#include <cstring>
#include <map>
#include <optional>
#include <string>

extern char * * environ __attribute__((weak));

namespace nix {

std::optional<std::string> getEnv(const std::string & key)
{
    char * value = getenv(key.c_str());
    if (!value) return {};
    return std::string(value);
}

std::optional<std::string> getEnvNonEmpty(const std::string & key) {
    auto value = getEnv(key);
    if (value == "") return {};
    return value;
}

std::map<std::string, std::string> getEnv()
{
    std::map<std::string, std::string> env;
    for (size_t i = 0; environ[i]; ++i) {
        auto s = environ[i];
        auto eq = strchr(s, '=');
        if (!eq)
            // invalid env, just keep going
            continue;
        env.emplace(std::string(s, eq), std::string(eq + 1));
    }
    return env;
}


void clearEnv()
{
    for (auto & name : getEnv())
        unsetenv(name.first.c_str());
}

void replaceEnv(const std::map<std::string, std::string> & newEnv)
{
    clearEnv();
    for (auto & newEnvVar : newEnv)
        setenv(newEnvVar.first.c_str(), newEnvVar.second.c_str(), 1);
}

}