/*
 * Bittorrent Client using Qt and libtorrent.
 * Copyright (C) 2015  Vladimir Golovnev <glassez@yandex.ru>
 * Copyright (C) 2012  Christophe Dumez <chris@qbittorrent.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * In addition, as a special exception, the copyright holders give permission to
 * link this program with the OpenSSL project's "OpenSSL" library (or with
 * modified versions of it that use the same license as the "OpenSSL" library),
 * and distribute the linked executables. You must obey the GNU General Public
 * License in all respects for all of the code used other than "OpenSSL".  If you
 * modify file(s), you may extend this exception to your version of the file(s),
 * but you are not obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 */

#include "rss_parser.h"

#include <QDateTime>
#include <QDebug>
#include <QGlobalStatic>
#include <QHash>
#include <QMetaObject>
#include <QRegularExpression>
#include <QStringList>
#include <QVariant>
#include <QXmlStreamEntityResolver>
#include <QXmlStreamReader>

#include "base/global.h"
#include "rss_article.h"

namespace
{
    class XmlStreamEntityResolver final : public QXmlStreamEntityResolver
    {
    public:
        QString resolveUndeclaredEntity(const QString &name) override
        {
            // (X)HTML entities declared in:
            //     http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent
            //     http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent
            //     http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent
            static const QHash<QString, QString> HTMLEntities
            {
                {u"nbsp"_s,   u"&#160;"_s}, // no-break space = non-breaking space, U+00A0 ISOnum
                {u"iexcl"_s,  u"&#161;"_s}, // inverted exclamation mark, U+00A1 ISOnum
                {u"cent"_s,   u"&#162;"_s}, // cent sign, U+00A2 ISOnum
                {u"pound"_s,  u"&#163;"_s}, // pound sign, U+00A3 ISOnum
                {u"curren"_s, u"&#164;"_s}, // currency sign, U+00A4 ISOnum
                {u"yen"_s,    u"&#165;"_s}, // yen sign = yuan sign, U+00A5 ISOnum
                {u"brvbar"_s, u"&#166;"_s}, // broken bar = broken vertical bar, U+00A6 ISOnum
                {u"sect"_s,   u"&#167;"_s}, // section sign, U+00A7 ISOnum
                {u"uml"_s,    u"&#168;"_s}, // diaeresis = spacing diaeresis, U+00A8 ISOdia
                {u"copy"_s,   u"&#169;"_s}, // copyright sign, U+00A9 ISOnum
                {u"ordf"_s,   u"&#170;"_s}, // feminine ordinal indicator, U+00AA ISOnum
                {u"laquo"_s,  u"&#171;"_s}, // left-pointing double angle quotation mark = left pointing guillemet, U+00AB ISOnum
                {u"not"_s,    u"&#172;"_s}, // not sign = angled dash, U+00AC ISOnum
                {u"shy"_s,    u"&#173;"_s}, // soft hyphen = discretionary hyphen, U+00AD ISOnum
                {u"reg"_s,    u"&#174;"_s}, // registered sign = registered trade mark sign, U+00AE ISOnum
                {u"macr"_s,   u"&#175;"_s}, // macron = spacing macron = overline = APL overbar, U+00AF ISOdia
                {u"deg"_s,    u"&#176;"_s}, // degree sign, U+00B0 ISOnum
                {u"plusmn"_s, u"&#177;"_s}, // plus-minus sign = plus-or-minus sign, U+00B1 ISOnum
                {u"sup2"_s,   u"&#178;"_s}, // superscript two = superscript digit two = squared, U+00B2 ISOnum
                {u"sup3"_s,   u"&#179;"_s}, // superscript three = superscript digit three = cubed, U+00B3 ISOnum
                {u"acute"_s,  u"&#180;"_s}, // acute accent = spacing acute, U+00B4 ISOdia
                {u"micro"_s,  u"&#181;"_s}, // micro sign, U+00B5 ISOnum
                {u"para"_s,   u"&#182;"_s}, // pilcrow sign = paragraph sign, U+00B6 ISOnum
                {u"middot"_s, u"&#183;"_s}, // middle dot = Georgian comma = Greek middle dot, U+00B7 ISOnum
                {u"cedil"_s,  u"&#184;"_s}, // cedilla = spacing cedilla, U+00B8 ISOdia
                {u"sup1"_s,   u"&#185;"_s}, // superscript one = superscript digit one, U+00B9 ISOnum
                {u"ordm"_s,   u"&#186;"_s}, // masculine ordinal indicator, U+00BA ISOnum
                {u"raquo"_s,  u"&#187;"_s}, // right-pointing double angle quotation mark = right pointing guillemet, U+00BB ISOnum
                {u"frac14"_s, u"&#188;"_s}, // vulgar fraction one quarter = fraction one quarter, U+00BC ISOnum
                {u"frac12"_s, u"&#189;"_s}, // vulgar fraction one half = fraction one half, U+00BD ISOnum
                {u"frac34"_s, u"&#190;"_s}, // vulgar fraction three quarters = fraction three quarters, U+00BE ISOnum
                {u"iquest"_s, u"&#191;"_s}, // inverted question mark = turned question mark, U+00BF ISOnum
                {u"Agrave"_s, u"&#192;"_s}, // latin capital letter A with grave = latin capital letter A grave, U+00C0 ISOlat1
                {u"Aacute"_s, u"&#193;"_s}, // latin capital letter A with acute, U+00C1 ISOlat1
                {u"Acirc"_s,  u"&#194;"_s}, // latin capital letter A with circumflex, U+00C2 ISOlat1
                {u"Atilde"_s, u"&#195;"_s}, // latin capital letter A with tilde, U+00C3 ISOlat1
                {u"Auml"_s,   u"&#196;"_s}, // latin capital letter A with diaeresis, U+00C4 ISOlat1
                {u"Aring"_s,  u"&#197;"_s}, // latin capital letter A with ring above = latin capital letter A ring, U+00C5 ISOlat1
                {u"AElig"_s,  u"&#198;"_s}, // latin capital letter AE = latin capital ligature AE, U+00C6 ISOlat1
                {u"Ccedil"_s, u"&#199;"_s}, // latin capital letter C with cedilla, U+00C7 ISOlat1
