Filter.java

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package org.apache.sling.scripting.sightly.impl.filter;

import org.apache.sling.scripting.sightly.compiler.expression.Expression;

/**
 * A filter is a transformation which performs modifications on expressions. Unlike plugins, filters are always applied on an expression.
 * Whether the filter transformation is actually necessary is decided by the filter. The application order of filters is given by filter
 * priority.
 */
public interface Filter extends Comparable<Filter> {

    /**
     * Transform the given expression
     *
     * @param expression        the original expression
     * @param expressionContext the expression's context
     * @return a transformed expression. If the filter is not applicable
     * to the given expression, then the original expression shall be returned
     */
    Expression apply(Expression expression, ExpressionContext expressionContext);

    /**
     * The priority with which filters are applied. This establishes order between filters. Filters with
     * lower priority are applied first.
     *
     * @return an integer representing the filter's priority
     */
    int priority();

}