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#include "textfileformat.h"
#include "fileutils.h"
#include "qtcassert.h"

#include <QTextCodec>
#include <QStringList>
#include <QCoreApplication>
#include <QDebug>

enum { debug = 0 };

#include <exception>

namespace Utils {

QDebug operator<<(QDebug d, const TextFileFormat &format)
{
    QDebug nsp = d.nospace();
    nsp << "TextFileFormat: ";
    if (format.codec) {
        nsp << format.codec->name();
        foreach (const QByteArray &alias, format.codec->aliases())
            nsp << ' ' << alias;
    } else {
        nsp << "NULL";
    }
    nsp << " hasUtf8Bom=" << format.hasUtf8Bom
        << (format.lineTerminationMode == TextFileFormat::LFLineTerminator ? " LF" : " CRLF");
    return d;
}

/*!
    \class Utils::TextFileFormat

    \brief Describes the format of a text file and provides autodetection.

    The format comprises
    \list
    \o Encoding represented by a pointer to a QTextCodec
    \o Presence of an UTF8 Byte Order Marker (BOM)
    \o Line feed storage convention
    \endlist

    The class also provides convenience functions to read text files and return them
    as strings or string lists and to write out files.
*/

TextFileFormat::TextFileFormat() :
    lineTerminationMode(NativeLineTerminator), hasUtf8Bom(false), codec(0)
{
}

/*!
    \brief Detect the format of text data.
*/

TextFileFormat TextFileFormat::detect(const QByteArray &data)
{
    TextFileFormat result;
    if (data.isEmpty())
        return result;
    const int bytesRead = data.size();
    const unsigned char *buf = reinterpret_cast<const unsigned char *>(data.constData());
    // code taken from qtextstream
    if (bytesRead >= 4 && ((buf[0] == 0xff && buf[1] == 0xfe && buf[2] == 0 && buf[3] == 0)
                           || (buf[0] == 0 && buf[1] == 0 && buf[2] == 0xfe && buf[3] == 0xff))) {
        result.codec = QTextCodec::codecForName("UTF-32");
    } else if (bytesRead >= 2 && ((buf[0] == 0xff && buf[1] == 0xfe)
                                  || (buf[0] == 0xfe && buf[1] == 0xff))) {
        result.codec = QTextCodec::codecForName("UTF-16");
    } else if (bytesRead >= 3 && ((buf[0] == 0xef && buf[1] == 0xbb) && buf[2] == 0xbf)) {
        result.codec = QTextCodec::codecForName("UTF-8");
        result.hasUtf8Bom = true;
    }
    // end code taken from qtextstream
    const int newLinePos = data.indexOf('\n');
    if (newLinePos == -1) {
        result.lineTerminationMode = NativeLineTerminator;
    } else if (newLinePos == 0) {
        result.lineTerminationMode = LFLineTerminator;
    } else {
        result.lineTerminationMode = data.at(newLinePos - 1) == '\r' ? CRLFLineTerminator : LFLineTerminator;
    }
    return result;
}

/*!
    \brief Returns a piece of text suitable as display for a encoding error.
*/

QByteArray TextFileFormat::decodingErrorSample(const QByteArray &data)
{
    const int p = data.indexOf('\n', 16384);
    return p < 0 ? data : data.left(p);
}

enum { textChunkSize = 65536 };

static bool verifyDecodingError(const QString &text, const QTextCodec *codec,
                                const char *data, const int dataSize,
                                const bool possibleHeader)
{
    const QByteArray verifyBuf = codec->fromUnicode(text); // slow
    // the minSize trick lets us ignore unicode headers
    const int minSize = qMin(verifyBuf.size(), dataSize);
    return (minSize < dataSize - (possibleHeader? 4 : 0)
            || memcmp(verifyBuf.constData() + verifyBuf.size() - minSize,
                      data + dataSize - minSize,
                      minSize));
}

// Decode a potentially large file in chunks and append it to target
// using the append function passed on (fits QStringList and QString).

template <class Target>
bool decodeTextFileContent(const QByteArray &dataBA,
                           const TextFileFormat &format,
                           Target *target,
                           void (Target::*appendFunction)(const QString &))
{
    QTC_ASSERT(format.codec, return  false; )

    QTextCodec::ConverterState state;
    bool hasDecodingError = false;

    const char *start = dataBA.constData();
    const char *data = start;
    const char *end  = data + dataBA.size();
    // Process chunkwise as QTextCodec allocates too much memory when doing it in one
    // go. An alternative to the code below would be creating a decoder from the codec,
    // but its failure detection does not seem be working reliably.
    for (const char *data = start; data < end; ) {
        const char *chunkStart = data;
        const int chunkSize = qMin(int(textChunkSize), int(end - chunkStart));
        QString text = format.codec->toUnicode(chunkStart, chunkSize, &state);
        data += chunkSize;
        // Process until the end of the current multi-byte character. Remaining might
        // actually contain more than needed so try one-be-one. If EOF is reached with
        // and characters remain->encoding error.
        for ( ; state.remainingChars && data < end ; ++data)
            text.append(format.codec->toUnicode(data, 1, &state));
        if (state.remainingChars)
            hasDecodingError = true;
        if (!hasDecodingError)
            hasDecodingError =
                verifyDecodingError(text, format.codec, chunkStart, data - chunkStart,
                                    chunkStart == start);
        if (format.lineTerminationMode == TextFileFormat::CRLFLineTerminator)
            text.remove(QLatin1Char('\r'));
        (target->*appendFunction)(text);
    }
    return !hasDecodingError;
}