                {u"Egrave"_s, u"&#200;"_s}, // latin capital letter E with grave, U+00C8 ISOlat1
                {u"Eacute"_s, u"&#201;"_s}, // latin capital letter E with acute, U+00C9 ISOlat1
                {u"Ecirc"_s,  u"&#202;"_s}, // latin capital letter E with circumflex, U+00CA ISOlat1
                {u"Euml"_s,   u"&#203;"_s}, // latin capital letter E with diaeresis, U+00CB ISOlat1
                {u"Igrave"_s, u"&#204;"_s}, // latin capital letter I with grave, U+00CC ISOlat1
                {u"Iacute"_s, u"&#205;"_s}, // latin capital letter I with acute, U+00CD ISOlat1
                {u"Icirc"_s,  u"&#206;"_s}, // latin capital letter I with circumflex, U+00CE ISOlat1
                {u"Iuml"_s,   u"&#207;"_s}, // latin capital letter I with diaeresis, U+00CF ISOlat1
                {u"ETH"_s,    u"&#208;"_s}, // latin capital letter ETH, U+00D0 ISOlat1
                {u"Ntilde"_s, u"&#209;"_s}, // latin capital letter N with tilde, U+00D1 ISOlat1
                {u"Ograve"_s, u"&#210;"_s}, // latin capital letter O with grave, U+00D2 ISOlat1
                {u"Oacute"_s, u"&#211;"_s}, // latin capital letter O with acute, U+00D3 ISOlat1
                {u"Ocirc"_s,  u"&#212;"_s}, // latin capital letter O with circumflex, U+00D4 ISOlat1
                {u"Otilde"_s, u"&#213;"_s}, // latin capital letter O with tilde, U+00D5 ISOlat1
                {u"Ouml"_s,   u"&#214;"_s}, // latin capital letter O with diaeresis, U+00D6 ISOlat1
                {u"times"_s,  u"&#215;"_s}, // multiplication sign, U+00D7 ISOnum
                {u"Oslash"_s, u"&#216;"_s}, // latin capital letter O with stroke = latin capital letter O slash, U+00D8 ISOlat1
                {u"Ugrave"_s, u"&#217;"_s}, // latin capital letter U with grave, U+00D9 ISOlat1
                {u"Uacute"_s, u"&#218;"_s}, // latin capital letter U with acute, U+00DA ISOlat1
                {u"Ucirc"_s,  u"&#219;"_s}, // latin capital letter U with circumflex, U+00DB ISOlat1
                {u"Uuml"_s,   u"&#220;"_s}, // latin capital letter U with diaeresis, U+00DC ISOlat1
                {u"Yacute"_s, u"&#221;"_s}, // latin capital letter Y with acute, U+00DD ISOlat1
                {u"THORN"_s,  u"&#222;"_s}, // latin capital letter THORN, U+00DE ISOlat1
                {u"szlig"_s,  u"&#223;"_s}, // latin small letter sharp s = ess-zed, U+00DF ISOlat1
                {u"agrave"_s, u"&#224;"_s}, // latin small letter a with grave = latin small letter a grave, U+00E0 ISOlat1
                {u"aacute"_s, u"&#225;"_s}, // latin small letter a with acute, U+00E1 ISOlat1
                {u"acirc"_s,  u"&#226;"_s}, // latin small letter a with circumflex, U+00E2 ISOlat1
                {u"atilde"_s, u"&#227;"_s}, // latin small letter a with tilde, U+00E3 ISOlat1
                {u"auml"_s,   u"&#228;"_s}, // latin small letter a with diaeresis, U+00E4 ISOlat1
                {u"aring"_s,  u"&#229;"_s}, // latin small letter a with ring above = latin small letter a ring, U+00E5 ISOlat1
                {u"aelig"_s,  u"&#230;"_s}, // latin small letter ae = latin small ligature ae, U+00E6 ISOlat1
                {u"ccedil"_s, u"&#231;"_s}, // latin small letter c with cedilla, U+00E7 ISOlat1
                {u"egrave"_s, u"&#232;"_s}, // latin small letter e with grave, U+00E8 ISOlat1
                {u"eacute"_s, u"&#233;"_s}, // latin small letter e with acute, U+00E9 ISOlat1
                {u"ecirc"_s,  u"&#234;"_s}, // latin small letter e with circumflex, U+00EA ISOlat1
                {u"euml"_s,   u"&#235;"_s}, // latin small letter e with diaeresis, U+00EB ISOlat1
                {u"igrave"_s, u"&#236;"_s}, // latin small letter i with grave, U+00EC ISOlat1
                {u"iacute"_s, u"&#237;"_s}, // latin small letter i with acute, U+00ED ISOlat1
                {u"icirc"_s,  u"&#238;"_s}, // latin small letter i with circumflex, U+00EE ISOlat1
                {u"iuml"_s,   u"&#239;"_s}, // latin small letter i with diaeresis, U+00EF ISOlat1
                {u"eth"_s,    u"&#240;"_s}, // latin small letter eth, U+00F0 ISOlat1
                {u"ntilde"_s, u"&#241;"_s}, // latin small letter n with tilde, U+00F1 ISOlat1
                {u"ograve"_s, u"&#242;"_s}, // latin small letter o with grave, U+00F2 ISOlat1
                {u"oacute"_s, u"&#243;"_s}, // latin small letter o with acute, U+00F3 ISOlat1
                {u"ocirc"_s,  u"&#244;"_s}, // latin small letter o with circumflex, U+00F4 ISOlat1
                {u"otilde"_s, u"&#245;"_s}, // latin small letter o with tilde, U+00F5 ISOlat1
                {u"ouml"_s,   u"&#246;"_s}, // latin small letter o with diaeresis, U+00F6 ISOlat1
                {u"divide"_s, u"&#247;"_s}, // division sign, U+00F7 ISOnum
                {u"oslash"_s, u"&#248;"_s}, // latin small letter o with stroke, = latin small letter o slash, U+00F8 ISOlat1
                {u"ugrave"_s, u"&#249;"_s}, // latin small letter u with grave, U+00F9 ISOlat1
                {u"uacute"_s, u"&#250;"_s}, // latin small letter u with acute, U+00FA ISOlat1
                {u"ucirc"_s,  u"&#251;"_s}, // latin small letter u with circumflex, U+00FB ISOlat1
                {u"uuml"_s,   u"&#252;"_s}, // latin small letter u with diaeresis, U+00FC ISOlat1
                {u"yacute"_s, u"&#253;"_s}, // latin small letter y with acute, U+00FD ISOlat1
                {u"thorn"_s,  u"&#254;"_s}, // latin small letter thorn, U+00FE ISOlat1
                {u"yuml"_s,   u"&#255;"_s}, // latin small letter y with diaeresis, U+00FF ISOlat1

