/*
 * Copyright (C) 2006 Google Inc.
 *
 * 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.elasticsearch.injection.guice;

import org.elasticsearch.common.Classes;
import org.elasticsearch.injection.guice.internal.BindingImpl;
import org.elasticsearch.injection.guice.internal.Errors;
import org.elasticsearch.injection.guice.internal.ErrorsException;
import org.elasticsearch.injection.guice.internal.InstanceBindingImpl;
import org.elasticsearch.injection.guice.internal.InternalContext;
import org.elasticsearch.injection.guice.internal.InternalFactory;
import org.elasticsearch.injection.guice.internal.MatcherAndConverter;
import org.elasticsearch.injection.guice.internal.Scoping;
import org.elasticsearch.injection.guice.internal.SourceProvider;
import org.elasticsearch.injection.guice.internal.ToStringBuilder;
import org.elasticsearch.injection.guice.spi.BindingTargetVisitor;
import org.elasticsearch.injection.guice.spi.ConvertedConstantBinding;
import org.elasticsearch.injection.guice.spi.Dependency;
import org.elasticsearch.injection.guice.spi.ProviderBinding;
import org.elasticsearch.injection.guice.spi.ProviderKeyBinding;
import org.elasticsearch.injection.guice.util.Providers;

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import static java.util.Collections.emptySet;

/**
 * Default {@link Injector} implementation.
 *
 * @author crazybob@google.com (Bob Lee)
 * @see InjectorBuilder
 */
class InjectorImpl implements Injector, Lookups {
    final State state;
    BindingsMultimap bindingsMultimap = new BindingsMultimap();

    /**
     * Just-in-time binding cache. Guarded by state.lock()
     */
    Map<Key<?>, BindingImpl<?>> jitBindings = new HashMap<>();

    Lookups lookups = new DeferredLookups(this);

    InjectorImpl(State state) {
        this.state = state;
        localContext = new ThreadLocal<>();
    }

    /**
     * Indexes bindings by type.
     */
    void index() {
        for (Binding<?> binding : state.getExplicitBindingsThisLevel().values()) {
            index(binding);
        }
    }

    <T> void index(Binding<T> binding) {
        bindingsMultimap.put(binding.getKey().getTypeLiteral(), binding);
    }

    @Override
    public <T> List<Binding<T>> findBindingsByType(TypeLiteral<T> type) {
        return bindingsMultimap.getAll(type);
    }

    /**
     * Gets a binding implementation.  First, it check to see if the parent has a binding.  If the
     * parent has a binding and the binding is scoped, it will use that binding.  Otherwise, this
     * checks for an explicit binding. If no explicit binding is found, it looks for a just-in-time
     * binding.
     */
    public <T> BindingImpl<T> getBindingOrThrow(Key<T> key, Errors errors) throws ErrorsException {
        // Check explicit bindings, i.e. bindings created by modules.
        BindingImpl<T> binding = state.getExplicitBinding(key);
        if (binding != null) {
            return binding;
        }

        // Look for an on-demand binding.
        return getJustInTimeBinding(key, errors);
    }

    /**
     * Returns a just-in-time binding for {@code key}, creating it if necessary.
     *
     * @throws ErrorsException if the binding could not be created.
     */
    private <T> BindingImpl<T> getJustInTimeBinding(Key<T> key, Errors errors) throws ErrorsException {
        synchronized (state.lock()) {
            // first try to find a JIT binding that we've already created
            @SuppressWarnings("unchecked") // we only store bindings that match their key
            BindingImpl<T> binding = (BindingImpl<T>) jitBindings.get(key);

            if (binding != null) {
                return binding;
            }

            return createJustInTimeBindingRecursive(key, errors);
        }
    }

    /**
     * Returns true if the key type is Provider (but not a subclass of Provider).
     */
    static boolean isProvider(Key<?> key) {
        return key.getTypeLiteral().getRawType().equals(Provider.class);
    }

    /**
     * Returns true if the key type is MembersInjector (but not a subclass of MembersInjector).
     */
    static boolean isMembersInjector(Key<?> key) {
        return key.getTypeLiteral().getRawType().equals(MembersInjector.class) && key.hasAnnotationType() == false;
    }

    private <T> BindingImpl<MembersInjector<T>> createMembersInjectorBinding(Key<MembersInjector<T>> key, Errors errors)
        throws ErrorsException {
        Type membersInjectorType = key.getTypeLiteral().getType();
        if ((membersInjectorType instanceof ParameterizedType) == false) {
            throw errors.cannotInjectRawMembersInjector().toException();
        }

