package io.jstach.rainbowgum;

import java.lang.System.Logger.Level;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.function.Function;

import org.eclipse.jdt.annotation.Nullable;

import io.jstach.rainbowgum.LogConfig.ChangePublisher.ChangeType;
import io.jstach.rainbowgum.LogProperty.Property;
import io.jstach.rainbowgum.LogPublisher.PublisherFactory;
import io.jstach.rainbowgum.LogRouter.RootRouter;
import io.jstach.rainbowgum.LogRouter.Route;
import io.jstach.rainbowgum.LogRouter.Router;
import io.jstach.rainbowgum.annotation.CaseChanging;

/**
 * Routes messages to a publisher by providing a {@link Route} from a logger name and
 * level.
 */
public sealed interface LogRouter extends LogLifecycle {

        /**
         * Finds a route.
         * @param loggerName topic.
         * @param level level.
         * @return route never <code>null</code>.
         */
        public Route route(String loggerName, java.lang.System.Logger.Level level);

        /**
         * Creates (or reuses in the case of logging off) an event builder.
         * @param loggerName logger name of the event.
         * @param level level that the event should be set to.
         * @return builder.
         * @apiNote using the builder is slightly slower and possibly more garbage (if the
         * builder is not marked for escape analysis) than just manually checking
         * {@link Route#isEnabled()} and constructing the event using the LogEvent static
         * "<code>of</code>" factory methods.
         */
        default LogEvent.Builder eventBuilder(String loggerName, Level level) {
                var route = route(loggerName, level);
                if (route.isEnabled()) {
                        return new LogEventBuilder(route, level, loggerName);
                }
                return NoOpLogEventBuilder.NOOP;
        }

        /**
         * Global router which is always available.
         * @return global root router.
         */
        public static RootRouter global() {
                return GlobalLogRouter.INSTANCE;
        }

        /**
         * Creates a <strong>static</strong> router based on the level. Use a
         * {@link LevelResolver} to resolve the level first.
         * @param logger to publish events that are equal or above level.
         * @param level threshold of the router.
         * @return immutable static router.
         * @apiNote This method is for facades that do not have named level methods but are
         * passed the level on every log method like the System Logger.
         */
        public static LogRouter ofLevel(LogEventLogger logger, Level level) {
                return new LevelRouter(level, logger);
        }

        /**
         * A route is similar to a SLF4J Logger or System Logger but has a much simpler
         * contract.
         *
         * The proper usage of Route in most cases is to call {@link #isEnabled()} before
         * calling {@link #log(LogEvent)}.
         *
         * That is {@link #log(LogEvent)} does not do any checking if the event is allowed
         * furthermore by first checking if {@link #isEnabled()} is true one can decide
         * whether or not to create a {@link LogEvent}.
         */
        public sealed interface Route extends LogEventLogger {

                /**
                 * Determines if {@link #log(LogEvent)} maybe called.
                 * @return true if log can be called.
                 */
                public boolean isEnabled();

                /**
                 * Route singletons and utilities.
                 */
                @CaseChanging
                public enum Routes implements Route {

                        /**
                         * A route that is a NOOP and is always disabled.
                         */
                        NotFound {
                                @Override
                                public void log(LogEvent event) {
                                }

                                @Override
                                public boolean isEnabled() {
                                        return false;
                                }

                        };

                }

        }

        /**
         * Router flags for adhoc router customization.
         */
        public enum RouteFlag {

                /**
                 * The route will not use the global level resolver and will only use the level
                 * config directly on the router.
                 */
                IGNORE_GLOBAL_LEVEL_RESOLVER;

        }

        /**
         * Root router is a router that has child routers.
         */
        sealed interface RootRouter extends LogRouter permits InternalRootRouter {

                /**
                 * Level resolver to find levels for a log name.
                 * @return level resolver.
                 */
                public LevelResolver levelResolver();

                /**
                 * Register for a router changes usually involving the level resolver being
                 * updated by config.
                 * @param router consumer that will be called with the updated router.
                 * @apiNote its best to use the router in the consumer accept argument and not
                 * this router even if they are usually the same.
                 */
                public void onChange(Consumer<? super RootRouter> router);

