#include <thread>

#ifdef NO_PCRE
#include <regex>
namespace rgx = std;
#else
#include "regex-pcre.hpp"
#endif

#include "nginx-util.hpp"
#include "px5g-openssl.hpp"


#ifndef NO_UBUS
static constexpr auto UBUS_TIMEOUT = 1000;
#endif

// once a year:
static constexpr auto CRON_INTERVAL = std::string_view{"3 3 12 12 *"};

static constexpr auto LAN_SSL_LISTEN =
    std::string_view{"/var/lib/nginx/lan_ssl.listen"};

static constexpr auto LAN_SSL_LISTEN_DEFAULT =
    std::string_view{"/var/lib/nginx/lan_ssl.listen.default"};

static constexpr auto ADD_SSL_FCT = std::string_view{"add_ssl"};

static constexpr auto SSL_SESSION_CACHE_ARG =
    [](const std::string_view & /*name*/) -> std::string
    { return "shared:SSL:32k"; };

static constexpr auto SSL_SESSION_TIMEOUT_ARG = std::string_view{"64m"};


using _Line =
    std::array< std::string (*)(const std::string &, const std::string &), 2 >;

class Line {

private:

    _Line _line;

public:

    explicit Line(const _Line & line) noexcept : _line{line} {}

    template<const _Line & ...xn>
    static auto build() noexcept -> Line
    {
        return Line{_Line{
            [](const std::string & p, const std::string & b) -> std::string
            { return (... + xn[0](p, b)); },
            [](const std::string & p, const std::string & b) -> std::string
            { return (... + xn[1](p, b)); }
        }};
    }


    [[nodiscard]] auto STR(const std::string & param, const std::string & begin)
        const -> std::string
    { return _line[0](param, begin); }


    [[nodiscard]] auto RGX() const -> rgx::regex
    { return rgx::regex{_line[1]("", "")}; }

};


auto get_if_missed(const std::string & conf, const Line & LINE,
                   const std::string & val,
                   const std::string & indent="\n    ", bool compare=true)
    -> std::string;


auto delete_if(const std::string & conf, const rgx::regex & rgx,
               const std::string & val="", bool compare=false)
    -> std::string;


void add_ssl_directives_to(const std::string & name, bool isdefault);


void create_ssl_certificate(const std::string & crtpath,
                            const std::string & keypath,
                            int days=792);


void use_cron_to_recreate_certificate(const std::string & name);


void add_ssl_if_needed(const std::string & name);


void del_ssl_directives_from(const std::string & name, bool isdefault);


void del_ssl(const std::string & name);


constexpr auto _begin = _Line{
    [](const std::string & /*param*/, const std::string & begin) -> std::string
    { return begin; },

    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return R"([{;](?:\s*#[^\n]*(?=\n))*(\s*))"; }
};


constexpr auto _space = _Line{
    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return std::string{" "}; },

    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return R"(\s+)"; }
};


constexpr auto _newline = _Line{
    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return std::string{"\n"}; },

    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return std::string{"\n"}; }
};


constexpr auto _end = _Line{
    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return std::string{";"}; },

    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    { return std::string{R"(\s*;(?:[\t ]*#[^\n]*)?)"}; }
};


template<char clim='\0'>
constexpr auto _capture = _Line{
    [](const std::string & param, const std::string & /*begin*/) -> std::string
    { return '\'' + param + '\''; },

    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    {
        const auto lim = clim=='\0' ? std::string{"\\s"} : std::string{clim};
        return std::string{R"(((?:(?:"[^"]*")|(?:[^'")"} +
            lim + "][^" + lim + "]*)|(?:'[^']*'))+)";
    }
};


template<const std::string_view & strptr, char clim='\0'>
constexpr auto _escape = _Line{
    [](const std::string &  /*param*/, const std::string & /*begin*/)
        -> std::string
    {
        return clim=='\0' ?
            std::string{strptr.data()} :
            clim + std::string{strptr.data()} + clim;
    },