/*!
    \brief Decode data to a plain string.
*/

bool TextFileFormat::decode(const QByteArray &data, QString *target) const
{
    target->clear();
    return decodeTextFileContent<QString>(data, *this, target, &QString::push_back);
}

/*!
    \brief Decode data to a list of strings.

    Intended for use with progress bars loading large files.
*/

bool TextFileFormat::decode(const QByteArray &data, QStringList *target) const
{
    target->clear();
    if (data.size() > textChunkSize)
        target->reserve(5 + data.size() / textChunkSize);
    return decodeTextFileContent<QStringList>(data, *this, target, &QStringList::append);
}

// Read text file contents to string or stringlist.
template <class Target>
TextFileFormat::ReadResult readTextFile(const QString &fileName, const QTextCodec *defaultCodec,
                                        Target *target, TextFileFormat *format, QString *errorString,
                                        QByteArray *decodingErrorSampleIn = 0)
{
    if (decodingErrorSampleIn)
        decodingErrorSampleIn->clear();

    QByteArray data;
    try {
        Utils::FileReader reader;
        if (!reader.fetch(fileName, errorString))
            return TextFileFormat::ReadIOError;
        data = reader.data();
    } catch (const std::bad_alloc &) {
        *errorString = QCoreApplication::translate("Utils::TextFileFormat", "Out of memory.");
        return TextFileFormat::ReadMemoryAllocationError;
    }

    *format = TextFileFormat::detect(data);
    if (!format->codec)
        format->codec = defaultCodec ? defaultCodec : QTextCodec::codecForLocale();

    if (!format->decode(data, target)) {
        *errorString = QCoreApplication::translate("Utils::TextFileFormat", "An encoding error was encountered.");
        if (decodingErrorSampleIn)
            *decodingErrorSampleIn = TextFileFormat::decodingErrorSample(data);
        return TextFileFormat::ReadEncodingError;
    }
    return TextFileFormat::ReadSuccess;
}

/*!
    \brief Read text file into a list of strings.
*/

TextFileFormat::ReadResult
    TextFileFormat::readFile(const QString &fileName, const QTextCodec *defaultCodec,
                             QStringList *plainTextList, TextFileFormat *format, QString *errorString,
                             QByteArray *decodingErrorSample /* = 0 */)
{
    const TextFileFormat::ReadResult result =
        readTextFile(fileName, defaultCodec,
                     plainTextList, format, errorString, decodingErrorSample);
    if (debug)
        qDebug().nospace() << Q_FUNC_INFO << fileName << ' ' << *format
                           << " returns " << result << '/' << plainTextList->size() << " chunks";
    return result;
}

/*!
    \brief Read text file into a string.
*/

TextFileFormat::ReadResult
    TextFileFormat::readFile(const QString &fileName, const QTextCodec *defaultCodec,
                             QString *plainText, TextFileFormat *format, QString *errorString,
                             QByteArray *decodingErrorSample /* = 0 */)
{
    const TextFileFormat::ReadResult result =
        readTextFile(fileName, defaultCodec,
                     plainText, format, errorString, decodingErrorSample);
    if (debug)
        qDebug().nospace() << Q_FUNC_INFO << fileName << ' ' << *format
                           << " returns " << result << '/' << plainText->size() << " characters";
    return result;
}

/*!
    \brief Write out a text file.
*/

bool TextFileFormat::writeFile(const QString &fileName, QString plainText, QString *errorString) const
{
    QTC_ASSERT(codec, return false;)

    // Does the user want CRLF? If that is native,
    // let QFile do the work, else manually add.
    QIODevice::OpenMode fileMode = QIODevice::NotOpen;
    if (lineTerminationMode == CRLFLineTerminator) {
        if (NativeLineTerminator == CRLFLineTerminator) {
            fileMode |= QIODevice::Text;
        } else {
            plainText.replace(QLatin1Char('\n'), QLatin1String("\r\n"));
        }
    }

    Utils::FileSaver saver(fileName, fileMode);
    if (saver.hasError()) {
        *errorString = saver.errorString();
        return false;
    }
    if (hasUtf8Bom && codec->name() == "UTF-8")
        saver.write("\xef\xbb\xbf", 3);
    saver.write(codec->fromUnicode(plainText));
    const bool ok = saver.finalize(errorString);
    if (debug)
        qDebug().nospace() << Q_FUNC_INFO << fileName << ' ' << *this <<  ' ' << plainText.size()
                           << " bytes, returns " << ok;
    return ok;
}

} // namespace Utils