                /**
                 * If a logger name configuration is changeable.
                 * @param loggerName logger name.
                 * @return true if config changes are allowed.
                 */
                public boolean isChangeable(String loggerName);

        }

        /**
         * Router routes messages to a publisher.
         */
        sealed interface Router extends LogRouter, LogEventLogger {

                /**
                 * The router name given if no router is explicitly declared.
                 */
                public static final String DEFAULT_ROUTER_NAME = LogProperties.DEFAULT_NAME;

                /**
                 * Level resolver.
                 * @return level resolver.
                 */
                LevelResolver levelResolver();

                /**
                 * Log publisher.
                 * @return publisher.
                 */
                LogPublisher publisher();

                /**
                 * Whether or not the publisher is synchronous. A synchronous publisher generally
                 * blocks.
                 * @return true if the publisher is synchronous.
                 */
                default boolean synchronous() {
                        return publisher().synchronous();
                }

                @Override
                default void log(LogEvent event) {
                        publisher().log(event);
                }

                /**
                 * Creates a builder from config.
                 * @param name name of the route which the publisher will inherit.
                 * @param config config.
                 * @return builder.
                 */
                static Builder builder(String name, LogConfig config) {
                        return new Builder(name, config);
                }

                /**
                 * Creates a router.
                 *
                 * @see AbstractRouter
                 */
                @FunctionalInterface
                public interface RouterFactory {

                        /**
                         * Builder will call this factory if passed in.
                         * @param publisher publisher from builder.
                         * @param levelResolver level resolver from builder.
                         * @param name name from builder.
                         * @param config config from builder.
                         * @return router.
                         */
                        public Router create(LogPublisher publisher, LevelResolver levelResolver, String name, LogConfig config);

                        /**
                         * Creates a router from a function.
                         * @param function <strong>the function may return <code>null</code></strong>
                         * which indicates to ignore.
                         * @return factory.
                         */
                        static RouterFactory of(@SuppressWarnings("exports") Function<LogEvent, @Nullable LogEvent> function) {
                                return (pub, lr, n, c) -> new AbstractRouter(n, pub, lr) {
                                        @Override
                                        protected @Nullable LogEvent transformOrNull(LogEvent event) {
                                                return function.apply(event);
                                        }
                                };
                        }

                }

                /**
                 * Router builder.
                 */
                public final class Builder extends LevelResolver.AbstractBuilder<Builder> implements LogConfig.ConfigSupport {

                        private final LogConfig config;

                        private final String name;

                        private final EnumSet<RouteFlag> flags = EnumSet.noneOf(RouteFlag.class);

                        private RouterFactory factory = (publisher, levelResolver, n, c) -> new SimpleRouter(n, publisher,
                                        levelResolver);

                        private List<LogProvider<LogAppender>> appenders = new ArrayList<>();

                        private Builder(String name, LogConfig config) {
                                this.name = Objects.requireNonNull(name);
                                this.config = config;
                        }

                        private @Nullable PublisherFactory publisher;

                        @Override
                        protected Builder self() {
                                return this;
                        }

                        /**
                         * Gets the currently bound config.
                         * @return config.
                         */
                        @Override
                        public LogConfig config() {
                                return this.config;
                        }

                        /**
                         * Adds a flag.
                         * @param flag flag added if not already added.
                         * @return this.
                         */
                        public Builder flag(RouteFlag flag) {
                                flags.add(flag);
                                return this;
                        }

                        /**
                         * Adds an appender by giving an appender builder to a consumer.
                         * @param name appender name.
                         * @param consumer consumer.
                         * @return this builder.
                         */
                        public Builder appender(String name, Consumer<LogAppender.Builder> consumer) {
                                var builder = LogAppender.builder(name);
                                consumer.accept(builder);
                                this.appenders.add(builder.build());
                                return this;
                        }

                        /**
                         * Adds an appender.
                         * @param appender appender provider.
                         * @return this builder.
                         */
                        public Builder appender(LogProvider<LogAppender> appender) {
                                this.appenders.add(Objects.requireNonNull(appender));
                                return self();
                        }

