Create the Qt File Filter => showOpen/SaveFilePicker options mapper

As a preparatory measure for using showXFilePicker, the Qt file
filter has to be transformed to the format used by the showXFilePicker
(sXFP) options. A class structure reflecting the options was created. Based on
an input in the form of a qt file filter, it will parse the filter to
the sXFP options format. Unit tests were added and the code is not yet
used in non-test env, next change will use it.

Task-number: QTBUG-99611
Change-Id: I277286467a7b5ce6f323c19bdd31740a41b6a6be
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

2 files changed, 284 insertions, 0 deletions

diff --git a/src/gui/platform/wasm/qlocalfileapi.cpp b/src/gui/platform/wasm/qlocalfileapi.cpp
new file mode 100644
index 0000000000..ec7ae40391
--- /dev/null
+++ b/src/gui/platform/wasm/qlocalfileapi.cpp
@@ -0,0 +1,197 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "qlocalfileapi_p.h"
+#include <private/qstdweb_p.h>
+#include <QtCore/QRegularExpression>
+
+QT_BEGIN_NAMESPACE
+namespace LocalFileApi {
+namespace {
+std::optional<emscripten::val> qtFilterListToTypes(const QStringList &filterList)
+{
+    using namespace qstdweb;
+    using namespace emscripten;
+
+    auto types = emscripten::val::array();
+
+    for (const auto &fileFilter : filterList) {
+        auto type = Type::fromQt(fileFilter);
+        if (type)
+            types.call<void>("push", type->asVal());
+    }
+
+    return types["length"].as<int>() == 0 ? std::optional<emscripten::val>() : types;
+}
+}
+
+Type::Type(QStringView description, std::optional<Accept> accept)
+    : m_storage(emscripten::val::object())
+{
+    m_storage.set("description", description.trimmed().toString().toStdString());
+    if (accept)
+        m_storage.set("accept", accept->asVal());
+}
+
+Type::~Type() = default;
+
+std::optional<Type> Type::fromQt(QStringView type)
+{
+    using namespace emscripten;
+
+    // Accepts either a string in format:
+    // GROUP3
+    // or in this format:
+    // GROUP1 (GROUP2)
+    // Group 1 is treated as the description, whereas group 2 or 3 are treated as the filter list.
+    static QRegularExpression regex(
+            QString(QStringLiteral("(?:(?:([^(]*)\\(([^()]+)\\)[^)]*)|([^()]+))")));
+    const auto match = regex.match(type);
+
+    if (!match.hasMatch())
+        return std::nullopt;
+
+    constexpr size_t DescriptionIndex = 1;
+    constexpr size_t FilterListFromParensIndex = 2;
+    constexpr size_t PlainFilterListIndex = 3;
+
+    const auto description = match.hasCaptured(DescriptionIndex)
+            ? match.capturedView(DescriptionIndex)
+            : QStringView();
+    const auto filterList = match.capturedView(match.hasCaptured(FilterListFromParensIndex)
+                                                       ? FilterListFromParensIndex
+                                                       : PlainFilterListIndex);
+
+    auto accept = Type::Accept::fromQt(filterList);
+    if (!accept)
+        return std::nullopt;
+
+    return Type(description, std::move(*accept));
+}
+
+emscripten::val Type::asVal() const
+{
+    return m_storage;
+}
+
+Type::Accept::Accept() : m_storage(emscripten::val::object()) { }
+
+Type::Accept::~Accept() = default;
+
+std::optional<Type::Accept> Type::Accept::fromQt(QStringView qtRepresentation)
+{
+    Accept accept;
+
+    // Used for accepting multiple extension specifications on a filter list.
+    // The next group of non-empty characters.
+    static QRegularExpression internalRegex(QString(QStringLiteral("([^\\s]+)\\s*")));
+    int offset = 0;
+    auto internalMatch = internalRegex.match(qtRepresentation, offset);
+    MimeType mimeType;
+
+    while (internalMatch.hasMatch()) {
+        auto webExtension = MimeType::Extension::fromQt(internalMatch.capturedView(1));
+
+        if (!webExtension)
+            return std::nullopt;
+
+        mimeType.addExtension(*webExtension);
+
+        internalMatch = internalRegex.match(qtRepresentation, internalMatch.capturedEnd());
+    }
+
+    accept.addMimeType(mimeType);
+    return accept;
+}
+
+void Type::Accept::addMimeType(MimeType mimeType)
+{
+    // The mime type provided here does not seem to have any effect at the result at all.
+    m_storage.set("application/octet-stream", mimeType.asVal());
+}
+
+emscripten::val Type::Accept::asVal() const
+{
+    return m_storage;
+}
+
+Type::Accept::MimeType::MimeType() : m_storage(emscripten::val::array()) { }
+
+Type::Accept::MimeType::~MimeType() = default;
+
