#include <algorithm>
#include <cctype>
#include <string>
#include <vector>

#include "urls.h"

using std::find;
using std::find_if;

#ifndef _MSC_VER
using std::isalnum;
using std::isalpha;
using std::isdigit;
#endif

using std::search;
using std::string;
using std::vector;

bool not_url_char(char);

string::const_iterator
url_end(string::const_iterator, string::const_iterator);

string::const_iterator
url_beg(string::const_iterator, string::const_iterator);
vector<string> find_urls(const string& s)
{
	vector<string> ret;
	typedef string::const_iterator iter;
	iter b = s.begin(), e = s.end();

	// look through the entire input
	while (b != e) {

		// look for one or more letters followed by `://'
		b = url_beg(b, e);

		// if we found it
		if (b != e) {
			// get the rest of the \s-1URL\s0
			iter after = url_end(b, e);

			// remember the \s-1URL\s0
			ret.push_back(string(b, after));

			// advance `b' and check for more \s-1URL\s0s on this line
			b = after;
		}
	}
	return ret;
}

string::const_iterator
url_end(string::const_iterator b, string::const_iterator e)
{
	return find_if(b, e, not_url_char);
}

bool not_url_char(char c)
{
	// characters, in addition to alphanumerics, that can appear in a \s-1URL\s0
	static const string url_ch = "~;/?:@=&$-_.+!*'(),";

	// see whether `c' can appear in a \s-1URL\s0 and return the negative
	return !(isalnum(c) ||
	         find(url_ch.begin(), url_ch.end(), c) != url_ch.end());
}

string::const_iterator
url_beg(string::const_iterator b, string::const_iterator e)
{
	static const string sep = "://";

	typedef string::const_iterator iter;

	// `i' marks where the separator was found
	iter i = b;

	while ((i = search(i, e, sep.begin(), sep.end())) != e) {

		// make sure the separator isn't at the beginning or end of the line
		if (i != b && i + sep.size() != e) {

			// `beg' marks the beginning of the protocol-name
			iter beg = i;
			while (beg != b && isalpha(beg[-1]))
				--beg;

			// is there at least one appropriate character before and after the separator?
			if (beg != i && !not_url_char(i[sep.size()]))
				return beg;
		}

		// the separator we found wasn't part of a \s-1URL\s0; advance `i' past this separator
		i += sep.size();
	}
	return e;
}