Spreadsheet: Add a CSV reader and writer

This is not utilised yet.

8 files changed, 989 insertions, 0 deletions

diff --git a/Applications/Spreadsheet/CMakeLists.txt b/Applications/Spreadsheet/CMakeLists.txt
index a80b4f07b7..9ba555450d 100644
--- a/Applications/Spreadsheet/CMakeLists.txt
+++ b/Applications/Spreadsheet/CMakeLists.txt
@@ -15,6 +15,7 @@ set(SOURCES
     CondFormattingViewUI.h
     HelpWindow.cpp
     JSIntegration.cpp
+    Readers/XSV.cpp
     Spreadsheet.cpp
     SpreadsheetModel.cpp
     SpreadsheetView.cpp
diff --git a/Applications/Spreadsheet/Readers/CSV.h b/Applications/Spreadsheet/Readers/CSV.h
new file mode 100644
index 0000000000..866ae67141
--- /dev/null
+++ b/Applications/Spreadsheet/Readers/CSV.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "XSV.h"
+#include <AK/Forward.h>
+#include <AK/StringView.h>
+
+namespace Reader {
+
+class CSV : public XSV {
+public:
+    CSV(StringView source, ParserBehaviour behaviours = default_behaviours())
+        : XSV(source, { ",", "\"", ParserTraits::Repeat }, behaviours)
+    {
+    }
+};
+
+}
diff --git a/Applications/Spreadsheet/Readers/Test/TestXSV.cpp b/Applications/Spreadsheet/Readers/Test/TestXSV.cpp
new file mode 100644
index 0000000000..b80093d556
--- /dev/null
+++ b/Applications/Spreadsheet/Readers/Test/TestXSV.cpp
@@ -0,0 +1,110 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/TestSuite.h>
+
+#include "../CSV.h"
+#include "../XSV.h"
+#include <LibCore/File.h>
+
+TEST_CASE(should_parse_valid_data)
+{
+    {
+        auto data = R"~~~(Foo, Bar, Baz
+                      1, 2, 3
+                      4, 5, 6
+                      """x", y"z, 9)~~~";
+        auto csv = Reader::CSV { data, Reader::default_behaviours() | Reader::ParserBehaviour::ReadHeaders | Reader::ParserBehaviour::TrimLeadingFieldSpaces };
+        EXPECT(!csv.has_error());
+
+        EXPECT_EQ(csv[0]["Foo"], "1");
+        EXPECT_EQ(csv[2]["Foo"], "\"x");
+        EXPECT_EQ(csv[2]["Bar"], "y\"z");
+    }
+
+    {
+        auto data = R"~~~(Foo, Bar, Baz
+                      1     	 , 2, 3
+                      4, "5 "       , 6
+                      """x", y"z, 9                       )~~~";
+        auto csv = Reader::CSV { data, Reader::default_behaviours() | Reader::ParserBehaviour::ReadHeaders | Reader::ParserBehaviour::TrimLeadingFieldSpaces | Reader::ParserBehaviour::TrimTrailingFieldSpaces };
+        EXPECT(!csv.has_error());
+
+        EXPECT_EQ(csv[0]["Foo"], "1");
+        EXPECT_EQ(csv[1]["Bar"], "5 ");
+        EXPECT_EQ(csv[2]["Foo"], "\"x");
+        EXPECT_EQ(csv[2]["Baz"], "9");
+    }
+}
+
+TEST_CASE(should_fail_nicely)
+{
+    {
+        auto data = R"~~~(Foo, Bar, Baz
+                      x, y)~~~";
+        auto csv = Reader::CSV { data, Reader::default_behaviours() | Reader::ParserBehaviour::ReadHeaders | Reader::ParserBehaviour::TrimLeadingFieldSpaces };
+        EXPECT(csv.has_error());
+        EXPECT_EQ(csv.error(), Reader::ReadError::NonConformingColumnCount);
+    }
+
+    {
+        auto data = R"~~~(Foo, Bar, Baz
+                      x, y, "z)~~~";
+        auto csv = Reader::CSV { data, Reader::default_behaviours() | Reader::ParserBehaviour::ReadHeaders | Reader::ParserBehaviour::TrimLeadingFieldSpaces };
+        EXPECT(csv.has_error());
+        EXPECT_EQ(csv.error(), Reader::ReadError::QuoteFailure);
+    }
+}
+
+TEST_CASE(should_iterate_rows)
+{
+    auto data = R"~~~(Foo, Bar, Baz
+                      1, 2, 3
+                      4, 5, 6
+                      """x", y"z, 9)~~~";
+    auto csv = Reader::CSV { data, Reader::default_behaviours() | Reader::ParserBehaviour::ReadHeaders | Reader::ParserBehaviour::TrimLeadingFieldSpaces };
