/**************************************************************************
 *                                                                        *
 *  Regina - A Normal Surface Theory Calculator                           *
 *  Computational Engine                                                  *
 *                                                                        *
 *  Copyright (c) 1999-2025, Ben Burton                                   *
 *  For further details contact Ben Burton (bab@debian.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.                       *
 *                                                                        *
 *  As an exception, when this program is distributed through (i) the     *
 *  App Store by Apple Inc.; (ii) the Mac App Store by Apple Inc.; or     *
 *  (iii) Google Play by Google Inc., then that store may impose any      *
 *  digital rights management, device limits and/or redistribution        *
 *  restrictions that are required by its terms of service.               *
 *                                                                        *
 *  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, see <https://www.gnu.org/licenses/>. *
 *                                                                        *
 **************************************************************************/

#include <cstring>
#include <fstream>
#include "core/engine.h"
#include "file/xml/xmlcallback.h"
#include "file/xml/xmlpacketreader.h"
#include "file/xml/xmltreeresolver.h"
#include "file/xml/xmltrireader.h"
#include "packet/container.h"
#include "utilities/stringutils.h"
#include "utilities/zstr.h"

namespace regina {

namespace {
    /**
     * Reads the outermost \<regina ...\> or \<reginadata ...\> XML element.
     */
    class ReginaDataReader : public regina::XMLPacketReader {
        private:
            std::shared_ptr<Container> container;
                /**< Sits above the entire packet tree read from file. */
            bool isReginaData;
                /**< Are we actually reading a \<regina ...\> or
                     \<reginadata ...\> element? */
            std::string version_;
                /**< The version of Regina that created this file, or
                     the empty string if this is not known. */

        public:
            /**
             * Create a new top-level reader.
             */
            ReginaDataReader(XMLTreeResolver& resolver) :
                    XMLPacketReader(resolver, nullptr, false, {}, {}),
                    container(new Container()), isReginaData(false) {
            }

            std::shared_ptr<Packet> packetToCommit() override {
                if (isReginaData)
                    return container;
                else
                    return nullptr;
            }

            const std::string& version() const {
                return version_;
            }

            void startElement(const std::string& n,
                    const regina::xml::XMLPropertyDict& props,
                    XMLElementReader*) override {
                if (n == "regina" || n == "reginadata") {
                    isReginaData = true;

                    auto it = props.find("engine");
                    if (it != props.end())
                        version_ = stripWhitespace(it->second);
                }
            }
    };

    /**
     * The number of characters by which we expect to have finished the
     * <reginadata ...> opening tag in an old pre-utf8 XML data stream.
     */
    const int regDataOpenBy = 200;

    /**
     * The size of the XML chunks that are sent through to libxml2 for parsing.
     *
     * Since we plan to perform surgery on pre-utf8 data streams, the chunk
     * size must be large enough to catch the regina engine version in the
     * first bite.  In particular, we require regChunkSize > regDataOpenBy.
     */
    const int regChunkSize = 1024;
}

std::shared_ptr<Packet> open(const char* filename) {
    std::ifstream file(filename, std::ios_base::in | std::ios_base::binary);
    // We don't test whether the file was opened, since open(std::istream&)
    // tests this for us as the first thing it does.
    return regina::open(file);
}

std::shared_ptr<Packet> open(std::istream& s) {
    // Note: open(const char*) relies on us testing here whether s was
    // successfully opened.  If anyone removes this test, then they
    // should add a corresponding test to open(const char*) instead.
    if (! s)
        return nullptr;

    // We declare buf outside the try-catch block because it is dynamically
    // allocated, and so we need to deallocate it if an exception is caught.
    char* buf = nullptr;

    // The following try-catch block is to catch decompression errors.
    try {
        zstr::istream in(s); // Can handle both compressed and uncompressed.