                        /**
                         * Sets the publisher. Only one publisher to router.
                         * @param publisher publisher.
                         * @return this builder.
                         */
                        public Builder publisher(PublisherFactory publisher) {
                                this.publisher = publisher;
                                return self();
                        }

                        /**
                         * Factory to use for creating the router.
                         * @param factory router factory.
                         * @return this.
                         */
                        public Builder factory(RouterFactory factory) {
                                this.factory = Objects.requireNonNull(factory);
                                return this;
                        }

                        Router build() {
                                return build(this.factory);
                        }

                        /**
                         * Builds the router.
                         * @param factory to create the router.
                         * @return router.
                         */
                        Router build(RouterFactory factory) {
                                String name = this.name;
                                String routerLevelPrefix = LogProperties.interpolateNamedKey(LogProperties.ROUTE_LEVEL_PREFIX, name);
                                var levelResolverBuilder = LevelResolver.builder();
                                var currentConfig = buildLevelConfigOrNull();
                                if (currentConfig != null) {
                                        levelResolverBuilder.config(currentConfig);
                                }
                                levelResolverBuilder.config(config.properties(), routerLevelPrefix);
                                if (!flags.contains(RouteFlag.IGNORE_GLOBAL_LEVEL_RESOLVER)) {
                                        levelResolverBuilder.config(config.levelResolver());
                                }
                                var levelResolver = levelResolverBuilder.build();
                                if (currentConfig == null) {
                                        /*
                                         * If no config is provided in this route the global level might not
                                         * be set.
                                         */
                                        var level = levelResolver.resolveLevel("");
                                        Objects.requireNonNull(level);
                                        if (level == System.Logger.Level.ALL) {
                                                /*
                                                 * The global root level was not set or set to ALL. This is a bug
                                                 * if this happens as the builders and other places will turn ALL
                                                 * -> TRACE.
                                                 */
                                                levelResolverBuilder.config(StaticLevelResolver.INFO);
                                                levelResolver = levelResolverBuilder.build();
                                                // throw new IllegalStateException("Global Level Resolver should
                                                // not resolve to Level.ALL");
                                        }
                                }

                                var _levelResolver = levelResolver;
                                /*
                                 * This routers level resolver needs to be notified if config changes.
                                 */
                                config.changePublisher().subscribe(c -> {
                                        _levelResolver.clear();
                                });
                                var publisher = this.publisher;

                                List<LogProvider<LogAppender>> appenders = new ArrayList<>(this.appenders);
                                if (appenders.isEmpty()) {
                                        DefaultAppenderRegistry.appenders(config, name) //
                                                .stream() //
                                                .forEach(appenders::add);
                                }

                                if (publisher == null) {
                                        publisher = Property.builder() //
                                                .ofProviderRef() //
                                                .map(r -> config.publisherRegistry().provide(r)) //
                                                .buildWithName(LogProperties.ROUTE_PUBLISHER_PROPERTY, name)
                                                .get(config.properties())
                                                .value(() -> LogPublisher.SyncLogPublisher.builder().build());
                                }

                                var apps = new LogAppender.Appenders(name, config, appenders);
                                var pub = publisher.create(name, config, apps);
                                /*
                                 * Register the publisher for lookup like status checks.
                                 */
                                config.serviceRegistry().put(LogPublisher.class, name, pub);
                                return factory.create(pub, levelResolver, name, config);
                        }

                }

        }

        /**
         * A user supplied router usually for filtering or transforming purposes. The method
         * required to implement is {@link #transformOrNull(LogEvent)}.
         *
         * @see RouterFactory
         */
        @SuppressWarnings("javadoc") // TODO Eclipse bug.
        public non-sealed abstract class AbstractRouter implements Router, Route {

                private final String name;

                private final LogPublisher publisher;

                private final LevelResolver levelResolver;

                /**
                 * Router tuple of publisher and resolver.
                 * @param name router name not <code>null</code>.
                 * @param publisher not <code>null</code>.
                 * @param levelResolver not <code>null</code>.
                 */
                protected AbstractRouter(String name, LogPublisher publisher, LevelResolver levelResolver) {
                        super();
                        this.name = name;
                        this.publisher = publisher;
                        this.levelResolver = levelResolver;
                }

