/*
 * Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance with
 * the License. A copy of the License is located at
 *
 * http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.services.lambda.runtime.events;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class HttpUtils {

    private static final String DEFAULT_ENCODING = "UTF-8";

    /**
     * Regex which matches any of the sequences that we need to fix up after
     * URLEncoder.encode().
     */
    private static final Pattern ENCODED_CHARACTERS_PATTERN;
    static {
        StringBuilder pattern = new StringBuilder()
                .append(Pattern.quote("+"))
                .append("|")
                .append(Pattern.quote("*"))
                .append("|")
                .append(Pattern.quote("%7E"))
                .append("|")
                .append(Pattern.quote("%2F"));

        ENCODED_CHARACTERS_PATTERN = Pattern.compile(pattern.toString());
    }

    /**
     * Encode a string for use in the path of a URL; uses URLEncoder.encode,
     * (which encodes a string for use in the query portion of a URL), then
     * applies some postfilters to fix things up per the RFC. Can optionally
     * handle strings which are meant to encode a path (ie include '/'es
     * which should NOT be escaped).
     *
     * @param value the value to encode
     * @param path true if the value is intended to represent a path
     * @return the encoded value
     */
    public static String urlEncode(final String value, final boolean path) {
        if (value == null) {
            return "";
        }

        try {
            String encoded = URLEncoder.encode(value, DEFAULT_ENCODING);

            Matcher matcher = ENCODED_CHARACTERS_PATTERN.matcher(encoded);
            StringBuffer buffer = new StringBuffer(encoded.length());

            while (matcher.find()) {
                String replacement = matcher.group(0);

                if ("+".equals(replacement)) {
                    replacement = "%20";
                } else if ("*".equals(replacement)) {
                    replacement = "%2A";
                } else if ("%7E".equals(replacement)) {
                    replacement = "~";
                } else if (path && "%2F".equals(replacement)) {
                    replacement = "/";
                }

                matcher.appendReplacement(buffer, replacement);
            }

            matcher.appendTail(buffer);
            return buffer.toString();

        } catch (UnsupportedEncodingException ex) {
            throw new RuntimeException(ex);
        }
    }
}