                // Latin Extended-A
                {u"OElig"_s,   u"&#338;"_s}, //  latin capital ligature OE, U+0152 ISOlat2
                {u"oelig"_s,   u"&#339;"_s}, //  latin small ligature oe, U+0153 ISOlat2
                // ligature is a misnomer, this is a separate character in some languages
                {u"Scaron"_s,  u"&#352;"_s}, //  latin capital letter S with caron, U+0160 ISOlat2
                {u"scaron"_s,  u"&#353;"_s}, //  latin small letter s with caron, U+0161 ISOlat2
                {u"Yuml"_s,    u"&#376;"_s}, //  latin capital letter Y with diaeresis, U+0178 ISOlat2

                // Spacing Modifier Letters
                {u"circ"_s,    u"&#710;"_s}, //  modifier letter circumflex accent, U+02C6 ISOpub
                {u"tilde"_s,   u"&#732;"_s}, //  small tilde, U+02DC ISOdia

                // General Punctuation
                {u"ensp"_s,    u"&#8194;"_s}, // en space, U+2002 ISOpub
                {u"emsp"_s,    u"&#8195;"_s}, // em space, U+2003 ISOpub
                {u"thinsp"_s,  u"&#8201;"_s}, // thin space, U+2009 ISOpub
                {u"zwnj"_s,    u"&#8204;"_s}, // zero width non-joiner, U+200C NEW RFC 2070
                {u"zwj"_s,     u"&#8205;"_s}, // zero width joiner, U+200D NEW RFC 2070
                {u"lrm"_s,     u"&#8206;"_s}, // left-to-right mark, U+200E NEW RFC 2070
                {u"rlm"_s,     u"&#8207;"_s}, // right-to-left mark, U+200F NEW RFC 2070
                {u"ndash"_s,   u"&#8211;"_s}, // en dash, U+2013 ISOpub
                {u"mdash"_s,   u"&#8212;"_s}, // em dash, U+2014 ISOpub
                {u"lsquo"_s,   u"&#8216;"_s}, // left single quotation mark, U+2018 ISOnum
                {u"rsquo"_s,   u"&#8217;"_s}, // right single quotation mark, U+2019 ISOnum
                {u"sbquo"_s,   u"&#8218;"_s}, // single low-9 quotation mark, U+201A NEW
                {u"ldquo"_s,   u"&#8220;"_s}, // left double quotation mark, U+201C ISOnum
                {u"rdquo"_s,   u"&#8221;"_s}, // right double quotation mark, U+201D ISOnum
                {u"bdquo"_s,   u"&#8222;"_s}, // double low-9 quotation mark, U+201E NEW
                {u"dagger"_s,  u"&#8224;"_s}, // dagger, U+2020 ISOpub
                {u"Dagger"_s,  u"&#8225;"_s}, // double dagger, U+2021 ISOpub
                {u"permil"_s,  u"&#8240;"_s}, // per mille sign, U+2030 ISOtech
                {u"lsaquo"_s,  u"&#8249;"_s}, // single left-pointing angle quotation mark, U+2039 ISO proposed
                // lsaquo is proposed but not yet ISO standardized
                {u"rsaquo"_s,  u"&#8250;"_s}, // single right-pointing angle quotation mark, U+203A ISO proposed
                // rsaquo is proposed but not yet ISO standardized

                // Currency Symbols
                {u"euro"_s,   u"&#8364;"_s}, //  euro sign, U+20AC NEW

                // Latin Extended-B
                {u"fnof"_s,     u"&#402;"_s}, // latin small letter f with hook = function   = florin, U+0192 ISOtech