+    EXPECT(!csv.has_error());
+
+    bool ran = false;
+    for (auto row : csv)
+        ran = !row[0].is_empty();
+
+    EXPECT(ran);
+}
+
+BENCHMARK_CASE(fairly_big_data)
+{
+    auto file_or_error = Core::File::open(__FILE__ ".data", Core::IODevice::OpenMode::ReadOnly);
+    EXPECT_EQ_FORCE(file_or_error.is_error(), false);
+
+    auto data = file_or_error.value()->read_all();
+    auto csv = Reader::CSV { data, Reader::default_behaviours() | Reader::ParserBehaviour::ReadHeaders };
+
+    EXPECT(!csv.has_error());
+    EXPECT_EQ(csv.size(), 100000u);
+}
+
+TEST_MAIN(XSV)
diff --git a/Applications/Spreadsheet/Readers/XSV.cpp b/Applications/Spreadsheet/Readers/XSV.cpp
new file mode 100644
index 0000000000..d87c86748e
--- /dev/null
+++ b/Applications/Spreadsheet/Readers/XSV.cpp
@@ -0,0 +1,272 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "XSV.h"
+#include <AK/StringBuilder.h>
+
+namespace Reader {
+
+ParserBehaviour operator&(ParserBehaviour left, ParserBehaviour right)
+{
+    return static_cast<ParserBehaviour>(static_cast<u32>(left) & static_cast<u32>(right));
+}
+
+ParserBehaviour operator|(ParserBehaviour left, ParserBehaviour right)
+{
+    return static_cast<ParserBehaviour>(static_cast<u32>(left) | static_cast<u32>(right));
+}
+
+void XSV::set_error(ReadError error)
+{
+    if (m_error == ReadError::None)
+        m_error = error;
+}
+
+Vector<String> XSV::headers() const
+{
+    Vector<String> headers;
+    for (auto& field : m_names)
+        headers.append(field.is_string_view ? field.as_string_view : field.as_string.view());
+
+    return headers;
+}
+
+void XSV::parse()
+{
+    if ((m_behaviours & ParserBehaviour::ReadHeaders) != ParserBehaviour::None)
+        read_headers();
+
+    while (!has_error() && !m_lexer.is_eof())
+        m_rows.append(read_row());
+
+    if (!m_lexer.is_eof())
+        set_error(ReadError::DataPastLogicalEnd);
+}
+
+void XSV::read_headers()
+{
+    if (!m_names.is_empty()) {
+        set_error(ReadError::InternalError);
+        m_names.clear();
+    }
+
+    m_names = read_row(true);
+}
+
+Vector<XSV::Field> XSV::read_row(bool header_row)
+{
+    Vector<Field> row;
+    bool first = true;
+    while (!(m_lexer.is_eof() || m_lexer.next_is('\n') || m_lexer.next_is("\r\n")) && (first || m_lexer.consume_specific(m_traits.separator))) {
+        first = false;
+        row.append(read_one_field());
+    }
+
+    if (!m_lexer.is_eof()) {
+        auto crlf_ok = m_lexer.consume_specific("\r\n");
+        if (!crlf_ok) {
+            auto lf_ok = m_lexer.consume_specific('\n');
+            if (!lf_ok)
+                set_error(ReadError::DataPastLogicalEnd);
+        }
+    }
+
+    if (!header_row && (m_behaviours & ParserBehaviour::ReadHeaders) != ParserBehaviour::None && row.size() != m_names.size())
+        set_error(ReadError::NonConformingColumnCount);
+
+    return row;
+}
+
+XSV::Field XSV::read_one_field()
+{
+    if ((m_behaviours & ParserBehaviour::TrimLeadingFieldSpaces) != ParserBehaviour::None)
+        m_lexer.consume_while(is_any_of(" \t\v"));
+
+    bool is_quoted = false;
+    Field field;
+    if (m_lexer.next_is(m_traits.quote.view())) {
+        is_quoted = true;
+        field = read_one_quoted_field();
+    } else {
+        field = read_one_unquoted_field();
+    }
+
+    if ((m_behaviours & ParserBehaviour::TrimTrailingFieldSpaces) != ParserBehaviour::None) {
+        m_lexer.consume_while(is_any_of(" \t\v"));
+
+        if (!is_quoted) {
+            // Also have to trim trailing spaces from unquoted fields.
