#include "parallel_finder.h"

#include <mutex>
#include <thread>

using std::mutex, std::thread, std::lock_guard;

ParallelFinder::ParallelFinder(const vector<string> &word_list,
                               size_t thread_count)
    : word_list_(word_list), thread_count_(thread_count) {}

vector<const string *>
ParallelFinder::find_prefix(string_view search_term) const {
  vector<const string *> result;
  mutex result_mutex;

  vector<thread> threads;
  for (size_t thread_index = 0; thread_index < thread_count_; ++thread_index) {
    const size_t first_word_index =
        thread_index * (word_list_.size() / thread_count_);
    const size_t last_word_index =
        (thread_index == thread_count_ - 1)
            ? word_list_.size()
            : (thread_index + 1) * (word_list_.size() / thread_count_);

    threads.emplace_back(
        [](const vector<string> &word_list, const string_view &search_term,
           vector<const string *> &result, size_t start_index, size_t end_index,
           mutex &result_mutex) {
          for (size_t index = start_index; index < end_index; ++index) {
            const auto &current_word = word_list[index];
            if (current_word.starts_with(search_term)) {
              const lock_guard<mutex> lock(result_mutex);
              result.push_back(&current_word);
            }
          }
        },
        cref(word_list_), cref(search_term), ref(result), first_word_index,
        last_word_index, ref(result_mutex));
  }

  for (auto &thread : threads) {
    thread.join();
  }

  return result;
}