package io.jstach.rainbowgum;

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.Queue;
import java.util.ServiceLoader;
import java.util.UUID;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;

import org.eclipse.jdt.annotation.Nullable;

import io.jstach.rainbowgum.LogProperty.Property;
import io.jstach.rainbowgum.LogRouter.RootRouter;
import io.jstach.rainbowgum.LogRouter.Router;
import io.jstach.rainbowgum.spi.RainbowGumServiceProvider;

//@formatter:off
/**
 * The main entry point and configuration of RainbowGum logging.
 * <p>
 * RainbowGum logging loads configuration through the service loader. While you can
 * manually set RainbowGum using {@link #set(Supplier)} it is better to register
 * implementations through the ServiceLoader so that RainbowGum will load prior to any
 * external logging.
 * <p>
 * To register a custom RainbowGum:
 *
 *
{@snippet class="snippets.RainbowGumProviderExample" region="provider" :

class RainbowGumProviderExample implements RainbowGumProvider {

        @Override
        public Optional<RainbowGum> provide(LogConfig config) {

                Property<Integer> bufferSize = Property.builder() //
                        .ofInt()
                        .orElse(1024)
                        .build("logging.custom.async.bufferSize");

                LogProvider<LogOutput> output = Property.builder()
                        .ofProvider(LogOutput::of)
                        .orElse(LogOutput.ofStandardOut())
                        .withKey("logging.custom.output")
                        .provider(o -> o);

                var gum = RainbowGum.builder() //
                        .route(r -> {
                                r.publisher(PublisherFactory //
                                        .async() //
                                        .bufferSize(r.value(bufferSize)) //
                                        .build());
                                r.appender("console", a -> {
                                        a.output(output);
                                });
                                r.level(Level.INFO);
                        })
                        .build();

                return Optional.of(gum);
        }

}
}
 */
//@formatter:on
@SuppressWarnings("InvalidInlineTag")
public sealed interface RainbowGum extends AutoCloseable, LogEventLogger {

        /**
         * Gets the currently statically bound RainbowGum and will try to load and find one if
         * there is none currently bound. <strong> This is a blocking operation as in locks
         * are used and will block indefinitely till a gum has loaded. </strong> If that is
         * not desired see {@link #getOrNull()}.
         * @return current RainbowGum or new loaded one.
         */
        public static RainbowGum of() {
                return RainbowGumHolder.get();
        }

        /**
         * Gets the currently statically bound RainbowGum or <code>null</code> if none are
         * <strong>finished binding</strong>. Unlike {@link #of()} this will never load or
         * start an instance but rather just gets the currently bound one. It will also never
         * block and does not wait if one is currently being loaded.
         * @return current RainbowGum or <code>null</code>
         */
        public static @Nullable RainbowGum getOrNull() {
                return RainbowGumHolder.current();
        }

        /**
         * Provides the service loader default based RainbowGum.
         * @return RainbowGum.
         */
        public static RainbowGum defaults() {
                return RainbowGumServiceProvider.provide();
        }

        /**
         * Creates a RainbowGum that will <strong>ALWAYS</strong> use the global router.
         * @param config config.
         * @return rainbow gum that always uses global router.
         */
        public static RainbowGum queued(LogConfig config) {
                return new SimpleRainbowGum(config, LogRouter.global(), UUID.randomUUID());
        }

        /**
         * Sets the global default RainbowGum. The supplied {@link RainbowGum} must not
         * already be started.
         * @param supplier the supplier will be memoized when {@linkplain Supplier#get()
         * accessed} and {@link RainbowGum#start()} will be called.
         */
        public static void set(Supplier<RainbowGum> supplier) {
                RainbowGumHolder.set(supplier);
        }

        /**
         * Subscribes to notification of a new RainbowGum becoming the globally bound one (see
         * {@link #set(Supplier)}, {@link #set(RainbowGum)}, {@link Builder#set()}). This is
         * primarily for components like SLF4J's logger factory that are themselves
         * bootstrapped once (often before "the real" RainbowGum has loaded, e.g. a
         * framework's own pre-boot sequence) and otherwise have no way of finding out that a
         * different RainbowGum has since replaced the one they captured.
         * <p>
         * Only a {@linkplain java.lang.ref.WeakReference weak reference} to
         * <code>consumer</code> is retained, so subscribing does not by itself keep the
         * consumer (or whatever it is attached to) reachable - the caller is responsible for
         * keeping a strong reference to <code>consumer</code> for as long as it needs to keep
         * receiving notifications, otherwise it may silently stop being called once garbage
         * collected.
         * @param consumer called with the newly bound global RainbowGum. Never called while
         * any RainbowGum internal lock is held.
         */
        public static void onGlobalChange(Consumer<RainbowGum> consumer) {
                RainbowGumHolder.globalChangePublisher.add(consumer);
        }