+            StringView view;
+            if (field.is_string_view)
+                view = field.as_string_view;
+            else
+                view = field.as_string;
+
+            if (!view.is_empty()) {
+                ssize_t i = view.length() - 1;
+                for (; i >= 0; --i) {
+                    if (!view.substring_view(i, 1).is_one_of(" ", "\t", "\v"))
+                        break;
+                }
+                view = view.substring_view(0, i + 1);
+            }
+
+            if (field.is_string_view)
+                field.as_string_view = view;
+            else
+                field.as_string = field.as_string.substring(0, view.length());
+        }
+    }
+
+    return field;
+}
+
+XSV::Field XSV::read_one_quoted_field()
+{
+    if (!m_lexer.consume_specific(m_traits.quote))
+        set_error(ReadError::InternalError);
+
+    size_t start = m_lexer.tell(), end = start;
+    bool is_copy = false;
+    StringBuilder builder;
+    auto allow_newlines = (m_behaviours & ParserBehaviour::AllowNewlinesInFields) != ParserBehaviour::None;
+
+    for (; !m_lexer.is_eof();) {
+        char ch;
+        switch (m_traits.quote_escape) {
+        case ParserTraits::Backslash:
+            if (m_lexer.consume_specific('\\') && m_lexer.consume_specific(m_traits.quote)) {
+                // If there is an escaped quote, we have no choice but to make a copy.
+                if (!is_copy) {
+                    is_copy = true;
+                    builder.append(m_source.substring_view(start, end - start));
+                }
+                builder.append(m_traits.quote);
+                end = m_lexer.tell();
+                continue;
+            }
+            break;
+        case ParserTraits::Repeat:
+            if (m_lexer.consume_specific(m_traits.quote)) {
+                if (m_lexer.consume_specific(m_traits.quote)) {
+                    // If there is an escaped quote, we have no choice but to make a copy.
+                    if (!is_copy) {
+                        is_copy = true;
+                        builder.append(m_source.substring_view(start, end - start));
+                    }
+                    builder.append(m_traits.quote);
+                    end = m_lexer.tell();
+                    continue;
+                }
+                for (size_t i = 0; i < m_traits.quote.length(); ++i)
+                    m_lexer.retreat();
+                goto end;
+            }
+            break;
+        }
+
+        if (m_lexer.next_is(m_traits.quote.view()))
+            goto end;
+
+        if (!allow_newlines) {
+            if (m_lexer.next_is('\n') || m_lexer.next_is("\r\n"))
+                goto end;
+        }
+
+        ch = m_lexer.consume();
+        if (is_copy)
+            builder.append(ch);
+        end = m_lexer.tell();
+        continue;
+
+    end:
+        break;
+    }
+
+    if (!m_lexer.consume_specific(m_traits.quote))
+        set_error(ReadError::QuoteFailure);
+
+    if (is_copy)
+        return { {}, builder.to_string(), false };
+
+    return { m_source.substring_view(start, end - start), {}, true };
+}
+
+XSV::Field XSV::read_one_unquoted_field()
+{
+    size_t start = m_lexer.tell(), end = start;
+    bool allow_quote_in_field = (m_behaviours & ParserBehaviour::QuoteOnlyInFieldStart) != ParserBehaviour::None;
+
+    for (; !m_lexer.is_eof();) {
+        if (m_lexer.next_is(m_traits.separator.view()))
+            break;
+
+        if (m_lexer.next_is("\r\n") || m_lexer.next_is("\n"))
+            break;
+
+        if (m_lexer.consume_specific(m_traits.quote)) {
+            if (!allow_quote_in_field)
+                set_error(ReadError::QuoteFailure);
+            end = m_lexer.tell();