    [](const std::string & /*param*/, const std::string & /*begin*/)
        -> std::string
    {
        std::string ret{};
        for (char c : strptr) {
                switch(c) {
                    case '^': ret += '\\'; [[fallthrough]];
                    case '_': [[fallthrough]];
                    case '-': ret += c;
                    break;
                    default:
                        if ((isalpha(c)!=0) || (isdigit(c)!=0)) { ret += c; }
                        else { ret += std::string{"["}+c+"]"; }
                }
        }
        return "(?:"+ret+"|'"+ret+"'"+"|\""+ret+"\""+")";
    }
};


constexpr std::string_view _server_name = "server_name";

constexpr std::string_view _include = "include";

constexpr std::string_view _ssl_certificate = "ssl_certificate";

constexpr std::string_view _ssl_certificate_key = "ssl_certificate_key";

constexpr std::string_view _ssl_session_cache = "ssl_session_cache";

constexpr std::string_view _ssl_session_timeout = "ssl_session_timeout";


// For a compile time regex lib, this must be fixed, use one of these options:
// * Hand craft or macro concat them (loosing more or less flexibility).
// * Use Macro concatenation of __VA_ARGS__ with the help of:
//   https://p99.gforge.inria.fr/p99-html/group__preprocessor__for.html
// * Use constexpr---not available for strings or char * for now---look at lib.

static const auto CRON_CMD = Line::build
    < _space, _escape<NGINX_UTIL>, _space, _escape<ADD_SSL_FCT,'\''>, _space,
        _capture<>, _newline >();

static const auto NGX_SERVER_NAME =
    Line::build<_begin, _escape<_server_name>, _space, _capture<';'>, _end>();

static const auto NGX_INCLUDE_LAN_LISTEN = Line::build
    <_begin, _escape<_include>, _space, _escape<LAN_LISTEN,'\''>, _end>();

static const auto NGX_INCLUDE_LAN_LISTEN_DEFAULT = Line::build
    < _begin, _escape<_include>, _space,
        _escape<LAN_LISTEN_DEFAULT, '\''>, _end >();

static const auto NGX_INCLUDE_LAN_SSL_LISTEN = Line::build
    <_begin, _escape<_include>, _space, _escape<LAN_SSL_LISTEN, '\''>, _end>();

static const auto NGX_INCLUDE_LAN_SSL_LISTEN_DEFAULT = Line::build
    < _begin, _escape<_include>, _space,
        _escape<LAN_SSL_LISTEN_DEFAULT, '\''>, _end >();

static const auto NGX_SSL_CRT = Line::build
    <_begin, _escape<_ssl_certificate>, _space, _capture<';'>, _end>();

static const auto NGX_SSL_KEY = Line::build
    <_begin, _escape<_ssl_certificate_key>, _space, _capture<';'>, _end>();

static const auto NGX_SSL_SESSION_CACHE = Line::build
    <_begin, _escape<_ssl_session_cache>, _space, _capture<';'>, _end>();

static const auto NGX_SSL_SESSION_TIMEOUT = Line::build
    <_begin, _escape<_ssl_session_timeout>, _space, _capture<';'>, _end>();


auto get_if_missed(const std::string & conf, const Line & LINE,
                   const std::string & val,
                   const std::string & indent, bool compare)
    -> std::string
{
    if (!compare || val.empty()) {
        return rgx::regex_search(conf, LINE.RGX()) ? "" : LINE.STR(val, indent);
    }

    rgx::smatch match; // assuming last capture has the value!

    for (auto pos = conf.begin();
         rgx::regex_search(pos, conf.end(), match, LINE.RGX());
         pos += match.position(0) + match.length(0))
    {
        const std::string value = match.str(match.size() - 1);

        if (value==val || value=="'"+val+"'" || value=='"'+val+'"') {
            return "";
        }
    }

    return LINE.STR(val, indent);
}


auto delete_if(const std::string & conf, const rgx::regex & rgx,
               const std::string & val, const bool compare)
    -> std::string
{
    std::string ret{};
    auto pos = conf.begin();

    for (rgx::smatch match;
         rgx::regex_search(pos, conf.end(), match, rgx);
         pos += match.position(0) + match.length(0))
    {
        const std::string value = match.str(match.size() - 1);
        auto len = match.position(1);
        if (compare && value!=val && value!="'"+val+"'" && value!='"'+val+'"') {
            len = match.position(0) + match.length(0);
        }
        ret.append(pos, pos + len);
    }