                // Greek
                {u"Alpha"_s,    u"&#913;"_s}, // greek capital letter alpha, U+0391
                {u"Beta"_s,     u"&#914;"_s}, // greek capital letter beta, U+0392
                {u"Gamma"_s,    u"&#915;"_s}, // greek capital letter gamma, U+0393 ISOgrk3
                {u"Delta"_s,    u"&#916;"_s}, // greek capital letter delta, U+0394 ISOgrk3
                {u"Epsilon"_s,  u"&#917;"_s}, // greek capital letter epsilon, U+0395
                {u"Zeta"_s,     u"&#918;"_s}, // greek capital letter zeta, U+0396
                {u"Eta"_s,      u"&#919;"_s}, // greek capital letter eta, U+0397
                {u"Theta"_s,    u"&#920;"_s}, // greek capital letter theta, U+0398 ISOgrk3
                {u"Iota"_s,     u"&#921;"_s}, // greek capital letter iota, U+0399
                {u"Kappa"_s,    u"&#922;"_s}, // greek capital letter kappa, U+039A
                {u"Lambda"_s,   u"&#923;"_s}, // greek capital letter lambda, U+039B ISOgrk3
                {u"Mu"_s,       u"&#924;"_s}, // greek capital letter mu, U+039C
                {u"Nu"_s,       u"&#925;"_s}, // greek capital letter nu, U+039D
                {u"Xi"_s,       u"&#926;"_s}, // greek capital letter xi, U+039E ISOgrk3
                {u"Omicron"_s,  u"&#927;"_s}, // greek capital letter omicron, U+039F
                {u"Pi"_s,       u"&#928;"_s}, // greek capital letter pi, U+03A0 ISOgrk3
                {u"Rho"_s,      u"&#929;"_s}, // greek capital letter rho, U+03A1
                {u"Sigma"_s,    u"&#931;"_s}, // greek capital letter sigma, U+03A3 ISOgrk3
                {u"Tau"_s,      u"&#932;"_s}, // greek capital letter tau, U+03A4
                {u"Upsilon"_s,  u"&#933;"_s}, // greek capital letter upsilon, U+03A5 ISOgrk3
                {u"Phi"_s,      u"&#934;"_s}, // greek capital letter phi, U+03A6 ISOgrk3
                {u"Chi"_s,      u"&#935;"_s}, // greek capital letter chi, U+03A7
                {u"Psi"_s,      u"&#936;"_s}, // greek capital letter psi, U+03A8 ISOgrk3
                {u"Omega"_s,    u"&#937;"_s}, // greek capital letter omega, U+03A9 ISOgrk3
                {u"alpha"_s,    u"&#945;"_s}, // greek small letter alpha, U+03B1 ISOgrk3
                {u"beta"_s,     u"&#946;"_s}, // greek small letter beta, U+03B2 ISOgrk3
                {u"gamma"_s,    u"&#947;"_s}, // greek small letter gamma, U+03B3 ISOgrk3
                {u"delta"_s,    u"&#948;"_s}, // greek small letter delta, U+03B4 ISOgrk3
                {u"epsilon"_s,  u"&#949;"_s}, // greek small letter epsilon, U+03B5 ISOgrk3
                {u"zeta"_s,     u"&#950;"_s}, // greek small letter zeta, U+03B6 ISOgrk3
                {u"eta"_s,      u"&#951;"_s}, // greek small letter eta, U+03B7 ISOgrk3
                {u"theta"_s,    u"&#952;"_s}, // greek small letter theta, U+03B8 ISOgrk3
                {u"iota"_s,     u"&#953;"_s}, // greek small letter iota, U+03B9 ISOgrk3
                {u"kappa"_s,    u"&#954;"_s}, // greek small letter kappa, U+03BA ISOgrk3
                {u"lambda"_s,   u"&#955;"_s}, // greek small letter lambda, U+03BB ISOgrk3
                {u"mu"_s,       u"&#956;"_s}, // greek small letter mu, U+03BC ISOgrk3
                {u"nu"_s,       u"&#957;"_s}, // greek small letter nu, U+03BD ISOgrk3
                {u"xi"_s,       u"&#958;"_s}, // greek small letter xi, U+03BE ISOgrk3
                {u"omicron"_s,  u"&#959;"_s}, // greek small letter omicron, U+03BF NEW
                {u"pi"_s,       u"&#960;"_s}, // greek small letter pi, U+03C0 ISOgrk3
                {u"rho"_s,      u"&#961;"_s}, // greek small letter rho, U+03C1 ISOgrk3
                {u"sigmaf"_s,   u"&#962;"_s}, // greek small letter final sigma, U+03C2 ISOgrk3
                {u"sigma"_s,    u"&#963;"_s}, // greek small letter sigma, U+03C3 ISOgrk3
                {u"tau"_s,      u"&#964;"_s}, // greek small letter tau, U+03C4 ISOgrk3
                {u"upsilon"_s,  u"&#965;"_s}, // greek small letter upsilon, U+03C5 ISOgrk3
                {u"phi"_s,      u"&#966;"_s}, // greek small letter phi, U+03C6 ISOgrk3
                {u"chi"_s,      u"&#967;"_s}, // greek small letter chi, U+03C7 ISOgrk3
                {u"psi"_s,      u"&#968;"_s}, // greek small letter psi, U+03C8 ISOgrk3
                {u"omega"_s,    u"&#969;"_s}, // greek small letter omega, U+03C9 ISOgrk3
                {u"thetasym"_s, u"&#977;"_s}, // greek theta symbol, U+03D1 NEW
                {u"upsih"_s,    u"&#978;"_s}, // greek upsilon with hook symbol, U+03D2 NEW
                {u"piv"_s,      u"&#982;"_s}, // greek pi symbol, U+03D6 ISOgrk3

                // General Punctuation
                {u"bull"_s,     u"&#8226;"_s}, // bullet = black small circle, U+2022 ISOpub
                // bullet is NOT the same as bullet operator, U+2219
                {u"hellip"_s,   u"&#8230;"_s}, // horizontal ellipsis = three dot leader, U+2026 ISOpub
                {u"prime"_s,    u"&#8242;"_s}, // prime = minutes = feet, U+2032 ISOtech
                {u"Prime"_s,    u"&#8243;"_s}, // double prime = seconds = inches, U+2033 ISOtech
                {u"oline"_s,    u"&#8254;"_s}, // overline = spacing overscore, U+203E NEW
                {u"frasl"_s,    u"&#8260;"_s}, // fraction slash, U+2044 NEW

                // Letterlike Symbols
                {u"weierp"_s,   u"&#8472;"_s}, // script capital P = power set = Weierstrass p, U+2118 ISOamso
                {u"image"_s,    u"&#8465;"_s}, // black-letter capital I = imaginary part, U+2111 ISOamso
                {u"real"_s,     u"&#8476;"_s}, // black-letter capital R = real part symbol, U+211C ISOamso
                {u"trade"_s,    u"&#8482;"_s}, // trade mark sign, U+2122 ISOnum
                {u"alefsym"_s,  u"&#8501;"_s}, // alef symbol = first transfinite cardinal, U+2135 NEW
                // alef symbol is NOT the same as hebrew letter alef,
                //     U+05D0 although the same glyph could be used to depict both characters

