/*
 * Copyright 2010 the original author or authors.
 *
 * 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.
 */

package org.gradle.groovy.scripts.internal;

import groovy.lang.GroovyClassLoader;
import groovy.lang.GroovyCodeSource;
import groovy.lang.Script;
import groovyjarjarasm.asm.ClassWriter;
import org.apache.commons.lang.StringUtils;
import org.codehaus.groovy.ast.expr.ConstantExpression;
import org.codehaus.groovy.ast.stmt.ReturnStatement;
import org.codehaus.groovy.ast.stmt.Statement;
import org.codehaus.groovy.control.*;
import org.codehaus.groovy.control.messages.SyntaxErrorMessage;
import org.codehaus.groovy.syntax.SyntaxException;
import org.gradle.api.GradleException;
import org.gradle.groovy.scripts.ScriptCompilationException;
import org.gradle.groovy.scripts.ScriptSource;
import org.gradle.groovy.scripts.Transformer;
import org.gradle.internal.UncheckedException;
import org.gradle.util.Clock;
import org.gradle.util.GFileUtils;
import org.gradle.util.WrapUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.lang.reflect.Field;
import java.net.URLClassLoader;
import java.security.CodeSource;
import java.util.List;

/**
 * @author Hans Dockter
 */
public class DefaultScriptCompilationHandler implements ScriptCompilationHandler {
    private Logger logger = LoggerFactory.getLogger(DefaultScriptCompilationHandler.class);
    private static final String EMPTY_SCRIPT_MARKER_FILE_NAME = "emptyScript.txt";
    private final EmptyScriptGenerator emptyScriptGenerator;

    public DefaultScriptCompilationHandler(EmptyScriptGenerator emptyScriptGenerator) {
        this.emptyScriptGenerator = emptyScriptGenerator;
    }

    public void compileToDir(ScriptSource source, ClassLoader classLoader, File classesDir,
                             Transformer transformer, Class<? extends Script> scriptBaseClass) {
        Clock clock = new Clock();
        GFileUtils.deleteDirectory(classesDir);
        GFileUtils.mkdirs(classesDir);
        CompilerConfiguration configuration = createBaseCompilerConfiguration(scriptBaseClass);
        configuration.setTargetDirectory(classesDir);
        try {
            compileScript(source, classLoader, configuration, classesDir, transformer);
        } catch (GradleException e) {
            GFileUtils.deleteDirectory(classesDir);
            throw e;
        }

        logger.debug("Timing: Writing script to cache at {} took: {}", classesDir.getAbsolutePath(),
                clock.getTime());
    }

    private void compileScript(final ScriptSource source, ClassLoader classLoader, CompilerConfiguration configuration,
                               File classesDir, final Transformer transformer) {
        logger.info("Compiling {} using {}.", source.getDisplayName(), transformer != null ? transformer.getClass().getSimpleName() : "no transformer");

        final EmptyScriptDetector emptyScriptDetector = new EmptyScriptDetector();
        final PackageStatementDetector packageDetector = new PackageStatementDetector();
        GroovyClassLoader groovyClassLoader = new GroovyClassLoader(classLoader, configuration, false) {
            @Override
            protected CompilationUnit createCompilationUnit(CompilerConfiguration compilerConfiguration,
                                                            CodeSource codeSource) {
                CompilationUnit compilationUnit = new CompilationUnit(compilerConfiguration, codeSource, this) {
                    // This creepy bit of code is here to put the full source path of the script into the debug info for
                    // the class.  This makes it possible for a debugger to find the source file for the class.  By default
                    // Groovy will only put the filename into the class, but that does not help a debugger for Gradle
                    // because it does not know where Gradle scripts might live.
                    @Override
                    protected groovyjarjarasm.asm.ClassVisitor createClassVisitor() {
                        return new ClassWriter(ClassWriter.COMPUTE_MAXS) {
                            // ignore the sourcePath that is given by Groovy (this is only the filename) and instead
                            // insert the full path if our script source has a source file
                            @Override
                            public void visitSource(String sourcePath, String debugInfo) {
                                super.visitSource(source.getFileName(), debugInfo);
                            }
                        };
                    }
                };

                if (transformer != null) {
                    transformer.register(compilationUnit);
                }

                compilationUnit.addPhaseOperation(packageDetector, Phases.CANONICALIZATION);
                compilationUnit.addPhaseOperation(emptyScriptDetector, Phases.CANONICALIZATION);
                return compilationUnit;
            }
        };
        String scriptText = source.getResource().getText();
        String scriptName = source.getClassName();
        GroovyCodeSource codeSource = new GroovyCodeSource(scriptText == null ? "" : scriptText, scriptName, "/groovy/script");
        try {
            groovyClassLoader.parseClass(codeSource, false);
        } catch (MultipleCompilationErrorsException e) {
            wrapCompilationFailure(source, e);
        } catch (CompilationFailedException e) {
            throw new GradleException(String.format("Could not compile %s.", source.getDisplayName()), e);
        }

