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Java script engine for JShell.
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package ch.obermuhlner.scriptengine.jshell;

import jdk.jshell.*;
import jdk.jshell.execution.DirectExecutionControl;
import jdk.jshell.execution.LocalExecutionControlProvider;
import jdk.jshell.spi.ExecutionControl;
import jdk.jshell.spi.ExecutionControlProvider;
import jdk.jshell.spi.ExecutionEnv;

import javax.script.*;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.*;
import java.util.stream.Collectors;

/**
 * Compiled script of a {@link JShellScriptEngine}.
 */
public class JShellCompiledScript extends CompiledScript {
    private final JShellScriptEngine engine;
    private final List snippets;

    JShellCompiledScript(JShellScriptEngine engine, String script) throws ScriptException {
        this.engine = engine;

        try (JShell jshell = JShell.builder()
                .executionEngine(new LocalExecutionControlProvider(), null)
                .build()) {
            this.snippets = compileScript(jshell, script);
        }
    }

    @Override
    public Object eval(ScriptContext context) throws ScriptException {
        Bindings globalBindings = context.getBindings(ScriptContext.GLOBAL_SCOPE);
        Bindings engineBindings = context.getBindings(ScriptContext.ENGINE_SCOPE);

        final AccessDirectExecutionControl accessDirectExecutionControl = new AccessDirectExecutionControl();
        try (JShell jshell = JShell.builder()
                .executionEngine(new AccessDirectExecutionControlProvider(accessDirectExecutionControl), null)
                .build()) {
            pushVariables(jshell, accessDirectExecutionControl, globalBindings, engineBindings);
            Object result = evaluateSnippets(jshell, accessDirectExecutionControl);
            pullVariables(jshell, accessDirectExecutionControl, globalBindings, engineBindings);

            return result;
        }
    }

    private void pushVariables(JShell jshell, AccessDirectExecutionControl accessDirectExecutionControl, Bindings globalBindings, Bindings engineBindings) throws ScriptException {
        Map variables = mergeBindings(globalBindings, engineBindings);
        VariablesTransfer.setVariables(variables);

        for (Map.Entry entry : variables.entrySet()) {
            String name = entry.getKey();
            Object value = entry.getValue();
            String type = determineType(value);
            String script = type + " " + name + " = (" + type + ") " + VariablesTransfer.class.getName() + ".getVariableValue(\"" + name + "\");";
            evaluateSnippet(jshell, accessDirectExecutionControl, script);
        }
    }

    private void pullVariables(JShell jshell, AccessDirectExecutionControl accessDirectExecutionControl, Bindings globalBindings, Bindings engineBindings) throws ScriptException {
        try {
            jshell.variables().forEach(varSnippet -> {
                String name = varSnippet.name();
                String script = VariablesTransfer.class.getName() + ".setVariableValue(\"" + name + "\", " + name + ");";
                try {
                    evaluateSnippet(jshell, accessDirectExecutionControl, script);
                    Object value = VariablesTransfer.getVariableValue(name);
                    setBindingsValue(globalBindings, engineBindings, name, value);
                } catch (ScriptException e) {
                    throw new ScriptRuntimeException(e);
                }
            });
        } catch (ScriptRuntimeException e) {
            throw (ScriptException) e.getCause();
        }

        VariablesTransfer.clear();
    }

    private void setBindingsValue(Bindings globalBindings, Bindings engineBindings, String name, Object value) {
        if (!engineBindings.containsKey(name) && globalBindings.containsKey(name)) {
            globalBindings.put(name, value);
        } else {
            engineBindings.put(name, value);
        }
    }

    private String determineType(Object value) {
        if (value == null) {
            return Object.class.getCanonicalName();
        }