+            continue;
+        }
+
+        m_lexer.consume();
+        end = m_lexer.tell();
+    }
+
+    return { m_source.substring_view(start, end - start), {}, true };
+}
+
+StringView XSV::Row::operator[](StringView name) const
+{
+    ASSERT(!m_xsv.m_names.is_empty());
+    auto it = m_xsv.m_names.find([&](auto&& entry) { return name == entry; });
+    ASSERT(!it.is_end());
+
+    return (*this)[it.index()];
+}
+
+StringView XSV::Row::operator[](size_t column) const
+{
+    auto& field = m_xsv.m_rows[m_index][column];
+    if (field.is_string_view)
+        return field.as_string_view;
+    return field.as_string;
+}
+
+const XSV::Row XSV::operator[](size_t index) const
+{
+    return const_cast<XSV&>(*this)[index];
+}
+
+XSV::Row XSV::operator[](size_t index)
+{
+    ASSERT(m_rows.size() > index);
+    return Row { *this, index };
+}
+
+}
diff --git a/Applications/Spreadsheet/Readers/XSV.h b/Applications/Spreadsheet/Readers/XSV.h
new file mode 100644
index 0000000000..0b32ca767d
--- /dev/null
+++ b/Applications/Spreadsheet/Readers/XSV.h
@@ -0,0 +1,208 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/GenericLexer.h>
+#include <AK/String.h>
+#include <AK/StringView.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+
+namespace Reader {
+
+enum class ParserBehaviour : u32 {
+    None = 0,
+    ReadHeaders = 1,
+    AllowNewlinesInFields = ReadHeaders << 1,
+    TrimLeadingFieldSpaces = ReadHeaders << 2,
+    TrimTrailingFieldSpaces = ReadHeaders << 3,
+    QuoteOnlyInFieldStart = ReadHeaders << 4,
+};
+
+ParserBehaviour operator&(ParserBehaviour left, ParserBehaviour right);
+ParserBehaviour operator|(ParserBehaviour left, ParserBehaviour right);
+
+struct ParserTraits {
+    String separator;
+    String quote { "\"" };
+    enum {
+        Repeat,
+        Backslash,
+    } quote_escape { Repeat };
+};
+
+#define ENUMERATE_READ_ERRORS()                                                   \
+    E(None, "No errors")                                                          \
+    E(NonConformingColumnCount, "Header count does not match given column count") \
+    E(QuoteFailure, "Quoting failure")                                            \
+    E(InternalError, "Internal error")                                            \
+    E(DataPastLogicalEnd, "Exrta data past the logical end of the rows")
+
+enum class ReadError {
+#define E(name, _) name,
+    ENUMERATE_READ_ERRORS()
+#undef E
+};
+
+inline constexpr ParserBehaviour default_behaviours()
+{
+    return ParserBehaviour::QuoteOnlyInFieldStart;
+}
+
+class XSV {
+public:
+    XSV(StringView source, const ParserTraits& traits, ParserBehaviour behaviours = default_behaviours())
+        : m_source(source)
+        , m_lexer(m_source)
+        , m_traits(traits)
+        , m_behaviours(behaviours)
+    {
+        parse();
+    }
+
+    virtual ~XSV() { }
+
+    bool has_error() const { return m_error != ReadError::None; }
+    ReadError error() const { return m_error; }
+    String error_string() const
+    {
+        switch (m_error) {
+#define E(x, y)        \
+    case ReadError::x: \
+        return y;
+
+            ENUMERATE_READ_ERRORS();
+#undef E
+        }
+        ASSERT_NOT_REACHED();
+    }
+
+    size_t size() const { return m_rows.size(); }
+    Vector<String> headers() const;
+
+    class Row {
+    public:
+        explicit Row(XSV& xsv, size_t index)
+            : m_xsv(xsv)
+            , m_index(index)
+        {
+        }
+
+        StringView operator[](StringView name) const;
+        StringView operator[](size_t column) const;
+
+        size_t index() const { return m_index; }
+
+        // FIXME: Implement begin() and end(), keeping `Field' out of the API.
