/* Remaining items before Project 2:
 * 	# Set home directory automatically so ~ works for everyone
 * 	# Switch the input routine to use GNU Readline
 * 	# Unify code paths in handle_pipes to provide a natural spot for redirection
 */

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<signal.h>
#include<string.h>
#include<time.h>
#include<wait.h>
#include<fcntl.h>
#include<readline/readline.h>
#include<readline/history.h>
#include "string_helpers.h"

#define PROMPT_LIMIT 512
void handle_pipes(char*, int);
void run_with_redirects(char *linebuffer);

char debug = 0;
void handle_ctrlc(int signal){
	write(1, "^C", 2);
	fsync(1);
}

struct variable{
	char *name;
	char *value;
};


int main(){
	size_t max_variables = 128;
	size_t actual_variables = 0;
	struct variable *variables = malloc(max_variables * sizeof(struct variable));
	size_t linebuffer_limit = 8192;
	char *linebuffer = malloc(linebuffer_limit);
	char working_directory[512];
	getcwd(working_directory, 512);
	ssize_t readlen;
	struct sigaction ctrlc_action;
	char *user_home = getenv("HOME"); //"/home/seth/"; // TODO:  Set this automatically
	char prompt[PROMPT_LIMIT];
	ctrlc_action.sa_handler = handle_ctrlc;
	sigaction(SIGINT, &ctrlc_action, 0);
	while(1){
		snprintf(prompt, PROMPT_LIMIT, "%s:  ", working_directory);
		char *cmdbuffer = readline(prompt);
		if(!cmdbuffer)
			break;
		if(!*cmdbuffer)
			continue;
		add_history(cmdbuffer);
		strncpy(linebuffer, cmdbuffer, linebuffer_limit);
		free(cmdbuffer);
		if(debug) printf("You entered:  \"%s\" (%ld bytes)\n", linebuffer, readlen);
		/* Shell expansions */
		for(size_t i = 0; linebuffer[i]; i++){
			if(linebuffer[i] == '~'){
				int length = strlen(user_home);
				move_right(linebuffer + i, length - 1);
				strncpy(linebuffer + i, user_home, length);				
			}
		}
		for(size_t i = 0; linebuffer[i]; i++){
			if(linebuffer[i] == '$'){
				char *varname = linebuffer + i + 1;
				char *varname_end = varname;
				while(*varname_end != ' ' && *varname_end != '\n' && *varname_end)
					varname_end++;
				char old_varname_end = *varname_end;
				*varname_end = 0;
				for(int j = 0; j < actual_variables; j++)
					if(!strcmp(variables[j].name, varname)){
						int shift = 1 + strlen(varname) - strlen(variables[j].value); // 1 for the $
						if(shift > 0){
							*varname_end = old_varname_end;
							move_left(varname_end, shift);
						} else if(shift < 0) {
							*varname_end = old_varname_end;
							move_right(varname_end - 1, -shift);
						}
						memcpy(linebuffer + i, variables[j].value, strlen(variables[j].value));
						goto found_it;
					}
				// if we never found it
				*varname_end = old_varname_end;
found_it:;
			}
		}
		/* Shell Builtins */
		if(!strncmp(linebuffer, "export ", 7)){
			char *varname = 7 + linebuffer;
			char *equals = varname;
			while(*equals != '=')
				++equals;
			*equals = 0;
			char* value = equals + 1;
			struct variable new_var;
			new_var.name = malloc(strlen(varname));
			strcpy(new_var.name, varname);
			new_var.value = malloc(strlen(value));
			strcpy(new_var.value, value);
			variables[actual_variables] = new_var;
			actual_variables++;
			continue;
		}
		if(!strncmp(linebuffer, "cd ", 3)){
			chdir(linebuffer + 3);
			getcwd(working_directory, 512);
			continue;
		}
		if(!strncmp(linebuffer, "debug", 5)){
			debug = !debug;
			continue;
		}
		if(!strncmp(linebuffer, "exit", 4)){
			break;
		}
		/* Most shells have a few more builtins than that */

