src/tint/utils/string_stream.h

// Copyright 2023 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef SRC_TINT_UTILS_STRING_STREAM_H_
#define SRC_TINT_UTILS_STRING_STREAM_H_

#include <functional>
#include <iomanip>
#include <iterator>
#include <limits>
#include <sstream>
#include <string>
#include <utility>

#include "src/tint/utils/unicode.h"

namespace tint::utils {

/// Stringstream wrapper which automatically resets the locale and sets floating point emission
/// settings needed for Tint.
class StringStream {
    using SetWRetTy = decltype(std::setw(std::declval<int>()));
    using SetPrecisionRetTy = decltype(std::setprecision(std::declval<int>()));
    using SetFillRetTy = decltype(std::setfill(std::declval<char>()));

    /// Evaluates to true if `T` is the return type of std::setw, std:setprecision or std::setfill.
    template <typename T>
    static constexpr bool IsSetType = std::is_same_v<SetWRetTy, std::decay_t<T>> ||
                                      std::is_same_v<SetPrecisionRetTy, std::decay_t<T>> ||
                                      std::is_same_v<SetFillRetTy, std::decay_t<T>>;

  public:
    /// Constructor
    StringStream();
    /// Destructor
    ~StringStream();

    /// @returns the format flags for the stream
    std::ios_base::fmtflags flags() const { return sstream_.flags(); }

    /// @param flags the flags to set
    /// @returns the original format flags
    std::ios_base::fmtflags flags(std::ios_base::fmtflags flags) { return sstream_.flags(flags); }

    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    template <typename T,
              typename std::enable_if_t<std::is_integral_v<std::decay_t<T>>, bool> = true>
    StringStream& operator<<(T&& value) {
        return EmitValue(std::forward<T>(value));
    }

    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    StringStream& operator<<(const char* value) { return EmitValue(value); }
    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    StringStream& operator<<(const std::string& value) { return EmitValue(value); }
    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    StringStream& operator<<(std::string_view value) { return EmitValue(value); }

    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    StringStream& operator<<(const void* value) { return EmitValue(value); }

    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    template <typename T,
              typename std::enable_if_t<std::is_floating_point_v<std::decay_t<T>>, bool> = true>
    StringStream& operator<<(T&& value) {
        return EmitFloat(std::forward<T>(value));
    }

    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    template <typename T>
    StringStream& EmitValue(T&& value) {
        sstream_ << std::forward<T>(value);
        return *this;
    }

    /// Emit `value` to the stream
    /// @param value the value to emit
    /// @returns a reference to this
    template <typename T>
    StringStream& EmitFloat(const T& value) {
        // Try printing the float in fixed point, with a smallish limit on the precision
        std::stringstream fixed;
        fixed.flags(fixed.flags() | std::ios_base::showpoint | std::ios_base::fixed);
        fixed.imbue(std::locale::classic());
        fixed.precision(20);
        fixed << value;

        std::string str = fixed.str();

        // If this string can be parsed without loss of information, use it.
        // (Use double here to dodge a bug in older libc++ versions which would incorrectly read
        // back FLT_MAX as INF.)
        double roundtripped;
        fixed >> roundtripped;

        // Strip trailing zeros from the number.
        auto float_equal_no_warning = std::equal_to<T>();
        if (float_equal_no_warning(value, static_cast<T>(roundtripped))) {
            while (str.length() >= 2 && str[str.size() - 1] == '0' && str[str.size() - 2] != '.') {
                str.pop_back();
            }

            sstream_ << str;
            return *this;
        }

        // Resort to scientific, with the minimum precision needed to preserve the whole float
        std::stringstream sci;
        sci.imbue(std::locale::classic());
        sci.precision(std::numeric_limits<T>::max_digits10);
        sci << value;
        sstream_ << sci.str();

        return *this;
    }

    /// Swaps streams
    /// @param other stream to swap too
    void swap(StringStream& other) { sstream_.swap(other.sstream_); }

    /// repeat queues the character c to be written to the printer n times.
    /// @param c the character to print `n` times
    /// @param n the number of times to print character `c`
    void repeat(char c, size_t n) { std::fill_n(std::ostream_iterator<char>(sstream_), n, c); }

    /// The callback to emit a `endl` to the stream
    using StdEndl = std::ostream& (*)(std::ostream&);

    /// @param manipulator the callback to emit too
    /// @returns a reference to this
    StringStream& operator<<(StdEndl manipulator) {
        // call the function, and return it's value
        manipulator(sstream_);
        return *this;
    }

    /// @param manipulator the callback to emit too
    /// @returns a reference to this
    StringStream& operator<<(decltype(std::hex) manipulator) {
        // call the function, and return it's value
        manipulator(sstream_);
        return *this;
    }

    /// @param value the value to emit
    /// @returns a reference to this
    template <typename T, typename std::enable_if_t<IsSetType<T>, int> = 0>
    StringStream& operator<<(T&& value) {
        // call the function, and return it's value
        sstream_ << std::forward<T>(value);
        return *this;
    }

    /// @returns the current location in the output stream
    uint32_t tellp() { return static_cast<uint32_t>(sstream_.tellp()); }

    /// @returns the string contents of the stream
    std::string str() const { return sstream_.str(); }

  private:
    std::stringstream sstream_;
};

/// Writes the CodePoint to the stream.
/// @param out the stream to write to
/// @param codepoint the CodePoint to write
/// @returns out so calls can be chained
utils::StringStream& operator<<(utils::StringStream& out, CodePoint codepoint);

}  // namespace tint::utils

#endif  // SRC_TINT_UTILS_STRING_STREAM_H_