        /**
         * Sets a Rainbow Gum and provides a supplier that will start it globally.
         * @param gum that will be set immediatly.
         * @return supplier that will set, get and start the supplied gum and if it is not the
         * same will throw {@link IllegalStateException}.
         */
        public static Supplier<? extends RainbowGum> set(RainbowGum gum) {
                UUID instanceId = gum.instanceId();
                RainbowGum.set(() -> gum);
                return () -> {
                        var of = RainbowGum.of();
                        /*
                         * TODO this is a hack. The holder lock should be used to make this not
                         * happen.
                         */
                        if (!instanceId.equals(of.instanceId())) {
                                throw new IllegalStateException("Another rainbow gum registered itself as the global. "
                                                + "This is rare reace condition and probably a bug");
                        }
                        return of;
                };
        }

        /**
         * The config associated with this instance.
         * @return config.
         */
        public LogConfig config();

        /**
         * The router that will route log messages to publishers.
         * @return router
         */
        public RootRouter router();

        /**
         * Starts the rainbow gum and returns it. It is returned for try-with usage
         * convenience.
         * @return the started RainbowGum.
         */
        default RainbowGum start() {
                router().start(config());
                return this;
        }

        /**
         * Unique id of rainbow gum instance.
         * @return random id created on creation.
         */
        public UUID instanceId();

        /**
         * Will close the RainbowGum and all registered components as well as removed from the
         * shutdown hooks. If the rainbow gum is set as global it will no longer be global and
         * replaced with the bootstrapping in memory queue. {@inheritDoc}
         */
        @Override
        public void close();

        /**
         * This append call is mainly for testing as it does not avoid making events that do
         * not need to be made if no logging needs to be done. {@inheritDoc}
         */
        @Override
        default void log(LogEvent event) {
                var r = router().route(event.loggerName(), event.level());
                if (r.isEnabled()) {
                        r.log(event);
                }
        }

        /**
         * Use to build a custom {@link RainbowGum} which will use the {@link LogConfig}
         * provided by the service loader.
         * @return builder.
         */
        public static Builder builder() {
                ServiceLoader<RainbowGumServiceProvider> loader = ServiceLoader.load(RainbowGumServiceProvider.class);
                var config = RainbowGumServiceProvider.provideConfig(loader);
                return builder(config);
        }

        /**
         * Use to build a custom {@link RainbowGum} with supplied config.
         * @param config the config
         * @return builder.
         * @see #builder()
         */
        public static Builder builder(LogConfig config) {
                return new Builder(config);
        }

        /**
         * Use to build a custom {@link RainbowGum} with supplied config.
         * @param config consumer that has first argument as config builder.
         * @return builder.
         * @see #builder()
         * @apiNote this method is for ergonomic fluent reasons.
         */
        public static Builder builder(Consumer<? super LogConfig.Builder> config) {
                var b = LogConfig.builder();
                config.accept(b);
                return builder(b.build());
        }

        /**
         * RainbowGum Builder.
         */
        public class Builder {

                private final LogConfig config;

                private final List<Router> routes = new ArrayList<>();

                private Builder(LogConfig config) {
                        this.config = config;
                }

                /**
                 * Adds a router.
                 * @param route a router.
                 * @return builder.
                 */
                public Builder route(Router route) {
                        this.routes.add(route);
                        return this;
                }

                /**
                 * Adds a route by using a consumer of the route builder.
                 * @param name name of router.
                 * @param consumer consumer is passed router builder. The consumer does not need
                 * to call {@link Router#builder(String,LogConfig)}
                 * @return builder.
                 * @see io.jstach.rainbowgum.LogRouter.Router.Builder
                 */
                public Builder route(String name, Consumer<Router.Builder> consumer) {
                        var builder = Router.builder(name, config);
                        consumer.accept(builder);
                        return route(builder.build());
                }

                /**
                 * Adds a route by using a consumer of the route builder.
                 * @param consumer consumer is passed router builder. The consumer does not need
                 * to call {@link Router#builder(String,LogConfig)}
                 * @return builder.
                 * @see io.jstach.rainbowgum.LogRouter.Router.Builder
                 */
                public Builder route(Consumer<Router.Builder> consumer) {
                        var builder = Router.builder(Router.DEFAULT_ROUTER_NAME, config);
                        consumer.accept(builder);
                        return route(builder.build());
                }

