/**
 * @file auto_fd.hh
 */

#ifndef __auto_fd_hh
#define __auto_fd_hh

#include <assert.h>
#include <unistd.h>
#include <sys/select.h>

#include <new>
#include <exception>

/**
 * Resource management class for file descriptors.
 *
 * @see auto_ptr
 */
class auto_fd {
public:
    /**
     * Wrapper for the posix pipe(2) function that stores the file descriptor
     * results in an auto_fd array.
     *
     * @param af An array of atleast two auto_fd elements, where the first
     * contains the reader end of the pipe and the second contains the writer.
     * @return The result of the pipe(2) function.
     */
    static int pipe(auto_fd *af)
    {
	int retval, fd[2];

	assert(fd != NULL);

	if ((retval = ::pipe(fd)) == 0) {
	    af[0] = fd[0];
	    af[1] = fd[1];
	}

	return(retval);
    };

    /**
     * Construct an auto_fd to manage the given file descriptor.
     *
     * @param fd The file descriptor to be managed.
     */
    auto_fd(int fd = -1)
	: af_fd(fd)
    {
	assert(fd >= -1);
	assert(fd < (int)FD_SETSIZE);
    };

    /**
     * Non-const copy constructor.  Management of the file descriptor will be
     * transferred from the source to this object and the source will be
     * cleared.
     *
     * @param af The source of the file descriptor.
     */
    auto_fd(auto_fd &af)
	: af_fd(af.release()) { };

    /**
     * Const copy constructor.  The file descriptor from the source will be
     * dup(2)'d and the new descriptor stored in this object.
     *
     * @param af The source of the file descriptor.
     */
    auto_fd(const auto_fd &af)
	: af_fd(-1)
    {
	if (af.af_fd != -1 && (this->af_fd = dup(af.af_fd)) == -1) {
	    throw std::bad_alloc();
	}
    };

    /**
     * Destructor that will close the file descriptor managed by this object.
     */
    ~auto_fd() { this->reset(); };

    /** @return The file descriptor as a pain integer. */
    operator int(void) const { return(this->af_fd); };

    /**
     * Replace the current descriptor with the given one.  The current
     * descriptor will be closed.
     *
     * @param fd The file descriptor to store in this object.
     * @return *this
     */
    auto_fd &operator=(int fd)
    {
	assert(fd >= -1);
	assert(fd < (int)FD_SETSIZE);

	this->reset(fd);
	return(*this);
    };

    /**
     * Transfer management of the given file descriptor to this object.
     *
     * @param af The old manager of the file descriptor.
     * @return *this
     */
    auto_fd &operator=(auto_fd &af)
    {
	this->reset(af.release());
	return(*this);
    };

    /**
     * Return a pointer that can be passed to functions that require an out
     * parameter for file descriptors (e.g. openpty).
     *
     * @return A pointer to the internal integer.
     */
    int *out(void)
    {
	this->reset();
	return(&this->af_fd);
    };

    /**
     * Stop managing the file descriptor in this object and return its value.
     *
     * @return The file descriptor.
     */
    int release(void)
    {
	int retval = this->af_fd;

	this->af_fd = -1;
	return(retval);
    };

    /**
     * @return The file descriptor.
     */
    int get(void) const { return(this->af_fd); };

    /**
     * Closes the current file descriptor and replaces its value with the given
     * one.
     *
     * @param fd The new file descriptor to be managed.
     */
    void reset(int fd = -1)
    {
	assert(fd >= -1);
	assert(fd < (int)FD_SETSIZE);

	if (this->af_fd != fd) {
	    if (this->af_fd != -1) {
		close(this->af_fd);
	    }
	    this->af_fd = fd;
	}
    };

private:
    int af_fd;  /*< The managed file descriptor. */
};

#endif