#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include <dirent.h>
#include <signal.h>
#include <errno.h>
#include <fcntl.h>
#include "yeeshell.h"

/* record cmdline history */
char *history[CMDLINE_HISTORY_MAX_QUANTITY];
int cmdline_amount = 0;

/* if true, print additional output */
int verbose = 0;

/* next job ID to allocate */
int nextjid = 1;

/* environment variable */
extern char **environ;

/* The job list */
struct job_t jobs[JOBS_MAX_QUANTITY];

int main()
{
	char *cmdline = NULL, *pwd = NULL;
	char *args[ARGS_MAX_QUANTITY];
	int status = 1;
	pwd = (char *)calloc(PATH_MAX_SIZE, sizeof(char));
	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
	{
		history[i] = (char *)calloc(CMDLINE_MAX_SIZE, sizeof(char));
	}

	/* Install the signal handlers */
	Signal(SIGINT, sigint_handler);	  /* ctrl-c */
	Signal(SIGTSTP, sigtstp_handler); /* ctrl-z */
	Signal(SIGCHLD, sigchld_handler); /* Terminated or stopped child */
	Signal(SIGQUIT, sigquit_handler);

	/* initiate job list */
	initjobs(jobs);

	/* execute the shell's read, parse and execution loop */
	do
	{
		if (!getcwd(pwd, PATH_MAX_SIZE))
		{
			printf("yeeshell: The current path cannot be obtained!\n");
			exit(0);
		}
		printf("[root@yeeshell %s]# ", pwd);
		cmdline = readline();
		strcpy(history[cmdline_amount++], cmdline);
		status = execute(cmdline, args);
		free(cmdline);
	} while (status);
	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
	{
		free(history[i]);
	}
	exit(EXIT_SUCCESS);
}

char *readline()
{
	char *cmdline = NULL;
	ssize_t bufsize = 0;
	getline(&cmdline, &bufsize, stdin);
	return cmdline;
}

int parseline(char *cmdline, char **args)
{
	static char array[CMDLINE_MAX_SIZE]; /* holds local copy of command line */
	char *buf = array;					 /* ptr that traverses command line */
	char *delim;						 /* points to first space delimiter */
	int argc;							 /* number of args */
	int bg;								 /* background job? */

	strcpy(buf, cmdline);
	buf[strlen(buf) - 1] = ' ';	  /* replace trailing '\n' with space */
	while (*buf && (*buf == ' ')) /* ignore leading spaces */
	{
		buf++;
	}

	/* Build the argv list */
	argc = 0;
	if (*buf == '\'')
	{
		buf++;
		delim = strchr(buf, '\'');
	}
	else
	{
		delim = strchr(buf, ' ');
	}

	while (delim)
	{
		args[argc++] = buf;
		*delim = '\0';
		buf = delim + 1;
		while (*buf && (*buf == ' ')) /* ignore spaces */
		{
			buf++;
		}

		if (*buf == '\'')
		{
			buf++;
			delim = strchr(buf, '\'');
		}
		else
		{
			delim = strchr(buf, ' ');
		}
	}
	args[argc] = NULL;

	if (argc == 0) /* ignore blank line */
	{
		return 1;
	}

	/* should the job run in the background? */
	if ((bg = (*args[argc - 1] == '&')) != 0)
	{
		args[--argc] = NULL;
	}
	return bg;
}

int check_redirect(char **args, char *redirect_filename, char **redirect_args)
{
	int i = 0, j = 0, redirect_flag = REDIRECT_NO;
	while (args[i] != NULL)
	{
		if (!strcmp(args[i], ">"))
		{
			redirect_flag = REDIRECT_OUT;
			break;
		}
		else if (!strcmp(args[i], "<"))
		{
			redirect_flag = REDIRECT_IN;
			break;
		}
		i++;
	}

