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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 ******************************************************************************/

package org.apache.sling.scripting.sightly.impl.engine.extension.use;

import java.io.StringReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;

import javax.script.Bindings;
import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

import org.apache.commons.io.IOUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.sling.api.resource.Resource;
import org.apache.sling.api.scripting.SlingBindings;
import org.apache.sling.api.scripting.SlingScript;
import org.apache.sling.scripting.api.CachedScript;
import org.apache.sling.scripting.api.ScriptCache;
import org.apache.sling.scripting.api.resource.ScriptingResourceResolverProvider;
import org.apache.sling.servlets.resolver.bundle.tracker.BundledRenderUnit;
import org.apache.sling.scripting.core.ScriptNameAwareReader;
import org.apache.sling.scripting.sightly.impl.engine.SightlyScriptEngineFactory;
import org.apache.sling.scripting.sightly.impl.engine.bundled.BundledUnitManagerImpl;
import org.apache.sling.scripting.sightly.impl.utils.BindingsUtils;
import org.apache.sling.scripting.sightly.impl.utils.ScriptUtils;
import org.apache.sling.scripting.sightly.render.RenderContext;
import org.apache.sling.scripting.sightly.use.ProviderOutcome;
import org.apache.sling.scripting.sightly.use.UseProvider;
import org.osgi.framework.Constants;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Reference;
import org.osgi.service.metatype.annotations.AttributeDefinition;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Use provider that interprets the identifier as a script path, and runs the respective script using a script engine that matches the
 * script extension.
 * <p>
 * This provider returns a non-failure outcome only if the evaluated script actually returns something. For more details check the
 * implementation of the {@link SlingScript#eval(SlingBindings)} method for the available script engines from your platform.
 */
@Component(
        service = UseProvider.class,
        configurationPid = "org.apache.sling.scripting.sightly.impl.engine.extension.use.ScriptUseProvider",
        property = {
                Constants.SERVICE_RANKING + ":Integer=0"
        }
)
public class ScriptUseProvider implements UseProvider {

    @interface Configuration {

        @AttributeDefinition(
                name = "Service Ranking",
                description = "The Service Ranking value acts as the priority with which this Use Provider is queried to return an " +
                        "Use-object. A higher value represents a higher priority."
        )
        int service_ranking() default 0;

    }

    private static final Logger log = LoggerFactory.getLogger(ScriptUseProvider.class);

    @Reference
    private ScriptingResourceResolverProvider scriptingResourceResolverProvider;

    @Reference
    private BundledUnitManagerImpl bundledUnitManager;

    @Reference
    private ScriptEngineManager scriptEngineManager;

    @Reference
    private ScriptCache scriptCache;

    @Override
    public ProviderOutcome provide(String scriptName, RenderContext renderContext, Bindings arguments) {
        Bindings globalBindings = renderContext.getBindings();
        Bindings bindings = BindingsUtils.merge(globalBindings, arguments);
        String extension = scriptExtension(scriptName);
        if (extension == null || extension.equals(SightlyScriptEngineFactory.EXTENSION)) {
            return ProviderOutcome.failure();
        }
        URL script = bundledUnitManager.getScript(bindings, scriptName);
        if (script != null) {
            String scriptUrlAsString = script.toExternalForm();
            bindings.remove(BundledRenderUnit.VARIABLE);
            bindings.put(ScriptEngine.FILENAME, scriptUrlAsString);
            try {
                ScriptEngine scriptEngine = scriptEngineManager.getEngineByExtension(extension);
                if (scriptEngine != null) {
                    if (scriptEngine instanceof Compilable) {
                        CompiledScript compiledScript;
                        CachedScript cachedScript = scriptCache.getScript(scriptUrlAsString);
                        if (cachedScript == null) {
                            Compilable compilableScriptEngine = (Compilable) scriptEngine;
                            ScriptNameAwareReader reader =
                                    new ScriptNameAwareReader(new StringReader(IOUtils.toString(script, StandardCharsets.UTF_8)),
                                            scriptUrlAsString);
                            compiledScript = compilableScriptEngine.compile(reader);
                        } else {
                            compiledScript = cachedScript.getCompiledScript();
                        }
                        return ProviderOutcome.notNullOrFailure(compiledScript.eval(bindings));
                    } else {
                        ScriptNameAwareReader reader =
                                new ScriptNameAwareReader(new StringReader(IOUtils.toString(script, StandardCharsets.UTF_8)),
                                        scriptUrlAsString);
                        return ProviderOutcome
                                .notNullOrFailure(scriptEngine.eval(reader, bindings));
                    }
                }
            } catch (Exception e) {
                return ProviderOutcome.failure(e);
            }
        }
        Resource scriptResource = ScriptUtils.resolveScript(scriptingResourceResolverProvider.getRequestScopedResourceResolver(),
                renderContext, scriptName);
        if (scriptResource == null) {
            log.debug("Path does not match an existing resource: {}", scriptName);
            return ProviderOutcome.failure();
        }
        return evalScript(scriptResource, bindings);
    }

    private ProviderOutcome evalScript(Resource scriptResource, Bindings bindings) {
        SlingScript slingScript = scriptResource.adaptTo(SlingScript.class);
        if (slingScript == null) {
            return ProviderOutcome.failure();
        }
        SlingBindings slingBindings = new SlingBindings();
        slingBindings.putAll(bindings);
        Object scriptEval = slingScript.eval(slingBindings);
        return ProviderOutcome.notNullOrFailure(scriptEval);
    }

    private String scriptExtension(String path) {
        String extension = StringUtils.substringAfterLast(path, ".");
        if (StringUtils.isEmpty(extension)) {
            extension = null;
        }
        return extension;
    }

}