escape_for_file_name.cpp

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/*
 * Copyright 2025 MusicScience37 (Kenta Kabashima)
 *
 * 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.
 */
#include "stat_bench/util/escape_for_file_name.h"
 
#include <array>
#include <cstddef>
#include <cstdint>
#include <string>
#include <string_view>
 
namespace stat_bench {
namespace util {
 
namespace {

constexpr std::string_view safe_chars =
    "!+-"
    "0123456789"
    "@"
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "^_"
    "abcdefghijklmnopqrstuvwxyz"
    "{}~";

constexpr std::size_t num_8bit_chars = 256;

[[nodiscard]] constexpr auto create_safe_char_table()
    -> std::array<bool, num_8bit_chars> {
    std::array<bool, num_8bit_chars> table{};
    for (std::size_t i = 0; i < num_8bit_chars; ++i) {
        table[i] = false;
    }
    for (const char c : safe_chars) {
        table[static_cast<std::uint8_t>(c)] = true;
    }
    return table;
}

[[nodiscard]] auto is_safe_char(char c) -> bool {
    static constexpr auto table = create_safe_char_table();
    return table[static_cast<std::uint8_t>(c)];
}
 
}  // namespace
 
auto escape_for_file_name(const Utf8String& input) -> Utf8String {
    std::string output;
    for (const char c : input.str()) {
        if (!is_safe_char(c)) {
            output.push_back('%');
            constexpr std::string_view hex_chars = "0123456789ABCDEF";
            const auto byte =
                static_cast<unsigned>(static_cast<std::uint8_t>(c));
            constexpr unsigned mask = 0xFU;
            output.push_back(hex_chars[(byte >> 4U) & mask]);
            output.push_back(hex_chars[byte & mask]);
        } else {
            output.push_back(c);
        }
    }
    return Utf8String(output);
}
 
}  // namespace util
}  // namespace stat_bench