42sh/src/expansion/expansion.c

#define _POSIX_C_SOURCE 200809L
#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "../utils/ast/ast.h"
#include "../utils/hash_map/hash_map.h"
#include "../utils/string_utils/string_utils.h"
#include "../utils/vars/vars.h"

static bool is_var_start_char(char c)
{
    return isalpha(c) || c == '_';
}

static bool is_var_char(char c)
{
    return isalnum(c) || c == '_';
}

static bool is_special_var_char(char c)
{
    return c == '@' || c == '*' || c == '?' || c == '$' || isdigit(c)
        || c == '#';
}

size_t parse_var_name(char *str, char **res)
{
    char *brace = NULL;
    size_t i = 1; // skip the '$'

    if (str[i] == '{' && str[i + 1] != 0 && str[i + 1] != '}')
    {
        if (is_special_var_char(str[i + 1]) && str[i + 2] == '}')
        {
            // Special variable like ${1}, ${?}
            *res = strndup(str + i + 1, 1);
            return 4; // length of ${X}
        }

        brace = str + i;
        i++; // skip the '{'
    }
    else if (is_special_var_char(str[i]))
    {
        *res = strndup(str + i, 1);
        return 2; // length of $X
    }

    if (!is_var_start_char(str[i]))
    {
        // Not a valid variable start
        *res = NULL;
        return 0;
    }

    while (1)
    {
        if (str[i] == '}' && *brace == '{')
        {
            *res = strndup(str + 2, i - 2);
            return i + 1;
        }
        else if (!is_var_char(str[i]))
        {
            if (brace != NULL)
            {
                // Missing closing '}'
                *res = NULL;
                return 0;
            }
            break;
        }
        i++;
    }

    *res = strndup(str + 1, i - 1);
    return i;
}

static bool expand_var(char **str, size_t pos, const struct hash_map *vars)
{
    char *var_name = NULL;
    size_t r = parse_var_name(*str + pos, &var_name);
    if (r > 0 && var_name != NULL)
    {
        char *value = get_var_or_env(vars, var_name);
        if (value == NULL)
            // Undefined variable: expand to empty string
            value = "";

        char *p = insert_into(*str, value, pos, r);
        free(var_name);
        if (p == NULL)
        {
            // error: insertion failed
            return false;
        }
        *str = p;
        return true;
    }
    return false;
}

struct ast_command *expand(struct ast_command *command,
                           const struct hash_map *vars)
{
    if (command == NULL)
        return NULL;

    char *str;
    size_t len;
    bool in_quotes;
    struct list *l = command->command;

    while (l != NULL)
    {
        in_quotes = false;
        str = (char *)l->data;
        len = strlen(str);

        for (size_t i = 0; str[i] != 0; i++)
        {
            if (str[i] == '\'')
            {
                // remove quote
                in_quotes = !in_quotes;
                memmove(str + i, str + i + 1, strlen(str + i + 1) + 1);
                i--;
            }
            else if (in_quotes)
            {
                continue; // do nothing
            }
            else if (str[i] == '$' && str[i + 1] != 0 && !isspace(str[i + 1]))
            {
                // variable expansion
                bool r = expand_var(&str, i, vars);
                if (r == false || str == NULL)
                    return NULL;

                i--; // -1 because loop will increment i
            }
        }

        if (in_quotes)
        {
            // error: quote not closed
            fprintf(stderr, "Error: quote not closed in string: %s\n", str);
            return NULL;
        }

        if (len != strlen(str))
        {
            char *new_str = realloc(str, strlen(str) + 1);
            if (new_str == NULL)
            {
                // error: realloc fail
                return NULL;
            }
            l->data = new_str;
        }

        l = l->next;
    }
    return command;
}