/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.validator.routines;

import java.io.Serializable;
import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URLDecoder;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.HashSet;
import java.util.Locale;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.commons.validator.GenericValidator;

/**
 * <p><strong>URL Validation</strong> routines.</p>
 * Behavior of validation is modified by passing in options:
 * <ul>
 * <li>ALLOW_2_SLASHES - [FALSE]  Allows double '/' characters in the path
 * component.</li>
 * <li>NO_FRAGMENT- [FALSE]  By default fragments are allowed, if this option is
 * included then fragments are flagged as illegal.</li>
 * <li>ALLOW_ALL_SCHEMES - [FALSE] By default only http, https, and ftp are
 * considered valid schemes.  Enabling this option will let any scheme pass validation.</li>
 * </ul>
 *
 * <p>Originally based in on php script by Debbie Dyer, validation.php v1.2b, Date: 03/07/02,
 * https://javascript.internet.com. However, this validation now bears little resemblance
 * to the php original.</p>
 * <pre>
 *   Example of usage:
 *   Construct a UrlValidator with valid schemes of "http", and "https".
 *
 *    String[] schemes = {"http","https"}.
 *    UrlValidator urlValidator = new UrlValidator(schemes);
 *    if (urlValidator.isValid("ftp://foo.bar.com/")) {
 *       System.out.println("URL is valid");
 *    } else {
 *       System.out.println("URL is invalid");
 *    }
 *
 *    prints "URL is invalid"
 *   If instead the default constructor is used.
 *
 *    UrlValidator urlValidator = new UrlValidator();
 *    if (urlValidator.isValid("ftp://foo.bar.com/")) {
 *       System.out.println("URL is valid");
 *    } else {
 *       System.out.println("URL is invalid");
 *    }
 *
 *   prints out "URL is valid"
 *  </pre>
 *
 * @see
 * <a href="https://www.ietf.org/rfc/rfc2396.txt">
 *  Uniform Resource Identifiers (URI): Generic Syntax
 * </a>
 *
 * @since 1.4
 */
public class UrlValidator implements Serializable {

    private static final long serialVersionUID = 7557161713937335013L;

    private static final int MAX_UNSIGNED_16_BIT_INT = 0xFFFF; // port max

    /**
     * Allows all validly formatted schemes to pass validation instead of
     * supplying a set of valid schemes.
     */
    public static final long ALLOW_ALL_SCHEMES = 1 << 0;

    /**
     * Allow two slashes in the path component of the URL.
     */
    public static final long ALLOW_2_SLASHES = 1 << 1;

    /**
     * Enabling this options disallows any URL fragments.
     */
    public static final long NO_FRAGMENTS = 1 << 2;

    /**
     * Allow local URLs, such as https://localhost/ or https://machine/ .
     * This enables a broad-brush check, for complex local machine name
     *  validation requirements you should create your validator with
     *  a {@link RegexValidator} instead ({@link #UrlValidator(RegexValidator, long)})
     */
    public static final long ALLOW_LOCAL_URLS = 1 << 3; // CHECKSTYLE IGNORE MagicNumber

    /**
     * Protocol scheme (for example, http, ftp, https).
     */
    private static final String SCHEME_REGEX = "^\\p{Alpha}[\\p{Alnum}\\+\\-\\.]*";
    private static final Pattern SCHEME_PATTERN = Pattern.compile(SCHEME_REGEX);

    // Drop numeric, and  "+-." for now
    // TODO does not allow for optional userinfo.
    // Validation of character set is done by isValidAuthority
    private static final String AUTHORITY_CHARS_REGEX = "\\p{Alnum}\\-\\."; // allows for IPV4 but not IPV6
    // Captured inside [ ] in AUTHORITY_REGEX and validated by InetAddressValidator.isValidInet6Address, so the
    // dot is allowed for IPv4-mapped/embedded forms (for example ::ffff:1.2.3.4 or 2001:db8::1.2.3.4), not just ::FFFF:
    private static final String IPV6_REGEX = "[0-9a-fA-F:.]+"; // the brackets remove the port-prefix ':' ambiguity

    // userinfo    = *( unreserved / pct-encoded / sub-delims / ":" )
    // unreserved    = ALPHA / DIGIT / "-" / "." / "_" / "~"
    // sub-delims    = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="
    // We assume that password has the same valid chars as user info
    private static final String USERINFO_CHARS_REGEX = "[a-zA-Z0-9%-._~!$&'()*+,;=]";

    // since neither ':' nor '@' are allowed chars, we don't need to use non-greedy matching
    private static final String USERINFO_FIELD_REGEX =
            USERINFO_CHARS_REGEX + "+" + // At least one character for the name
            "(?::" + USERINFO_CHARS_REGEX + "*)?@"; // colon and password may be absent

