/** 
 * @file llprocess.cpp
 * @brief Utility class for launching, terminating, and tracking the state of processes.
 *
 * $LicenseInfo:firstyear=2008&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#include "linden_common.h"
#include "llprocess.h"
#include "llsdserialize.h"
#include "llsingleton.h"
#include "llstring.h"
#include "stringize.h"

#include <boost/foreach.hpp>
#include <iostream>
#include <stdexcept>

/// Need an exception to avoid constructing an invalid LLProcess object, but
/// internal use only
struct LLProcessError: public std::runtime_error
{
	LLProcessError(const std::string& msg): std::runtime_error(msg) {}
};

LLProcessPtr LLProcess::create(const LLSDParamAdapter<Params>& params)
{
	try
	{
		return LLProcessPtr(new LLProcess(params));
	}
	catch (const LLProcessError& e)
	{
		LL_WARNS("LLProcess") << e.what() << LL_ENDL;
		return LLProcessPtr();
	}
}

LLProcess::LLProcess(const LLSDParamAdapter<Params>& params):
	mProcessID(0),
	mAutokill(params.autokill)
{
	if (! params.validateBlock(true))
	{
		throw LLProcessError(STRINGIZE("not launched: failed parameter validation\n"
									   << LLSDNotationStreamer(params)));
	}

	launch(params);
}

LLProcess::~LLProcess()
{
	if (mAutokill)
	{
		kill();
	}
}

bool LLProcess::isRunning(void)
{
	mProcessID = isRunning(mProcessID, mDesc);
	return (mProcessID != 0);
}

std::ostream& operator<<(std::ostream& out, const LLProcess::Params& params)
{
	std::string cwd(params.cwd);
	if (! cwd.empty())
	{
		out << "cd " << LLStringUtil::quote(cwd) << ": ";
	}
	out << LLStringUtil::quote(params.executable);
	BOOST_FOREACH(const std::string& arg, params.args)
	{
		out << ' ' << LLStringUtil::quote(arg);
	}
	return out;
}

/*****************************************************************************
*   Windows specific
*****************************************************************************/
#if LL_WINDOWS

static std::string WindowsErrorString(const std::string& operation);

/**
 * Wrap a Windows Job Object for use in managing child-process lifespan.
 *
 * On Windows, we use a Job Object to constrain the lifespan of any
 * autokill=true child process to the viewer's own lifespan:
 * http://stackoverflow.com/questions/53208/how-do-i-automatically-destroy-child-processes-in-windows
 * (thanks Richard!).
 *
 * We manage it using an LLSingleton for a couple of reasons:
 *
 * # Lazy initialization: if some viewer session never launches a child
 *   process, we should never have to create a Job Object.
 * # Cross-DLL support: be wary of C++ statics when multiple DLLs are
 *   involved.
 */
class LLJob: public LLSingleton<LLJob>
{
public:
	void assignProcess(const std::string& prog, HANDLE hProcess)
	{
		// If we never managed to initialize this Job Object, can't use it --
		// but don't keep spamming the log, we already emitted warnings when
		// we first tried to create.
		if (! mJob)
			return;

		if (! AssignProcessToJobObject(mJob, hProcess))
		{
			LL_WARNS("LLProcess") << WindowsErrorString(STRINGIZE("AssignProcessToJobObject("
																  << prog << ")")) << LL_ENDL;
		}
	}

private:
	friend class LLSingleton<LLJob>;
	LLJob():
		mJob(0)
	{
		mJob = CreateJobObject(NULL, NULL);
		if (! mJob)
		{
			LL_WARNS("LLProcess") << WindowsErrorString("CreateJobObject()") << LL_ENDL;
			return;
		}

		JOBOBJECT_EXTENDED_LIMIT_INFORMATION jeli = { 0 };

		// Configure all child processes associated with this new job object
		// to terminate when the calling process (us!) terminates.
		jeli.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
		if (! SetInformationJobObject(mJob, JobObjectExtendedLimitInformation, &jeli, sizeof(jeli)))
		{
			LL_WARNS("LLProcess") << WindowsErrorString("SetInformationJobObject()") << LL_ENDL;
			// This Job Object is useless to us
			CloseHandle(mJob);
			// prevent assignProcess() from trying to use it
			mJob = 0;
		}
	}