	if (redirect_flag == 1) /* redirect output */
	{
		strcpy(redirect_filename, args[i + 1]);
		for (j = 0; j < i; j++)
		{
			redirect_args[j] = args[j];
		}
	}
	else if (redirect_flag == 2) /* redirect input */
	{
		redirect_filename = args[0];
		i++;
		while (args[i] != NULL)
		{
			redirect_args[j++] = args[i++];
		}
	}
	return redirect_flag;
}

int execute(char *cmdline, char **args)
{
	int bg = 0, i = 0, redirect_flag = 0, fd = 1;
	pid_t pid;
	char *redirect_filename = NULL;
	redirect_filename = (char *)calloc(32, sizeof(char));
	char *redirect_args[ARGS_MAX_QUANTITY];
	sigset_t mask_all, mask_prev;
	sigprocmask(SIG_BLOCK, NULL, &mask_all);
	sigaddset(&mask_all, SIGCHLD);
	bg = parseline(cmdline, args);
	redirect_flag = check_redirect(args, redirect_filename, redirect_args);

	if (args[0] == NULL)
	{
		return 1;
	}
	if (!built_in(args))
	{
		/* Prevent child processes from ending between parent processes, that is, between addJob and deleteJob. */
		sigprocmask(SIG_BLOCK, &mask_all, &mask_prev); /* Shield SIGCHLD */

		if ((pid = fork()) == 0) /* Child process */
		{
			if (redirect_flag == 1)
			{
				fd = open(redirect_filename, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR | S_IXUSR);
				close(1);
				dup2(1, fd);
			}
			else if (redirect_flag == 2)
			{
				fd = open(redirect_filename, O_RDONLY, S_IRUSR);
				close(0);
				dup2(0, fd);
			}

			/* The child process inherits the parent's signal mask and will inherit it after exec, 
            so it needs to restore the signal mask before executing. */
			sigprocmask(SIG_SETMASK, &mask_prev, NULL); /* Child process, unblock SIGCHLD */

			/* Set the pid of the current process to the group number of the process group it belongs to. */
			/* avoid being grouped with tsh */
			setpgid(0, 0);
			if (execvp(args[0], args) <= 0)
			{
				printf("%s: Command not found\n", args[0]);
				free(redirect_filename);
				free(redirect_args);
				exit(0);
			}
		}
		else
		{
			if (bg) /* bg task */
			{
				addjob(jobs, pid, BG, cmdline);
			}
			else /* fg task */
			{
				addjob(jobs, pid, FG, cmdline);
			}

			sigprocmask(SIG_SETMASK, &mask_prev, NULL);

			if (bg) /* Don't wait for background tasks to finish */
			{
				printf("[%d](%d)%s", pid2jid(pid), pid, cmdline);
			}
			else /* Wait for foreground tasks to finish */
			{
				waitfg(pid);
			}
		}
	}
	close(fd);
	free(redirect_filename);
	free(redirect_args);
	return 1;
}

int built_in(char **args)
{
	if (!strcmp(args[0], "exit"))
	{
		exit(0);
	}
	else if (!strcmp(args[0], "cd"))
	{
		return builtin_cd(args);
	}
	else if (!strcmp(args[0], "history"))
	{
		return builtin_history(args);
	}
	else if (!strcmp(args[0], "mytop"))
	{
		return builtin_mytop(args);
	}
	else if (!strcmp(args[0], "jobs"))
	{
		return builtin_jobs(args);
	}
	else
	{
		return 0;
	}
}

int builtin_cd(char **args)
{
	if (args[1] == NULL)
	{
		return 1;
	}
	else
	{
		if (chdir(args[1]) != 0)
		{
			perror("yeeshell");
		}
		return 1;
	}
}

int builtin_history(char **args)
{
	int n = 0;
	if (args[1] == NULL)
	{
		n = cmdline_amount;
	}
	else
	{
		n = atoi(args[1]) < cmdline_amount ? atoi(args[1]) : cmdline_amount;
	}
	printf("ID\tCommandline\n");
	for (int i = 0; i < n; i++)
	{
		printf("%d\t%s\n", i + 1, history[i]);
	}
	return 1;
}

