/*
    UsenetSearch is Free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    UsenetSearch is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with UsenetSearch.  If not, see <https://www.gnu.org/licenses/>.
*/

#include "usenetsearch/ThreadPool.h"

#include <memory>
#include <mutex>

namespace usenetsearch {

ThreadPool::ThreadPool()
{
    m_threadStates = std::make_shared<ThreadStates>();
}

ThreadPool::~ThreadPool()
{
    m_stopping = true;
    JoinThreads();
}

void ThreadPool::JoinThreads()
{
    std::lock_guard<std::mutex> threadsLock(m_threadsMutex);
    std::lock_guard<std::mutex> threadStatesLock(m_threadStatesMutex);
    for (auto& thread: m_threads)
    {
        if (thread->joinable()) thread->join();
    }
    m_threads.clear();
    m_threadStates->clear();
}

void ThreadPool::MaxThreads(std::uint16_t max)
{
    m_maxThreads = max;
}

void ThreadPool::Queue(std::function<void()> fn)
{
    if (m_stopping == true) return; // not accepting new work.
    if (m_maxThreads <= 1)
    {
        // single threaded case.
        fn();
        return;
    }
    // Wait for an available thread.
    while (m_threads.size() >= m_maxThreads)
    {
        auto foundThread = m_threads.end();
        for (auto it = m_threads.begin(); it != m_threads.end(); ++it)
        {
            const auto& t = (*it);
            if (!t) continue;
                if (t->joinable()) t->join();
                foundThread = it;
                break;
        }
        if (foundThread != m_threads.end()) m_threads.erase(foundThread);
    }
    // Spawn a new thread.
    auto thread = std::make_unique<std::thread>(fn);
    m_threads.emplace_back(std::move(thread));
}

} // namespace usenetsearch