#include <cassert>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <regex>
#include <sstream>
#include <string>
#include <string_view>
#include <vector>

using namespace std;
using filesystem::path;

const regex LIBRE{R"/(\s*#\s*include\s*<([^>]*)>\s*)/"};
const regex HEADER{R"/(\s*#\s*include\s*"([^"]*)"\s*)/"};

path operator""_p(const char* data, std::size_t sz) {return path(data, data + sz);}

bool Preprocess(const path& file_path, const vector<path>& include_directories, istream& source, ostream& destination) {
    string line = ""s;
    int line_number = 1;
 
    while (getline(source, line)) {
        smatch m, m_1;
        
        if (!regex_match(line, m_1, LIBRE) && !regex_match(line, m, HEADER)) {
            destination << line << endl;
            
        } else {
            
            ifstream input;           
            path path, path_1;
 
            if (m.empty()) {
                path = string(m_1[1]);
                
            } else {
                path = string(m[1]);
                path_1 = file_path.parent_path()/path;
                input.open(path_1);
            }
 
            for (const auto& entry_dir : include_directories) {
                
                if (input.is_open() && input) {
                    break;
                }
                
                path_1 = entry_dir / path;
                input.open(path_1);
            }
 
            if (!input) {
                cout << "unknown include file "sv << path.string() 
                     << " at file "sv << file_path.string()
                     << " at line "sv << line_number << endl;
                
                return false;
            }
            
            if (!Preprocess(path_1, include_directories, input, destination)) {
                return false;
            }
        }
        
        ++line_number;
    }
 
    return true;
}

bool Preprocess(const path& in_file, const path& out_file, const vector<path>& include_directories) {
    
    ifstream input(in_file); 
    if (!input) {
        cerr << in_file << endl;
        return false;
    }
    
    ofstream output(out_file);
    if (!output) {
        cerr << out_file << endl;
        return false;
    }
 
    return Preprocess(in_file, include_directories, input, output);
}

string GetFileContents(string file) {
    ifstream stream(file);

    return {(istreambuf_iterator<char>(stream)), istreambuf_iterator<char>()};
}

void Test() {
    error_code err;
    filesystem::remove_all("sources"_p, err);
    filesystem::create_directories("sources"_p / "include2"_p / "lib"_p, err);
    filesystem::create_directories("sources"_p / "include1"_p, err);
    filesystem::create_directories("sources"_p / "dir1"_p / "subdir"_p, err);

    {
        ofstream file("sources/a.cpp");
        file << "// this comment before include\n"
                "#include \"dir1/b.h\"\n"
                "// text between b.h and c.h\n"
                "#include \"dir1/d.h\"\n"
                "\n"
                "int SayHello() {\n"
                "    cout << \"hello, world!\" << endl;\n"
                "#   include<dummy.txt>\n"
                "}\n"sv;
    }
    {
        ofstream file("sources/dir1/b.h");
        file << "// text from b.h before include\n"
                "#include \"subdir/c.h\"\n"
                "// text from b.h after include"sv;
    }
    {
        ofstream file("sources/dir1/subdir/c.h");
        file << "// text from c.h before include\n"
                "#include <std1.h>\n"
                "// text from c.h after include\n"sv;
    }
    {
        ofstream file("sources/dir1/d.h");
        file << "// text from d.h before include\n"
                "#include \"lib/std2.h\"\n"
                "// text from d.h after include\n"sv;
    }
    {
        ofstream file("sources/include1/std1.h");
        file << "// std1\n"sv;
    }
    {
        ofstream file("sources/include2/lib/std2.h");
        file << "// std2\n"sv;
    }

    assert((!Preprocess("sources"_p / "a.cpp"_p, "sources"_p / "a.in"_p,
                                  {"sources"_p / "include1"_p,"sources"_p / "include2"_p})));

    ostringstream test_out;
    test_out << "// this comment before include\n"
                "// text from b.h before include\n"
                "// text from c.h before include\n"
                "// std1\n"
                "// text from c.h after include\n"
                "// text from b.h after include\n"
                "// text between b.h and c.h\n"
                "// text from d.h before include\n"
                "// std2\n"
                "// text from d.h after include\n"
                "\n"
                "int SayHello() {\n"
                "    cout << \"hello, world!\" << endl;\n"sv;

    assert(GetFileContents("sources/a.in"s) == test_out.str());
}

int main() {
    Test();
}