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rx-java Observables for jdbc

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package com.github.davidmoten.rx.jdbc;

import static com.github.davidmoten.rx.RxUtil.concatButIgnoreFirstSequence;
import static com.github.davidmoten.rx.jdbc.Util.TO_EMPTY_PARAMETER_LIST;

import java.util.List;

import rx.Observable;

/**
 * Utility methods for queries.
 */
final class Queries {

    /**
     * Private constructor to prevent instantiation.
     */
    private Queries() {
        // prevent instantiation
    }

    /**
     * Returns the number of parameters required to run this query once. Roughly
     * corresponds to the number of ? characters in the sql but have to watch
     * out for ? characters within quoted strings.
     * 
     * @return number of parameters in query sql
     */
    static int numParamsPerQuery(Query query) {
        return Util.parametersCount(query.sql());
    }

    /**
     * Returns query.getParameters() {@link Observable} but only after query
     * dependencies have been fully emitted (and ignored).
     * 
     * @return query parameters
     */
    static Observable parametersAfterDependencies(Query query) {
        return concatButIgnoreFirstSequence(query.depends(), query.parameters());
    }

    /**
     * Returns {@link Observable} with one item 1 but only after query
     * dependencies have been fully emitted (and ignored).
     * 
     * @param query
     * 
     * @return {@link Observable} with one element 1
     */
    static Observable singleIntegerAfterDependencies(Query query) {
        return concatButIgnoreFirstSequence(query.depends(), Observable.just(1));
    }

    /**
     * If the number of parameters in a query is >0 then group the parameters in
     * lists of that number in size but only after the dependencies have been
     * completed. If the number of parameteres is zero then return an observable
     * containing one item being an empty list.
     * 
     * @param query
     * @return
     */
    static Observable> bufferedParameters(Query query) {
        int numParamsPerQuery = numParamsPerQuery(query);
        if (numParamsPerQuery > 0)
            return parametersAfterDependencies(query).buffer(numParamsPerQuery);
        else
            return singleIntegerAfterDependencies(query).map(TO_EMPTY_PARAMETER_LIST);
    }
}