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Kiwi is a utility library. We really like Google's Guava, and also use Apache Commons. But if they don't have something we need, and we think it is useful, this is where we put it.

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package org.kiwiproject.jdbc;

import static org.kiwiproject.base.KiwiPreconditions.checkArgumentNotNull;

import java.util.List;
import java.util.Optional;
import java.util.function.Supplier;

/**
 * Simple enum that represents the values for SQL {@code ORDER BY} clauses.
 * 
 * This is useful in building queries, for example when using JDBI and the SQL objects API you might
 * need to add dynamic ordering based on user input but want to ensure no SQL injection attack is possible.
 * So you would accept user input and then use {@link #from(String)} to get a {@link SqlOrder} instance.
 * Then, you could use it in a JDBI {@code SqlQuery} annotation as one example.
 */
public enum SqlOrder {

    ASC, DESC;

    /**
     * Given a string value, return a {@link SqlOrder}, ignoring case and leading/trailing whitespace.
     *
     * @param value the value to convert from
     * @return the SqlOrder enum corresponding to the given value
     * @throws IllegalArgumentException if an invalid value is provided that does not map to a SqlOrder enum constant
     */
    public static SqlOrder from(String value) {
        var trimmedValue = Optional.ofNullable(value).map(String::trim).orElse("");

        if ("ASC".equalsIgnoreCase(trimmedValue)) {
            return ASC;
        } else if ("DESC".equalsIgnoreCase(trimmedValue)) {
            return DESC;
        }

        throw new IllegalArgumentException("Invalid SQL order: " + value);
    }

    /**
     * Perform a search in either ascending or descending order using the given {@link Supplier} instances.
     * If this instance is {@link #ASC} then the ascending search is executed, otherwise if {@link #DESC} the
     * descending search is executed.
     *
     * @param ascSearch  the logic to perform an ascending search
     * @param descSearch the logic to perform a descending search
     * @param         the result type
     * @return a list of results in either ascending or descending order based on this instance
     */
    public  List searchWith(Supplier> ascSearch, Supplier> descSearch) {
        checkArgumentNotNull(ascSearch, "Ascending search must be specified");
        checkArgumentNotNull(descSearch, "Descending search must be specified");

        if (this == ASC) {
            return ascSearch.get();
        }

        return descSearch.get();
    }

    /**
     * Return a string that can be used directly in a SQL {@code ORDER BY} clause.
     *
     * @return a string that can be used in a SQL query
     */
    public String toSql() {
        return name();
    }
}