Application: gvSIG desktop

package org.gvsig.expressionevaluator.impl.function.programming;

import java.util.Iterator;

import org.apache.commons.lang3.Range;

import static org.gvsig.expressionevaluator.ExpressionBuilder.FUNCTION_RANGE;

import org.gvsig.expressionevaluator.ExpressionRuntimeException;

import org.gvsig.expressionevaluator.Function;

import org.gvsig.expressionevaluator.Interpreter;

import org.gvsig.expressionevaluator.spi.AbstractFunction;

public class RangeFunction extends AbstractFunction {

    public RangeFunction() {

        super(

            Function.GROUP_PROGRAMMING, 

            FUNCTION_RANGE, 

            Range.between(1,3),

            "",

            FUNCTION_RANGE+"({{start}}, stop, step)",

            null,

            "Iterable",

            false

        );

    }

    @Override

    public boolean allowConstantFolding() {

        return false;

    }    

    @Override

    public Object call(Interpreter interpreter, final Object[] args) throws Exception {

        switch(args.length) {

            case 1:

                return new Iterable<Long>() {

                    @Override

                    public Iterator<Long> iterator() {

                        return new XRangeIterator(0, getLong(args, 0), 1);

                    }

                };

            case 2:

                return new Iterable<Long>() {

                    @Override

                    public Iterator<Long> iterator() {

                        return new XRangeIterator(getLong(args, 0), getLong(args, 1), 1);

                    }

                };

            case 3:

                return new Iterable<Long>() {

                    @Override

                    public Iterator<Long> iterator() {

                        return new XRangeIterator(getLong(args, 0), getLong(args, 1), getLong(args, 2));

                    }

                };

            default:

                // Aqui no deberia llegar, el interprete deberia producir un error

                // antes, al comprobar el numero de argumentos de esta funcion.

                throw new ExpressionRuntimeException("Incorrect number of arguments in function range.");

        }

    }

    private static class XRangeIterator implements Iterator<Long> {

        private final long start;

        private final long stop;

        private final long step;

        private long current;

        public XRangeIterator(long start, long stop, long step) {

            this.start = start;

            this.stop = stop;

            this.step = step;

            this.current = start;

        }

        @Override

        public boolean hasNext() {

            return this.current < this.stop;

        }

        @Override

        public Long next() {

            long n = this.current;

            this.current += this.step;

            return n;

        }

    }

}