#include "nix/util/util.hh"
#include "nix/util/users.hh"
#include "nix/util/environment-variables.hh"
#include "nix/util/file-system.hh"

#include <pwd.h>
#include <sys/types.h>
#include <unistd.h>

namespace nix {

namespace fs { using namespace std::filesystem; }

std::string getUserName()
{
    auto pw = getpwuid(geteuid());
    std::string name = pw ? pw->pw_name : getEnv("USER").value_or("");
    if (name.empty())
        throw Error("cannot figure out user name");
    return name;
}

Path getHomeOf(uid_t userId)
{
    std::vector<char> buf(16384);
    struct passwd pwbuf;
    struct passwd * pw;
    if (getpwuid_r(userId, &pwbuf, buf.data(), buf.size(), &pw) != 0
        || !pw || !pw->pw_dir || !pw->pw_dir[0])
        throw Error("cannot determine user's home directory");
    return pw->pw_dir;
}

Path getHome()
{
    static Path homeDir = []()
    {
        std::optional<std::string> unownedUserHomeDir = {};
        auto homeDir = getEnv("HOME");
        if (homeDir) {
            // Only use $HOME if doesn't exist or is owned by the current user.
            struct stat st;
            int result = stat(homeDir->c_str(), &st);
            if (result != 0) {
                if (errno != ENOENT) {
                    warn("couldn't stat $HOME ('%s') for reason other than not existing ('%d'), falling back to the one defined in the 'passwd' file", *homeDir, errno);
                    homeDir.reset();
                }
            } else if (st.st_uid != geteuid()) {
                unownedUserHomeDir.swap(homeDir);
            }
        }
        if (!homeDir) {
            homeDir = getHomeOf(geteuid());
            if (unownedUserHomeDir.has_value() && unownedUserHomeDir != homeDir) {
                warn("$HOME ('%s') is not owned by you, falling back to the one defined in the 'passwd' file ('%s')", *unownedUserHomeDir, *homeDir);
            }
        }
        return *homeDir;
    }();
    return homeDir;
}

bool isRootUser() {
    return getuid() == 0;
}

}