        XMLTreeResolver resolver;

        ReginaDataReader reader(resolver);
        regina::XMLCallback callback(reader, std::cerr);

        // Instead of using the simpler regina::xml::XMLParser::parse_stream(),
        // we split the stream into parseable chunks manually.  This allows us
        // to perform surgery on pre-utf8 streams and tell the parser that old
        // files actually store their data in latin1 (which the old file format
        // neglected to specify in the XML prologue).
        {
            regina::xml::XMLParser parser(callback);

            buf = new char[regChunkSize];
            int chunkRead;
            bool seenFirstChunk = false;
            while (callback.state() != XMLCallback::State::Aborted) {
                // Read in the next chunk.
                try {
                    for (chunkRead = 0; chunkRead < regChunkSize; ++chunkRead) {
                        int c = in.get();
                        if (c == EOF)
                            break;
                        buf[chunkRead] = static_cast<char>(c);
                    }
                } catch (const zstr::Exception& e) {
                    std::cerr << "ERROR: Could not read stream: "
                        << e.what() << std::endl;
                    delete[] buf;
                    return nullptr;
                }
                if (chunkRead == 0)
                    break;

                // Parse the chunk that has just been read.
                // Interesting things (i.e., surgery) can only happen in the
                // first chunk.
                if (seenFirstChunk) {
                    parser.parse_chunk(std::string(buf, chunkRead));
                    continue;
                }

                seenFirstChunk = true;

                // This is the first chunk in the data stream.  See if we
                // need to perform surgery upon it.
                //
                // We will be fairly rigid in looking for substrings, since
                // we are only trying to match old pre-utf8 data files.  If
                // future versions of the calculation engine change the
                // opening "signature" then this does not matter, since they
                // will not need surgery anyway.
                //
                // If anything looks out of place, just abort the surgery
                // and send everything straight through to the XML parser,
                // in the hope that either the file is new enough to not
                // need surgery (i.e., it uses utf8 already) or it's old but
                // only uses plain ASCII.

                char tmp = buf[regDataOpenBy];
                buf[regDataOpenBy] = 0;

                char* start = ::strstr(buf, "<reginadata engine=\"");
                if (! start) {
                    buf[regDataOpenBy] = tmp;
                    parser.parse_chunk(std::string(buf, chunkRead));
                    continue;
                }
                start += 20; /* Length of "<reginadata engine=\"" */

                char* finish = ::strchr(start, '"');
                if ((! finish) || finish == start) {
                    // Never found a closing quote, or else the engine version
                    // string is empty.
                    buf[regDataOpenBy] = tmp;
                    parser.parse_chunk(std::string(buf, chunkRead));
                    continue;
                }

                // We've found the engine version.
                buf[regDataOpenBy] = tmp;

                tmp = *finish;
                *finish = 0;

                if (versionUsesUTF8(start)) {
                    // No need for surgery.
                    *finish = tmp;
                    parser.parse_chunk(std::string(buf, chunkRead));
                    continue;
                }

                // Surgery is required.
                // Make sure there is somewhere to squeeze in an encoding.
                start = ::strstr(buf, "encoding=");
                if (start) {
                    // Someone else seems to have done it already.. *shrug*
                    *finish = tmp;
                    parser.parse_chunk(std::string(buf, chunkRead));
                    continue;
                }

                start = ::strstr(buf, "?>");
                if (! start) {
                    // Can't find the end of the <?xml ...?> opening sequence!
                    *finish = tmp;
                    parser.parse_chunk(std::string(buf, chunkRead));
                    continue;
                }

                // Good to go.  Parse the chunk with a new encoding squeezed in
                // just before the "?>".
                *finish = tmp;

                parser.parse_chunk(std::string(buf, start - buf));
                parser.parse_chunk(" encoding=\"ISO-8859-1\"");
                parser.parse_chunk(std::string(start,
                    chunkRead - (start - buf)));
            }

            parser.finish();
            delete[] buf;
            buf = nullptr; // Be safe in case we enter the catch block later.
        }

        // See if we read anything.
        // If so, break it away from the top-level container and return it.
        if (auto p = reader.packetToCommit()) {
            // Resolve any dangling packet references.
            resolver.resolveDelayed();

            // As reader is destroyed, it will automatically orphan the
            // child packet that we return and delete the old parent container.
            return p->firstChild();
        } else
            return nullptr;
    } catch (const zstr::Exception& e) {
        std::cerr << "ERROR: Could not open: " << e.what() << std::endl;
        delete[] buf;
        return nullptr;
    }
}

} // namespace regina