42sh/src/lexer/lexer.c

#include "lexer.h"

#include <ctype.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#include "io_backend/io_backend.h"
#include "utils/string_utils/string_utils.h"

static char *end_last_token;
static ssize_t remaining_chars;

/* @brief: saves state for the next call the the lexer.
 *
 */
static void save_state(char *stream, ssize_t i)
{
    remaining_chars -= i;
    end_last_token = stream + i;
    return;
}

/* @return: true if a special character from the grammar was found,
 *          false otherwise.
 *
 */
static bool is_special_char(char c)
{
    return c == '\'' || c == '\n' || c == ';';
}

/* @return: true if a keyword from the grammar was found, false otherwise.
 *
 */
static bool is_keyword(char *stream, ssize_t i)
{
    if (i == 2)
    {
        return strcmp(stream, "if") == 0 || strcmp(stream, "fi") == 0;
    }
    if (i == 4)
    {
        return strcmp(stream, "then") || strcmp(stream, "else")
            || strcmp(stream, "elif");
    }
    return false;
}

char *new_token(char *begin, ssize_t size)
{
    char *res = calloc(size + 1, sizeof(char));
    if (res == NULL)
        return NULL;
    strncpy(res, begin, size);
    return res;
}

char *stream_init(void)
{
    char *stream;

    if (remaining_chars == 0)
    {
        remaining_chars = stream_read(&stream);
    }
    else
    {
        stream = end_last_token;
    }

    char *trimed_stream = trim_blank_left(stream);
    remaining_chars -= trimed_stream - stream;
    stream = trimed_stream;

    return stream;
}

char *peek_token(void)
{
    char *stream = stream_init();

    ssize_t i = 0;

    while (i < remaining_chars)
    {
        if (is_special_char(stream[i]))
        {
            if (i == 0) // where we create spe_char token
                i++;
            break;
        }
        if (isblank(stream[i]))
        {
            break;
        }
        else if (is_keyword(stream, i))
        {
            i++;
            break;
        }
        i++;
    }

    return new_token(stream, i);
}

char *pop_token(void)
{
    char *stream = stream_init();

    ssize_t i = 0;

    while (i < remaining_chars)
    {
        if (is_special_char(stream[i]))
        {
            if (i == 0) // where we create spe_char token
                i++;
            break;
        }
        if (isblank(stream[i]))
        {
            break;
        }
        else if (is_keyword(stream, i))
        {
            i++;
            break;
        }
        i++;
    }

    save_state(stream, i);

    return new_token(stream, i);
}