error('Expected to close ' + this.tag);
                }
                stream.upTo('>');
                stream.skip();
                this.contents = this.unescape(this.contents);
                return;
            }
            child = new XML_Element(null, null, this);
            child.parseStream(stream);
        } else {
            this.contents += ch;
        }
    }
};
