#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <unistd.h>
#include <sys/wait.h>


#include "lift.h"


#define STAGES 2


#define FAIL_PAUSE 0x01
#define FAIL_EXIT  0x02


unsigned    failures = 0;
const char* program_name;


void fail
(
	const char* source,
	int         mode,
	const char* format,
	...
)
{
	va_list args;
	va_start( args, format );

	perror( source );
	if( format != NULL )
	{
		fputs( program_name, stderr );
		fputs( ": ", stderr );
		vfprintf( stderr, format, args );
		fputc( '\n', stderr );
	}

	va_end( args );

	++failures;
	if( failures == STAGES || ( mode & FAIL_PAUSE ) )
	{
		pause();
	}

	if( failures == STAGES || ( mode & FAIL_EXIT ) )
	{
		exit( EXIT_FAILURE );
	}
}


void checked_take_foreground()
{
	signal( SIGTTOU, SIG_IGN );
	if( tcsetpgrp( 0, getpgrp() ) < 0 )
	{
		fail( "tcsetpgrp()", FAIL_EXIT, NULL );
	}

	signal( SIGTTOU, SIG_DFL );
}


void checked_exec
(
	char *const* command_line
)
{
	execvp( command_line[ 0 ], command_line );
	fail( "execvp()", FAIL_EXIT, "unable to execute %s", command_line[ 0 ] );
}


int main
(
	int         argc,
	char *const argv[]
)
{
	program_name = argv[ 0 ];

	struct passwd* passwd = getpwuid( getuid() );
	if( passwd == NULL )
	{
		fail( "getpwuid()", FAIL_PAUSE | FAIL_EXIT, NULL );
	}

	pid_t pid = fork();
	if( pid < 0 )
	{
		fail( "fork()", 0, NULL );
	} else if( pid == 0 )
	{
		if( setpgid( 0, 0 ) < 0 )
		{
			fail( "setpgid()", FAIL_EXIT, NULL );
		}

		checked_take_foreground();

		char formatted_pid[ 16 ];
		snprintf( formatted_pid, sizeof formatted_pid, "%d", getpid() );

		setenv( LIFT_PID_ENV, formatted_pid, 1 );
		checked_exec( argc > 1 ? &argv[ 1 ] : (char *const[]){ DEFAULT_PATH, NULL } );
	} else
	{
		int status;
		pid_t res = wait( &status );

		checked_take_foreground();
		if( res < 0 )
		{
			fail( "wait()", FAIL_PAUSE | FAIL_EXIT, NULL );
		}

		if( WIFEXITED( status ) )
		{
			if( status == 0 )
			{
				return 0;
			}

			fprintf( stderr, "Session unlifted by exit code %d\n", WEXITSTATUS( status ) );
		} else if( WIFSIGNALED( status ) )
		{
			fprintf( stderr, "Session unlifted by %s\n", strsignal( WTERMSIG( status ) ) );
		}
	}

	checked_exec( (char *const[]){ passwd->pw_shell, NULL } );
}