		/* Maybe the user specified a program */
		handle_pipes(linebuffer, 0);
	}

	write(1, "\n", 1);
	free(linebuffer);
	return 0;
}

void handle_pipes(char *linebuffer, int input){
	char *secondcmd;
	if(secondcmd = strstr(linebuffer, "|")){
		*secondcmd = 0; // This'll overwrite the | with a terminator
		char *end_of_first = secondcmd - 1;
		while(*end_of_first == ' '){
			*end_of_first = 0;
			--end_of_first;
		}
		while(*++secondcmd == ' ') *secondcmd = ' ';

		if(debug) {
			printf("First command:  \"%s\"\n", linebuffer);
			printf("Second command:  \"%s\"\n", secondcmd);
		}
		int pipefd[2];
		pipe(pipefd);
		// Run first command
		pid_t pid = fork();
		if(!pid) { // Set up and exec the first command, the one in linebuffer
			dup2(pipefd[1], 1);
			dup2(input, 0);
			close(pipefd[0]);
			// Pipes are done, redirects are next
			run_with_redirects(linebuffer);
		}
		// Run second command
		close(pipefd[1]);
		handle_pipes(secondcmd, pipefd[0]);
		wait(0);
		return;
	}
	pid_t pid = fork();
	if(!pid) { // Set up and exec the first command, the one in linebuffer
		dup2(input, 0);
		// Pipes are done, redirects are next
		run_with_redirects(linebuffer);
	}
	wait(0);
}

/* echo hi >afile
 * ["echo", "hi", ">afile"] then filename = argv[i]+1
 * echo hi > afile
 * ["echo", "hi", ">", "afile] then filename = argv[i+1]
 * > afile echo goose
 * [">", "afile", "echo", "goose"]
 * ["echo", "goose"]
 */
void open_and_redirect(int flags, char ** argv, int i, int over_fd, int oplen){
	char *filename = argv[i+1];
	if(argv[i][oplen])
		filename = argv[i] + oplen;
	int fd = open(filename, flags, 0644);
	if(fd == -1) {
		perror("open");
		exit(1);
	}
	int j, offset;
	if(argv[i+1] == filename)
		offset = 2; 
	else
		offset = 1; 
	for(j = i + offset; argv[j]; j++)
		argv[j-offset] = argv[j];
	argv[j - offset] = 0;
	dup2(fd, over_fd); // here
}

void run_with_redirects(char *linebuffer){
	size_t length;
	char **argv = split(linebuffer, &length);
	for(int i = 0; argv[i]; i++){
		if(!strncmp("<", argv[i], 2)){
			open_and_redirect(O_RDONLY, argv, i, 0, 1);
		}
		if(argv[i] && !strncmp("2>", argv[i], 2)){
			int oplen = 2, append_create = O_TRUNC; // here
			if(!strncmp("2>>", argv[i], 3)) { // here
				oplen = 3; // here
				append_create = O_APPEND;
			}
			open_and_redirect(O_WRONLY | O_CREAT | append_create, argv, i, 2, oplen);
		}
		if(argv[i] && '>' == argv[i][0]){ // segfault prevention:  If argv[i] == 0, then we don't try to dereference
			int oplen = 1, append_create = O_TRUNC;
			if(!strncmp(">>", argv[i], 2)) {
				oplen = 2;
				append_create = O_APPEND;
			}
			open_and_redirect(O_WRONLY | O_CREAT | append_create, argv, i, 1, oplen);
		}
	}	

	if(debug){
		printf("[");
		for(int i = 0; argv[i]; i++)
			printf("%s, ", argv[i]);
		printf("\b\b]\n");
	}

	execvp(argv[0], argv);
	free(argv);
	perror("exec");
	exit(1);
}