        Class clazz = value.getClass();
        while (clazz != null) {
            if(isValidType(clazz)) {
                return clazz.getCanonicalName();
            }
            for(Class interfaceClazz : clazz.getInterfaces()) {
                if(isValidType(interfaceClazz)) {
                    return interfaceClazz.getCanonicalName();
                }
            }
            clazz = clazz.getSuperclass();
        }

        return Object.class.getCanonicalName();
    }

    private boolean isValidType(Class clazz) {
        if(clazz.getCanonicalName() == null) {
            return false;
        }

        if((clazz.getModifiers() & (Modifier.PRIVATE | Modifier.PROTECTED)) != 0) {
            return false;
        }

        return true;
    }

    private Map mergeBindings(Bindings... bindingsToMerge) {
        Map variables = new HashMap<>();

        for (Bindings bindings : bindingsToMerge) {
            if (bindings != null) {
                for (Map.Entry globalEntry : bindings.entrySet()) {
                    variables.put(globalEntry.getKey(), globalEntry.getValue());
                }
            }
        }

        return variables;
    }

    private Object evaluateSnippets(JShell jshell, AccessDirectExecutionControl accessDirectExecutionControl) throws ScriptException {
        Object result = null;

        for (String snippetScript : snippets) {
            result = evaluateSnippet(jshell, accessDirectExecutionControl, snippetScript);
        }

        return result;
    }

    private Object evaluateSnippet(JShell jshell, AccessDirectExecutionControl accessDirectExecutionControl, String snippetScript) throws ScriptException {
        Object result = null;

        List events = jshell.eval(snippetScript);

        for (SnippetEvent event : events) {
            if (event.status() == Snippet.Status.VALID && event.exception() == null) {
                result = accessDirectExecutionControl.getLastValue();
            } else {
                throwAsScriptException(jshell, event);
            }
        }
        return result;
    }

    private void throwAsScriptException(JShell jshell, SnippetEvent event) throws ScriptException {
        if (event.exception() != null) {
            JShellException exception = event.exception();
            String message = exception.getMessage() == null ? "" : ": " + exception.getMessage();
            if (exception instanceof EvalException) {
                EvalException evalException = (EvalException) exception;
                throw new ScriptException(evalException.getExceptionClassName() + message + "\n" + event.snippet().source());
            }
            throw new ScriptException(message + "\n" + event.snippet().source());
        }

        Snippet snippet = event.snippet();
        Optional optionalDiag = jshell.diagnostics(snippet).findAny();
        if (optionalDiag.isPresent()) {
            Diag diag = optionalDiag.get();
            throw new ScriptException(diag.getMessage(null) + "\n" + snippet);
        }

        if (snippet instanceof DeclarationSnippet) {
            DeclarationSnippet declarationSnippet = (DeclarationSnippet) snippet;
            List unresolvedDependencies = jshell.unresolvedDependencies(declarationSnippet).collect(Collectors.toList());
            if (!unresolvedDependencies.isEmpty()) {
                throw new ScriptException("Unresolved dependencies: " + unresolvedDependencies + "\n" + snippet);
            }
        }

        throw new ScriptException("Unknown error\n" + snippet);
    }

    @Override
    public ScriptEngine getEngine() {
        return engine;
    }

    private static List compileScript(JShell jshell, String script) throws ScriptException {
        List snippets = new ArrayList<>();

        while (!script.isEmpty()) {
            SourceCodeAnalysis.CompletionInfo completionInfo = jshell.sourceCodeAnalysis().analyzeCompletion(script);
            if (!completionInfo.completeness().isComplete()) {
                throw new ScriptException("Incomplete script\n" + script);
            }

            snippets.add(completionInfo.source());

            script = completionInfo.remaining();
        }

        return snippets;
    }

    private static class ScriptRuntimeException extends RuntimeException {
        public ScriptRuntimeException(ScriptException cause) {
            super(cause);
        }
    }

    private static class AccessDirectExecutionControl extends DirectExecutionControl {
        private Object lastValue;

        @Override
        protected String invoke(Method doitMethod) throws Exception {
            lastValue = doitMethod.invoke(null);
            return valueString(lastValue);
        }

        public Object getLastValue() {
            return lastValue;
        }
    }

    private static class AccessDirectExecutionControlProvider implements ExecutionControlProvider {
        private AccessDirectExecutionControl accessDirectExecutionControl;

        AccessDirectExecutionControlProvider(AccessDirectExecutionControl accessDirectExecutionControl) {
            this.accessDirectExecutionControl = accessDirectExecutionControl;
        }

        @Override
        public String name() {
            return "accessdirect";
        }

        @Override
        public ExecutionControl generate(ExecutionEnv env, Map parameters) throws Throwable {
            return accessDirectExecutionControl;
        }
    }
}