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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.time.OffsetDateTime;
import java.time.format.DateTimeParseException;

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.LongNode;

/**
 * http://docs.jsonata.org/numeric-functions.html
 * 
 * $toMillis(timestamp)
 * 
 * Convert a timestamp string in the ISO 8601 format to the number of
 * milliseconds since the Unix Epoch (1 January, 1970 UTC) as a number.
 * 
 * An error is thrown if the string is not in the correct format.
 * 
 * Examples
 * 
 * $toMillis("2017-11-07T15:07:54.972Z")==1510067274972
 */
public class ToMillisFunction extends FunctionBase implements Function {

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

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

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

		// Make sure that we have the right number of arguments
		if (argCount == 1) {
			if (!useContext) {
				argTimestamp = FunctionUtils.getValuesListExpression(expressionVisitor, ctx, 0);
			}
			// if arg is an array, return its length. Any other type of
			// input returns 1.
			if (argTimestamp == null) {
				return null;
			}
			// Check the type of the argument
			if (argTimestamp.isTextual()) {
				try {
					/*
					 * The string passed to us might contain an ISO 8601 format string that
					 * specifies an offset element. The java.time.Instant class will throw a
					 * DateTimeParseException when attempting to parse these strings. We need to use
					 * the java.time.OffsetDateTime class instead.
					 */
					Long millis = OffsetDateTime.parse(argTimestamp.asText()).toInstant().toEpochMilli();
					result = new LongNode(millis);
				} catch (DateTimeParseException e) {
					/*
					 * The string argument does not contain a valid ISO 8601 format datetime string.
					 * Throw a suitable exception.
					 */
					final String msg = String.format(Constants.ERR_MSG_TO_MILLIS_ISO_8601_FORMAT,
							argTimestamp.asText());
					throw new EvaluateRuntimeException(msg);
				}
			} else {
				// The argument is a neither a number or a string. Throw a suitable
				// exception.
				throw new EvaluateRuntimeException(ERR_ARG1BADTYPE);
			}
		} else {
			throw new EvaluateRuntimeException(argCount == 0 ? ERR_BAD_CONTEXT : ERR_ARG2BADTYPE);
		}

		return result;
	}

	@Override
	public int getMaxArgs() {
		return 2;
	}
	@Override
	public int getMinArgs() {
		return 0; // account for context variable
	}

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