                // Arrows
                {u"larr"_s,     u"&#8592;"_s}, // leftwards arrow, U+2190 ISOnum
                {u"uarr"_s,     u"&#8593;"_s}, // upwards arrow, U+2191 ISOnum
                {u"rarr"_s,     u"&#8594;"_s}, // rightwards arrow, U+2192 ISOnum
                {u"darr"_s,     u"&#8595;"_s}, // downwards arrow, U+2193 ISOnum
                {u"harr"_s,     u"&#8596;"_s}, // left right arrow, U+2194 ISOamsa
                {u"crarr"_s,    u"&#8629;"_s}, // downwards arrow with corner leftwards = carriage return, U+21B5 NEW
                {u"lArr"_s,     u"&#8656;"_s}, // leftwards double arrow, U+21D0 ISOtech
                // Unicode does not say that lArr is the same as the 'is implied by' arrow
                //    but also does not have any other character for that function. So lArr can
                //    be used for 'is implied by' as ISOtech suggests
                {u"uArr"_s,     u"&#8657;"_s}, // upwards double arrow, U+21D1 ISOamsa
                {u"rArr"_s,     u"&#8658;"_s}, // rightwards double arrow, U+21D2 ISOtech
                // Unicode does not say this is the 'implies' character but does not have
                //     another character with this function so rArr can be used for 'implies'
                //     as ISOtech suggests
                {u"dArr"_s,     u"&#8659;"_s}, // downwards double arrow, U+21D3 ISOamsa
                {u"hArr"_s,     u"&#8660;"_s}, // left right double arrow, U+21D4 ISOamsa

                // Mathematical Operators
                {u"forall"_s,   u"&#8704;"_s}, // for all, U+2200 ISOtech
                {u"part"_s,     u"&#8706;"_s}, // partial differential, U+2202 ISOtech
                {u"exist"_s,    u"&#8707;"_s}, // there exists, U+2203 ISOtech
                {u"empty"_s,    u"&#8709;"_s}, // empty set = null set, U+2205 ISOamso
                {u"nabla"_s,    u"&#8711;"_s}, // nabla = backward difference, U+2207 ISOtech
                {u"isin"_s,     u"&#8712;"_s}, // element of, U+2208 ISOtech
                {u"notin"_s,    u"&#8713;"_s}, // not an element of, U+2209 ISOtech
                {u"ni"_s,       u"&#8715;"_s}, // contains as member, U+220B ISOtech
                {u"prod"_s,     u"&#8719;"_s}, // n-ary product = product sign, U+220F ISOamsb
                // prod is NOT the same character as U+03A0 'greek capital letter pi' though
                //     the same glyph might be used for both
                {u"sum"_s,      u"&#8721;"_s}, // n-ary summation, U+2211 ISOamsb
                // sum is NOT the same character as U+03A3 'greek capital letter sigma'
                //     though the same glyph might be used for both
                {u"minus"_s,    u"&#8722;"_s}, // minus sign, U+2212 ISOtech
                {u"lowast"_s,   u"&#8727;"_s}, // asterisk operator, U+2217 ISOtech
                {u"radic"_s,    u"&#8730;"_s}, // square root = radical sign, U+221A ISOtech
                {u"prop"_s,     u"&#8733;"_s}, // proportional to, U+221D ISOtech
                {u"infin"_s,    u"&#8734;"_s}, // infinity, U+221E ISOtech
                {u"ang"_s,      u"&#8736;"_s}, // angle, U+2220 ISOamso
                {u"and"_s,      u"&#8743;"_s}, // logical and = wedge, U+2227 ISOtech
                {u"or"_s,       u"&#8744;"_s}, // logical or = vee, U+2228 ISOtech
                {u"cap"_s,      u"&#8745;"_s}, // intersection = cap, U+2229 ISOtech
                {u"cup"_s,      u"&#8746;"_s}, // union = cup, U+222A ISOtech
                {u"int"_s,      u"&#8747;"_s}, // integral, U+222B ISOtech
                {u"there4"_s,   u"&#8756;"_s}, // therefore, U+2234 ISOtech
                {u"sim"_s,      u"&#8764;"_s}, // tilde operator = varies with = similar to, U+223C ISOtech
                // tilde operator is NOT the same character as the tilde, U+007E,
                //     although the same glyph might be used to represent both
                {u"cong"_s,     u"&#8773;"_s}, // approximately equal to, U+2245 ISOtech
                {u"asymp"_s,    u"&#8776;"_s}, // almost equal to = asymptotic to, U+2248 ISOamsr
                {u"ne"_s,       u"&#8800;"_s}, // not equal to, U+2260 ISOtech
                {u"equiv"_s,    u"&#8801;"_s}, // identical to, U+2261 ISOtech
                {u"le"_s,       u"&#8804;"_s}, // less-than or equal to, U+2264 ISOtech
                {u"ge"_s,       u"&#8805;"_s}, // greater-than or equal to, U+2265 ISOtech
                {u"sub"_s,      u"&#8834;"_s}, // subset of, U+2282 ISOtech
                {u"sup"_s,      u"&#8835;"_s}, // superset of, U+2283 ISOtech
                {u"nsub"_s,     u"&#8836;"_s}, // not a subset of, U+2284 ISOamsn
                {u"sube"_s,     u"&#8838;"_s}, // subset of or equal to, U+2286 ISOtech
                {u"supe"_s,     u"&#8839;"_s}, // superset of or equal to, U+2287 ISOtech
                {u"oplus"_s,    u"&#8853;"_s}, // circled plus = direct sum, U+2295 ISOamsb
                {u"otimes"_s,   u"&#8855;"_s}, // circled times = vector product, U+2297 ISOamsb
                {u"perp"_s,     u"&#8869;"_s}, // up tack = orthogonal to = perpendicular, U+22A5 ISOtech
                {u"sdot"_s,     u"&#8901;"_s}, // dot operator, U+22C5 ISOamsb
                // dot operator is NOT the same character as U+00B7 middle dot