    // Optional userinfo ("user:pass@") precedes the host so it may come before either host form: a bracketed IPv6
    // literal (group 1) or a hostname/IPv4 host (group 2). Group 3 is the port, group 4 any trailing remainder.
    private static final String AUTHORITY_REGEX =
            "(?:" + USERINFO_FIELD_REGEX + ")?(?:\\[(" + IPV6_REGEX + ")\\]|([" + AUTHORITY_CHARS_REGEX + "]*))(?::(\\d*))?(.*)?";
    private static final Pattern AUTHORITY_PATTERN = Pattern.compile(AUTHORITY_REGEX);

    private static final int PARSE_AUTHORITY_IPV6 = 1;

    private static final int PARSE_AUTHORITY_HOST_IP = 2; // excludes userinfo, if present

    private static final int PARSE_AUTHORITY_PORT = 3; // excludes leading colon

    /**
     * Should always be empty. The code currently allows spaces.
     */
    private static final int PARSE_AUTHORITY_EXTRA = 4;

    private static final String PATH_REGEX = "^(/[-\\w:@&?=+,.!/~*'%$_;\\(\\)]*)?$";
    private static final Pattern PATH_PATTERN = Pattern.compile(PATH_REGEX);

    private static final String QUERY_REGEX = "^(\\S*)$";
    private static final Pattern QUERY_PATTERN = Pattern.compile(QUERY_REGEX);

    /**
     * If no schemes are provided, default to this set.
     */
    private static final String[] DEFAULT_SCHEMES = {"http", "https", "ftp"}; // Must be lower-case

    /**
     * Singleton instance of this class with default schemes and options.
     */
    private static final UrlValidator DEFAULT_URL_VALIDATOR = new UrlValidator();

    /**
     * Returns the singleton instance of this class with default schemes and options.
     *
     * @return singleton instance with default schemes and options
     */
    public static UrlValidator getInstance() {
        return DEFAULT_URL_VALIDATOR;
    }

    /**
     * Tests whether the given flag is on. If the flag is not a power of 2
     * (for example, 3) this tests whether the combination of flags is on.
     *
     * @param flag Flag value to check.
     * @param options what to check
     * @return whether the specified flag value is on.
     */
    private static boolean isOn(final long flag, final long options) {
        return (options & flag) > 0;
    }

    /**
     * Holds the set of current validation options.
     */
    private final long options;

    /**
     * The set of schemes that are allowed to be in a URL.
     */
    private final Set<String> allowedSchemes; // Must be lower-case

    /**
     * Regular expressions used to manually validate authorities if IANA
     * domain name validation isn't desired.
     */
    private final RegexValidator authorityValidator;

    /**
     * The domain validator.
     */
    private final DomainValidator domainValidator;

    /**
     * Constructs a new instance with default properties.
     */
    public UrlValidator() {
        this(null);
    }

    /**
     * Constructs a new instance with the given validation options.
     *
     * @param options The options should be set using the public constants declared in
     * this class.  To set multiple options you simply add them together.  For example,
     * ALLOW_2_SLASHES + NO_FRAGMENTS enables both of those options.
     */
    public UrlValidator(final long options) {
        this(null, null, options);
    }

    /**
     * Constructs a new instance with the given validation options.
     *
     * @param authorityValidator Regular expression validator used to validate the authority part
     * This allows the user to override the standard set of domains.
     * @param options Validation options. Set using the public constants of this class.
     * To set multiple options, simply add them together:
     * <p>{@code ALLOW_2_SLASHES + NO_FRAGMENTS}</p>
     * enables both of those options.
     */
    public UrlValidator(final RegexValidator authorityValidator, final long options) {
        this(null, authorityValidator, options);
    }

    /**
     * Behavior of validation is modified by passing in several strings options:
     *
     * @param schemes Pass in one or more URL schemes to consider valid, passing in
     *        a null will default to "http,https,ftp" being valid.
     *        If a non-null schemes is specified then all valid schemes must
     *        be specified. Setting the ALLOW_ALL_SCHEMES option will
     *        ignore the contents of schemes.
     */
    public UrlValidator(final String[] schemes) {
        this(schemes, 0L);
    }

    /**
     * Behavior of validation is modified by passing in options:
     *
     * @param schemes The set of valid schemes. Ignored if the ALLOW_ALL_SCHEMES option is set.
     * @param options The options should be set using the public constants declared in
     * this class.  To set multiple options you simply add them together.  For example,
     * ALLOW_2_SLASHES + NO_FRAGMENTS enables both of those options.
     */
    public UrlValidator(final String[] schemes, final long options) {
        this(schemes, null, options);
    }