int builtin_jobs(char **args)
{
	/* To prevent interruptions, block all signals. */
	sigset_t mask_all, mask_prev;
	sigfillset(&mask_all);
	sigprocmask(SIG_SETMASK, &mask_all, &mask_prev);

	for (int i = 0; i < JOBS_MAX_QUANTITY; i++)
	{
		if (jobs[i].pid != 0)
		{
			printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
			switch (jobs[i].state)
			{
			case BG:
				printf("Running ");
				break;
			case FG:
				printf("Foreground ");
				break;
			case ST:
				printf("Stopped ");
				break;
			default:
				printf("listjobs: Internal error: job[%d].state=%d ",
					   i, jobs[i].state);
			}
			printf("%s", jobs[i].cmdline);
		}
	}

	sigprocmask(SIG_SETMASK, &mask_prev, NULL); /* unclock */
	return 1;
}

int builtin_mytop(char **args)
{
}

int do_bgfg(char **args)
{
	/* initialize variables */
	struct job_t *currentJob;
	int jid;
	pid_t pid;
	sigset_t mask_all, mask_prev;
	sigfillset(&mask_all);

	sigprocmask(SIG_SETMASK, &mask_all, &mask_prev);

	/* bg or fg has the argument? */
	if (args[1] == NULL)
	{
		printf("%s command requires PID or %%jobid argument\n", args[0]);
		return 1;
	}
	/* if process by jid, gets the corresponding Job structure*/
	else if (args[1][0] == '%')
	{
		jid = atoi(args[1][1]);
		currentJob = getjobjid(jobs, jid);
		if (currentJob == NULL)
		{
			printf("%%%d: No such job\n", jid);
			return 1;
		}
		pid = currentJob->pid;
	}
	/* if process by pid, gets the corresponding Job structure */
	else
	{
		pid = atoi(args[1]);
		currentJob = getjobpid(jobs, pid);
		if (pid <= 0)
		{
			printf("%s: argument must be a PID or %%jobid\n", args[0]);
			return 1;
		}
		currentJob = getjobpid(jobs, pid);
		if (currentJob == NULL)
		{
			printf("(%d): No such process\n", pid);
			return 1;
		}
	}

	/* bg or fg? */
	if (!strcmp(args[0], "bg")) /* if bg */
	{
		currentJob->state = BG;
		printf("[%d] (%d) %s", currentJob->jid, pid, currentJob->cmdline);
		sigprocmask(SIG_SETMASK, &mask_prev, NULL);
		kill(-pid, SIGCONT); /* send the SIGCONT to the pid */
		return 1;
	}
	else if (!strcmp(args[0], "fg")) /* if fg */
	{
		currentJob->state = FG;
		sigprocmask(SIG_SETMASK, &mask_prev, NULL);
		kill(-pid, SIGCONT);	 /* send the SIGCONT to the pid */
		waitfg(currentJob->pid); /* Child process switched to FG, so wait for it to finish */
		return 1;
	}
	else if (!strcmp(args[0], "kill"))
	{
		sigprocmask(SIG_SETMASK, &mask_prev, NULL);
		kill(-pid, SIGQUIT);
		return 1;
	}
	return 1;
}

void waitfg(pid_t pid)
{
	sigset_t m;
	sigemptyset(&m);
	while (pid == fgpid(jobs))
	{
		/* Wake up when there is a signal to check whether the foreground process PID change, */
		/* change means that the foreground process is over. */
		sigsuspend(&m);
	}
	return;
}

void initjobs(struct job_t *jobs)
{
	int i;

	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
		clearjob(&jobs[i]);
}

int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
{
	int i;

	if (pid < 1)
		return 0;

