/*
 * Copyright 2004-present the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.security.web.authentication.www;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.jspecify.annotations.Nullable;

import org.springframework.security.crypto.codec.Hex;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

final class DigestAuthUtils {

	private static final String[] EMPTY_STRING_ARRAY = new String[0];

	private DigestAuthUtils() {
	}

	static String encodePasswordInA1Format(@Nullable String username, @Nullable String realm,
			@Nullable String password) {
		String a1 = username + ":" + realm + ":" + password;

		return md5Hex(a1);
	}

	static String @Nullable [] splitIgnoringQuotes(String str, char separatorChar) {
		if (str == null) {
			return null;
		}
		int len = str.length();
		if (len == 0) {
			return EMPTY_STRING_ARRAY;
		}
		List<String> list = new ArrayList<>();
		int i = 0;
		int start = 0;
		boolean match = false;
		while (i < len) {
			if (str.charAt(i) == '"') {
				i++;
				while (i < len) {
					if (str.charAt(i) == '"') {
						i++;
						break;
					}
					i++;
				}
				match = true;
				continue;
			}
			if (str.charAt(i) == separatorChar) {
				if (match) {
					list.add(str.substring(start, i));
					match = false;
				}
				start = ++i;
				continue;
			}
			match = true;
			i++;
		}
		if (match) {
			list.add(str.substring(start, i));
		}
		return list.toArray(new String[0]);
	}

	/**
	 * Computes the <code>response</code> portion of a Digest authentication header. Both
	 * the server and user agent should compute the <code>response</code> independently.
	 * Provided as a static method to simplify the coding of user agents.
	 * @param passwordAlreadyEncoded true if the password argument is already encoded in
	 * the correct format. False if it is plain text.
	 * @param username the user's login name.
	 * @param realm the name of the realm.
	 * @param password the user's password in plaintext or ready-encoded.
	 * @param httpMethod the HTTP request method (GET, POST etc.)
	 * @param uri the request URI.
	 * @param qop the qop directive, or null if not set.
	 * @param nonce the nonce supplied by the server
	 * @param nc the "nonce-count" as defined in RFC 2617.
	 * @param cnonce opaque string supplied by the client when qop is set.
	 * @return the MD5 of the digest authentication response, encoded in hex
	 * @throws IllegalArgumentException if the supplied qop value is unsupported.
	 */
	static String generateDigest(boolean passwordAlreadyEncoded, @Nullable String username, @Nullable String realm,
			@Nullable String password, String httpMethod, @Nullable String uri, @Nullable String qop,
			@Nullable String nonce, @Nullable String nc, @Nullable String cnonce) throws IllegalArgumentException {
		String a2 = httpMethod + ":" + uri;
		String a1Md5 = (!passwordAlreadyEncoded) ? DigestAuthUtils.encodePasswordInA1Format(username, realm, password)
				: password;
		String a2Md5 = md5Hex(a2);
		if (qop == null) {
			// as per RFC 2069 compliant clients (also reaffirmed by RFC 2617)
			return md5Hex(a1Md5 + ":" + nonce + ":" + a2Md5);
		}
		if ("auth".equals(qop)) {
			// As per RFC 2617 compliant clients
			return md5Hex(a1Md5 + ":" + nonce + ":" + nc + ":" + cnonce + ":" + qop + ":" + a2Md5);
		}
		throw new IllegalArgumentException("This method does not support a qop: '" + qop + "'");
	}

	/**
	 * Takes an array of <code>String</code>s, and for each element removes any instances
	 * of <code>removeCharacter</code>, and splits the element based on the
	 * <code>delimiter</code>. A <code>Map</code> is then generated, with the left of the
	 * delimiter providing the key, and the right of the delimiter providing the value.
	 * <p>
	 * Will trim both the key and value before adding to the <code>Map</code>.
	 * </p>
	 * @param array the array to process
	 * @param delimiter to split each element using (typically the equals symbol)
	 * @param removeCharacters one or more characters to remove from each element prior to
	 * attempting the split operation (typically the quotation mark symbol) or
	 * <code>null</code> if no removal should occur
	 * @return a <code>Map</code> representing the array contents, or <code>null</code> if
	 * the array to process was null or empty
	 */
	static @Nullable Map<String, String> splitEachArrayElementAndCreateMap(String @Nullable [] array, String delimiter,
			String removeCharacters) {
		if ((array == null) || (array.length == 0)) {
			return null;
		}
		Map<String, String> map = new HashMap<>();
		for (String s : array) {
			String postRemove = (removeCharacters != null) ? StringUtils.replace(s, removeCharacters, "") : s;
			String[] splitThisArrayElement = split(postRemove, delimiter);
			if (splitThisArrayElement == null) {
				continue;
			}
			map.put(splitThisArrayElement[0].trim(), splitThisArrayElement[1].trim());
		}
		return map;
	}

	/**
	 * Splits a <code>String</code> at the first instance of the delimiter.
	 * <p>
	 * Does not include the delimiter in the response.
	 * </p>
	 * @param toSplit the string to split
	 * @param delimiter to split the string up with
	 * @return a two element array with index 0 being before the delimiter, and index 1
	 * being after the delimiter (neither element includes the delimiter)
	 * @throws IllegalArgumentException if an argument was invalid
	 */
	static String @Nullable [] split(String toSplit, String delimiter) {
		Assert.hasLength(toSplit, "Cannot split a null or empty string");
		Assert.hasLength(delimiter, "Cannot use a null or empty delimiter to split a string");
		Assert.isTrue(delimiter.length() == 1, "Delimiter can only be one character in length");
		int offset = toSplit.indexOf(delimiter);
		if (offset < 0) {
			return null;
		}
		String beforeDelimiter = toSplit.substring(0, offset);
		String afterDelimiter = toSplit.substring(offset + 1);
		return new String[] { beforeDelimiter, afterDelimiter };
	}

	static String md5Hex(String data) {
		try {
			MessageDigest digest = MessageDigest.getInstance("MD5");
			return new String(Hex.encode(digest.digest(data.getBytes())));
		}
		catch (NoSuchAlgorithmException ex) {
			throw new IllegalStateException("No MD5 algorithm available!");
		}
	}

}