    /**
     * Customizable constructor. Validation behavior is modified by passing in options.
     *
     * @param schemes The set of valid schemes. Ignored if the ALLOW_ALL_SCHEMES option is set.
     * @param authorityValidator Regular expression validator used to validate the authority part
     * @param options Validation options. Set using the public constants of this class.
     * To set multiple options, simply add them together:
     * <p>{@code ALLOW_2_SLASHES + NO_FRAGMENTS}</p>
     * enables both of those options.
     */
    public UrlValidator(final String[] schemes, final RegexValidator authorityValidator, final long options) {
        this(schemes, authorityValidator, options, DomainValidator.getInstance(isOn(ALLOW_LOCAL_URLS, options)));
    }

    /**
     * Customizable constructor. Validation behavior is modified by passing in options.
     *
     * @param schemes The set of valid schemes. Ignored if the ALLOW_ALL_SCHEMES option is set.
     * @param authorityValidator Regular expression validator used to validate the authority part
     * @param options Validation options. Set using the public constants of this class.
     * To set multiple options, simply add them together:
     * <p>{@code ALLOW_2_SLASHES + NO_FRAGMENTS}</p>
     * enables both of those options.
     * @param domainValidator The DomainValidator to use; must agree with ALLOW_LOCAL_URLS setting
     * @since 1.7
     */
    public UrlValidator(String[] schemes, final RegexValidator authorityValidator, final long options, final DomainValidator domainValidator) {
        this.options = options;
        if (domainValidator == null) {
            throw new IllegalArgumentException("DomainValidator must not be null");
        }
        if (domainValidator.isAllowLocal() != (options & ALLOW_LOCAL_URLS) > 0) {
            throw new IllegalArgumentException("DomainValidator disagrees with ALLOW_LOCAL_URLS setting");
        }
        this.domainValidator = domainValidator;

        if (isOn(ALLOW_ALL_SCHEMES)) {
            allowedSchemes = Collections.emptySet();
        } else {
            if (schemes == null) {
                schemes = DEFAULT_SCHEMES;
            }
            allowedSchemes = new HashSet<>(schemes.length);
            for (final String scheme : schemes) {
                allowedSchemes.add(scheme.toLowerCase(Locale.ENGLISH));
            }
        }

        this.authorityValidator = authorityValidator;
    }

    /**
     * Returns the number of times the token appears in the target.
     *
     * @param token Token value to be counted.
     * @param target Target value to count tokens in.
     * @return The number of tokens.
     */
    protected int countToken(final String token, final String target) {
        int tokenIndex = 0;
        int count = 0;
        while (tokenIndex != -1) {
            tokenIndex = target.indexOf(token, tokenIndex);
            if (tokenIndex > -1) {
                tokenIndex++;
                count++;
            }
        }
        return count;
    }

    /**
     * Tests whether the given flag is off.  If the flag is not a power of 2
     * (for example, 3) this tests whether the combination of flags is off.
     *
     * @param flag Flag value to check.
     * @return whether the specified flag value is off.
     */
    private boolean isOff(final long flag) {
        return (options & flag) == 0;
    }

    /**
     * Tests whether the given flag is on.  If the flag is not a power of 2
     * (for example, 3) this tests whether the combination of flags is on.
     *
     * @param flag Flag value to check.
     * @return whether the specified flag value is on.
     */
    private boolean isOn(final long flag) {
        return (options & flag) > 0;
    }

    /**
     * <p>Checks if a field has a valid URL address.</p>
     *
     * Note that the method calls #isValidAuthority()
     * which checks that the domain is valid.
     *
     * @param value The value validation is being performed on.  A {@code null}
     * value is considered invalid.
     * @return true if the URL is valid.
     */
    public boolean isValid(final String value) {
        if (value == null) {
            return false;
        }
        final URI uri; // ensure value is a valid URI
        try {
            uri = new URI(value);
        } catch (final URISyntaxException e) {
            return false;
        }
        // OK, perform additional validation
        final String scheme = uri.getScheme();
        if (!isValidScheme(scheme)) {
            return false;
        }
        final String authority = uri.getRawAuthority();
        if ("file".equals(scheme) && GenericValidator.isBlankOrNull(authority)) { // Special case - file: allows an empty authority
            return true; // this is a local file - nothing more to do here
        }
        // Validate the authority
        if ("file".equals(scheme) && authority != null && authority.contains(":") || !isValidAuthority(authority)) {
            return false;
        }
        if (!isValidPath(uri.getRawPath()) || !isValidQuery(uri.getRawQuery()) || !isValidFragment(uri.getRawFragment())) {
            return false;
        }
        return true;
    }

    /**
     * Returns true if the authority is properly formatted.  An authority is the combination
     * of hostname and port.  A {@code null} authority value is considered invalid.
     * Note: this implementation validates the domain unless a RegexValidator was provided.
     * If a RegexValidator was supplied, and it matches, then the authority is regarded
     * as valid with no further checks, otherwise the method checks against the
     * AUTHORITY_PATTERN and the DomainValidator (ALLOW_LOCAL_URLS)
     *
     * @param authority Authority value to validate, allows IDN
     * @return true if authority (hostname and port) is valid.
     */
    protected boolean isValidAuthority(final String authority) {
        if (authority == null) {
            return false;
        }