                @Override
                public final boolean synchronous() {
                        return Router.super.synchronous();
                }

                @Override
                public final void log(LogEvent event) {
                        var e = transformOrNull(event);
                        if (e != null) {
                                Router.super.log(e);
                        }
                }

                /**
                 * Implement for custom filtering or transformation.
                 * @param event usually from logging facade.
                 * @return event to be pushed to logger or not if <code>null</code>.
                 */
                protected abstract @Nullable LogEvent transformOrNull(LogEvent event);

                @Override
                public final Route route(String loggerName, Level level) {
                        if (levelResolver().isEnabled(loggerName, level)) {
                                return this;
                        }
                        return Route.Routes.NotFound;
                }

                @Override
                public final void start(LogConfig config) {
                        publisher.start(config);
                }

                @Override
                public final void close() {
                        publisher.close();

                }

                @Override
                public final boolean isEnabled() {
                        return true;
                }

                @Override
                public final LevelResolver levelResolver() {
                        return this.levelResolver;
                }

                @Override
                public final LogPublisher publisher() {
                        return this.publisher;
                }

                @Override
                public String toString() {
                        return getClass() + "[name=" + name + ", publisher=" + publisher + ", levelResolver=" + levelResolver + "]";
                }

        }

}

record LevelRouter(Level loggerLevel, LogEventLogger logger) implements LogRouter, Route {

        @Override
        public void start(LogConfig config) {
        }

        @Override
        public void close() {
        }

        @Override
        public void log(LogEvent event) {
                logger.log(event);
        }

        @Override
        public boolean isEnabled() {
                return true;
        }

        @Override
        public Route route(String loggerName, Level level) {
                if (LevelResolver.checkEnabled(level, loggerLevel)) {
                        return this;
                }
                return Routes.NotFound;
        }
}

record SimpleRouter(String name, LogPublisher publisher, LevelResolver levelResolver) implements Router, Route {

        @Override
        public void close() {
                publisher.close();
        }

        @Override
        public Route route(String loggerName, java.lang.System.Logger.Level level) {
                if (levelResolver().isEnabled(loggerName, level)) {
                        return this;
                }
                return Route.Routes.NotFound;
        }

        @Override
        public boolean isEnabled() {
                return true;
        }

        @Override
        public void start(LogConfig config) {
                publisher.start(config);
        }

}

sealed interface InternalRootRouter extends RootRouter {

        /**
         * Sets the root router.
         * @param router root router.
         */
        static void setRouter(RootRouter router) {
                if (GlobalLogRouter.INSTANCE == router) {
                        return;
                }
                GlobalLogRouter.INSTANCE.drain((InternalRootRouter) router);
        }

        static InternalRootRouter of(List<? extends Router> routes, LogConfig config) {

                if (routes.isEmpty()) {
                        throw new IllegalArgumentException("atleast one route is required");
                }
                List<Router> sorted = new ArrayList<>();
                /*
                 * We add the async routers first
                 */
                Set<Router> matched = Collections.newSetFromMap(new IdentityHashMap<Router, Boolean>());
                for (var r : routes) {
                        if (!r.synchronous()) {
                                if (matched.add(r)) {
                                        sorted.add(r);
                                }
                        }
                }
                for (var r : routes) {
                        if (r.synchronous()) {
                                if (matched.add(r)) {
                                        sorted.add(r);
                                }
                        }
                }
                routes = sorted;
                LevelResolver.Builder resolverBuilder = LevelResolver.builder();
                routes.stream().map(Router::levelResolver).forEach(resolverBuilder::resolver);
                var globalLevelResolver = resolverBuilder.build();

                Router[] array = routes.toArray(new Router[] {});

                RouteChangePublisher changePublisher = new RouteChangePublisher(
                                s -> config.changePublisher().allowedChanges(s).contains(ChangeType.LEVEL));
                if (array.length == 1) {
                        var r = array[0];
                        return r.synchronous() ? new SingleSyncRootRouter(r, changePublisher)
                                        : new SingleAsyncRootRouter(r, changePublisher);
                }
                return new CompositeLogRouter(array, globalLevelResolver, changePublisher);
        }

        default boolean isEnabled(String loggerName, java.lang.System.Logger.Level level) {
                return route(loggerName, level).isEnabled();