                /**
                 * Builds an un-started {@link RainbowGum}.
                 * @return an un-started {@link RainbowGum}.
                 */
                public RainbowGum build() {
                        return build(UUID.randomUUID());
                }

                /**
                 * Builds an un-started {@link RainbowGum}.
                 * @param instanceId unique id for rainbow gum instance.
                 * @return an un-started {@link RainbowGum}.
                 */
                private RainbowGum build(UUID instanceId) {
                        var routes = this.routes;
                        var config = this.config;
                        if (routes.isEmpty()) {
                                List<String> routeNames = Property.builder() //
                                        .ofList()
                                        .build(LogProperties.ROUTES_PROPERTY)
                                        .get(config.properties())
                                        .value(List.of());
                                if (routeNames.isEmpty()) {
                                        routes = List.of(Router.builder(Router.DEFAULT_ROUTER_NAME, config).build());
                                }
                                else {
                                        routes = routeNames.stream().map(n -> Router.builder(n, config).build()).toList();
                                }
                        }
                        var root = InternalRootRouter.of(routes, config);
                        config.changePublisher().subscribe(c -> {
                                root.changePublisher().publish(root);
                        });
                        return new SimpleRainbowGum(config, root, instanceId);
                }

                /**
                 * Builds, starts and sets the RainbowGum as the global one picked up by logging
                 * facades.
                 * @return started and set rainbow that can be used in a try-close.
                 */
                public RainbowGum set() {
                        UUID instanceId = UUID.randomUUID();
                        RainbowGum.set(() -> build(instanceId));
                        var gum = RainbowGum.of();
                        /*
                         * TODO this is a hack. The holder lock should be used to make this not
                         * happen.
                         */
                        if (!instanceId.equals(gum.instanceId())) {
                                throw new IllegalStateException("Another rainbow gum registered itself as the global. "
                                                + "This is rare reace condition and probably a bug");
                        }
                        return gum;
                }

                /**
                 * Removes the currently set Rainbow Gum which will close it if one exists and
                 * will be replaced by the default provision process if {@link RainbowGum#of()} is
                 * called before {@link #set()}.
                 * @apiNote This is largely an internal detail for unit testing the provision
                 * process.
                 */
                public void unset() {
                        RainbowGumHolder.remove(null);
                }

                /**
                 * For returning an optional for the LogProvider contract.
                 * @return optional that always has a rainbow gum.
                 * @apiNote this method is for ergonomics.
                 */
                public Optional<RainbowGum> optional() {
                        return Optional.of(this.build());
                }

                /**
                 * For returning an optional for the LogProvider contract.
                 * @param condition condition to check if this rainbow gum should be used.
                 * @return optional rainbow gum.
                 * @apiNote this method is for ergonomics.
                 */
                public Optional<RainbowGum> optional(Function<? super LogConfig, Boolean> condition) {
                        var cond = condition.apply(config);
                        if (cond) {
                                return Optional.of(this.build());
                        }
                        return Optional.empty();
                }

        }

}

final class RainbowGumHolder {

        /*
         * TODO perhaps a StampedLock would be better performance wise.
         */
        private static final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

        private static Supplier<RainbowGum> supplier = RainbowGumServiceProvider::provide;

        private static volatile @Nullable RainbowGum rainbowGum = null;

        static final GlobalChangePublisher globalChangePublisher = new GlobalChangePublisher();

        static @Nullable RainbowGum current() {
                if (lock.readLock().tryLock()) {
                        try {
                                return rainbowGum;
                        }
                        finally {
                                lock.readLock().unlock();
                        }
                }
                return null;
        }

        static RainbowGum get() {
                lock.readLock().lock();
                try {
                        var r = rainbowGum;
                        if (r != null) {
                                return r;
                        }
                }
                finally {
                        lock.readLock().unlock();
                }
                if (lock.writeLock().isHeldByCurrentThread()) {
                        throw new IllegalStateException("RainbowGum component tried to log too early. "
                                        + "This is usually caused by dependencies calling logging.");
                }
                RainbowGum newlyStarted = null;
                lock.writeLock().lock();
                try {
                        var r = rainbowGum;
                        if (r != null) {
                                return r;
                        }
                        r = supplier.get();
                        start(r);
                        rainbowGum = r;
                        newlyStarted = r;
                        return r;

