/* Copyright (C) 2004 J.F.Dockes
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the
 *   Free Software Foundation, Inc.,
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
#ifndef _EXECMD_H_INCLUDED_
#define _EXECMD_H_INCLUDED_
#include <signal.h>
#include <string>
#include <vector>
#include <stack>
#ifndef NO_NAMESPACES
using std::string;
using std::vector;
using std::stack;
#endif

#include "netcon.h"

/** 
 * Callback function object to advise of new data arrival, or just periodic 
 * heartbeat if cnt is 0. 
 *
 * To interrupt the command, the code using ExecCmd should either
 * raise an exception inside newData() (and catch it in doexec's caller), or 
 * call ExecCmd::setKill() 
 * 
 */
class ExecCmdAdvise {
 public:
    virtual ~ExecCmdAdvise() {}
    virtual void newData(int cnt) = 0;
};

/** 
 * Callback function object to get more input data. Data has to be provided
 * in the initial input string, set it to empty to signify eof.
 */
class ExecCmdProvide {
 public:
    virtual ~ExecCmdProvide() {}
    virtual void newData() = 0;
};

/**
 * Execute command possibly taking both input and output (will do
 * asynchronous io as appropriate for things to work).
 *
 * Input to the command can be provided either once in a parameter to doexec
 * or provided in chunks by setting a callback which will be called to 
 * request new data. In this case, the 'input' parameter to doexec may be
 * empty (but not null)
 *
 * Output from the command is normally returned in a single string, but a
 * callback can be set to be called whenever new data arrives, in which case
 * it is permissible to consume the data and erase the string.
 * 
 * Note that SIGPIPE should be ignored and SIGCLD blocked when calling doexec,
 * else things might fail randomly. (This is not done inside the class because
 * of concerns with multithreaded programs).
 *
 */
class ExecCmd {
 public:
    // Use vfork instead of fork. This must not be called in a multithreaded 
    // program.
    static void useVfork(bool on)
    {
	o_useVfork  = on;
    }
    /** 
     * Add/replace environment variable before executing command. This must
     * be called before doexec() to have an effect (possibly multiple
     * times for several variables).
     * @param envassign an environment assignment string ("name=value")
     */
    void putenv(const string &envassign);
    void putenv(const string &name, const string& value);

    /** 
     * Set function objects to call whenever new data is available or on
     * select timeout / whenever new data is needed to send. Must be called
     * before doexec()
     */
    void setAdvise(ExecCmdAdvise *adv) {m_advise = adv;}
    void setProvide(ExecCmdProvide *p) {m_provide = p;}

    /**
     * Set select timeout in milliseconds. The default is 1 S. 
     * This is NOT a time after which an error will occur, but the period of
     * the calls to the cancellation check routine.
     */
    void setTimeout(int mS) {if (mS > 30) m_timeoutMs = mS;}

    /** 
     * Set destination for stderr data. The default is to let it alone (will 
     * usually go to the terminal or to wherever the desktop messages go).
     * There is currently no option to put stderr data into a program variable
     * If the parameter can't be opened for writing, the command's
     * stderr will be closed.
     */
    void setStderr(const string &stderrFile) {m_stderrFile = stderrFile;}

    /**
     * Execute command. 
     *
     * Both input and output can be specified, and asynchronous 
     * io (select-based) is used to prevent blocking. This will not
     * work if input and output need to be synchronized (ie: Q/A), but
     * works ok for filtering.
     * The function is exception-safe. In case an exception occurs in the 
     * advise callback, fds and pids will be cleaned-up properly.
     *
     * @param cmd the program to execute. This must be an absolute file name 
     *   or exist in the PATH.
     * @param args the argument vector (NOT including argv[0]).
     * @param input Input to send TO the command.
     * @param output Output FROM the command.
     * @return the exec ouput status (0 if ok), or -1
     */
    int doexec(const string &cmd, const vector<string>& args, 
	       const string *input = 0, 
	       string *output = 0);

    /*
     * The next four methods can be used when a Q/A dialog needs to be 
     * performed with the command
     */
    int startExec(const string &cmd, const vector<string>& args, 
		  bool has_input, bool has_output);
    int send(const string& data);
    int receive(string& data, int cnt = -1);
    int getline(string& data);
    int wait();
    /** Wait with WNOHANG set. 
	@return true if process exited, false else.
	@param O: status, the wait(2) call's status value */
    bool maybereap(int *status);

    pid_t getChildPid() {return m_pid;}

    /** 
     * Cancel/kill command. This can be called from another thread or
     * from the advise callback, which could also raise an exception to 
     * accomplish the same thing
     */
    void setKill() {m_killRequest = true;}

