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/**
 * This file is part of Graylog.
 *
 * Graylog is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Graylog is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Graylog.  If not, see .
 */
package org.graylog.plugins.pipelineprocessor.functions.urls;

import org.graylog.plugins.pipelineprocessor.EvaluationContext;
import org.graylog.plugins.pipelineprocessor.ast.functions.AbstractFunction;
import org.graylog.plugins.pipelineprocessor.ast.functions.FunctionArgs;
import org.graylog.plugins.pipelineprocessor.ast.functions.FunctionDescriptor;
import org.graylog.plugins.pipelineprocessor.ast.functions.ParameterDescriptor;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

import static com.google.common.collect.ImmutableList.of;

public class UrlDecode extends AbstractFunction {
    public static final String NAME = "urldecode";

    private final ParameterDescriptor valueParam;
    private final ParameterDescriptor charsetParam;

    public UrlDecode() {
        valueParam = ParameterDescriptor.string("value").description("The string to decode").build();
        charsetParam = ParameterDescriptor.type("charset", String.class, Charset.class).optional()
                .description("The name of a supported character encoding such as \"UTF-8\" or \"US-ASCII\". Default: \"UTF-8\"")
                .transform(Charset::forName)
                .build();
    }

    @Override
    public String evaluate(FunctionArgs args, EvaluationContext context) {
        final String value = valueParam.required(args, context);
        final Charset charset = charsetParam.optional(args, context).orElse(StandardCharsets.UTF_8);

        if (value == null) {
            return null;
        }

        try {
            return URLDecoder.decode(value, charset.name());
        } catch (UnsupportedEncodingException e) {
            throw new IllegalArgumentException("Unsupported character encoding", e);
        }
    }

    @Override
    public FunctionDescriptor descriptor() {
        return FunctionDescriptor.builder()
                .name(NAME)
                .returnType(String.class)
                .params(of(valueParam, charsetParam))
                .description("Decodes a application/x-www-form-urlencoded string using a specific encoding scheme.")
                .build();
    }
}