#include <regex.h>
#include <stdio.h>
#include <string.h>

// Receives a regular expression by command line argument
// Test texts given in standard input against the regular expression
// http://pubs.opengroup.org/onlinepubs/009695399/functions/regcomp.html
// Compile with: gcc -Wall -Wextra -std=c11 -o test_regex test_regex.c
// Adapted from: https://stackoverflow.com/questions/1085083/regular-expressions-in-c-examples

#define SZ_LINE 1024

int main(int argc, char* argv[])
{
	// One argument is mandatory: the regular expression
	if ( argc <= 1 )
		return fprintf(stderr, "usage: test_regex 'regular expression' [extended|icase|nosub|newline]\n"), 1;

	// set flags in arguments
	int cflags = 0;
	for ( int index = 2; index < argc; ++index )
	{
		if ( strcmp(argv[index], "extended") == 0 )
			cflags |= REG_EXTENDED;
		else if ( strcmp(argv[index], "icase") == 0 )
			cflags |= REG_ICASE;
		else if ( strcmp(argv[index], "NOSUB") == 0 )
			cflags |= REG_NOSUB;
		else if ( strcmp(argv[index], "newline") == 0 )
			cflags |= REG_NEWLINE;
		else
			fprintf(stderr, "warning: ignoring flag: %s\n", argv[index]);
	}

	// Compile the regular expression
	regex_t regex;
	int error = regcomp(&regex, argv[1], cflags);
	if ( error )
		return fprintf(stderr, "error: could not compile regex '%s'\n", argv[1]), 1;

	// While there are lines in stdin
	char line[SZ_LINE];
	while ( fgets(line, SZ_LINE, stdin) )
	{
		// Execute regular expression against line
		error = regexec(&regex, line, 0, NULL, 0);
		if ( error == 0 )
			puts("Match");
		else if (error == REG_NOMATCH)
			puts("No match");
		else
		{
			char msgbuf[100];
			regerror(error, &regex, msgbuf, sizeof(msgbuf));
			fprintf(stderr, "Regex match failed: %s\n", msgbuf);
			break;
		}
	}

	// Free memory allocated to the pattern buffer by regcomp()
	regfree(&regex);
	return 0;
}