// Laboratorio 1 - Esercizio 1
// Matteo Schiff - s295565

#include <stdbool.h>
#include <ctype.h>
#include <stdio.h>

char *cercaRegexp(char *src, char *regexp);

// NOTE: regexp has to be incremented after calling this function
bool checkChar(char src, char **regexp)
{
    switch (**regexp)
    {
    case '.':
        return true;
    case '[':
        (*regexp)++;
        int negate = **regexp == '^';

        if (negate)
            (*regexp)++;

        do
        {
            if (src == **regexp) {
            	while (**regexp != ']')
		    (*regexp)++;
		return !negate;
	    }
            (*regexp)++;
        } while (**regexp != ']');

        return negate;
    case '\\':
        (*regexp)++;
        if (**regexp == 'a') {
            return islower(src);
        } else if (**regexp == 'A') {
            return isupper(src);
        }
        return false; // NOTE: regex is not valid
    default:
        return src == **regexp;
    }
}

bool matchSubstring(char *src, char *regexp)
{
    char *cur_s = src;
    char *cur_meta = regexp;

    while (*cur_meta != 0)
    {
        // match failed if regex check is false or if we reached the end
        // of the string without reaching the end of the regex
        if (*cur_s == 0 || !checkChar(*cur_s, &cur_meta)) 
            return false;

        cur_s++;
        cur_meta++;
    }

    return true;
}

char *searchRegexp(char *src, char *regexp)
{
    char *cur_s = src;

    while (*cur_s != 0)
    {
        if (matchSubstring(cur_s, regexp))
            return cur_s;
        cur_s++;
    }
    return 0;
}

int main(int argc, char ** argv) {
    if (argc != 3) {
        puts("USAGE: ./esercizio1 string regexp");
        return 1;
    }

    char * substr = searchRegexp(argv[1], argv[2]);

    if (!substr) {
        puts("No matches");
    } else {
        puts(substr);
    }
    return 0;
}