+
+    private:
+        XSV& m_xsv;
+        size_t m_index { 0 };
+    };
+
+    template<bool const_>
+    class RowIterator {
+    public:
+        explicit RowIterator(const XSV& xsv, size_t init_index = 0) requires(const_)
+            : m_xsv(const_cast<XSV&>(xsv))
+            , m_index(init_index)
+        {
+        }
+
+        explicit RowIterator(XSV& xsv, size_t init_index = 0) requires(!const_)
+            : m_xsv(xsv)
+            , m_index(init_index)
+        {
+        }
+
+        Row operator*() const { return Row { m_xsv, m_index }; }
+        Row operator*() requires(!const_) { return Row { m_xsv, m_index }; }
+
+        RowIterator& operator++()
+        {
+            ++m_index;
+            return *this;
+        }
+
+        bool is_end() const { return m_index == m_xsv.m_rows.size(); }
+        bool operator==(const RowIterator& other) const
+        {
+            return m_index == other.m_index && &m_xsv == &other.m_xsv;
+        }
+        bool operator==(const RowIterator<!const_>& other) const
+        {
+            return m_index == other.m_index && &m_xsv == &other.m_xsv;
+        }
+
+    private:
+        XSV& m_xsv;
+        size_t m_index { 0 };
+    };
+
+    const Row operator[](size_t index) const;
+    Row operator[](size_t index);
+
+    auto begin() { return RowIterator<false>(*this); }
+    auto end() { return RowIterator<false>(*this, m_rows.size()); }
+
+    auto begin() const { return RowIterator<true>(*this); }
+    auto end() const { return RowIterator<true>(*this, m_rows.size()); }
+
+    using ConstIterator = RowIterator<true>;
+    using Iterator = RowIterator<false>;
+
+private:
+    struct Field {
+        StringView as_string_view;
+        String as_string; // This member only used if the parser couldn't use the original source verbatim.
+        bool is_string_view { true };
+
+        bool operator==(StringView other) const
+        {
+            if (is_string_view)
+                return other == as_string_view;
+            return as_string == other;
+        }
+    };
+    void set_error(ReadError error);
+    void parse();
+    void read_headers();
+    Vector<Field> read_row(bool header_row = false);
+    Field read_one_field();
+    Field read_one_quoted_field();
+    Field read_one_unquoted_field();
+
+    StringView m_source;
+    GenericLexer m_lexer;
+    const ParserTraits& m_traits;
+    ParserBehaviour m_behaviours;
+    Vector<Field> m_names;
+    Vector<Vector<Field>> m_rows;
+    ReadError m_error { ReadError::None };
+};
+
+}
diff --git a/Applications/Spreadsheet/Writers/CSV.h b/Applications/Spreadsheet/Writers/CSV.h
new file mode 100644
index 0000000000..49940fbdf1
--- /dev/null
+++ b/Applications/Spreadsheet/Writers/CSV.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "XSV.h"
+#include <AK/Forward.h>
+#include <AK/StringView.h>
+
+namespace Writer {
+
+template<typename ContainerType>
+class CSV : public XSV<ContainerType> {
+public:
+    CSV(OutputStream& output, const ContainerType& data, const Vector<StringView>& headers = {}, WriterBehaviour behaviours = default_behaviours())
+        : XSV<ContainerType>(output, data, { ",", "\"", WriterTraits::Repeat }, headers, behaviours)
+    {
+    }
+};
+
+}
diff --git a/Applications/Spreadsheet/Writers/Test/TestXSVWriter.cpp b/Applications/Spreadsheet/Writers/Test/TestXSVWriter.cpp
new file mode 100644
index 0000000000..4971658431
--- /dev/null
+++ b/Applications/Spreadsheet/Writers/Test/TestXSVWriter.cpp
@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/TestSuite.h>
+
+#include "../CSV.h"
+#include "../XSV.h"
+#include <AK/MemoryStream.h>
+
+TEST_CASE(can_write)
+{
+    Vector<Vector<int>> data = {
+        { 1, 2, 3 },
+        { 4, 5, 6 },
+        { 7, 8, 9 },
+    };
