#include <sys/stat.h>
#include <stdexcept>
#include <iostream>
#include <fstream>
#include <string>
#include <map>
#include <utility>
#include <regex>
#include <locale>
#include <clocale>
#include <stdio.h>
#include <codecvt>

using namespace std;

// Map of found words + number of occasions
typedef map<wstring, int> WordMap;
// For ordering
typedef pair<wstring, int> WordFrequency;

// Since we don't know which locales current system have installed let's try this list
const vector<string> RU_LOCALES = { "ru_RU.UTF-8", "ru_RU", "ru" };

// Yep, I googled this one
bool FileExists(const char* name) {
	struct stat buffer;
	return (stat(name, &buffer) == 0);
}

// Just in case basic checks for input parameters
int CheckParams(int argc, char *argv[]) {
	if (argc < 3) {
		throw invalid_argument("Invalid parameters. Two arguments required: input filename and output filename");
	}
	if (!FileExists(argv[1])) {
		char* msg = new char[256];
		snprintf(msg, 256, "Cannot open file \"%s\"", argv[1]);
		throw invalid_argument(msg);
	}
	return 0;
}

int main(int argc, char *argv[]) {
	// Enterprise level code here we go
	try {
		CheckParams(argc, argv);
	}
	catch (const exception& e) {
		cerr << e.what();
		return 0;
	}
	// Just kidding
	for (unsigned int i = 0; i < RU_LOCALES.size(); i++) {
		try {
			locale::global(locale(locale(RU_LOCALES[i]), new codecvt_utf8<wchar_t>));
			break;
		}
		catch (const exception&) {
			if (RU_LOCALES.size()-1 == i) {
				cout << "Warning: Cannot set locale \"ru\". Cyrillic characters may not be detected correctly" << endl;
			}
		}
	}
	wstring token;
	WordMap words;
	wifstream input;
	wofstream output;
	input.open(argv[1]);
	output.open(argv[2]);
	// Variables for tranforming and parsing text
	wregex rx(L"[[:alpha:]]+");
	wsmatch word;
	locale currentLocale("");
	while (!input.eof()) {
		input >> token;
		// To lowercase
		transform(
			token.begin(),
			token.end(),
			token.begin(),
			[&currentLocale] (wchar_t c) {
				return tolower(c, currentLocale);
			}
		);
		auto from(token.cbegin());
		// Find words with regex and shove them into a map
		while (regex_search(from, token.cend(), word, rx))
		{
			auto node = words.find(word[0]);
			// if it's already in there increment counter
			if (node != words.cend()) {
				node->second++;
			}
			else {
				words.insert(make_pair(word[0], 1));
			}
			from += word.position() + word.length();
		}
	}
	// Now make an ordered list of words
	vector<WordFrequency> ordered;
	for (auto it = words.cbegin(); it != words.cend(); it++) {
		ordered.push_back(*it);
	}
	sort(
		ordered.begin(),
		ordered.end(),
		[](WordFrequency elem1, WordFrequency elem2) -> bool {
			// first sort by frequency, then lexicographically
			return elem1.second > elem2.second
				|| elem1.second == elem2.second && elem1.first < elem2.first;
		}
	);
	// We did it boys
	for (auto it = ordered.cbegin(); it != ordered.cend(); it++) {
		output << it->second << ' ' << it->first << endl;
	}
	return 0;
}