    /**
     * Get rid of current process (become ready for start). 
     */
    void zapChild() {setKill(); (void)wait();}

    ExecCmd()
	: m_advise(0), m_provide(0), m_timeoutMs(1000)
    {
	reset();
    }
    ~ExecCmd();

    /**
     * Utility routine: check if/where a command is found according to the
     * current PATH (or the specified one
     * @param cmd command name
     * @param exe on return, executable path name if found
     * @param path exec seach path to use instead of getenv(PATH)
     * @return true if found
     */
    static bool which(const string& cmd, string& exe, const char* path = 0);

    /**
     * Execute command and return stdout output in a string
     * @param cmd input: command and args
     * @param out output: what the command printed
     * @return true if exec status was 0
     */
    static bool backtick(const std::vector<std::string> cmd, std::string& out);

    friend class ExecCmdRsrc;
 private:
    static bool      o_useVfork;

    vector<string>   m_env;
    ExecCmdAdvise   *m_advise;
    ExecCmdProvide  *m_provide;
    bool             m_killRequest;
    int              m_timeoutMs;
    string           m_stderrFile;
    // Pipe for data going to the command
    int              m_pipein[2];
    NetconP          m_tocmd;
    // Pipe for data coming out
    int              m_pipeout[2];
    NetconP          m_fromcmd;
    // Subprocess id
    pid_t            m_pid;
    // Saved sigmask
    sigset_t         m_blkcld;

    // Reset internal state indicators. Any resources should have been
    // previously freed
    void reset() {
	m_killRequest = false;
	m_pipein[0] = m_pipein[1] = m_pipeout[0] = m_pipeout[1] = -1;
	m_pid = -1;
	sigemptyset(&m_blkcld);
    }
    // Child process code
    inline void dochild(const string &cmd, const char **argv, 
			const char **envv, bool has_input, bool has_output);
    /* Copyconst and assignment private and forbidden */
    ExecCmd(const ExecCmd &) {}
    ExecCmd& operator=(const ExecCmd &) {return *this;};
};


/** 
 * Rexecute self process with the same arguments. 
 *
 * Note that there are some limitations:
 *  - argv[0] has to be valid: an executable name which will be found in 
 *    the path when exec is called in the initial working directory. This is 
 *    by no means guaranteed. The shells do this, but argv[0] could be an
 *    arbitrary string.
 *  - The initial working directory must be found and remain valid.
 *  - We don't try to do anything with fd 0,1,2. If they were changed by the
 *    program, their initial meaning won't be the same as at the moment of the 
 *    initial invocation.
 *  - We don't restore the signals. Signals set to be blocked 
 *    or ignored by the program will remain ignored even if this was not their
 *    initial state.
 *  - The environment is also not restored.
 *  - Others system aspects ?
 *  - Other program state: application-dependant. Any external cleanup 
 *    (temp files etc.) must be performed by the application. ReExec() 
 *    duplicates the atexit() function to make this easier, but the 
 *    ReExec().atexit() calls must be done explicitely, this is not automatic
 * 
 * In short, this is usable in reasonably controlled situations and if there 
 * are no security issues involved, but this does not perform miracles.
 */
class ReExec {
public:
    ReExec() {}
    ReExec(int argc, char *argv[]);
    void init(int argc, char *argv[]);
    int atexit(void (*function)(void))
    {
	m_atexitfuncs.push(function);
	return 0;
    }
    void reexec();
    const string& getreason() {return m_reason;}
    // Insert new args into the initial argv. idx designates the place
    // before which the new args are inserted (the default of 1
    // inserts after argv[0] which would probably be an appropriate
    // place for additional options)
    void insertArgs(const vector<string>& args, int idx = 1);
    void removeArg(const string& arg);
private:
    vector<string> m_argv;
    string m_curdir;
    int    m_cfd;
    string m_reason;
    stack<void (*)(void)> m_atexitfuncs;
};

#endif /* _EXECMD_H_INCLUDED_ */