+
+    auto buffer = ByteBuffer::create_uninitialized(1024);
+    OutputMemoryStream stream { buffer };
+
+    Writer::CSV csv(stream, data);
+
+    auto expected_output = R"~(1,2,3
+4,5,6
+7,8,9
+)~";
+
+    EXPECT_EQ(StringView { stream.bytes() }, expected_output);
+}
+
+TEST_CASE(can_write_with_header)
+{
+    Vector<Vector<int>> data = {
+        { 1, 2, 3 },
+        { 4, 5, 6 },
+        { 7, 8, 9 },
+    };
+
+    auto buffer = ByteBuffer::create_uninitialized(1024);
+    OutputMemoryStream stream { buffer };
+
+    Writer::CSV csv(stream, data, { "A", "B\"", "C" });
+
+    auto expected_output = R"~(A,"B""",C
+1,2,3
+4,5,6
+7,8,9
+)~";
+
+    EXPECT_EQ(StringView { stream.bytes() }, expected_output);
+}
+
+TEST_CASE(can_write_with_different_behaviours)
+{
+    Vector<Vector<String>> data = {
+        { "Well", "Hello\"", "Friends" },
+        { "We\"ll", "Hello,", "   Friends" },
+    };
+
+    auto buffer = ByteBuffer::create_uninitialized(1024);
+    OutputMemoryStream stream { buffer };
+
+    Writer::CSV csv(stream, data, { "A", "B\"", "C" }, Writer::WriterBehaviour::QuoteOnlyInFieldStart | Writer::WriterBehaviour::WriteHeaders);
+
+    auto expected_output = R"~(A,B",C
+Well,Hello",Friends
+We"ll,"Hello,",   Friends
+)~";
+
+    EXPECT_EQ(StringView { stream.bytes() }, expected_output);
+}
+
+TEST_MAIN(XSV)
diff --git a/Applications/Spreadsheet/Writers/XSV.h b/Applications/Spreadsheet/Writers/XSV.h
new file mode 100644
index 0000000000..7a065f87d1
--- /dev/null
+++ b/Applications/Spreadsheet/Writers/XSV.h
@@ -0,0 +1,215 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/GenericLexer.h>
+#include <AK/OwnPtr.h>
+#include <AK/Stream.h>
+#include <AK/String.h>
+#include <AK/StringView.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+
+namespace Writer {
+
+enum class WriterBehaviour : u32 {
+    None = 0,
+    WriteHeaders = 1,
+    AllowNewlinesInFields = WriteHeaders << 1,
+    QuoteOnlyInFieldStart = WriteHeaders << 2,
+    QuoteAll = WriteHeaders << 3,
+};
+
+inline WriterBehaviour operator&(WriterBehaviour left, WriterBehaviour right)
+{
+    return static_cast<WriterBehaviour>(static_cast<u32>(left) & static_cast<u32>(right));
+}
+
+inline WriterBehaviour operator|(WriterBehaviour left, WriterBehaviour right)
+{
+    return static_cast<WriterBehaviour>(static_cast<u32>(left) | static_cast<u32>(right));
+}
+
+struct WriterTraits {
+    String separator;
+    String quote { "\"" };
+    enum {
+        Repeat,
+        Backslash,
+    } quote_escape { Repeat };
+};
+
+#define ENUMERATE_WRITE_ERRORS()                                                  \
+    E(None, "No errors")                                                          \
+    E(NonConformingColumnCount, "Header count does not match given column count") \
+    E(InternalError, "Internal error")
+
+enum class WriteError {
+#define E(name, _) name,
+    ENUMERATE_WRITE_ERRORS()
+#undef E
+};
+
+inline constexpr WriterBehaviour default_behaviours()
+{
+    return WriterBehaviour::None;
+}
+
+template<typename ContainerType>
+class XSV {
+public:
+    XSV(OutputStream& output, const ContainerType& data, const WriterTraits& traits, const Vector<StringView>& headers = {}, WriterBehaviour behaviours = default_behaviours())
+        : m_data(data)
+        , m_traits(traits)
+        , m_behaviours(behaviours)
+        , m_names(headers)
+        , m_output(output)
+    {
+        if (!headers.is_empty())
+            m_behaviours = m_behaviours | WriterBehaviour::WriteHeaders;
+
+        generate();
+    }
+
+    virtual ~XSV() { }
+
+    bool has_error() const { return m_error != WriteError::None; }
+    WriteError error() const { return m_error; }
+    String error_string() const
+    {
+        switch (m_error) {
