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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.ExprContext;
import com.api.jsonata4java.expressions.generated.MappingExpressionParser.Function_callContext;
import com.api.jsonata4java.expressions.generated.MappingExpressionParser.Function_declContext;
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;
import com.fasterxml.jackson.databind.node.TextNode;

/**
 * From http://docs.jsonata.org/object-functions.html
 * 
 * $spread(object)
 * 
 * Splits an object containing key/value pairs into an array of objects, each of
 * which has a single key/value pair from the input object. If the parameter is
 * an array of objects, then the resultant array contains an object for every
 * key/value pair in every object in the supplied array.
 * 
 */
public class SpreadFunction extends FunctionBase implements Function {

	public static String ERR_BAD_CONTEXT = String.format(Constants.ERR_MSG_BAD_CONTEXT, Constants.FUNCTION_SPREAD);
	public static String ERR_ARG1BADTYPE = String.format(Constants.ERR_MSG_ARG1_BAD_TYPE, Constants.FUNCTION_SPREAD);
	public static String ERR_ARG2BADTYPE = String.format(Constants.ERR_MSG_ARG2_BAD_TYPE, Constants.FUNCTION_SPREAD);
	public static String ERR_ARG1_MUST_BE_ARRAY_OF_OBJECTS = String
			.format(Constants.ERR_MSG_ARG1_MUST_BE_ARRAY_OF_OBJECTS, Constants.FUNCTION_SPREAD);

	public JsonNode invoke(ExpressionsVisitor expressionVisitor, Function_callContext ctx) {
		// Create the variable to return
		SelectorArrayNode result = new SelectorArrayNode(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;
			}
		}
		boolean argIsArray = 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) {
					ExprContext exprCtx = ctx.exprValues().exprList().expr(0);
					if (exprCtx instanceof Function_declContext) {
						argObject = new TextNode("");
					}
				}
			}

			if (argObject == null) {
				return null;
			}
			if (argObject.isObject()) {
				ObjectNode obj = (ObjectNode) argObject;
				if (obj.size() > 0) {
					addObject(result, obj);
				} else {
					return null;
				}
			} else if (argObject.isArray()) {
				argIsArray = true;
				ArrayNode objArray = (ArrayNode) argObject;
				if (objArray.size() == 0) {
					return null;
				}
				// process each object in the array
				for (int i = 0; i < objArray.size(); i++) {
					JsonNode node = objArray.get(i);
					if (node.isObject()) {
						ObjectNode obj = (ObjectNode) node;
						addObject(result, obj);
					} else {
						// jsonata.js 1.8 just keeps non-objects
						// throw new EvaluateRuntimeException(ERR_ARG1_MUST_BE_ARRAY_OF_OBJECTS);
						result.add(node);
					}

				}
			} else {
				/*
				 * The input argument is not an object nor array of objects. Throw a suitable
				 * exception
				 */
				// throw new EvaluateRuntimeException(ERR_ARG1BADTYPE);
				// jsonata.js 1.8 just adds the argument
				result.add(argObject);
			}
		} else {
			throw new EvaluateRuntimeException(argCount == 0 ? ERR_BAD_CONTEXT : ERR_ARG2BADTYPE);
		}

		if (result != null && argIsArray == false) {
			JsonNode test = ExpressionsVisitor.unwrapArray(result);
			if (test.isArray() && test instanceof SelectorArrayNode) {
				result = (SelectorArrayNode) test;
			} else {
				return test;
			}
		}
		return result;
	}

	@Override
	public int getMaxArgs() {
		return 1;
	}

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

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

	public void addObject(SelectorArrayNode result, ObjectNode obj) {
		for (Iterator it = obj.fieldNames(); it.hasNext();) {
			String key = it.next();
			ObjectNode cell = JsonNodeFactory.instance.objectNode();
			cell.set(key, obj.get(key));
			result.add(cell);
		}
	}
}