        }

        default void drain(InternalRootRouter delegate) {

        }

        @Override
        default void onChange(Consumer<? super RootRouter> router) {
                changePublisher().add(router);
        }

        public RouteChangePublisher changePublisher();

        @Override
        default boolean isChangeable(String loggerName) {
                return changePublisher().loggerChangeable.apply(loggerName);
        }

        final class RouteChangePublisher {

                private final Collection<Consumer<? super RootRouter>> consumers = new CopyOnWriteArrayList<Consumer<? super RootRouter>>();

                private final Function<String, Boolean> loggerChangeable;

                RouteChangePublisher(Function<String, Boolean> loggerChangeable) {
                        super();
                        this.loggerChangeable = loggerChangeable;
                }

                void add(Consumer<? super RootRouter> consumer) {
                        consumers.add(consumer);
                }

                void publish(RootRouter router) {
                        for (var c : consumers) {
                                c.accept(router);
                        }
                }

                void transferTo(RouteChangePublisher changePublisher) {
                        changePublisher.consumers.addAll(consumers);
                        this.consumers.clear();
                }

        }

}

record SingleSyncRootRouter(Router router, RouteChangePublisher changePublisher) implements InternalRootRouter {

        @Override
        public void start(LogConfig config) {
                router.start(config);
        }

        @Override
        public void close() {
                router.close();
        }

        @Override
        public LevelResolver levelResolver() {
                return router.levelResolver();
        }

        @Override
        public Route route(String loggerName, Level level) {
                return router.route(loggerName, level);
        }

}

record SingleAsyncRootRouter(Router router, RouteChangePublisher changePublisher) implements InternalRootRouter {

        @Override
        public void start(LogConfig config) {
                router.start(config);
        }

        @Override
        public void close() {
                router.close();
        }

        @Override
        public LevelResolver levelResolver() {
                return router.levelResolver();
        }

        @Override
        public Route route(String loggerName, Level level) {
                return router.route(loggerName, level);
        }

}

@SuppressWarnings("ArrayRecordComponent") // TODO revisit perf
record CompositeLogRouter(Router[] routers, LevelResolver levelResolver,
                RouteChangePublisher changePublisher) implements InternalRootRouter, Route {

        @Override
        public Route route(String loggerName, Level level) {
                /*
                 * The assumption is the provided level resolver is a cached composite level
                 * resolver of all the routers.
                 */
                if (levelResolver.isEnabled(loggerName, level)) {
                        return this;
                }
                return Routes.NotFound;
        }

        @Override
        public void log(LogEvent event) {
                for (var router : routers) {
                        var route = router.route(event.loggerName(), event.level());
                        if (route.isEnabled()) {
                                /*
                                 * We assume async routers are earlier in the array.
                                 */
                                if (!router.synchronous()) {
                                        /*
                                         * Now all events are frozen from here onward to guarantee that the
                                         * synchronous routers see the same thing as the async routers.
                                         *
                                         * Freeze is a noop if it already frozen.
                                         */
                                        event = event.freeze();
                                }
                                route.log(event);
                        }
                }
        }

        @Override
        public boolean isEnabled() {
                return true;
        }

        @Override
        public void start(LogConfig config) {
                for (var r : routers) {
                        r.start(config);
                }
        }

        @Override
        public void close() {
                for (var r : routers) {
                        r.close();
                }
        }
}

final class QueueEventsRouter implements InternalRootRouter, Route {

        private final ConcurrentLinkedQueue<LogEvent> events = new ConcurrentLinkedQueue<>();

        private final LevelResolver levelResolver;

        private final LevelResolver errorLevelResolver;

        private final RouteChangePublisher changePublisher = new RouteChangePublisher(s -> true);

        static QueueEventsRouter of() {
                return new QueueEventsRouter(StaticLevelResolver.of(queueLevel()), StaticLevelResolver.of(errorLevel()));
        }