    ret.append(pos, conf.end());
    return ret;
}


void add_ssl_directives_to(const std::string & name, const bool isdefault)
{
    const std::string prefix = std::string{CONF_DIR} + name;

    std::string conf = read_file(prefix+".conf");

    const std::string & const_conf = conf; // iteration needs const string.
    rgx::smatch match; // captures str(1)=indentation spaces, str(2)=server name
    for (auto pos = const_conf.begin();
        rgx::regex_search(pos, const_conf.end(), match, NGX_SERVER_NAME.RGX());
        pos += match.position(0) + match.length(0))
    {
        if (match.str(2).find(name) == std::string::npos) { continue; }

        const std::string indent = match.str(1);

        std::string adds = isdefault ?
            get_if_missed(conf, NGX_INCLUDE_LAN_SSL_LISTEN_DEFAULT,"",indent) :
            get_if_missed(conf, NGX_INCLUDE_LAN_SSL_LISTEN, "", indent);

        adds += get_if_missed(conf, NGX_SSL_CRT, prefix+".crt", indent);

        adds += get_if_missed(conf, NGX_SSL_KEY, prefix+".key", indent);

        adds += get_if_missed(conf, NGX_SSL_SESSION_CACHE,
                              SSL_SESSION_CACHE_ARG(name), indent, false);

        adds += get_if_missed(conf, NGX_SSL_SESSION_TIMEOUT,
                        std::string{SSL_SESSION_TIMEOUT_ARG}, indent, false);

        if (adds.length() > 0) {
            pos += match.position(0) + match.length(0);

            conf = std::string(const_conf.begin(), pos) + adds +
                    std::string(pos, const_conf.end());

            conf = isdefault ?
                delete_if(conf, NGX_INCLUDE_LAN_LISTEN_DEFAULT.RGX()) :
                delete_if(conf, NGX_INCLUDE_LAN_LISTEN.RGX());

            write_file(prefix+".conf", conf);

            std::cerr<<"Added SSL directives to "<<prefix<<".conf: ";
            std::cerr<<adds<<std::endl;
        }

        return;
    }

    auto errmsg = std::string{"add_ssl_directives_to error: "};
    errmsg += "cannot add SSL directives to " + name + ".conf, missing: ";
    errmsg += NGX_SERVER_NAME.STR(name, "\n    ") + "\n";
    throw std::runtime_error(errmsg.c_str());
}


template<typename T>
inline auto num2hex(T bytes) -> std::array<char, 2*sizeof(bytes)+1>
{
    constexpr auto n = 2*sizeof(bytes);
    std::array<char, n+1> str{};

    for (size_t i=0; i<n; ++i) {
        static const std::array<char, 17> hex{"0123456789ABCDEF"};
        static constexpr auto get = 0x0fU;
        str.at(i) = hex.at(bytes & get);

        static constexpr auto move = 4U;
        bytes >>= move;
    }

    str[n] = '\0';
    return str;
}


template<typename T>
inline auto get_nonce(const T salt=0) -> T
{
    T nonce = 0;

    std::ifstream urandom{"/dev/urandom"};

    static constexpr auto move = 6U;

    constexpr size_t steps = (sizeof(nonce)*8 - 1)/move + 1;

    for (size_t i=0; i<steps; ++i) {
        if (!urandom.good()) { throw std::runtime_error("get_nonce error"); }
        nonce = (nonce << move) + static_cast<unsigned>(urandom.get());
    }

    nonce ^= salt;

    return nonce;
}


void create_ssl_certificate(const std::string & crtpath,
                            const std::string & keypath,
                            const int days)
{
    size_t nonce = 0;

    try { nonce = get_nonce(nonce); }

    catch (...) { // the address of a variable should be random enough:
        auto addr = &crtpath;
        auto addrptr = static_cast<const size_t *>(
                        static_cast<const void *>(&addr) );
        nonce += *addrptr;
    }

    auto noncestr = num2hex(nonce);

    const auto tmpcrtpath = crtpath + ".new-" + noncestr.data();
    const auto tmpkeypath = keypath + ".new-" + noncestr.data();

    try {
        auto pkey = gen_eckey(NID_secp384r1);

        write_key(pkey, tmpkeypath);

        std::string subject {"/C=ZZ/ST=Somewhere/L=None/CN=OpenWrt/O=OpenWrt"};
        subject += noncestr.data();

        selfsigned(pkey, days, subject, tmpcrtpath);

        static constexpr auto to_seconds = 24*60*60;
        static constexpr auto leeway = 42;
        if (!checkend(tmpcrtpath, days*to_seconds - leeway)) {
            throw std::runtime_error("bug: created certificate is not valid!!");
        }

