// system headers
#include <algorithm>
#include <fcntl.h>
#include <unistd.h>
#include <functional>
#include <cstring>
#include <stdexcept>

// local headers
#include "includes/pipe_reader.h"

pipe_reader::pipe_reader(int pipe_fd) : pipe_fd_(pipe_fd) {
    // add O_NONBLOCK TO fd's flags to be able to read
    auto flags = fcntl(pipe_fd_, F_GETFL, 0);
    flags |= O_NONBLOCK;
    fcntl(pipe_fd_, F_SETFL, flags);
}

size_t pipe_reader::read(std::vector<std::string::value_type>& buffer) const {
    ssize_t rv = ::read(pipe_fd_, buffer.data(), buffer.size());

    if (rv == -1) {
        // no data available
        if (errno == EAGAIN)
            return 0;

        // TODO: introduce custom subprocess_error
        throw std::runtime_error{"unexpected error reading from pipe: " + std::string(strerror(errno))};
    }

    return rv;
}