Text Codecs Example

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#include <QtWidgets>

#include "previewform.h"

// Helpers for creating hex dumps
static void indent(QTextStream &str, int indent)
{
    for (int i = 0; i < indent; ++i)
        str << ' ';
}

static void formatHex(QTextStream &str, const QByteArray &data)
{
    const int fieldWidth = str.fieldWidth();
    const QTextStream::FieldAlignment alignment = str.fieldAlignment();
    const int base = str.integerBase();
    const QChar padChar = str.padChar();
    str.setIntegerBase(16);
    str.setPadChar(QLatin1Char('0'));
    str.setFieldAlignment(QTextStream::AlignRight);

    const unsigned char *p = reinterpret_cast<const unsigned char *>(data.constBegin());
    for (const unsigned char *end = p + data.size(); p < end; ++p) {
        str << ' ';
        str.setFieldWidth(2);
        str << unsigned(*p);
        str.setFieldWidth(fieldWidth);
    }
    str.setFieldAlignment(alignment);
    str.setPadChar(padChar);
    str.setIntegerBase(base);
}

static void formatPrintableCharacters(QTextStream &str, const QByteArray &data)
{
    for (int i = 0, size = data.size(); i < size; ++i) {
        const char c = data.at(i);
        switch (c) {
        case '\0':
            str << "\\0";
            break;
        case '\t':
            str << "\\t";
            break;
        case '\r':
            str << "\\r";
            break;
        case '\n':
            str << "\\n";
            break;
        default:
            if (c >= 32 && uchar(c) < 127)
                str << ' ' << c;
            else
                str << "..";
            break;
        }
    }
}

static QString formatHexDump(const QByteArray &data)
{
    enum { lineWidth = 16 };
    QString result;
    QTextStream str(&result);
    str.setIntegerBase(16);
    str.setPadChar(QLatin1Char('0'));
    const int fieldWidth = str.fieldWidth();
    const QTextStream::FieldAlignment alignment = str.fieldAlignment();
    for (int a = 0, size = data.size(); a < size; a += lineWidth) {
        str.setFieldAlignment(QTextStream::AlignRight);
        str.setFieldWidth(8);
        str << a;
        str.setFieldWidth(fieldWidth);
        str.setFieldAlignment(alignment);

        const int end = qMin(a + lineWidth, size);
        const QByteArray line = data.mid(a, end - a);

        formatHex(str, line);
        indent(str, 3 * (lineWidth - line.size()));

        str << ' ';
        formatPrintableCharacters(str, line);
        indent(str, 2 * (lineWidth - line.size()));
        str << '\n';
    }
    return result;
}

PreviewForm::PreviewForm(QWidget *parent)
    : QDialog(parent)
{
    setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
    encodingComboBox = new QComboBox;

    QLabel *encodingLabel = new QLabel(tr("&Encoding:"));
    encodingLabel->setBuddy(encodingComboBox);

    textEdit = new QPlainTextEdit;
    textEdit->setLineWrapMode(QPlainTextEdit::NoWrap);
    textEdit->setReadOnly(true);
    hexDumpEdit = new QPlainTextEdit;
    hexDumpEdit->setLineWrapMode(QPlainTextEdit::NoWrap);
    hexDumpEdit->setReadOnly(true);
    hexDumpEdit->setFont(QFontDatabase::systemFont(QFontDatabase::FixedFont));

    QDialogButtonBox *buttonBox =
        new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Cancel);
    okButton = buttonBox->button(QDialogButtonBox::Ok);

    connect(encodingComboBox, QOverload<int>::of(&QComboBox::activated),
            this, &PreviewForm::updateTextEdit);
    connect(buttonBox, &QDialogButtonBox::accepted, this, &QDialog::accept);
    connect(buttonBox, &QDialogButtonBox::rejected, this, &QDialog::reject);

    QGridLayout *mainLayout = new QGridLayout(this);
    mainLayout->addWidget(encodingLabel, 0, 0);
    mainLayout->addWidget(encodingComboBox, 0, 1);
    tabWidget = new QTabWidget;
    tabWidget->addTab(textEdit, tr("Preview"));
    tabWidget->addTab(hexDumpEdit, tr("Hex Dump"));
    mainLayout->addWidget(tabWidget, 1, 0, 1, 2);
    statusLabel = new QLabel;
    mainLayout->addWidget(statusLabel, 2, 0, 1, 2);
    mainLayout->addWidget(buttonBox, 3, 0, 1, 2);

    const QRect screenGeometry = QApplication::desktop()->screenGeometry(this);
    resize(screenGeometry.width() * 2 / 5, screenGeometry.height() / 2);
}

void PreviewForm::setCodecList(const QList<QTextCodec *> &list)
{
    encodingComboBox->clear();
    foreach (const QTextCodec *codec, list) {
        encodingComboBox->addItem(QLatin1String(codec->name()),
                                  QVariant(codec->mibEnum()));
    }
}

void PreviewForm::reset()
{
    decodedStr.clear();
    textEdit->clear();
    hexDumpEdit->clear();
    statusLabel->clear();
    statusLabel->setStyleSheet(QString());
    okButton->setEnabled(false);
    tabWidget->setCurrentIndex(0);
}

void PreviewForm::setEncodedData(const QByteArray &data)
{
    reset();
    encodedData = data;
    hexDumpEdit->setPlainText(formatHexDump(data));
    updateTextEdit();
}

void PreviewForm::updateTextEdit()
{
    int mib = encodingComboBox->itemData(
                      encodingComboBox->currentIndex()).toInt();
    const QTextCodec *codec = QTextCodec::codecForMib(mib);
    const QString name = QLatin1String(codec->name());

    QTextCodec::ConverterState state;
    decodedStr = codec->toUnicode(encodedData.constData(), encodedData.size(), &state);

    bool success = true;
    if (state.remainingChars) {
        success = false;
        const QString message =
            tr("%1: conversion error at character %2")
            .arg(name).arg(encodedData.size() - state.remainingChars + 1);
        statusLabel->setText(message);
        statusLabel->setStyleSheet(QStringLiteral("background-color: \"red\";"));
    } else if (state.invalidChars) {
        statusLabel->setText(tr("%1: %n invalid characters", 0, state.invalidChars).arg(name));
        statusLabel->setStyleSheet(QStringLiteral("background-color: \"yellow\";"));
    } else {
        statusLabel->setText(tr("%1: %n bytes converted", 0, encodedData.size()).arg(name));
        statusLabel->setStyleSheet(QString());
    }
    if (success)
        textEdit->setPlainText(decodedStr);
    else
        textEdit->clear();
    okButton->setEnabled(success);
}