                // Miscellaneous Technical
                {u"lceil"_s,    u"&#8968;"_s}, // left ceiling = APL upstile, U+2308 ISOamsc
                {u"rceil"_s,    u"&#8969;"_s}, // right ceiling, U+2309 ISOamsc
                {u"lfloor"_s,   u"&#8970;"_s}, // left floor = APL downstile, U+230A ISOamsc
                {u"rfloor"_s,   u"&#8971;"_s}, // right floor, U+230B ISOamsc
                {u"lang"_s,     u"&#9001;"_s}, // left-pointing angle bracket = bra, U+2329 ISOtech
                // lang is NOT the same character as U+003C 'less than sign'
                //     or U+2039 'single left-pointing angle quotation mark'
                {u"rang"_s,     u"&#9002;"_s}, // right-pointing angle bracket = ket, U+232A ISOtech
                // rang is NOT the same character as U+003E 'greater than sign'
                //     or U+203A 'single right-pointing angle quotation mark'

                // Geometric Shapes
                {u"loz"_s,      u"&#9674;"_s}, // lozenge, U+25CA ISOpub

                // Miscellaneous Symbols
                {u"spades"_s,   u"&#9824;"_s}, // black spade suit, U+2660 ISOpub
                {u"clubs"_s,    u"&#9827;"_s}, // black club suit = shamrock, U+2663 ISOpub
                {u"hearts"_s,   u"&#9829;"_s}, // black heart suit = valentine, U+2665 ISOpub
                {u"diams"_s,    u"&#9830;"_s}  // black diamond suit, U+2666 ISOpub
            };
            return HTMLEntities.value(name);
        }
    };

    // Ported to Qt from KDElibs4
    QDateTime parseDate(const QString &string)
    {
        const char16_t shortDay[][4] =
        {
            u"Mon", u"Tue", u"Wed",
            u"Thu", u"Fri", u"Sat",
            u"Sun"
        };
        const char16_t longDay[][10] =
        {
            u"Monday", u"Tuesday", u"Wednesday",
            u"Thursday", u"Friday", u"Saturday",
            u"Sunday"
        };
        const char16_t shortMonth[][4] =
        {
            u"Jan", u"Feb", u"Mar", u"Apr",
            u"May", u"Jun", u"Jul", u"Aug",
            u"Sep", u"Oct", u"Nov", u"Dec"
        };

        const QString str = string.trimmed();
        if (str.isEmpty())
            return QDateTime::currentDateTime();

        int nyear  = 6;   // indexes within string to values
        int nmonth = 4;
        int nday   = 2;
        int nwday  = 1;
        int nhour  = 7;
        int nmin   = 8;
        int nsec   = 9;
        // Also accept obsolete form "Weekday, DD-Mon-YY HH:MM:SS ±hhmm"
        QRegularExpression rx {u"^(?:([A-Z][a-z]+),\\s*)?(\\d{1,2})(\\s+|-)([^-\\s]+)(\\s+|-)(\\d{2,4})\\s+(\\d\\d):(\\d\\d)(?::(\\d\\d))?\\s+(\\S+)$"_s};
        QRegularExpressionMatch rxMatch;
        QStringList parts;
        if (str.indexOf(rx, 0, &rxMatch) == 0)
        {
            // Check that if date has '-' separators, both separators are '-'.
            parts = rxMatch.capturedTexts();
            const bool h1 = (parts[3] == u"-");
            const bool h2 = (parts[5] == u"-");
            if (h1 != h2)
                return QDateTime::currentDateTime();
        }
        else
        {
            // Check for the obsolete form "Wdy Mon DD HH:MM:SS YYYY"
            rx = QRegularExpression {u"^([A-Z][a-z]+)\\s+(\\S+)\\s+(\\d\\d)\\s+(\\d\\d):(\\d\\d):(\\d\\d)\\s+(\\d\\d\\d\\d)$"_s};
            if (str.indexOf(rx, 0, &rxMatch) != 0)
                return QDateTime::currentDateTime();

            nyear  = 7;
            nmonth = 2;
            nday   = 3;
            nwday  = 1;
            nhour  = 4;
            nmin   = 5;
            nsec   = 6;
            parts = rxMatch.capturedTexts();
        }

        bool ok[4];
        const int day = parts[nday].toInt(&ok[0]);
        int year = parts[nyear].toInt(&ok[1]);
        const int hour = parts[nhour].toInt(&ok[2]);
        const int minute = parts[nmin].toInt(&ok[3]);
        if (!ok[0] || !ok[1] || !ok[2] || !ok[3])
            return QDateTime::currentDateTime();

        int second = 0;
        if (!parts[nsec].isEmpty())
        {
            second = parts[nsec].toInt(&ok[0]);
            if (!ok[0])
                return QDateTime::currentDateTime();
        }

        const bool leapSecond = (second == 60);
        if (leapSecond)
            second = 59;   // apparently a leap second - validate below, once time zone is known
        int month = 0;
        for ( ; (month < 12) && (parts[nmonth] != shortMonth[month]); ++month);
        int dayOfWeek = -1;
        if (!parts[nwday].isEmpty())
        {
            // Look up the weekday name
            while ((++dayOfWeek < 7) && (shortDay[dayOfWeek] != parts[nwday]));
            if (dayOfWeek >= 7)
                for (dayOfWeek = 0; (dayOfWeek < 7) && (longDay[dayOfWeek] != parts[nwday]); ++dayOfWeek);
        }

