package lambda2sql;

import static java.lang.System.getProperty;

import static java.nio.file.Files.createTempDirectory;

import static java.util.Objects.requireNonNull;

import java.io.IOException;

import java.util.function.Predicate;

import com.trigersoft.jaque.expression.LambdaExpression;

/**

* A utility class for converting java lambdas to SQL.

* It must be initializes with {@link #init()} before any lambdas are created.

*/

public class Lambda2Sql {

private static final String DUMP_CLASSES_PROP = "jdk.internal.lambda.dumpProxyClasses";

/**

* Initializes the jdk.internal.lambda.dumpProxyClasses system property with a temporary directory.

* See https://bugs.openjdk.java.net/browse/JDK-8023524

*/

public static void init() {

try {

if( System.getProperty(DUMP_CLASSES_PROP) == null )

System.setProperty(DUMP_CLASSES_PROP, createTempDirectory("lambda").toString());

} catch (IOException e) {

throw new IllegalStateException(e);

}

}

/**

* Converts a predicate lambda to SQL. Make sure to {@link Lamda2Sql#init()} before creating the predicate.<br/>

* <pre>{@code person -> person.getAge() > 50 && person.isActive() }</pre>

* Becomes a string:

* <pre>{@code "age > 50 AND active" }</pre>

* Supported operators: >,>=,<,<=,=,!=,&&,||,!

*/

public static <T> String toSql(Predicate<T> predicate) {

requireNonNull(getProperty(DUMP_CLASSES_PROP), "Call init() before creating the predicate.");

LambdaExpression<Predicate<T>> lambdaExpression = LambdaExpression.parse(predicate);

return lambdaExpression.accept(new ToSqlVisitor()).toString();

}

}