src/tint/utils/text/styled_text.h

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#ifndef SRC_TINT_UTILS_TEXT_STYLED_TEXT_H_
#define SRC_TINT_UTILS_TEXT_STYLED_TEXT_H_

#include <string>
#include <string_view>
#include <tuple>
#include <type_traits>
#include <utility>

#include "src/tint/utils/containers/vector.h"
#include "src/tint/utils/text/string_stream.h"
#include "src/tint/utils/text/text_style.h"

namespace tint {

/// StyledText is a string builder with support for styled text spans.
class StyledText {
  public:
    /// Constructor - empty string
    StyledText();

    /// Copy constructor
    StyledText(const StyledText&);

    /// Constructor from unstyled text
    explicit StyledText(const std::string&);

    /// Constructor from unstyled text
    explicit StyledText(std::string_view);

    /// Move constructor
    StyledText(StyledText&&);

    /// Assignment copy operator
    StyledText& operator=(const StyledText& other);

    /// Assignment operator from unstyled text
    StyledText& operator=(std::string_view text);

    /// Clears the text and restore the default style
    void Clear();

    /// @returns the TextStyle of all future writes to this StyledText
    TextStyle Style() const { return spans_.Back().style; }

    /// Sets the style for all future writes to this StyledText
    StyledText& SetStyle(TextStyle style);

    /// @returns the unstyled text.
    std::string Plain() const;

    /// Appends the styled text of @p other to this StyledText.
    /// @note: Unlike `operator<<(const StyledText&)`, this StyledText's previous style will *not*
    /// be automatically restored.
    void Append(const StyledText& other);

    /// repeat queues the character @p c to be written to the StyledText n times.
    /// @param c the character to print @p n times
    /// @param n the number of times to print character @p c
    /// @returns this StyledText so calls can be chained.
    StyledText& Repeat(char c, size_t n);

    /// operator<<() appends @p value to this StyledText.
    /// @p value which is one of:
    ///  * a TextStyle, which sets the style of all future appends. Note that this fully replaces
    ///    the old style (no style combinations / overlays).
    ///  * a ScopedTextStyle, which will will use the span's style for each value, and then this
    ///    StyledText's previous style will be restored.
    ///  * a StyledText, which will be appended to this StyledText, and then this StyledText's
    ///    previous style will be restored.
    ///  * any other type will be stringified and appended to this StyledText using the current
    ///    TextStyle.
    template <typename VALUE>
    StyledText& operator<<(VALUE&& value) {
        using T = std::decay_t<VALUE>;
        if constexpr (std::is_same_v<T, TextStyle>) {
            SetStyle(std::forward<VALUE>(value));
        } else if constexpr (std::is_same_v<T, StyledText>) {
            auto old_style = Style();
            Append(value);
            *this << old_style;
        } else if constexpr (IsScopedTextStyle<T>) {
            auto old_style = Style();
            std::apply([&](auto&&... values) { ((*this << value.style << values), ...); },
                       value.values);
            *this << old_style;
        } else {
            size_t offset = stream_.Length();
            stream_ << value;
            spans_.Back().length += stream_.Length() - offset;
        }
        return *this;
    }

    /// Walk calls @p callback with each styled span in the StyledText.
    /// @param callback a function with the signature: void(std::string_view, TextStyle)
    template <typename CB>
    void Walk(CB&& callback) const {
        std::string text = stream_.str();
        size_t offset = 0;
        for (auto& span : spans_) {
            callback(text.substr(offset, span.length), span.style);
            offset += span.length;
        }
    }

    /// @returns the number of UTF-8 code units (bytes) have been written to the string.
    size_t Length() { return stream_.Length(); }

  private:
    struct Span {
        TextStyle style;
        size_t length = 0;
    };

    StringStream stream_;
    Vector<Span, 1> spans_{Span{}};
};

}  // namespace tint

#endif  // SRC_TINT_UTILS_TEXT_STYLED_TEXT_H_