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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.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import rx.Observable;
import rx.functions.Func1;

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

    private static final Func1> FLATTEN_NAMED_MAPS = new Func1>() {

        @SuppressWarnings("unchecked")
        @Override
        public Observable call(Parameter p) {
            if (p.value() instanceof Map) {
                List list = new ArrayList();
                for (Entry entry : ((Map) p.value()).entrySet()) {
                    list.add(new Parameter(entry.getKey(), entry.getValue()));
                }
                return Observable.from(list);
            } else
                return Observable.from(Arrays.asList(p));
        }
    };

    /**
     * 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);
    }

    /**
     * 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)
            // we don't check that parameters is empty after this because by
            // general design we want nothing to happen if a query is passed no
            // parameters when it expects them
            return parametersAfterDependencies(query).concatMap(FLATTEN_NAMED_MAPS)
                    .buffer(numParamsPerQuery);
        else
            return singleIntegerAfterDependencies(query).map(TO_EMPTY_PARAMETER_LIST);
    }

}