poi/src/java/org/apache/poi/hssf/record/formula/eval/UserDefinedFunction.java

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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
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       http://www.apache.org/licenses/LICENSE-2.0

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   distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.poi.hssf.record.formula.eval;

import org.apache.poi.hssf.record.formula.atp.AnalysisToolPak;
import org.apache.poi.hssf.record.formula.functions.FreeRefFunction;
import org.apache.poi.ss.formula.EvaluationWorkbook;
import org.apache.poi.ss.formula.OperationEvaluationContext;
import org.apache.poi.ss.formula.eval.NotImplementedException;
/**
 *
 * Common entry point for all user-defined (non-built-in) functions (where
 * <tt>AbstractFunctionPtg.field_2_fnc_index</tt> == 255)
 *
 * @author Josh Micich
 */
final class UserDefinedFunction implements FreeRefFunction {

	public static final FreeRefFunction instance = new UserDefinedFunction();

	private UserDefinedFunction() {
		// enforce singleton
	}

	public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec) {

		int nIncomingArgs = args.length;
		if(nIncomingArgs < 1) {
			throw new RuntimeException("function name argument missing");
		}

		ValueEval nameArg = args[0];
		FreeRefFunction targetFunc;
		if (nameArg instanceof NameEval) {
			targetFunc = findInternalUserDefinedFunction((NameEval) nameArg);
		} else if (nameArg instanceof NameXEval) {
			targetFunc = findExternalUserDefinedFunction(ec.getWorkbook(), (NameXEval) nameArg);
		} else {
			throw new RuntimeException("First argument should be a NameEval, but got ("
					+ nameArg.getClass().getName() + ")");
		}
		int nOutGoingArgs = nIncomingArgs -1;
		ValueEval[] outGoingArgs = new ValueEval[nOutGoingArgs];
		System.arraycopy(args, 1, outGoingArgs, 0, nOutGoingArgs);
		return targetFunc.evaluate(outGoingArgs, ec);
	}

	private static FreeRefFunction findExternalUserDefinedFunction(EvaluationWorkbook workbook,
			NameXEval n) {
		String functionName = workbook.resolveNameXText(n.getPtg());

		if(false) {
			System.out.println("received call to external user defined function (" + functionName + ")");
		}
		// currently only looking for functions from the 'Analysis TookPak'  e.g. "YEARFRAC" or "ISEVEN"
		// not sure how much this logic would need to change to support other or multiple add-ins.
		FreeRefFunction result = AnalysisToolPak.findFunction(functionName);
		if (result != null) {
			return result;
		}
		throw new NotImplementedException(functionName);
	}

	private static FreeRefFunction findInternalUserDefinedFunction(NameEval functionNameEval) {

		String functionName = functionNameEval.getFunctionName();
		if(false) {
			System.out.println("received call to internal user defined function  (" + functionName + ")");
		}
		// TODO find the implementation for the user defined function

		throw new NotImplementedException(functionName);
	}
}