package org.picketlink.http.internal.cors;

import java.util.Collection;
import java.util.Iterator;
import java.util.regex.Pattern;

import static java.util.regex.Pattern.compile;

/**
 * Utility functions for CORS requests.
 *
 * @author Giriraj Sharma
 */
public class CorsUtil {

    /**
     * Must match "token", 1 or more of any US-ASCII char except control chars or specific "separators", see:
     * http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2 and
     * http://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2
     *
     * Note use of regex character class subtraction and character class metacharacter rules.
     */
    private static final Pattern VALID = compile("^[\\x21-\\x7e&&[^]\\[}{()<>@,;:\\\\\"/?=]]+$");

    /**
     * Parses a header value consisting of zero or more space / comma / space + comma separated strings. The input string is
     * trimmed before splitting.
     *
     * @param headerValue The header value, may be {@code null}.
     *
     * @return A string array of the parsed string items, empty if none were found or the input was {@code null}.
     */
    public static String[] parseMultipleHeaderValues(final String headerValue) {

        if (headerValue == null)
            return new String[0]; // empty array

        String trimmedHeaderValue = headerValue.trim();

        if (trimmedHeaderValue.isEmpty())
            return new String[0];

        return trimmedHeaderValue.split("\\s*,\\s*|\\s+");
    }

    /**
     * Applies a {@code Aaa-Bbb-Ccc} format to a header name.
     *
     * @param name The header name to format, must not be an empty string or {@code null}.
     *
     * @return The formatted header name.
     *
     * @throws IllegalArgumentException On a empty or invalid header name.
     */
    public static String formatCanonical(final String name) {

        String nameTrimmed = name.trim();

        if (nameTrimmed.isEmpty())
            throw new IllegalArgumentException("The header field name must not be an empty string");

        assert (VALID != null);

        // Check for valid syntax
        if (!VALID.matcher(nameTrimmed).matches())
            throw new IllegalArgumentException("Invalid header field name syntax (see RFC 2616)");

        String[] tokens = nameTrimmed.toLowerCase().split("-");

        String out = "";

        for (int i = 0; i < tokens.length; i++) {

            char[] c = tokens[i].toCharArray();

            // Capitalise first char
            c[0] = Character.toUpperCase(c[0]);

            if (i >= 1)
                out = out + "-";

            out = out + new String(c);
        }

        return out;
    }

    public static String join(Collection<String> strings) {
        return join(strings, ", ");
    }

    public static String join(Collection<String> strings, String separator) {
        Iterator<String> iter = strings.iterator();
        StringBuilder sb = new StringBuilder();
        while (iter.hasNext()) {
            sb.append(iter.next());
            if (iter.hasNext()) {
                sb.append(separator);
            }
        }
        return sb.toString();
    }
}