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/**
 * (c) Copyright 2018, 2019 IBM Corporation
 * 1 New Orchard Road, 
 * Armonk, New York, 10504-1722
 * United States
 * +1 914 499 1900
 * support: Nathaniel Mills [email protected]
 *
 * 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
 *
 *    http://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 com.api.jsonata4java.expressions.functions;

import java.io.UnsupportedEncodingException;
import java.util.Base64;

import com.api.jsonata4java.expressions.EvaluateRuntimeException;
import com.api.jsonata4java.expressions.ExpressionsVisitor;
import com.api.jsonata4java.expressions.generated.MappingExpressionParser.Function_callContext;
import com.api.jsonata4java.expressions.utils.Constants;
import com.api.jsonata4java.expressions.utils.FunctionUtils;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.fasterxml.jackson.databind.node.TextNode;

/**
 * From http://docs.jsonata.org/string-functions.html:
 * 
 * $base64decode()
 * 
 * Converts base 64 encoded bytes to a string, using a UTF-8 Unicode codepage.
 * 
 * Examples
 * 
 * $base64decode("bXl1c2VyOm15cGFzcw==")=="myuser:mypass"
 * 
 */
public class Base64DecodeFunction extends FunctionBase implements Function {

	public static String ERR_BAD_CONTEXT = String.format(Constants.ERR_MSG_BAD_CONTEXT,
			Constants.FUNCTION_BASE64_DECODE);
	public static String ERR_ARG1BADTYPE = String.format(Constants.ERR_MSG_ARG1_BAD_TYPE,
			Constants.FUNCTION_BASE64_DECODE);
	public static String ERR_ARG2BADTYPE = String.format(Constants.ERR_MSG_ARG2_BAD_TYPE,
			Constants.FUNCTION_BASE64_DECODE);
	public static String ERR_RUNTIME_ERROR = String.format(Constants.ERR_MSG_RUNTIME_ERROR,
			Constants.FUNCTION_BASE64_DECODE);

	public JsonNode invoke(ExpressionsVisitor expressionVisitor, Function_callContext ctx) {
		// Create the variable to return
		JsonNode result = null;

		// Retrieve the number of arguments
		JsonNode argString = JsonNodeFactory.instance.nullNode();
		boolean useContext = FunctionUtils.useContextVariable(this, ctx, getSignature());
		int argCount = getArgumentCount(ctx);
		if (useContext) {
			argString = FunctionUtils.getContextVariable(expressionVisitor);
			if (argString != null && argString.isNull() == false) {
				// check to see if there is a valid context value
				if (!argString.isTextual()) {
					throw new EvaluateRuntimeException(ERR_BAD_CONTEXT);
				}
				argCount++;
			} else {
				useContext = false;
			}
		}

		// Make sure that we have the right number of arguments
		if (argCount == 1) {
			if (!useContext) {
				argString = FunctionUtils.getValuesListExpression(expressionVisitor, ctx, 0);
			}
			if (argString == null) {
				return null;
			}
			if (argString.isTextual()) {
				final String str = argString.textValue();

				try {
					result = new TextNode(new String(Base64.getDecoder().decode(str), "utf-8"));
				} catch (UnsupportedEncodingException e) {
					throw new EvaluateRuntimeException(ERR_RUNTIME_ERROR);
				}
			} else {
				throw new EvaluateRuntimeException(ERR_ARG1BADTYPE);
			}
		} else {
			throw new EvaluateRuntimeException(argCount == 0 ? ERR_BAD_CONTEXT : ERR_ARG2BADTYPE);
		}

		return result;
	}

	@Override
	public int getMaxArgs() {
		return 1;
	}
	@Override
	public int getMinArgs() {
		return 0; // account for context variable
	}

	@Override
	public String getSignature() {
		// accepts a string (or context variable), returns a string
		return "";
	}
}