    } catch (...) {
        std::cerr<<"create_ssl_certificate error: ";
        std::cerr<<"cannot create selfsigned certificate, ";
        std::cerr<<"removing temporary files ..."<<std::endl;

        if (remove(tmpcrtpath.c_str())!=0) {
            auto errmsg = "\t cannot remove "+tmpcrtpath;
            perror(errmsg.c_str());
        }

        if (remove(tmpkeypath.c_str())!=0) {
            auto errmsg = "\t cannot remove "+tmpkeypath;
            perror(errmsg.c_str());
        }

        throw;
    }

    if ( rename(tmpcrtpath.c_str(), crtpath.c_str())!=0 ||
         rename(tmpkeypath.c_str(), keypath.c_str())!=0 )
    {
        auto errmsg = std::string{"create_ssl_certificate warning: "};
        errmsg += "cannot move "+tmpcrtpath+" to "+crtpath;
        errmsg += " or "+tmpkeypath+" to "+keypath+", continuing ... ";
        perror(errmsg.c_str());
    }

}


void use_cron_to_recreate_certificate(const std::string & name)
{
    static const char * filename = "/etc/crontabs/root";

    std::string conf{};
    try { conf = read_file(filename); }
    catch (const std::ifstream::failure &) { /* is ok if not found, create. */ }

    const std::string add = get_if_missed(conf, CRON_CMD, name);

    if (add.length() > 0) {
#ifndef NO_UBUS
        auto service = ubus::call("service","list",UBUS_TIMEOUT).filter("cron");

        if (!service) {
            std::string errmsg{"use_cron_to_recreate_certificate error: "};
            errmsg += "Cron unavailable to re-create the ssl certificate for ";
            errmsg += name + "\n";
            throw std::runtime_error(errmsg.c_str());
        } // else active with or without instances:
#endif

        write_file(filename, std::string{CRON_INTERVAL}+add, std::ios::app);

#ifndef NO_UBUS
        call("/etc/init.d/cron", "reload");
#endif

        std::cerr<<"Rebuild the ssl certificate for '";
        std::cerr<<name<<"' annually with cron."<<std::endl;
    }
}


void add_ssl_if_needed(const std::string & name)
{
    try { add_ssl_directives_to(name, name==LAN_NAME); }
    catch (...) {
        std::cerr<<"add_ssl_if_needed error: ";
        std::cerr<<"cannot add SSL directives to "<<name<<".conf"<<std::endl;
        throw;
    }

    const auto crtpath = std::string{CONF_DIR} + name + ".crt";
    const auto keypath = std::string{CONF_DIR} + name + ".key";
    constexpr auto remaining_seconds = (365 + 32)*24*60*60;
    constexpr auto validity_days = 3*(365 + 31);

    bool is_valid = true;

    if (access(keypath.c_str(), R_OK) != 0 ||
        access(crtpath.c_str(), R_OK) != 0)
    { is_valid = false; }

    else {
        try {
            if (!checkend(crtpath, remaining_seconds)) {
                is_valid = false;
            }
        }
        catch (...) { // something went wrong, maybe it is in DER format:
            try {
                if (!checkend(crtpath, remaining_seconds, false)) {
                    is_valid = false;
                }
            }
            catch (...) { // it has neither DER nor PEM format, rebuild.
                is_valid = false;
            }
        }
    }

    if (!is_valid) { create_ssl_certificate(crtpath, keypath, validity_days); }

    try { use_cron_to_recreate_certificate(name); }
    catch (...) {
        std::cerr<<"add_ssl_if_needed warning: ";
        std::cerr<<"cannot use cron to rebuild certificate for "<<name<<"\n";
    }
}