	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
	{
		if (jobs[i].pid == 0)
		{
			jobs[i].pid = pid;
			jobs[i].state = state;
			jobs[i].jid = nextjid++;
			if (nextjid > JOBS_MAX_QUANTITY)
				nextjid = 1;
			strcpy(jobs[i].cmdline, cmdline);

			if (verbose)
			{
				printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
			}
			return 1;
		}
	}
	printf("Tried to create too many jobs\n");
	return 0;
}

void listjobs(struct job_t *jobs)
{
	for (int i = 0; i < JOBS_MAX_QUANTITY; i++)
	{
		if (jobs[i].pid != 0)
		{
			printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
			switch (jobs[i].state)
			{
			case BG:
				printf("Running ");
				break;
			case FG:
				printf("Foreground ");
				break;
			case ST:
				printf("Stopped ");
				break;
			default:
				printf("listjobs: Internal error: job[%d].state=%d ", i, jobs[i].state);
			}
			printf("%s", jobs[i].cmdline);
		}
	}
}

int deletejob(struct job_t *jobs, pid_t pid)
{
	int i;

	if (pid < 1)
		return 0;

	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
	{
		if (jobs[i].pid == pid)
		{
			clearjob(&jobs[i]);
			nextjid = maxjid(jobs) + 1;
			return 1;
		}
	}
	return 0;
}

void clearjob(struct job_t *job)
{
	job->pid = 0;
	job->jid = 0;
	job->state = UNDF;
	job->cmdline[0] = '\0';
}

int pid2jid(pid_t pid)
{
	int i;

	if (pid < 1)
		return 0;
	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
		if (jobs[i].pid == pid)
		{
			return jobs[i].jid;
		}
	return 0;
}

pid_t fgpid(struct job_t *jobs)
{
	for (int i = 0; i < JOBS_MAX_QUANTITY; i++)
		if (jobs[i].state == FG)
			return jobs[i].pid;
	return 0;
}

struct job_t *getjobpid(struct job_t *jobs, pid_t pid)
{
	int i;

	if (pid < 1)
		return NULL;
	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
		if (jobs[i].pid == pid)
			return &jobs[i];
	return NULL;
}

struct job_t *getjobjid(struct job_t *jobs, int jid)
{
	int i;

	if (jid < 1)
		return NULL;
	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
		if (jobs[i].jid == jid)
			return &jobs[i];
	return NULL;
}

int maxjid(struct job_t *jobs)
{
	int i, max = 0;

	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
	{
		if (jobs[i].jid > max)
		{
			max = jobs[i].jid;
		}
	}
	return max;
}

handler_t *Signal(int signum, handler_t *handler)
{
	struct sigaction action, old_action;

	action.sa_handler = handler;
	sigemptyset(&action.sa_mask); /* block sigs of type being handled */
	action.sa_flags = SA_RESTART; /* restart syscalls if possible */

	if (sigaction(signum, &action, &old_action) < 0)
		fprintf(stdout, "%s: %s\n", 'Signal Error', strerror(errno));
	return (old_action.sa_handler);
}

void sigchld_handler(int signal)
{
	pid_t pid;
	int status;
	while ((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0)
	{
		if (WIFEXITED(status)) /* Normal termination */
		{
			deletejob(jobs, pid);
		}
		if (WIFSTOPPED(status)) /* Task suspension */
		{
			struct job_t *job = getjobpid(jobs, pid);
			int jid = pid2jid(pid);
			printf("Job [%d] (%d) stopped by signal %d\n", jid, pid, WSTOPSIG(status));
			job->state = ST;
		}
		if (WIFSIGNALED(status)) /* Task terminated */
		{
			int jid = pid2jid(pid);
			printf("Job [%d] (%d) terminated by signal %d\n", jid, pid, WTERMSIG(status));
			deletejob(jobs, pid);
		}
	}
	return;
}

void sigint_handler(int signal)
{
	pid_t pid = fgpid(jobs);
	if (pid != 0)
	{
		kill(-pid, signal);
	}
	return;
}

void sigtstp_handler(int signal)
{
	pid_t pid = fgpid(jobs);
	if (pid > 0)
	{
		kill(-pid, signal);
	}
	return;
}

void sigquit_handler(int signal)
{
	printf("Terminating after receipt of SIGQUIT signal\n");
	exit(1);
}