/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

package org.opensearch.missingdoclet;

import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.ModuleElement;
import javax.lang.model.element.TypeElement;
import javax.lang.model.type.DeclaredType;
import javax.lang.model.type.TypeKind;
import javax.lang.model.util.ElementFilter;
import javax.lang.model.util.Elements;
import javax.tools.Diagnostic;

import com.sun.source.doctree.DocCommentTree;
import com.sun.source.doctree.ParamTree;
import com.sun.source.util.DocTrees;

import jdk.javadoc.doclet.Doclet;
import jdk.javadoc.doclet.DocletEnvironment;
import jdk.javadoc.doclet.Reporter;
import jdk.javadoc.doclet.StandardDoclet;

/**
 * Checks for missing javadocs, where missing also means "only whitespace" or "license header".
 * Has option --missing-level (package, class, method, parameter) so that we can improve over time.
 * Has option --missing-ignore to ignore individual elements (such as split packages).
 *   It isn't recursive, just ignores exactly the elements you tell it.
 * Has option --missing-method to apply "method" level to selected packages (fix one at a time).
 *   Matches package names exactly: so you'll need to list subpackages separately.
 *
 * Note: This by default ignores javadoc validation on overridden methods.
 */
// Original version of this class is ported from MissingDoclet code in Lucene,
// which is under the Apache Software Foundation under Apache 2.0 license
// See - https://github.com/apache/lucene-solr/tree/master/dev-tools/missing-doclet
public class MissingDoclet extends StandardDoclet {
    // checks that modules and packages have documentation
    private static final int PACKAGE = 0;
    // checks that classes, interfaces, enums, and annotation types have documentation
    private static final int CLASS = 1;
    // checks that methods, constructors, fields, and enumerated constants have documentation
    private static final int METHOD = 2;
    // checks that @param tags are present for any method/constructor parameters
    private static final int PARAMETER = 3;
    int level = PARAMETER;
    Reporter reporter;
    DocletEnvironment docEnv;
    DocTrees docTrees;
    Elements elementUtils;
    Set<String> ignored = Collections.emptySet();
    Set<String> methodPackages = Collections.emptySet();

    @Override
    public Set<Doclet.Option> getSupportedOptions() {
        Set<Doclet.Option> options = new HashSet<>();
        options.addAll(super.getSupportedOptions());
        options.add(new Doclet.Option() {
            @Override
            public int getArgumentCount() {
                return 1;
            }

            @Override
            public String getDescription() {
                return "level to enforce for missing javadocs: [package, class, method, parameter]";
            }

            @Override
            public Kind getKind() {
                return Option.Kind.STANDARD;
            }

            @Override
            public List<String> getNames() {
                return Collections.singletonList("--missing-level");
            }

            @Override
            public String getParameters() {
                return "level";
            }

            @Override
            public boolean process(String option, List<String> arguments) {
                switch (arguments.get(0)) {
                    case "package":
                        level = PACKAGE;
                        return true;
                    case "class":
                        level = CLASS;
                        return true;
                    case "method":
                        level = METHOD;
                        return true;
                    case "parameter":
                        level = PARAMETER;
                        return true;
                    default:
                        return false;
                }
            }
        });
        options.add(new Doclet.Option() {
            @Override
            public int getArgumentCount() {
                return 1;
            }

            @Override
            public String getDescription() {
                return "comma separated list of element names to ignore (e.g. as a workaround for split packages)";
            }

            @Override
            public Kind getKind() {
                return Option.Kind.STANDARD;
            }

            @Override
            public List<String> getNames() {
                return Collections.singletonList("--missing-ignore");
            }

            @Override
            public String getParameters() {
                return "ignoredNames";
            }

            @Override
            public boolean process(String option, List<String> arguments) {
                ignored = new HashSet<>(Arrays.asList(arguments.get(0).split(",")));
                return true;
            }
        });
        options.add(new Doclet.Option() {
            @Override
            public int getArgumentCount() {
                return 1;
            }

            @Override
            public String getDescription() {
                return "comma separated list of packages to check at 'method' level";
            }

            @Override
            public Kind getKind() {
                return Option.Kind.STANDARD;
            }

            @Override
            public List<String> getNames() {
                return Collections.singletonList("--missing-method");
            }

            @Override
            public String getParameters() {
                return "packages";
            }

            @Override
            public boolean process(String option, List<String> arguments) {
                methodPackages = new HashSet<>(Arrays.asList(arguments.get(0).split(",")));
                return true;
            }
        });
        return options;
    }

    @Override
    public void init(Locale locale, Reporter reporter) {
        this.reporter = reporter;
        super.init(locale, reporter);
    }