void del_ssl_directives_from(const std::string & name, const bool isdefault)
{
    const std::string prefix = std::string{CONF_DIR} + name;

    std::string conf = read_file(prefix+".conf");

    const std::string & const_conf = conf; // iteration needs const string.
    rgx::smatch match; // captures str(1)=indentation spaces, str(2)=server name
    for (auto pos = const_conf.begin();
        rgx::regex_search(pos, const_conf.end(), match, NGX_SERVER_NAME.RGX());
        pos += match.position(0) + match.length(0))
    {
        if (match.str(2).find(name) == std::string::npos) { continue; }

        const std::string indent = match.str(1);

        std::string adds = isdefault ?
            get_if_missed(conf, NGX_INCLUDE_LAN_LISTEN_DEFAULT,"",indent) :
            get_if_missed(conf, NGX_INCLUDE_LAN_LISTEN, "", indent);

        if (adds.length() > 0) {
            pos += match.position(1);

            conf = std::string(const_conf.begin(), pos) + adds
                    + std::string(pos, const_conf.end());

            conf = isdefault ?
                delete_if(conf, NGX_INCLUDE_LAN_SSL_LISTEN_DEFAULT.RGX())
                : delete_if(conf, NGX_INCLUDE_LAN_SSL_LISTEN.RGX());

            const auto crtpath = prefix+".crt";
            conf = delete_if(conf, NGX_SSL_CRT.RGX(), crtpath, true);

            const auto keypath = prefix+".key";
            conf = delete_if(conf, NGX_SSL_KEY.RGX(), keypath, true);

            conf = delete_if(conf, NGX_SSL_SESSION_CACHE.RGX());

            conf = delete_if(conf, NGX_SSL_SESSION_TIMEOUT.RGX());

            write_file(prefix+".conf", conf);

            std::cerr<<"Deleted SSL directives from "<<prefix<<".conf\n";
        }

        return;
    }

    auto errmsg = std::string{"del_ssl_directives_from error: "};
    errmsg += "cannot delete SSL directives from " + name + ".conf, missing: ";
    errmsg += NGX_SERVER_NAME.STR(name, "\n    ") + "\n";
    throw std::runtime_error(errmsg.c_str());
}


void del_ssl(const std::string & name)
{
    static const char * filename = "/etc/crontabs/root";

    try {
        const auto const_conf = read_file(filename);

        bool changed = false;
        auto conf = std::string{};

        size_t prev = 0;
        size_t curr = 0;
        while ((curr=const_conf.find('\n', prev)) != std::string::npos) {

            auto line = const_conf.substr(prev, curr-prev+1);

            if (line==delete_if(line,CRON_CMD.RGX(),std::string{name},true)) {
                conf += line;
            } else { changed = true; }

            prev = curr + 1;
        }

        if (changed) {
            write_file(filename, conf);

            std::cerr<<"Do not rebuild the ssl certificate for '";
            std::cerr<<name<<"' annually with cron anymore."<<std::endl;

#ifndef NO_UBUS
            if (ubus::call("service", "list", UBUS_TIMEOUT).filter("cron"))
            { call("/etc/init.d/cron", "reload"); }
#endif
        }

    } catch (...) {
        std::cerr<<"del_ssl warning: ";
        std::cerr<<"cannot delete cron job for "<<name<<" in "<<filename<<"\n";
    }

    try { del_ssl_directives_from(name, name==LAN_NAME); }
    catch (...) {
        std::cerr<<"del_ssl error: ";
        std::cerr<<"cannot delete SSL directives from "<<name<<".conf\n";
        throw;
    }

    const auto crtpath = std::string{CONF_DIR} + name + ".crt";

    if (remove(crtpath.c_str())!=0) {
        auto errmsg = "del_ssl warning: cannot remove "+crtpath;
        perror(errmsg.c_str());
    }

    const auto keypath = std::string{CONF_DIR} + name + ".key";

    if (remove(keypath.c_str())!=0) {
        auto errmsg = "del_ssl warning: cannot remove "+keypath;
        perror(errmsg.c_str());
    }
}


// reuse main(...) and common functions:
#define NGINX_OPENSSL
#include "nginx-util.cpp"