#include "common/Email.h"

#include <curl/curl.h>
#include <drogon/drogon.h>

#include <algorithm>
#include <cstddef>
#include <cstring>
#include <memory>
#include <sstream>

namespace visione::email
{
namespace
{
const Json::Value &mailConfig()
{
    return drogon::app().getCustomConfig()["mail"];
}

std::string configString(const std::string &key, const std::string &fallback)
{
    const auto &mail = mailConfig();
    return mail.get(key, fallback).asString();
}

int configInt(const std::string &key, int fallback)
{
    const auto &mail = mailConfig();
    return mail.get(key, fallback).asInt();
}

bool configBool(const std::string &key, bool fallback)
{
    const auto &mail = mailConfig();
    return mail.get(key, fallback).asBool();
}

struct SmtpDefaults
{
    std::string host;
    int port;
    std::string username;
    bool useTls;
    bool useStartTls;
    bool verifyPeer;
    bool verifyHost;
};

SmtpDefaults smtpDefaults(const std::string &provider)
{
    if (provider == "resend")
    {
        return {
            .host = "smtp.resend.com",
            .port = 465,
            .username = "resend",
            .useTls = true,
            .useStartTls = false,
            .verifyPeer = true,
            .verifyHost = true,
        };
    }

    return {
        .host = "127.0.0.1",
        .port = 1025,
        .username = "",
        .useTls = false,
        .useStartTls = false,
        .verifyPeer = false,
        .verifyHost = false,
    };
}

std::string smtpUrl(const std::string &host, int port, bool useTls)
{
    return (useTls ? "smtps://" : "smtp://") + host + ":" + std::to_string(port);
}

struct UploadContext
{
    const std::string *payload;
    size_t offset{0};
};

size_t readPayload(char *buffer, size_t size, size_t count, void *userData)
{
    auto *context = static_cast<UploadContext *>(userData);
    const auto capacity = size * count;
    const auto remaining = context->payload->size() - context->offset;
    const auto bytesToCopy = std::min(capacity, remaining);

    if (bytesToCopy == 0)
    {
        return 0;
    }

    std::memcpy(buffer,
                context->payload->data() + static_cast<std::ptrdiff_t>(context->offset),
                bytesToCopy);
    context->offset += bytesToCopy;
    return bytesToCopy;
}

bool ensureCurlInitialized()
{
    static const bool initialized = []() {
        const auto result = curl_global_init(CURL_GLOBAL_DEFAULT);
        if (result != CURLE_OK)
        {
            LOG_ERROR << "curl_global_init failed: " << curl_easy_strerror(result);
            return false;
        }
        return true;
    }();
    return initialized;
}
}  // namespace

std::string EmailService::deliveryName() const
{
    return configString("provider", "smtp");
}

bool EmailService::sendOtp(const std::string &to, const std::string &code) const
{
    const auto provider = deliveryName();
    const auto defaults = smtpDefaults(provider);
    const auto host = configString("host", defaults.host);
    const auto port = configInt("port", defaults.port);
    const auto username = configString("username", defaults.username);
    const auto password = configString("password", "");
    const auto from = configString("from", "");
    const auto useTls = configBool("use_tls", defaults.useTls);
    const auto useStartTls = configBool("use_starttls", defaults.useStartTls);
    const auto verifyPeer = configBool("verify_peer", defaults.verifyPeer);
    const auto verifyHost = configBool("verify_host", defaults.verifyHost);

    if (host.empty() || from.empty())
    {
        LOG_ERROR << "Email delivery configuration missing: host or from";
        return false;
    }
    if (provider == "resend" && password.empty())
    {
        LOG_ERROR << "Email delivery configuration missing: SMTP password for Resend";
        return false;
    }

    if (!ensureCurlInitialized())
    {
        return false;
    }

    std::ostringstream payload;
    payload << "To: <" << to << ">\r\n";
    payload << "From: Visione <" << from << ">\r\n";
    payload << "Subject: Codice OTP Visione\r\n";
    payload << "MIME-Version: 1.0\r\n";
    payload << "Content-Type: text/plain; charset=utf-8\r\n";
    payload << "\r\n";
    payload << "Il tuo codice OTP per Visione e': " << code << "\r\n";
    payload << "Scade tra 10 minuti.\r\n";
    const auto payloadString = payload.str();
    const auto url = smtpUrl(host, port, useTls);
    const auto mailFrom = "<" + from + ">";
    const auto recipientAddress = "<" + to + ">";

    using CurlHandle = std::unique_ptr<CURL, decltype(&curl_easy_cleanup)>;
    using CurlList = std::unique_ptr<curl_slist, decltype(&curl_slist_free_all)>;

    CurlHandle curl(curl_easy_init(), &curl_easy_cleanup);
    if (!curl)
    {
        LOG_ERROR << "Could not initialize libcurl SMTP handle";
        return false;
    }

    CurlList recipients(nullptr, &curl_slist_free_all);
    recipients.reset(curl_slist_append(nullptr, recipientAddress.c_str()));
    if (!recipients)
    {
        LOG_ERROR << "Could not build SMTP recipient list for " << to;
        return false;
    }

    UploadContext uploadContext{.payload = &payloadString};
    char errorBuffer[CURL_ERROR_SIZE] = {0};

    curl_easy_setopt(curl.get(), CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl.get(), CURLOPT_MAIL_FROM, mailFrom.c_str());
    curl_easy_setopt(curl.get(), CURLOPT_MAIL_RCPT, recipients.get());
    curl_easy_setopt(curl.get(), CURLOPT_READFUNCTION, readPayload);
    curl_easy_setopt(curl.get(), CURLOPT_READDATA, &uploadContext);
    curl_easy_setopt(curl.get(), CURLOPT_UPLOAD, 1L);
    curl_easy_setopt(curl.get(), CURLOPT_USERAGENT, "visione-backend/1.0");
    curl_easy_setopt(curl.get(), CURLOPT_CONNECTTIMEOUT, 10L);
    curl_easy_setopt(curl.get(), CURLOPT_TIMEOUT, 20L);
    curl_easy_setopt(curl.get(), CURLOPT_ERRORBUFFER, errorBuffer);
    curl_easy_setopt(curl.get(), CURLOPT_SSL_VERIFYPEER, verifyPeer ? 1L : 0L);
    curl_easy_setopt(curl.get(), CURLOPT_SSL_VERIFYHOST, verifyHost ? 2L : 0L);

    if (!username.empty())
    {
        curl_easy_setopt(curl.get(), CURLOPT_USERNAME, username.c_str());
    }
    if (!password.empty())
    {
        curl_easy_setopt(curl.get(), CURLOPT_PASSWORD, password.c_str());
    }
    if (useStartTls)
    {
        curl_easy_setopt(curl.get(), CURLOPT_USE_SSL, CURLUSESSL_ALL);
    }

    const auto result = curl_easy_perform(curl.get());
    if (result != CURLE_OK)
    {
        LOG_ERROR << "OTP email delivery failed via SMTP for "
                  << to
                  << ", provider="
                  << provider
                  << ", host="
                  << host
                  << ", port="
                  << port
                  << ", error="
                  << (errorBuffer[0] != '\0' ? errorBuffer : curl_easy_strerror(result));
        return false;
    }

    LOG_INFO << "OTP email sent via SMTP for " << to
             << ", provider=" << provider
             << ", host=" << host
             << ", port=" << port;
    return true;
}
}  // namespace visione::email