    @Override
    public boolean run(DocletEnvironment docEnv) {
        this.docEnv = docEnv;
        this.docTrees = docEnv.getDocTrees();
        this.elementUtils = docEnv.getElementUtils();
        for (var element : docEnv.getIncludedElements()) {
            check(element);
        }
        return true;
    }

    /**
     * Returns effective check level for this element
     */
    private int level(Element element) {
        String pkg = elementUtils.getPackageOf(element).getQualifiedName().toString();
        if (methodPackages.contains(pkg)) {
            return METHOD;
        } else {
            return level;
        }
    }

    /**
     * Check an individual element.
     * This checks packages and types from the doctrees.
     * It will recursively check methods/fields from encountered types when the level is "method"
     */
    private void check(Element element) {
        switch(element.getKind()) {
            case MODULE:
                // don't check the unnamed module, it won't have javadocs
                if (!((ModuleElement)element).isUnnamed()) {
                    checkComment(element);
                }
                break;
            case PACKAGE:
                checkComment(element);
                break;
            // class-like elements, check them, then recursively check their children (fields and methods)
            case CLASS:
            case INTERFACE:
            case ENUM:
            case ANNOTATION_TYPE:
                if (level(element) >= CLASS) {
                    checkComment(element);
                    for (var subElement : element.getEnclosedElements()) {
                        // don't recurse into enclosed types, otherwise we'll double-check since they are already in the included docTree
                        if (subElement.getKind() == ElementKind.METHOD ||
                            subElement.getKind() == ElementKind.CONSTRUCTOR ||
                            subElement.getKind() == ElementKind.FIELD ||
                            subElement.getKind() == ElementKind.ENUM_CONSTANT) {
                            check(subElement);
                        }
                    }
                }
                break;
            // method-like elements, check them if we are configured to do so
            case METHOD:
            case CONSTRUCTOR:
            case FIELD:
            case ENUM_CONSTANT:
                if (level(element) >= METHOD && !isSyntheticEnumMethod(element)) {
                    checkComment(element);
                }
                break;
            default:
                error(element, "I don't know how to analyze " + element.getKind() + " yet.");
        }
    }

    /**
     * Return true if the method is synthetic enum method (values/valueOf).
     * According to the doctree documentation, the "included" set never includes synthetic elements.
     * UweSays: It should not happen but it happens!
     */
    private boolean isSyntheticEnumMethod(Element element) {
        String simpleName = element.getSimpleName().toString();
        if (simpleName.equals("values") || simpleName.equals("valueOf")) {
            if (element.getEnclosingElement().getKind() == ElementKind.ENUM) {
                return true;
            }
        }
        return false;
    }

    /**
     * Checks that an element doesn't have missing javadocs.
     * In addition to truly "missing", check that comments aren't solely whitespace (generated by some IDEs)
     */
    private void checkComment(Element element) {
        // sanity check that the element is really "included", because we do some recursion into types
        if (!docEnv.isIncluded(element)) {
            return;
        }
        // check that this element isn't on our ignore list. This is only used as a workaround for "split packages".
        // ignoring a package isn't recursive (on purpose), we still check all the classes, etc. inside it.
        // we just need to cope with the fact package-info.java isn't there because it is split across multiple jars.
        if (ignored.contains(element.toString())) {
            return;
        }
        // Ignore classes annotated with @Generated and all enclosed elements in them.
        if (isGenerated(element)) {
            return;
        }
        Element enclosing = element.getEnclosingElement();
        if (enclosing != null && isGenerated(enclosing)) {
            return;
        }
        // If a package contains only generated classes, ignore the package as well.
        if (element.getKind() == ElementKind.PACKAGE) {
            List<? extends Element> enclosedElements = element.getEnclosedElements();
            Optional<?> elm = enclosedElements.stream().findFirst().filter(e -> ((e.getKind() != ElementKind.CLASS) || !isGenerated(e)));
            if (elm.isEmpty()) {
                return;
            }
        }
        var tree = docTrees.getDocCommentTree(element);
        if (tree == null || tree.getFirstSentence().isEmpty()) {
            // Check for methods that override other stuff and perhaps inherit their Javadocs.
            if (hasInheritedJavadocs(element)) {
                return;
            } else {
                error(element, "javadocs are missing");
            }
        } else {
            var normalized = tree.getFirstSentence().get(0).toString()
                .replace('\u00A0', ' ')
                .trim()
                .toLowerCase(Locale.ROOT);
            if (normalized.isEmpty()) {
                error(element, "blank javadoc comment");
            }
        }
        if (level >= PARAMETER) {
            checkParameters(element, tree);
        }
    }

