#include <algorithm>
#include <fcntl.h>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <sys/stat.h>
#include <unistd.h>
#include <unordered_map>
#include <vector>
#include <cstring>
#include <dirent.h>

#define PROC_LOCATION "/proc"

namespace Animia { namespace Linux {

std::vector<std::string> get_all_files_in_dir(const std::string& _dir) {
	std::vector<std::string> ret;

	DIR* dir = opendir(_dir.c_str());
	if (!dir)
		return ret;

	struct dirent* dp;
	while ((dp = readdir(dir)) != NULL) {
		if (!(!strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..")))
			ret.push_back(_dir + "/" + dp->d_name);
	}

	closedir(dir);
	return ret;
}

std::string basename(const std::string& path) {
	return path.substr(path.find_last_of("/") + 1, path.length());
}

std::string stem(const std::string& path) {
	std::string bn = basename(path);
	return bn.substr(0, path.find_last_of("."));
}

std::vector<int> get_all_pids() {
	std::vector<int> ret;

	for (const auto& dir : get_all_files_in_dir(PROC_LOCATION)) {
		int pid;
		try {
			pid = std::stoi(basename(dir));
		} catch (std::invalid_argument) {
			continue;
		}
		ret.push_back(pid);
	}

	return ret;
}

std::string get_process_name(int pid) {
	std::string path = PROC_LOCATION "/" + std::to_string(pid) + "/comm";
	std::ifstream t(path);
	std::stringstream buf;
	buf << t.rdbuf();

	std::string str = buf.str();
	str.erase(std::remove(str.begin(), str.end(), '\n'), str.end());
	return str;
}

static bool is_regular_file(std::string link) {
	struct stat sb;
	if (stat(link.c_str(), &sb) == -1)
		return false;
	return S_ISREG(sb.st_mode);
}

static bool are_flags_ok(int pid, int fd) {
	std::string path = PROC_LOCATION "/" + std::to_string(pid) + "/fdinfo/" + std::to_string(fd);
	std::ifstream t(path);
	std::stringstream buffer;
	buffer << t.rdbuf();
	std::string raw;
	int flags = 0;
	while (std::getline(buffer, raw)) {
		if (raw.rfind("flags:", 0) == 0) {
			flags = std::stoi(raw.substr(raw.find_last_not_of("0123456789") + 1));
		}
	}
	if (flags & O_WRONLY || flags & O_RDWR)
		return false;
	return true;
}

static std::string get_name_from_fd(std::string link) {
	size_t  exe_size = 1024;
	ssize_t exe_used;
	std::string ret;
	while (1) {
		ret = std::string(exe_size, '\0');
		exe_used = readlink(link.c_str(), &ret.front(), ret.length());
		if (exe_used == (ssize_t)-1)
			return NULL;

		if (exe_used < (ssize_t)1) {
			errno = ENOENT;
			return NULL;
		}

		if (exe_used < (ssize_t)(exe_size - 1))
			break;

		exe_size += 1024;
	}

	return ret.c_str();
}

std::vector<std::string> get_open_files(int pid) {
	std::vector<std::string> ret;
	std::string path = PROC_LOCATION "/" + std::to_string(pid) + "/fd";

	for (const auto& dir : get_all_files_in_dir(path)) {
		if (!are_flags_ok(pid, std::stoi(basename(dir))))
			continue;

		std::string buf = get_name_from_fd(dir);

		if (!is_regular_file(buf))
			continue;

		ret.push_back(buf);
	}
	return ret;
}

std::unordered_map<int, std::vector<std::string>> get_all_open_files() {
	std::unordered_map<int, std::vector<std::string>> map;
	std::vector<int> pids = get_all_pids();
	for (int i : pids)
		map[i] = get_open_files(i);
	return map;
}

} // namespace Linux
} // namespace Animia