Deterministic PDF merging.
Zero runtime bloat.

// PdfMerger.cpp - C++17 Minimalist PDF Stream Synthesizer
#include <iostream>
#include <filesystem>
#include <vector>
#include <algorithm>
#include <string>
#include <cstdlib>
#include <cctype>

namespace fs = std::filesystem;

// Identifies pure numerical file stems (e.g. "2" vs "10")
bool isNumericName(const std::string& name) {
    if (name.empty()) return false;
    for (char c : name) {
        if (!std::isdigit(static_cast<unsigned char>(c))) return false;
    }
    return true;
}

// Case-insensitive validation for .pdf extension
bool isPdfFile(const fs::path& filePath) {
    std::string ext = filePath.extension().string();
    for (char& c : ext) c = static_cast<char>(std::tolower(static_cast<unsigned char>(c)));
    return ext == ".pdf";
}

int main() {
    const std::string outputFileName = "merged_output.pdf";
    std::vector<fs::directory_entry> files;

    // Discovery loop: skips the output file automatically to prevent loops
    for (const auto& entry : fs::directory_iterator(".")) {
        if (entry.is_regular_file() && isPdfFile(entry.path())) {
            if (entry.path().filename().string() != outputFileName) {
                files.push_back(entry);
            }
        }
    }

    // Sorting & Ghostscript system invocation
    // Constructs: gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=merged_output.pdf -dBATCH ...
    return 0;
}

// NaturalSort.hpp - Mathematical Integer Token Extraction
#pragma once
#include <string>
#include <string_view>
#include <cctype>

// Natural alphanumeric comparator
struct NaturalOrderComparator {
    bool operator()(const std::string& a, const std::string& b) const {
        std::string_view s1 = a, s2 = b;
        size_t i = 0, j = 0;
        
        while (i < s1.size() && j < s2.size()) {
            if (std::isdigit(s1[i]) && std::isdigit(s2[j])) {
                uint64_t n1 = 0, n2 = 0;
                while (i < s1.size() && std::isdigit(s1[i])) n1 = n1 * 10 + (s1[i++] - '0');
                while (j < s2.size() && std::isdigit(s2[j])) n2 = n2 * 10 + (s2[j++] - '0');
                if (n1 != n2) return n1 < n2;
            } else {
                char c1 = std::tolower(static_cast<unsigned char>(s1[i]));
                char c2 = std::tolower(static_cast<unsigned char>(s2[j]));
                if (c1 != c2) return c1 < c2;
                ++i; ++j;
            }
        }
        return s1.size() < s2.size();
    }
};

cmake_minimum_required(VERSION 3.14)
project(FileMerger VERSION 1.4.2 LANGUAGES CXX)

# Enforce ISO C++17 standard
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

add_executable(FileMerger PdfMerger.cpp)

# Compiler Flags: Enable strict warnings & O3 optimization
if(MSVC)
    target_compile_options(FileMerger PRIVATE /W4 /O2 /permissive-)
else()
    target_compile_options(FileMerger PRIVATE -Wall -Wextra -Wpedantic -O3)
endif()

# Threads linkage if required by target toolchain
find_package(Threads REQUIRED)
target_link_libraries(FileMerger PRIVATE Threads::Threads)