        if (packageDetector.hasPackageStatement) {
            throw new UnsupportedOperationException(String.format("%s should not contain a package statement.",
                    StringUtils.capitalize(source.getDisplayName())));
        }
        if (emptyScriptDetector.isEmptyScript()) {
            GFileUtils.touch(new File(classesDir, EMPTY_SCRIPT_MARKER_FILE_NAME));
        }
    }

    private void wrapCompilationFailure(ScriptSource source, MultipleCompilationErrorsException e) {
        // Fix the source file name displayed in the error messages
        for (Object message : e.getErrorCollector().getErrors()) {
            if (message instanceof SyntaxErrorMessage) {
                try {
                    SyntaxErrorMessage syntaxErrorMessage = (SyntaxErrorMessage) message;
                    Field sourceField = SyntaxErrorMessage.class.getDeclaredField("source");
                    sourceField.setAccessible(true);
                    SourceUnit sourceUnit = (SourceUnit) sourceField.get(syntaxErrorMessage);
                    Field nameField = SourceUnit.class.getDeclaredField("name");
                    nameField.setAccessible(true);
                    nameField.set(sourceUnit, source.getDisplayName());
                } catch (Exception failure) {
                    throw UncheckedException.throwAsUncheckedException(failure);
                }
            }
        }

        SyntaxException syntaxError = e.getErrorCollector().getSyntaxError(0);
        Integer lineNumber = syntaxError == null ? null : syntaxError.getLine();
        throw new ScriptCompilationException(String.format("Could not compile %s.", source.getDisplayName()), e, source,
                lineNumber);
    }

    private CompilerConfiguration createBaseCompilerConfiguration(Class<? extends Script> scriptBaseClass) {
        CompilerConfiguration configuration = new CompilerConfiguration();
        configuration.setScriptBaseClass(scriptBaseClass.getName());
        return configuration;
    }

    public <T extends Script> Class<? extends T> loadFromDir(ScriptSource source, ClassLoader classLoader, File scriptCacheDir,
                                              Class<T> scriptBaseClass) {
        if (new File(scriptCacheDir, EMPTY_SCRIPT_MARKER_FILE_NAME).isFile()) {
            return emptyScriptGenerator.generate(scriptBaseClass);
        }
        
        try {
            URLClassLoader urlClassLoader = new URLClassLoader(WrapUtil.toArray(scriptCacheDir.toURI().toURL()),
                    classLoader);
            return urlClassLoader.loadClass(source.getClassName()).asSubclass(scriptBaseClass);
        } catch (Exception e) {
            File expectedClassFile = new File(scriptCacheDir, source.getClassName()+".class");
            if(!expectedClassFile.exists()){
                throw new GradleException(String.format("Could not load compiled classes for %s from cache. Expected class file %s does not exist.", source.getDisplayName(), expectedClassFile.getAbsolutePath()), e);
            }
            throw new GradleException(String.format("Could not load compiled classes for %s from cache.", source.getDisplayName()), e);
        }
    }

    private static class PackageStatementDetector extends CompilationUnit.SourceUnitOperation {
        private boolean hasPackageStatement;

        @Override
        public void call(SourceUnit source) throws CompilationFailedException {
            hasPackageStatement = source.getAST().getPackageName() != null;
        }
    }

    private static class EmptyScriptDetector extends CompilationUnit.SourceUnitOperation {
        private boolean emptyScript;

        @Override
        public void call(SourceUnit source) throws CompilationFailedException {
            emptyScript = isEmpty(source);
        }

        private boolean isEmpty(SourceUnit source) {
            if (!source.getAST().getMethods().isEmpty()) {
                return false;
            }
            List<Statement> statements = source.getAST().getStatementBlock().getStatements();
            if (statements.size() > 1) {
                return false;
            }
            if (statements.isEmpty()) {
                return true;
            }

            Statement statement = statements.get(0);
            if (statement instanceof ReturnStatement) {
                ReturnStatement returnStatement = (ReturnStatement) statement;
                if (returnStatement.getExpression() instanceof ConstantExpression) {
                    ConstantExpression constantExpression = (ConstantExpression) returnStatement.getExpression();
                    if (constantExpression.getValue() == null) {
                        return true;
                    }
                }
            }

            return false;
        }

        public boolean isEmptyScript() {
            return emptyScript;
        }
    }
}