        private static Level queueLevel() {
                return LogProperty.builder()
                        .build(LogProperties.GLOBAL_QUEUE_LEVEL_PROPERTY)
                        .map(LevelResolver::parseLevel)
                        .get(LogProperties.StandardProperties.SYSTEM_PROPERTIES)
                        .value(Level.INFO);
        }

        private static final Level errorLevel() {
                return LogProperty.builder()
                        .build(LogProperties.GLOBAL_QUEUE_ERROR_PROPERTY)
                        .map(LevelResolver::parseLevel)
                        .get(LogProperties.StandardProperties.SYSTEM_PROPERTIES)
                        .value(Level.ERROR);
        }

        private QueueEventsRouter(LevelResolver levelResolver, LevelResolver errorLevelResolver) {
                super();
                this.levelResolver = levelResolver;
                this.errorLevelResolver = errorLevelResolver;
        }

        @Override
        public LevelResolver levelResolver() {
                return levelResolver;
        }

        @Override
        public Route route(String loggerName, Level level) {
                if (levelResolver.isEnabled(loggerName, level)) {
                        return this;
                }
                return Routes.NotFound;
        }

        @Override
        public void start(LogConfig config) {
        }

        @Override
        public void close() {
                events.clear();
        }

        @Override
        public void log(LogEvent event) {
                events.add(event);
                if (errorLevelResolver.isEnabled(event.loggerName(), event.level())) {
                        MetaLog.error(event);
                }
        }

        @Override
        public void drain(InternalRootRouter delegate) {
                LogEvent e;
                while ((e = this.events.poll()) != null) {
                        delegate.route(e.loggerName(), e.level()).log(e);
                }
        }

        @Override
        public boolean isEnabled() {
                return true;
        }

        @Override
        public RouteChangePublisher changePublisher() {
                return this.changePublisher;
        }

}

@SuppressWarnings("ImmutableEnumChecker")
enum GlobalLogRouter implements InternalRootRouter, Route {

        INSTANCE;

        private volatile InternalRootRouter delegate = QueueEventsRouter.of();

        private final ReentrantLock drainLock = new ReentrantLock();

        static boolean isShutdownEvent(String loggerName, java.lang.System.Logger.Level level) {
                return loggerName.equals(LogLifecycle.SHUTDOWN)
                                && Boolean.parseBoolean(System.getProperty(LogLifecycle.SHUTDOWN));
        }

        @Override
        public LevelResolver levelResolver() {
                return delegate.levelResolver();
        }

        @Override
        public boolean isEnabled() {
                return true;
        }

        @Override
        public void log(LogEvent event) {
                InternalRootRouter d = delegate;
                if (d instanceof QueueEventsRouter q) {
                        q.log(event);
                }
                else {
                        String loggerName = event.loggerName();
                        var level = event.level();
                        var route = d.route(event.loggerName(), event.level());
                        if (route.isEnabled()) {
                                route.log(event);
                        }
                        if (isShutdownEvent(loggerName, level)) {
                                d.close();
                        }
                }
        }

        @Override
        public Route route(String loggerName, Level level) {
                return this.delegate.route(loggerName, level);
        }

        @Override
        public boolean isEnabled(String loggerName, Level level) {
                return this.delegate.isEnabled(loggerName, level);
        }

        @Override
        public RouteChangePublisher changePublisher() {
                return this.delegate.changePublisher();
        }

        @Override
        public void drain(InternalRootRouter delegate) {
                _drain(delegate);
        }

        private InternalRootRouter _drain(InternalRootRouter delegate) {
                if (delegate == this) {
                        throw new IllegalStateException("bug");
                }
                drainLock.lock();
                try {
                        var original = this.delegate;
                        if (original instanceof QueueEventsRouter q) {
                                q.changePublisher().transferTo(delegate.changePublisher());
                                delegate.changePublisher().publish(delegate);
                        }
                        this.delegate = Objects.requireNonNull(delegate);
                        original.drain(delegate);
                        return original;
                }
                finally {
                        drainLock.unlock();
                }
        }

        @Override
        public void start(LogConfig config) {
        }

        @Override
        public void close() {
                var d = _drain(QueueEventsRouter.of());
                d.close();
        }

}