path: root/shell.c

#include "queue.h"
#include "dynamic_array.h"
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>

enum modes { word_separation, whole_word };
enum {
    new_line        = 10,
    whitespace      = ' ',
    tab             = 9,
    backslash       = '\\',
    double_quotes   = '"'
};

/* two-letter tokens */
enum {
    append          = '>' + 1,
    and             = '&' + 1,
    or              = '|' + 1
};

struct param_type {
    int is_word;
    int escape_sequences;
    unsigned int double_quotes_counter;
    char stored_symbol;
    int empty_word_flag;
    int tokens;
    int wrong_command;
};

static void show_invitation()
{
    printf("> ");
}

static void print_error()
{
    fprintf(stderr, "Error: unmatched quotes\n");
}

static void init_params(struct param_type *params, enum modes *current_mode)
{
    params->is_word = 0;
    params->escape_sequences = 0;
    params->double_quotes_counter = 0;
    params->stored_symbol = ' ';
    params->empty_word_flag = 0;
    params->tokens = 0;
    params->wrong_command = 0;
    *current_mode = word_separation;
}

static void reset_params(struct param_type *params,
                             enum modes *current_mode,
                             struct queue *word_chain,
                             struct dynamic_array *tmp_word)
{
    init_params(params, current_mode);
    queue_clear(word_chain);
    dynarr_drop_word(tmp_word);
}

static int is_double_quotes_pair(struct param_type params)
{
    return !(params.double_quotes_counter % 2);
}

static int check_separation(int ch, struct param_type params)
{
    return (ch == whitespace || ch == tab) && params.is_word &&
            !params.escape_sequences;
}

static int single_tokens(int ch)
{
    return ch == '<' || ch == ';' || ch == '(' || ch == ')';
}

static void clean_input_buffer()
{
    int ch;
    while((ch = getchar() != new_line))
    {}
}

static void double_tokens_and_fg(int ch, struct param_type *params)
{
    int next_ch;
    next_ch = getchar();
    ungetc(next_ch, stdin);
    if(ch == '>' && next_ch == '>')
        params->tokens = append;
    else if(ch == '|' && next_ch == '|')
        params->tokens = or;
    else if(ch == '&' && next_ch == '&')
        params->tokens = and;
    else if(ch == '&') {
        while((ch = getchar()) != new_line) {
            if(ch != whitespace && ch != tab) {
                fprintf(stderr, "incorrect command\n");
                params->wrong_command = 1;
                return;
            }
        }
        params->tokens = '&';
    }
}

static int check_tokens(int ch, struct param_type *params)
{
    if(single_tokens(ch))
        params->tokens = ch;
    else
        double_tokens_and_fg(ch, params);
    return params->tokens;
}

static int ignore_spaces(int ch, struct param_type params)
{
    return (ch == whitespace || ch == tab) && !params.escape_sequences;
}

static int change_mode(int ch, struct param_type params)
{
    return ch == '"' && !params.escape_sequences;
}

static int start_escape_sequence(int ch, struct param_type params)
{
    return ch == backslash && !params.escape_sequences;
}

static void add_word(struct queue *word_chain,
                     struct dynamic_array *tmp_word,
                     struct param_type *params)
{
    dynarr_push_back(tmp_word, 0);
    char *word = malloc(tmp_word->last_element_index+1);
    dynarr_copy_array(tmp_word, word);
    queue_push(word_chain, word);
    dynarr_drop_word(tmp_word);
    params->is_word = 0;
}

#if 0
static void print_word(char *word)
{
    putchar('[');
    while(*word) {
        putchar(*word);
        ++word;
    }
    printf("]\n");
}

static void print_line(const struct queue *word_chain)
{
    queue_processing(word_chain, print_word);
}
#endif

static char** create_cmdline(const struct queue *word_chain,
                                   int word_counter)
{
    char **cmdline = malloc((word_counter + 1) * sizeof(char*));
    queue_copy_words_to_args(word_chain, cmdline);
    return cmdline;
}

static int check_cd(const char *arg)
{
    return !strcmp(arg, "cd");
}

static void change_directory(char **cmdline)
{
    int result;
    char *first_arg = cmdline[1];
    char *path = NULL;
    /* change to user home directory */
    if(first_arg == NULL) {
        path = getenv("HOME");
        if(!path) {
            perror("I don't know where's your home...");
            return;
        }
    } else {
        if(cmdline[2]) {
            perror("cd: too many arguments");
            return;
        }
        path = first_arg;
    }
    result = chdir(path);
    if(result == -1)
        perror(path);
}

static void clean_up_memory(struct queue *word_chain, char **cmdline)
{
    queue_clear(word_chain);
    free(cmdline);
}

static void clean_up_zombie_process()
{
    int pid;
    do {
        pid = wait4(-1, NULL, WNOHANG, NULL);
    } while(pid > 0);
}

static void run_external_program(struct queue *word_chain,
                                 struct param_type *params)
{
    int pid, wait_pid, result;
    if(word_chain->first == NULL) {
        fprintf(stderr, "empty command\n");
        return;
    }
    char **cmdline = create_cmdline(word_chain,
                                    queue_get_word_count(word_chain));
    if(check_cd(cmdline[0])) {
        change_directory(cmdline);
        clean_up_memory(word_chain, cmdline);
    }
    else {
        pid = fork();
        if(pid == -1) {
            perror("fork error");
            exit(1);
        }
        /* child process  */
        if(pid == 0) {
            execvp(cmdline[0], cmdline);
            perror(cmdline[0]);
            exit(1);
        }
        /* parent process */

        clean_up_memory(word_chain, cmdline);