        //       if (month >= 12 || dayOfWeek >= 7
        //       ||  (dayOfWeek < 0  &&  format == RFCDateDay))
        //         return QDateTime;
        const int i = parts[nyear].size();
        if (i < 4)
        {
            // It's an obsolete year specification with less than 4 digits
            year += ((i == 2) && (year < 50)) ? 2000 : 1900;
        }

        // Parse the UTC offset part
        int offset = 0;           // set default to '-0000'
        bool negOffset = false;
        if (parts.count() > 10)
        {
            rx = QRegularExpression {u"^([+-])(\\d\\d)(\\d\\d)$"_s};
            if (parts[10].indexOf(rx, 0, &rxMatch) == 0)
            {
                // It's a UTC offset ±hhmm
                parts = rxMatch.capturedTexts();
                offset = parts[2].toInt(&ok[0]) * 3600;
                const int offsetMin = parts[3].toInt(&ok[1]);
                if (!ok[0] || !ok[1] || offsetMin > 59)
                    return {};
                offset += offsetMin * 60;
                negOffset = (parts[1] == u"-");
                if (negOffset)
                    offset = -offset;
            }
            else
            {
                // Check for an obsolete time zone name
                const QByteArray zone = parts[10].toLatin1();
                if ((zone.length() == 1) && (isalpha(zone[0])) && (toupper(zone[0]) != 'J'))
                {
                    negOffset = true;    // military zone: RFC 2822 treats as '-0000'
                }
                else if ((zone != "UT") && (zone != "GMT"))
                { // treated as '+0000'
                    offset = (zone == "EDT")
                            ? -4 * 3600
                            : ((zone == "EST") || (zone == "CDT"))
                              ? -5 * 3600
                              : ((zone == "CST") || (zone == "MDT"))
                                ? -6 * 3600
                                : ((zone == "MST") || (zone == "PDT"))
                                  ? -7 * 3600
                                  : (zone == "PST")
                                    ? -8 * 3600
                                    : 0;
                    if (!offset)
                    {
                        // Check for any other alphabetic time zone
                        bool nonalpha = false;
                        for (int i = 0, end = zone.size(); (i < end) && !nonalpha; ++i)
                            nonalpha = !isalpha(zone[i]);
                        if (nonalpha)
                            return {};
                        // TODO: Attempt to recognize the time zone abbreviation?
                        negOffset = true;    // unknown time zone: RFC 2822 treats as '-0000'
                    }
                }
            }
        }

        const QDate qDate(year, month + 1, day);   // convert date, and check for out-of-range
        if (!qDate.isValid())
            return QDateTime::currentDateTime();

        const QTime qTime(hour, minute, second);
        QDateTime result(qDate, qTime, Qt::UTC);
        if (offset)
            result = result.addSecs(-offset);
        if (!result.isValid())
            return QDateTime::currentDateTime();    // invalid date/time

        if (leapSecond)
        {
            // Validate a leap second time. Leap seconds are inserted after 23:59:59 UTC.
            // Convert the time to UTC and check that it is 00:00:00.
            if ((hour*3600 + minute*60 + 60 - offset + 86400*5) % 86400)   // (max abs(offset) is 100 hours)
                return QDateTime::currentDateTime();    // the time isn't the last second of the day
        }

        return result;
    }
}

const int PARSINGRESULT_TYPEID = qRegisterMetaType<RSS::Private::ParsingResult>();

RSS::Private::Parser::Parser(const QString &lastBuildDate)
{
    m_result.lastBuildDate = lastBuildDate;
}

// read and create items from a rss document
void RSS::Private::Parser::parse(const QByteArray &feedData)
{
    QXmlStreamReader xml {feedData};
    XmlStreamEntityResolver resolver;
    xml.setEntityResolver(&resolver);
    bool foundChannel = false;

    while (xml.readNextStartElement())
    {
        if (xml.name() == u"rss")
        {
            // Find channels
            while (xml.readNextStartElement())
            {
                if (xml.name() == u"channel")
                {
                    parseRSSChannel(xml);
                    foundChannel = true;
                    break;
                }

                qDebug() << "Skip rss item: " << xml.name();
                xml.skipCurrentElement();
            }
            break;
        }
        if (xml.name() == u"feed")
        { // Atom feed
            parseAtomChannel(xml);
            foundChannel = true;
            break;
        }

        qDebug() << "Skip root item: " << xml.name();
        xml.skipCurrentElement();
    }

    if (xml.hasError())
    {
        m_result.error = tr("%1 (line: %2, column: %3, offset: %4).")
                .arg(xml.errorString()).arg(xml.lineNumber())
                .arg(xml.columnNumber()).arg(xml.characterOffset());
    }
    else if (!foundChannel)
    {
        m_result.error = tr("Invalid RSS feed.");
    }

    emit finished(m_result);
    m_result.articles.clear();
    m_result.error.clear();
    m_articleIDs.clear();
}

void RSS::Private::Parser::parseRssArticle(QXmlStreamReader &xml)
{
    QVariantHash article;
    QString altTorrentUrl;

    while (!xml.atEnd())
    {
        xml.readNext();
        const QString name(xml.name().toString());

        if (xml.isEndElement() && (name == u"item"))
            break;

        if (xml.isStartElement())
        {
            if (name == u"title")
            {
                article[Article::KeyTitle] = xml.readElementText().trimmed();
            }
            else if (name == u"enclosure")
            {
                if (xml.attributes().value(u"type"_s) == u"application/x-bittorrent")
                    article[Article::KeyTorrentURL] = xml.attributes().value(u"url"_s).toString();
                else if (xml.attributes().value(u"type"_s).isEmpty())
                    altTorrentUrl = xml.attributes().value(u"url"_s).toString();
            }
            else if (name == u"link")
            {
                const QString text {xml.readElementText().trimmed()};
                if (text.startsWith(u"magnet:", Qt::CaseInsensitive))
                    article[Article::KeyTorrentURL] = text; // magnet link instead of a news URL
                else
                    article[Article::KeyLink] = text;
            }
            else if (name == u"description")
            {
                article[Article::KeyDescription] = xml.readElementText(QXmlStreamReader::IncludeChildElements);
            }
            else if (name == u"pubDate")
            {
                article[Article::KeyDate] = parseDate(xml.readElementText().trimmed());
            }
            else if (name == u"author")
            {
                article[Article::KeyAuthor] = xml.readElementText().trimmed();
            }
            else if (name == u"guid")
            {
                article[Article::KeyId] = xml.readElementText().trimmed();
            }
            else
            {
                article[name] = xml.readElementText(QXmlStreamReader::IncludeChildElements);
            }
        }
    }