    // Ignore classes annotated with @Generated and all enclosed elements in them.
    private boolean isGenerated(Element element) {
        return element
            .getAnnotationMirrors()
            .stream()
            .anyMatch(m -> m
                .getAnnotationType()
                .toString() /* ClassSymbol.toString() returns class name */
                .equalsIgnoreCase("javax.annotation.Generated"));
    }

    private boolean hasInheritedJavadocs(Element element) {
        boolean hasOverrides = element.getAnnotationMirrors().stream()
            .anyMatch(ann -> ann.getAnnotationType().toString().equals(Override.class.getName()));

        if (hasOverrides) {
            // If an element has explicit @Overrides annotation, assume it does
            // have inherited javadocs somewhere.
            reporter.print(Diagnostic.Kind.NOTE, element, "javadoc empty but @Override declared, skipping.");
            return true;
        }

        // Check for methods up the types tree.
        if (element instanceof ExecutableElement) {
            ExecutableElement thisMethod = (ExecutableElement) element;
            Iterable<Element> superTypes =
                () -> superTypeForInheritDoc(thisMethod.getEnclosingElement()).iterator();

            for (Element sup : superTypes) {
                for (ExecutableElement supMethod : ElementFilter.methodsIn(sup.getEnclosedElements())) {
                    TypeElement clazz = (TypeElement) thisMethod.getEnclosingElement();
                    if (elementUtils.overrides(thisMethod, supMethod, clazz)) {
                        // We could check supMethod for non-empty javadoc here. Don't know if this makes
                        // sense though as all methods will be verified in the end so it'd fail on the
                        // top of the hierarchy (if empty) anyway.
                        reporter.print(Diagnostic.Kind.NOTE, element, "javadoc empty but method overrides another, skipping.");
                        return true;
                    }
                }
            }
        }

        return false;
    }


    /* Find types from which methods in type may inherit javadoc, in the proper order.*/
    private Stream<Element> superTypeForInheritDoc(Element type) {
        TypeElement clazz = (TypeElement) type;
        List<Element> interfaces = clazz.getInterfaces()
            .stream()
            .filter(tm -> tm.getKind() == TypeKind.DECLARED)
            .map(tm -> ((DeclaredType) tm).asElement())
            .collect(Collectors.toList());

        Stream<Element> result = interfaces.stream();
        result = Stream.concat(result, interfaces.stream().flatMap(this::superTypeForInheritDoc));

        if (clazz.getSuperclass().getKind() == TypeKind.DECLARED) {
            Element superClass = ((DeclaredType) clazz.getSuperclass()).asElement();
            result = Stream.concat(result, Stream.of(superClass));
            result = Stream.concat(result, superTypeForInheritDoc(superClass));
        }

        return result;
    }

    /** Checks there is a corresponding "param" tag for each method parameter */
    private void checkParameters(Element element, DocCommentTree tree) {
        if (element instanceof ExecutableElement) {
            // record each @param that we see
            Set<String> seenParameters = new HashSet<>();
            if (tree != null) {
                for (var tag : tree.getBlockTags()) {
                    if (tag instanceof ParamTree) {
                        var name = ((ParamTree)tag).getName().getName().toString();
                        seenParameters.add(name);
                    }
                }
            }
            // now compare the method's formal parameter list against it
            for (var param : ((ExecutableElement)element).getParameters()) {
                var name = param.getSimpleName().toString();
                if (!seenParameters.contains(name)) {
                    error(element, "missing javadoc @param for parameter '" + name + "'");
                }
            }
        }
    }

    /** logs a new error for the particular element */
    private void error(Element element, String message) {
        var fullMessage = new StringBuilder();
        switch (element.getKind()) {
            case MODULE:
            case PACKAGE:
                // for modules/packages, we don't have filename + line number, fully qualify
                fullMessage.append(element.toString());
                break;
            case METHOD:
            case CONSTRUCTOR:
            case FIELD:
            case ENUM_CONSTANT:
                // for method-like elements, include the enclosing type to make it easier
                fullMessage.append(element.getEnclosingElement().getSimpleName());
                fullMessage.append(".");
                fullMessage.append(element.getSimpleName());
                break;
            default:
                // for anything else, use a simple name
                fullMessage.append(element.getSimpleName());
                break;
        }

        fullMessage.append(" (");
        fullMessage.append(element.getKind().toString().toLowerCase(Locale.ROOT));
        fullMessage.append("): ");
        fullMessage.append(message);

        if (Runtime.version().feature() == 11 && element.getKind() == ElementKind.PACKAGE) {
            // Avoid JDK 11 bug:
            // https://bugs.openjdk.java.net/browse/JDK-8224082
            reporter.print(Diagnostic.Kind.ERROR, fullMessage.toString());
        } else {
            reporter.print(Diagnostic.Kind.ERROR, element, fullMessage.toString());
        }
    }
}