+void Type::Accept::MimeType::addExtension(Extension extension)
+{
+    m_storage.call<void>("push", extension.asVal());
+}
+
+emscripten::val Type::Accept::MimeType::asVal() const
+{
+    return m_storage;
+}
+
+Type::Accept::MimeType::Extension::Extension(QStringView extension)
+    : m_storage(extension.toString().toStdString())
+{
+}
+
+Type::Accept::MimeType::Extension::~Extension() = default;
+
+std::optional<Type::Accept::MimeType::Extension>
+Type::Accept::MimeType::Extension::fromQt(QStringView qtRepresentation)
+{
+    // Checks for a filter that matches everything:
+    // Any number of asterisks or any number of asterisks with a '.' between them.
+    // The web filter does not support wildcards.
+    static QRegularExpression qtAcceptAllRegex(
+            QRegularExpression::anchoredPattern(QString(QStringLiteral("[*]+|[*]+\\.[*]+"))));
+    if (qtAcceptAllRegex.match(qtRepresentation).hasMatch())
+        return std::nullopt;
+
+    // Checks for correctness. The web filter only allows filename extensions and does not filter
+    // the actual filenames, therefore we check whether the filter provided only filters for the
+    // extension.
+    static QRegularExpression qtFilenameMatcherRegex(
+            QRegularExpression::anchoredPattern(QString(QStringLiteral("(\\*?)(\\.[^*]+)"))));
+
+    auto extensionMatch = qtFilenameMatcherRegex.match(qtRepresentation);
+    if (extensionMatch.hasMatch())
+        return Extension(extensionMatch.capturedView(2));
+
+    // Mapping impossible.
+    return std::nullopt;
+}
+
+emscripten::val Type::Accept::MimeType::Extension::asVal() const
+{
+    return m_storage;
+}
+
+emscripten::val makeOpenFileOptions(const QStringList &filterList, bool acceptMultiple)
+{
+    auto options = emscripten::val::object();
+    if (auto typeList = LocalFileApi::qtFilterListToTypes(filterList)) {
+        options.set("types", std::move(*typeList));
+        options.set("excludeAcceptAllOption", true);
+    }
+
+    options.set("multiple", acceptMultiple);
+
+    return options;
+}
+
+emscripten::val makeSaveFileOptions(const QStringList &filterList, const std::string& suggestedName)
+{
+    auto options = emscripten::val::object();
+
+    if (!suggestedName.empty())
+        options.set("suggestedName", emscripten::val(suggestedName));
+
+    if (auto typeList = LocalFileApi::qtFilterListToTypes(filterList))
+        options.set("types", emscripten::val(std::move(*typeList)));
+
+    return options;
+}
+
+}  // namespace LocalFileApi
+
+QT_END_NAMESPACE
diff --git a/src/gui/platform/wasm/qlocalfileapi_p.h b/src/gui/platform/wasm/qlocalfileapi_p.h
new file mode 100644
index 0000000000..a8e7f666f9
--- /dev/null
+++ b/src/gui/platform/wasm/qlocalfileapi_p.h
@@ -0,0 +1,87 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QLOCALFILEAPI_P_H
+#define QLOCALFILEAPI_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <private/qglobal_p.h>
+#include <qstringview.h>
+#include <emscripten/val.h>
+#include <cstdint>
+#include <functional>
+
+QT_BEGIN_NAMESPACE
+
+namespace LocalFileApi {
+class Q_CORE_EXPORT Type {
+public:
+    class Accept {
+    public:
+        class MimeType {
+        public:
+            class Extension {
+            public:
+                static std::optional<Extension> fromQt(QStringView extension);
+
+                ~Extension();
+
+                emscripten::val asVal() const;
+
+            private:
+                explicit Extension(QStringView extension);
+
+                emscripten::val m_storage;
+            };
+
+            MimeType();
+            ~MimeType();
+
+            void addExtension(Extension type);
+
+            emscripten::val asVal() const;
+
+        private:
+            emscripten::val m_storage;
+        };
+
+        static std::optional<Accept> fromQt(QStringView type);
+
+        ~Accept();
+
+        void addMimeType(MimeType mimeType);
+
+        emscripten::val asVal() const;
+
+    private:
+        Accept();
+        emscripten::val m_storage;
+    };
+
+    Type(QStringView description, std::optional<Accept> accept);
+    ~Type();
+
+    static std::optional<Type> fromQt(QStringView type);
+    emscripten::val asVal() const;
+
+private:
+    emscripten::val m_storage;
+};
+
+Q_CORE_EXPORT emscripten::val makeOpenFileOptions(const QStringList &filterList, bool acceptMultiple);
+Q_CORE_EXPORT emscripten::val makeSaveFileOptions(const QStringList &filterList, const std::string& suggestedName);
+
+}  // namespace LocalFileApi
+QT_END_NAMESPACE
+
+#endif // QLOCALFILEAPI_P_H