    if (article[Article::KeyTorrentURL].toString().isEmpty())
        article[Article::KeyTorrentURL] = altTorrentUrl;

    addArticle(article);
}

void RSS::Private::Parser::parseRSSChannel(QXmlStreamReader &xml)
{
    while (!xml.atEnd())
    {
        xml.readNext();

        if (xml.isStartElement())
        {
            if (xml.name() == u"title")
            {
                m_result.title = xml.readElementText();
            }
            else if (xml.name() == u"lastBuildDate")
            {
                const QString lastBuildDate = xml.readElementText();
                if (!lastBuildDate.isEmpty())
                {
                    if (m_result.lastBuildDate == lastBuildDate)
                    {
                        qDebug() << "The RSS feed has not changed since last time, aborting parsing.";
                        return;
                    }
                    m_result.lastBuildDate = lastBuildDate;
                }
            }
            else if (xml.name() == u"item")
            {
                parseRssArticle(xml);
            }
        }
    }
}

void RSS::Private::Parser::parseAtomArticle(QXmlStreamReader &xml)
{
    QVariantHash article;
    bool doubleContent = false;

    while (!xml.atEnd())
    {
        xml.readNext();
        const QString name(xml.name().toString());

        if (xml.isEndElement() && (name == u"entry"))
            break;

        if (xml.isStartElement())
        {
            if (name == u"title")
            {
                article[Article::KeyTitle] = xml.readElementText().trimmed();
            }
            else if (name == u"link")
            {
                const QString link = (xml.attributes().isEmpty()
                                ? xml.readElementText().trimmed()
                                : xml.attributes().value(u"href"_s).toString());

                if (link.startsWith(u"magnet:", Qt::CaseInsensitive))
                {
                    article[Article::KeyTorrentURL] = link; // magnet link instead of a news URL
                }
                else
                {
                    // Atom feeds can have relative links, work around this and
                    // take the stress of figuring article full URI from UI
                    // Assemble full URI
                    article[Article::KeyLink] = (m_baseUrl.isEmpty() ? link : m_baseUrl + link);
                }
            }
            else if ((name == u"summary") || (name == u"content"))
            {
                if (doubleContent)
                { // Duplicate content -> ignore
                    xml.skipCurrentElement();
                    continue;
                }

                // Try to also parse broken articles, which don't use html '&' escapes
                // Actually works great for non-broken content too
                const QString feedText = xml.readElementText(QXmlStreamReader::IncludeChildElements).trimmed();
                if (!feedText.isEmpty())
                {
                    article[Article::KeyDescription] = feedText;
                    doubleContent = true;
                }
            }
            else if (name == u"updated")
            {
                // ATOM uses standard compliant date, don't do fancy stuff
                const QDateTime articleDate = QDateTime::fromString(xml.readElementText().trimmed(), Qt::ISODate);
                article[Article::KeyDate] = (articleDate.isValid() ? articleDate : QDateTime::currentDateTime());
            }
            else if (name == u"author")
            {
                while (xml.readNextStartElement())
                {
                    if (xml.name() == u"name")
                        article[Article::KeyAuthor] = xml.readElementText().trimmed();
                    else
                        xml.skipCurrentElement();
                }
            }
            else if (name == u"id")
            {
                article[Article::KeyId] = xml.readElementText().trimmed();
            }
            else
            {
                article[name] = xml.readElementText(QXmlStreamReader::IncludeChildElements);
            }
        }
    }

    addArticle(article);
}

void RSS::Private::Parser::parseAtomChannel(QXmlStreamReader &xml)
{
    m_baseUrl = xml.attributes().value(u"xml:base"_s).toString();

    while (!xml.atEnd())
    {
        xml.readNext();

        if (xml.isStartElement())
        {
            if (xml.name() == u"title")
            {
                m_result.title = xml.readElementText();
            }
            else if (xml.name() == u"updated")
            {
                const QString lastBuildDate = xml.readElementText();
                if (!lastBuildDate.isEmpty())
                {
                    if (m_result.lastBuildDate == lastBuildDate)
                    {
                        qDebug() << "The RSS feed has not changed since last time, aborting parsing.";
                        return;
                    }
                    m_result.lastBuildDate = lastBuildDate;
                }
            }
            else if (xml.name() == u"entry")
            {
                parseAtomArticle(xml);
            }
        }
    }
}

void RSS::Private::Parser::addArticle(QVariantHash article)
{
    QVariant &torrentURL = article[Article::KeyTorrentURL];
    if (torrentURL.toString().isEmpty())
        torrentURL = article.value(Article::KeyLink);

    // If item does not have an ID, fall back to some other identifier.
    QVariant &localId = article[Article::KeyId];
    if (localId.toString().isEmpty())
    {
        localId = article.value(Article::KeyTorrentURL);
        if (localId.toString().isEmpty())
        {
            localId = article.value(Article::KeyTitle);
            if (localId.toString().isEmpty())
            {
                // The article could not be uniquely identified
                // since it has no appropriate data.
                // Just ignore it.
                return;
            }
        }
    }

    if (m_articleIDs.contains(localId.toString()))
    {
        // The article could not be uniquely identified
        // since the Feed has duplicate identifiers.
        // Just ignore it.
        return;
    }

    m_articleIDs.insert(localId.toString());
    m_result.articles.prepend(article);
}