        // check manual authority validation if specified
        if (authorityValidator != null && authorityValidator.isValid(authority)) {
            return true;
        }
        // convert to ASCII if possible
        final String authorityASCII = DomainValidator.unicodeToASCII(authority);

        final Matcher authorityMatcher = AUTHORITY_PATTERN.matcher(authorityASCII);
        if (!authorityMatcher.matches()) {
            return false;
        }

        // We have to process IPV6 separately because that is parsed in a different group
        final String ipv6 = authorityMatcher.group(PARSE_AUTHORITY_IPV6);
        if (ipv6 != null) {
            final InetAddressValidator inetAddressValidator = InetAddressValidator.getInstance();
            if (!inetAddressValidator.isValidInet6Address(ipv6)) {
                return false;
            }
        } else {
            final String hostLocation = authorityMatcher.group(PARSE_AUTHORITY_HOST_IP);
            // check if authority is hostname or IP address:
            // try a hostname first since that's much more likely
            if (!domainValidator.isValid(hostLocation)) {
                // try an IPv4 address
                final InetAddressValidator inetAddressValidator = InetAddressValidator.getInstance();
                if (!inetAddressValidator.isValidInet4Address(hostLocation)) {
                    // isn't IPv4, so the URL is invalid
                    return false;
                }
            }
        }

        // the port is captured in the same group regardless of host form, so it must be
        // range checked for a bracketed IPv6 host too, not just the hostname/IPv4 branch
        final String port = authorityMatcher.group(PARSE_AUTHORITY_PORT);
        if (!GenericValidator.isBlankOrNull(port)) {
            try {
                final int iPort = Integer.parseInt(port);
                if (iPort < 0 || iPort > MAX_UNSIGNED_16_BIT_INT) {
                    return false;
                }
            } catch (final NumberFormatException nfe) {
                return false; // this can happen for big numbers
            }
        }

        final String extra = authorityMatcher.group(PARSE_AUTHORITY_EXTRA);
        if (extra != null && !extra.trim().isEmpty()) {
            return false;
        }

        return true;
    }

    /**
     * Returns true if the given fragment is null or fragments are allowed.
     *
     * @param fragment Fragment value to validate.
     * @return true if fragment is valid.
     */
    protected boolean isValidFragment(final String fragment) {
        if (fragment == null) {
            return true;
        }

        return isOff(NO_FRAGMENTS);
    }

    /**
     * Returns true if the path is valid.  A {@code null} value is considered invalid.
     *
     * @param path Path value to validate.
     * @return true if path is valid.
     */
    protected boolean isValidPath(final String path) {
        if (path == null || !PATH_PATTERN.matcher(path).matches()) {
            return false;
        }

        try {
            // This will convert '+' to space, but that is irrelevant for the purpose of validation
            final String decodedPath = URLDecoder.decode(path, StandardCharsets.UTF_8.name());
            // Don't omit host otherwise leading path may be taken as host if it starts with //
            final URI uri = new URI(null, "localhost", decodedPath, null);
            final String norm = uri.normalize().getPath();
            if (norm.startsWith("/../") // Trying to go via the parent dir
                    || norm.equals("/..")) { // Trying to go to the parent dir
                return false;
            }
            final int slash2Count = countToken("//", decodedPath);
            if (isOff(ALLOW_2_SLASHES) && slash2Count > 0) {
                return false;
            }
        } catch (final UnsupportedEncodingException | IllegalArgumentException | URISyntaxException e) {
            return false;
        }

        return true;
    }

    /**
     * Returns true if the query is null, or it's a properly formatted query string.
     *
     * @param query Query value to validate.
     * @return true if query is valid.
     */
    protected boolean isValidQuery(final String query) {
        if (query == null) {
            return true;
        }
        return QUERY_PATTERN.matcher(query).matches();
    }

    /**
     * Validate scheme. If schemes[] was initialized to a non-null,
     * then only those schemes are allowed.
     * Otherwise, the default schemes are "http", "https", "ftp".
     * Matching is case-blind.
     *
     * @param scheme The scheme to validate.  A {@code null} value is considered
     * invalid.
     * @return true if valid.
     */
    protected boolean isValidScheme(final String scheme) {
        if (scheme == null || !SCHEME_PATTERN.matcher(scheme).matches()
                || isOff(ALLOW_ALL_SCHEMES) && !allowedSchemes.contains(scheme.toLowerCase(Locale.ENGLISH))) {
            return false;
        }

        return true;
    }

}
