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Port of jsonata.js to Java to enable rules for JSON content
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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.util.Iterator;

import com.api.jsonata4java.expressions.EvaluateRuntimeException;
import com.api.jsonata4java.expressions.ExpressionsVisitor;
import com.api.jsonata4java.expressions.ExpressionsVisitor.SelectorArrayNode;
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.ArrayNode;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.fasterxml.jackson.databind.node.ObjectNode;

/**
 * From http://docs.jsonata.org/object-functions.html
 * 
 * $keys(object)
 * 
 * Returns the keys in an array of Strings. It is an error if the input is not
 * an object.
 * 
 * Example
 * 
 * $keys({"a":1,"b":2})==["a", "b"]
 * 
 */
public class KeysFunction extends FunctionBase implements Function {

	private static final long serialVersionUID = -6908272736871289545L;

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

	public JsonNode invoke(ExpressionsVisitor expressionVisitor, Function_callContext ctx) {
		// Create the variable to return
		ObjectNode result = new ObjectNode(JsonNodeFactory.instance);

		// Retrieve the number of arguments
		JsonNode argObject = JsonNodeFactory.instance.nullNode();
		boolean useContext = FunctionUtils.useContextVariable(this, ctx, getSignature());
		int argCount = getArgumentCount(ctx);
		if (useContext) {
			argObject = FunctionUtils.getContextVariable(expressionVisitor);
			if (argObject != null && argObject.isNull() == false) {
				argCount++;
			} else {
				useContext = false;
			}
		}

		// Make sure that we have the right number of arguments
		if (argCount == 1) {
			if (!useContext) {
				argObject = FunctionUtils.getValuesListExpression(expressionVisitor, ctx, 0);
			}
			if (argObject == null) {
				return null;
			}
			// Check the type of the argument
			String key = "";
			if (argObject.isObject()) {
				ObjectNode obj = (ObjectNode) argObject;
				for (Iterator it = obj.fieldNames(); it.hasNext();) {
					key = it.next();
					if (result.get(key) == null) {
						result.put(key,true);
					}
				}
			} else {
				if (argObject.isArray()) {
					findObjects((ArrayNode)argObject,result);
				} else {
					/*
					 * The input argument is not an array. Throw a suitable exception
					 */
					return null;
					// throw new EvaluateRuntimeException(ERR_ARG1BADTYPE);
				}
			}
		} else {
			throw new EvaluateRuntimeException(argCount == 0 ? ERR_BAD_CONTEXT : ERR_ARG2BADTYPE);
		}
		if (result.size() == 0) {
			return null;
		}
		SelectorArrayNode output = new SelectorArrayNode(JsonNodeFactory.instance);
		for (Iteratorit = result.fieldNames(); it.hasNext(); ) {
			output.add(it.next());
		}
		return ExpressionsVisitor.unwrapArray(output);
	}
	
	static void findObjects(ArrayNode array,ObjectNode result) {
		for (int i=0;i it = obj.fieldNames(); it.hasNext();) {
			key = it.next();
			if (result.get(key) == null) {
				result.put(key,true);
			}
//			value = obj.get(key);
//			if (value != null) {
//				if (value.isArray()) {
//					ArrayNode subArray = JsonNodeFactory.instance.arrayNode();
//					findObjects((ArrayNode)value,subArray);
//					if (subArray.size() > 0) {
//						result.add(subArray);
//					}
//				} else if (value.isObject()) {
//					// not implemented in jsonata.js
//				}
//			}
		}
	}

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

	@Override
	public String getSignature() {
		// accepts an object (or context variable), returns an array of strings
		return ">";
	}
}