	HANDLE mJob;
};

void LLProcess::launch(const LLSDParamAdapter<Params>& params)
{
	PROCESS_INFORMATION pinfo;
	STARTUPINFOA sinfo = { sizeof(sinfo) };

	// LLProcess::create()'s caller passes a Unix-style array of strings for
	// command-line arguments. Our caller can and should expect that these will be
	// passed to the child process as individual arguments, regardless of content
	// (e.g. embedded spaces). But because Windows invokes any child process with
	// a single command-line string, this means we must quote each argument behind
	// the scenes.
	std::string args = LLStringUtil::quote(params.executable);
	BOOST_FOREACH(const std::string& arg, params.args)
	{
		args += " ";
		args += LLStringUtil::quote(arg);
	}

	// So retarded.  Windows requires that the second parameter to
	// CreateProcessA be a writable (non-const) string...
	std::vector<char> args2(args.begin(), args.end());
	args2.push_back('\0');

	// Convert wrapper to a real std::string so we can use c_str(); but use a
	// named variable instead of a temporary so c_str() pointer remains valid.
	std::string cwd(params.cwd);
	const char * working_directory = 0;
	if (! cwd.empty())
		working_directory = cwd.c_str();
	if( ! CreateProcessA( NULL, &args2[0], NULL, NULL, FALSE, 0, NULL, working_directory, &sinfo, &pinfo ) )
	{
		throw LLProcessError(WindowsErrorString("CreateProcessA"));
	}

	// foo = pinfo.dwProcessId; // get your pid here if you want to use it later on
	// CloseHandle(pinfo.hProcess); // stops leaks - nothing else
	mProcessID = pinfo.hProcess;
	CloseHandle(pinfo.hThread); // stops leaks - nothing else

	mDesc = STRINGIZE(LLStringUtil::quote(params.executable) << " (" << pinfo.dwProcessId << ')');
	LL_INFOS("LLProcess") << "Launched " << params << " (" << pinfo.dwProcessId << ")" << LL_ENDL;

	// Now associate the new child process with our Job Object -- unless
	// autokill is false, i.e. caller asserts the child should persist.
	if (params.autokill)
	{
		LLJob::instance().assignProcess(mDesc, mProcessID);
	}
}

LLProcess::id LLProcess::isRunning(id handle, const std::string& desc)
{
	if (! handle)
		return 0;

	DWORD waitresult = WaitForSingleObject(handle, 0);
	if(waitresult == WAIT_OBJECT_0)
	{
		// the process has completed.
		if (! desc.empty())
		{
			LL_INFOS("LLProcess") << desc << " terminated" << LL_ENDL;
		}
		return 0;
	}

	return handle;
}

bool LLProcess::kill(void)
{
	if (! mProcessID)
		return false;

	LL_INFOS("LLProcess") << "killing " << mDesc << LL_ENDL;
	TerminateProcess(mProcessID, 0);
	return ! isRunning();
}

/// GetLastError()/FormatMessage() boilerplate
static std::string WindowsErrorString(const std::string& operation)
{
	int result = GetLastError();

	LPTSTR error_str = 0;
	if (FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
					   NULL,
					   result,
					   0,
					   (LPTSTR)&error_str,
					   0,
					   NULL)
		!= 0) 
	{
        // convert from wide-char string to multi-byte string
		char message[256];
		wcstombs(message, error_str, sizeof(message));
		message[sizeof(message)-1] = 0;
		LocalFree(error_str);
		// convert to std::string to trim trailing whitespace
		std::string mbsstr(message);
		mbsstr.erase(mbsstr.find_last_not_of(" \t\r\n"));
		return STRINGIZE(operation << " failed (" << result << "): " << mbsstr);
	}
	return STRINGIZE(operation << " failed (" << result
					 << "), but FormatMessage() did not explain");
}