        /* waiting for forground process */
        if(params->tokens != '&') {
            do {
                wait_pid = wait(&result);
            } while(wait_pid != pid);
        } else
            clean_up_zombie_process();
    }
}

static void command_processing(struct param_type *params,
                                enum modes *current_mode,
                                struct queue *word_chain,
                                struct dynamic_array *tmp_word)
{
    /* and odd number of double quotes  */
    if(!is_double_quotes_pair(*params)) {
        print_error();
        reset_params(params, current_mode, word_chain, tmp_word);
        show_invitation();
        return;
    }
    if(params->empty_word_flag || params->is_word) {
        if(params->empty_word_flag)
            dynarr_push_back(tmp_word, '\0');
        add_word(word_chain, tmp_word, params);
    }
    run_external_program(word_chain, params);
    if(params->tokens == '&' || params->tokens == 0)
        show_invitation();
    reset_params(params, current_mode, word_chain, tmp_word);
#if 0
    print_line(word_chain);
#endif
}

static int is_empty_word(int ch, struct param_type params)
{
    return (ch == whitespace || ch == tab) && !params.is_word &&
            params.empty_word_flag;
}

static void word_separation_processing(int ch, struct param_type *params,
                                  enum modes *current_mode,
                                  struct queue *word_chain,
                                  struct dynamic_array *tmp_word)
{
    /* could be a marker for the beginning of a blank word */
    params->stored_symbol = ch;
    if(is_empty_word(ch, *params)) {
        dynarr_push_back(tmp_word, '\0');
        add_word(word_chain, tmp_word, params);
        params->empty_word_flag = 0;
        return;
    }
    params->empty_word_flag = 0;
    if(change_mode(ch, *params)) {
        ++params->double_quotes_counter;
        *current_mode = whole_word;
        return;
    }
    if(start_escape_sequence(ch, *params)) {
        params->escape_sequences = 1;
        return;
    }
    if(check_tokens(ch, params)) {
        command_processing(params, current_mode, word_chain, tmp_word);
        return;
    }
    if(params->wrong_command) {
        clean_input_buffer();
        reset_params(params, current_mode, word_chain, tmp_word);
        show_invitation();
        return;
    }
    if(check_separation(ch, *params)) {
        add_word(word_chain, tmp_word, params);
        params->is_word = 0;
        return;
    }
    if(ignore_spaces(ch, *params))
        return;

    dynarr_push_back(tmp_word, ch);
    params->is_word = 1;
    params->escape_sequences = 0;
}

static int escape_double_quotes_or_backslash(int ch, struct param_type params)
{
    return params.escape_sequences &&
        (ch == double_quotes || ch == backslash);
}

static int double_quotes_again(int ch, struct param_type params)
{
    return ch == double_quotes && !params.is_word &&
        params.stored_symbol == '"';
}

static void whole_word_processing(int ch, struct param_type *params,
                                  enum modes *current_mode,
                                  struct queue *word_chain,
                                  struct dynamic_array *tmp_word)
{
    if(double_quotes_again(ch, *params)) {
        params->stored_symbol = '\0';
        params->empty_word_flag = 1;
        ++params->double_quotes_counter;
        *current_mode = word_separation;
        return;
    }
    params->stored_symbol = '\0';
    if(change_mode(ch, *params)) {
        ++params->double_quotes_counter;
        *current_mode = word_separation;
        return;
    }
    if(escape_double_quotes_or_backslash(ch, *params)) {
        dynarr_push_back(tmp_word, ch);
        params->escape_sequences = 0;
        params->is_word = 1;
        return;
    }
    if(start_escape_sequence(ch, *params)) {
        params->escape_sequences = 1;
        return;
    }
    /* backslash recovery */
    if(params->escape_sequences)
        dynarr_push_back(tmp_word, backslash);
    dynarr_push_back(tmp_word, ch);
    params->is_word = 1;
    params->escape_sequences = 0;
}

int main()
{
    int ch;
    struct param_type params;
    struct queue word_chain;
    struct dynamic_array tmp_word;
    enum modes current_mode = word_separation;
    queue_init(&word_chain);
    dynarr_create_array(&tmp_word);
    init_params(&params, &current_mode);
    show_invitation();
    while((ch = getchar()) != EOF) {
        clean_up_zombie_process();
        if(ch == new_line)
            command_processing(&params, &current_mode, &word_chain,
                                &tmp_word);
        else if(current_mode == word_separation)
            word_separation_processing(ch, &params, &current_mode, &word_chain,
                                       &tmp_word);
        else if(current_mode == whole_word)
            whole_word_processing(ch, &params, &current_mode, &word_chain,
                                  &tmp_word);
    }
    putchar(new_line);
    dynarr_clear(&tmp_word);
    return 0;
}