+#define E(x, y)         \
+    case WriteError::x: \
+        return y;
+
+            ENUMERATE_WRITE_ERRORS();
+#undef E
+        }
+        ASSERT_NOT_REACHED();
+    }
+
+private:
+    void set_error(WriteError error)
+    {
+        if (m_error == WriteError::None)
+            m_error = error;
+    }
+
+    void generate()
+    {
+        auto with_headers = (m_behaviours & WriterBehaviour::WriteHeaders) != WriterBehaviour::None;
+        if (with_headers) {
+            write_row(m_names);
+            if (m_output.write({ "\n", 1 }) != 1)
+                set_error(WriteError::InternalError);
+        }
+
+        for (auto&& row : m_data) {
+            if (with_headers) {
+                if (row.size() != m_names.size())
+                    set_error(WriteError::NonConformingColumnCount);
+            }
+
+            write_row(row);
+            if (m_output.write({ "\n", 1 }) != 1)
+                set_error(WriteError::InternalError);
+        }
+    }
+
+    template<typename T>
+    void write_row(T&& row)
+    {
+        bool first = true;
+        for (auto&& entry : row) {
+            if (!first) {
+                if (m_output.write(m_traits.separator.bytes()) != m_traits.separator.length())
+                    set_error(WriteError::InternalError);
+            }
+            first = false;
+            write_entry(entry);
+        }
+    }
+
+    template<typename T>
+    void write_entry(T&& entry)
+    {
+        auto string = String::formatted("{}", FormatIfSupported(entry));
+
+        auto safe_to_write_normally = !string.contains("\n") && !string.contains(m_traits.separator);
+        if (safe_to_write_normally) {
+            if ((m_behaviours & WriterBehaviour::QuoteOnlyInFieldStart) == WriterBehaviour::None)
+                safe_to_write_normally = !string.contains(m_traits.quote);
+            else
+                safe_to_write_normally = !string.starts_with(m_traits.quote);
+        }
+        if (safe_to_write_normally) {
+            if (m_output.write(string.bytes()) != string.length())
+                set_error(WriteError::InternalError);
+            return;
+        }
+
+        if (m_output.write(m_traits.quote.bytes()) != m_traits.quote.length())
+            set_error(WriteError::InternalError);
+
+        GenericLexer lexer(string);
+        while (!lexer.is_eof()) {
+            if (lexer.consume_specific(m_traits.quote)) {
+                switch (m_traits.quote_escape) {
+                case WriterTraits::Repeat:
+                    if (m_output.write(m_traits.quote.bytes()) != m_traits.quote.length())
+                        set_error(WriteError::InternalError);
+                    if (m_output.write(m_traits.quote.bytes()) != m_traits.quote.length())
+                        set_error(WriteError::InternalError);
+                    break;
+                case WriterTraits::Backslash:
+                    if (m_output.write({ "\\", 1 }) != 1)
+                        set_error(WriteError::InternalError);
+                    if (m_output.write(m_traits.quote.bytes()) != m_traits.quote.length())
+                        set_error(WriteError::InternalError);
+                    break;
+                }
+                continue;
+            }
+
+            auto ch = lexer.consume();
+            if (m_output.write({ &ch, 1 }) != 1)
+                set_error(WriteError::InternalError);
+        }
+
+        if (m_output.write(m_traits.quote.bytes()) != m_traits.quote.length())
+            set_error(WriteError::InternalError);
+    }
+
+    const ContainerType& m_data;
+    const WriterTraits& m_traits;
+    WriterBehaviour m_behaviours;
+    const Vector<StringView>& m_names;
+    WriteError m_error { WriteError::None };
+    OutputStream& m_output;
+};
+
+}