/*****************************************************************************
*   Non-Windows specific
*****************************************************************************/
#else // Mac and linux

#include <signal.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/wait.h>

// Attempt to reap a process ID -- returns true if the process has exited and been reaped, false otherwise.
static bool reap_pid(pid_t pid)
{
	pid_t wait_result = ::waitpid(pid, NULL, WNOHANG);
	if (wait_result == pid)
	{
		return true;
	}
	if (wait_result == -1 && errno == ECHILD)
	{
		// No such process -- this may mean we're ignoring SIGCHILD.
		return true;
	}
	
	return false;
}

void LLProcess::launch(const LLSDParamAdapter<Params>& params)
{
	// flush all buffers before the child inherits them
	::fflush(NULL);

	pid_t child = vfork();
	if (child == 0)
	{
		// child process

		std::string cwd(params.cwd);
		if (! cwd.empty())
		{
			// change to the desired child working directory
			if (::chdir(cwd.c_str()))
			{
				// chdir failed
				LL_WARNS("LLProcess") << "could not chdir(\"" << cwd << "\")" << LL_ENDL;
				// pointless to throw; this is child process...
				_exit(248);
			}
		}

		// create an argv vector for the child process
		std::vector<const char*> fake_argv;

		// add the executable path
		std::string executable(params.executable);
		fake_argv.push_back(executable.c_str());

		// and any arguments
		std::vector<std::string> args(params.args.begin(), params.args.end());
		BOOST_FOREACH(const std::string& arg, args)
		{
			fake_argv.push_back(arg.c_str());
		}

		// terminate with a null pointer
		fake_argv.push_back(NULL);

		::execv(executable.c_str(), const_cast<char* const*>(&fake_argv[0]));

		// If we reach this point, the exec failed.
		LL_WARNS("LLProcess") << "failed to launch: ";
		BOOST_FOREACH(const char* arg, fake_argv)
		{
			LL_CONT << arg << ' ';
		}
		LL_CONT << LL_ENDL;
		// Use _exit() instead of exit() per the vfork man page. Exit with a
		// distinctive rc: someday soon we'll be able to retrieve it, and it
		// would be nice to be able to tell that the child process failed!
		_exit(249);
	}

	// parent process
	mProcessID = child;

	mDesc = STRINGIZE(LLStringUtil::quote(params.executable) << " (" << mProcessID << ')');
	LL_INFOS("LLProcess") << "Launched " << params << " (" << mProcessID << ")" << LL_ENDL;
}

LLProcess::id LLProcess::isRunning(id pid, const std::string& desc)
{
	if (! pid)
		return 0;

	// Check whether the process has exited, and reap it if it has.
	if(reap_pid(pid))
	{
		// the process has exited.
		if (! desc.empty())
		{
			LL_INFOS("LLProcess") << desc << " terminated" << LL_ENDL;
		}
		return 0;
	}

	return pid;
}

bool LLProcess::kill(void)
{
	if (! mProcessID)
		return false;

	// Try to kill the process. We'll do approximately the same thing whether
	// the kill returns an error or not, so we ignore the result.
	LL_INFOS("LLProcess") << "killing " << mDesc << LL_ENDL;
	(void)::kill(mProcessID, SIGTERM);

	// This will have the side-effect of reaping the zombie if the process has exited.
	return ! isRunning();
}

/*==========================================================================*|
static std::list<pid_t> sZombies;

void LLProcess::orphan(void)
{
	// Disassociate the process from this object
	if(mProcessID != 0)
	{	
		// We may still need to reap the process's zombie eventually
		sZombies.push_back(mProcessID);
	
		mProcessID = 0;
	}
}

// static 
void LLProcess::reap(void)
{
	// Attempt to real all saved process ID's.
	
	std::list<pid_t>::iterator iter = sZombies.begin();
	while(iter != sZombies.end())
	{
		if(reap_pid(*iter))
		{
			iter = sZombies.erase(iter);
		}
		else
		{
			iter++;
		}
	}
}
|*==========================================================================*/

#endif