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package ganymede.notebook;
/*-
 * ##########################################################################
 * Ganymede
 * %%
 * Copyright (C) 2021, 2022 Allen D. Ball
 * %%
 * Licensed 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.
 * ##########################################################################
 */
import com.fasterxml.jackson.databind.JsonNode;
import java.io.InputStreamReader;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import lombok.NoArgsConstructor;
import lombok.ToString;
import lombok.extern.log4j.Log4j2;
import org.springframework.core.io.ClassPathResource;

import static java.nio.charset.StandardCharsets.UTF_8;
import static javax.script.ScriptContext.ENGINE_SCOPE;
import static lombok.AccessLevel.PROTECTED;

/**
 * Abstract
 * {@link.uri https://www.jcp.org/en/jsr/detail?id=223 target=newtab JSR 223}
 * {@link ScriptEngine} {@link Magic} base class.
 *
 * @see ScriptEngineManager
 *
 * @author {@link.uri mailto:[email protected] Allen D. Ball}
 */
@NoArgsConstructor(access = PROTECTED) @ToString @Log4j2
public abstract class AbstractScriptEngineMagic extends AbstractMagic implements AnnotatedScriptEngineMagic {
    /** See {@link #engine()}. */
    protected ScriptEngine engine = null;

    /**
     * Method to get the {@link ScriptEngine}.
     *
     * @return  The {@link ScriptEngine} if it can be instantiated;
     *          {@code null} otherwise.
     */
    protected ScriptEngine engine() {
        if (engine == null) {
            var manager = new ScriptEngineManager(context.getClassLoader());

            engine = manager.getEngineByName(getScriptEngineName());

            if (engine == null || (! initialize(engine))) {
                engine =
                    getExtensions().stream()
                    .map(t -> manager.getEngineByExtension(t))
                    .filter(Objects::nonNull)
                    .filter(this::initialize)
                    .findFirst().orElse(null);
            }
        }

        return engine;
    }

    /**
     * Method to initialize the {@link ScriptEngine}.  Default
     * implementation looks for a {@link Class} resource named with the
     * {@link Class#getSimpleName()} and one of the {@link ScriptEngine}'s
     * {@link javax.script.ScriptEngineFactory#getExtensions() extensions}.
     * A {@link ScriptEngine} instance that cannot be initialized will be
     * ignored.
     *
     * @return  {@code true} if the {@link ScriptEngine} can be initialized,
     *          {@code false} otherwise.
     */
    protected boolean initialize(ScriptEngine engine) {
        var initialized = true;
        var resource = getInitScript(engine.getFactory().getExtensions());

        if (initialized && resource != null) {
            try (var in = new InputStreamReader(resource.getInputStream(), UTF_8)) {
                engine.eval(in, context.context);
            } catch (Throwable throwable) {
                initialized = false;
                throwable.printStackTrace(System.err);
            }
        }

        return initialized;
    }

    /**
     * Method to locate {@link ScriptEngine} initialization script.
     *
     * @param   suffixes        The {@link List} of script suffixes.
     *
     * @return  Return the first resource that matches this class's simple
     *          name and suffix (and exists).
     */
    protected ClassPathResource getInitScript(List suffixes) {
        var resource =
            Optional.ofNullable(suffixes).stream()
            .flatMap(List::stream)
            .map(t -> getClass().getSimpleName() + "." + t)
            .map(t -> new ClassPathResource(t, getClass()))
            .filter(ClassPathResource::exists)
            .findFirst().orElse(null);

        return resource;
    }

    @Override
    public void execute(String line0, String code, JsonNode metadata) throws Exception {
        execute(Magic.getCellMagicCommand(line0), code);
    }

    /**
     * Method provided for subclass implementations to intercept calculation
     * of {@link ScriptEngine#ARGV} binding.
     *
     * @param   argv            The first line parsed as an array of
     *                          {@link String}s.
     * @param   code            The remainder of the cell.
     */
    protected void execute(String[] argv, String code) throws Exception {
        var bindings = context.context.getBindings(ENGINE_SCOPE);

        try {
            bindings.put(ScriptEngine.ARGV, argv);
            execute(code);
        } finally {
            bindings.remove(ScriptEngine.ARGV);
        }
    }

    /**
     * Target of {@link #execute(String[],String)}.  The {@code argv} is
     * available in the {@link javax.script.ScriptContext}
     * {@code ENGINE_SCOPE} {@link javax.script.Bindings} as
     * {@link ScriptEngine#ARGV ScriptEngine.ARGV}.
     *
     * @param   code            The remainder of the cell.
     */
    protected void execute(String code) {
        var engine = engine();

        if (engine != null) {
            try {
                if (! code.isBlank()) {
                    render(engine.eval(code, context.context));
                } else {
                    show();
                }
            } catch (Throwable throwable) {
                throwable.printStackTrace(System.err);
            }
        } else {
            System.err.format("No %s REPL available\n", getMagicNames()[0]);
        }
    }

    /**
     * Callback to render the results of
     * {@link ScriptEngine#eval(String,ScriptContext)}.  Made available for
     * template engines.  Default implementation does nothing.
     *
     * @param   object          The result of
     *                          {@link ScriptEngine#eval(String,ScriptContext)}.
     */
    protected void render(Object object) { }

    /**
     * Callback to show information about the {@link ScriptEngine} instance.
     * Default implementation does nothing.
     */
    protected void show() { }
}