                }
                finally {
                        lock.writeLock().unlock();
                        /*
                         * Published outside of the write lock so a subscriber can never deadlock or
                         * trip the "tried to log too early" reentrancy guard above by, say, trying to
                         * read a volatile field it owns - it is not calling back into this class.
                         */
                        if (newlyStarted != null) {
                                globalChangePublisher.publish(newlyStarted);
                        }
                }

        }

        static boolean remove(@Nullable RainbowGum gum) {
                lock.writeLock().lock();
                try {
                        var original = rainbowGum;
                        if (gum != null) {
                                if (original != gum) {
                                        return false;
                                }
                        }
                        /*
                         * Reset the global router
                         */
                        if (original != null) {
                                LogRouter.global().close();
                        }
                        rainbowGum = null;
                        supplier = RainbowGumServiceProvider::provide;
                        return true;
                }
                finally {
                        lock.writeLock().unlock();
                }
        }

        static void set(Supplier<RainbowGum> rainbowGumSupplier) {
                Objects.requireNonNull(rainbowGumSupplier);
                if (lock.writeLock().isHeldByCurrentThread()) {
                        throw new IllegalStateException("RainbowGum component tried to log too early. "
                                        + "This is usually caused by dependencies calling logging.");
                }
                lock.writeLock().lock();
                try {
                        rainbowGum = null;
                        supplier = rainbowGumSupplier;
                }
                finally {
                        lock.writeLock().unlock();
                }
        }

        private static void start(RainbowGum gum) {
                Objects.requireNonNull(gum);
                ShutdownManager.addShutdownHook(gum);
                gum.start();
                InternalRootRouter.setRouter(gum.router());
        }

}

/*
 * Unlike LogConfig.ChangePublisher/LogRouter.RouteChangePublisher (both scoped to a
 * single RainbowGum/router instance and torn down with it) this is a JVM-lifetime static
 * registry, so consumers are held only weakly - otherwise every SLF4J logger factory (or
 * any other subscriber) ever created over the life of the JVM, e.g. across many
 * short-lived RainbowGums in tests, would be pinned forever.
 */
final class GlobalChangePublisher {

        private final Queue<WeakReference<Consumer<RainbowGum>>> consumers = new ConcurrentLinkedQueue<>();

        void add(Consumer<RainbowGum> consumer) {
                consumers.add(new WeakReference<>(consumer));
        }

        void publish(RainbowGum gum) {
                for (var it = consumers.iterator(); it.hasNext();) {
                        var consumer = it.next().get();
                        if (consumer == null) {
                                it.remove();
                        }
                        else {
                                consumer.accept(gum);
                        }
                }
        }

}

final class SimpleRainbowGum implements RainbowGum, Shutdownable {

        private final LogConfig config;

        private final RootRouter router;

        private final AtomicInteger state = new AtomicInteger(0);

        private final UUID instanceId;

        private static final int INIT = 0;

        private static final int STARTED = 1;

        private static final int CLOSED = 2;

        public SimpleRainbowGum(LogConfig config, RootRouter router, UUID instanceId) {
                super();
                this.config = config;
                this.router = router;
                this.instanceId = instanceId;
        }

        @Override
        public LogConfig config() {
                return this.config;
        }

        @Override
        public RootRouter router() {
                return this.router;
        }

        @Override
        public RainbowGum start() {
                int current;
                if ((current = state.compareAndExchange(INIT, STARTED)) == INIT) {
                        return RainbowGum.super.start();
                }
                throw new IllegalStateException("Cannot start. This rainbowgum is " + stateLabel(current));
        }

        @Override
        public UUID instanceId() {
                return this.instanceId;
        }

        @Override
        public void close() {
                if (state.compareAndSet(STARTED, CLOSED)) {
                        RainbowGumHolder.remove(this);
                        try {
                                shutdown();
                        }
                        finally {
                                ShutdownManager.removeShutdownHook(this);
                        }
                        return;
                }
        }

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

        @Override
        public String toString() {
                return "SimpleRainbowGum [instanceId=" + instanceId + ", config=" + config + ", router=" + router + ", state="
                                + stateLabel(state.get()) + "]";
        }

        private static String stateLabel(int state) {
                return switch (state) {
                        case INIT -> "created";
                        case STARTED -> "started";
                        case CLOSED -> "closed";
                        default -> {
                                throw new IllegalArgumentException("" + state);
                        }
                };
        }

}