        @SuppressWarnings("unchecked") // safe because T came from Key<MembersInjector<T>>
        TypeLiteral<T> instanceType = (TypeLiteral<T>) TypeLiteral.get(
            ((ParameterizedType) membersInjectorType).getActualTypeArguments()[0]
        );
        MembersInjector<T> membersInjector = membersInjectorStore.get(instanceType, errors);

        InternalFactory<MembersInjector<T>> factory = new ConstantFactory<>(Initializables.of(membersInjector));

        return new InstanceBindingImpl<>(this, key, SourceProvider.UNKNOWN_SOURCE, factory, emptySet(), membersInjector);
    }

    /**
     * Creates a synthetic binding to {@code Provider<T>}, i.e. a binding to the provider from
     * {@code Binding<T>}.
     */
    private <T> BindingImpl<Provider<T>> createProviderBinding(Key<Provider<T>> key, Errors errors) throws ErrorsException {
        Type providerType = key.getTypeLiteral().getType();

        // If the Provider has no type parameter (raw Provider)...
        if ((providerType instanceof ParameterizedType) == false) {
            throw errors.cannotInjectRawProvider().toException();
        }

        Type entryType = ((ParameterizedType) providerType).getActualTypeArguments()[0];

        @SuppressWarnings("unchecked") // safe because T came from Key<Provider<T>>
        Key<T> providedKey = (Key<T>) key.ofType(entryType);

        BindingImpl<T> delegate = getBindingOrThrow(providedKey, errors);
        return new ProviderBindingImpl<>(this, key, delegate);
    }

    static class ProviderBindingImpl<T> extends BindingImpl<Provider<T>> implements ProviderBinding<Provider<T>> {
        final BindingImpl<T> providedBinding;

        ProviderBindingImpl(InjectorImpl injector, Key<Provider<T>> key, Binding<T> providedBinding) {
            super(injector, key, providedBinding.getSource(), createInternalFactory(providedBinding), Scoping.UNSCOPED);
            this.providedBinding = (BindingImpl<T>) providedBinding;
        }

        static <T> InternalFactory<Provider<T>> createInternalFactory(Binding<T> providedBinding) {
            final Provider<T> provider = providedBinding.getProvider();
            return (errors, context, dependency) -> provider;
        }

        @Override
        public <V> void acceptTargetVisitor(BindingTargetVisitor<? super Provider<T>, V> visitor) {
            visitor.visit();
        }

        @Override
        public String toString() {
            return new ToStringBuilder(ProviderKeyBinding.class).add("key", getKey())
                .add("providedKey", providedBinding.getKey())
                .toString();
        }
    }

    /**
     * Converts a constant string binding to the required type.
     *
     * @return the binding if it could be resolved, or null if the binding doesn't exist
     * @throws ErrorsException
     *          if there was an error resolving the binding
     */
    private <T> BindingImpl<T> convertConstantStringBinding(Key<T> key, Errors errors) throws ErrorsException {
        // Find a constant string binding.
        BindingImpl<String> stringBinding = state.getExplicitBinding(key.ofStringType());
        if (stringBinding == null || stringBinding.isConstant() == false) {
            return null;
        }

        String stringValue = stringBinding.getProvider().get();
        Object source = stringBinding.getSource();

        // Find a matching type converter.
        TypeLiteral<T> type = key.getTypeLiteral();
        MatcherAndConverter matchingConverter = state.getConverter(stringValue, type, errors, source);

        if (matchingConverter == null) {
            // No converter can handle the given type.
            return null;
        }

        // Try to convert the string. A failed conversion results in an error.
        try {
            @SuppressWarnings("unchecked") // This cast is safe because we double check below.
            T converted = (T) matchingConverter.getTypeConverter().convert(stringValue, type);

            if (converted == null) {
                throw errors.converterReturnedNull(stringValue, source, type, matchingConverter).toException();
            }

            if (type.getRawType().isInstance(converted) == false) {
                throw errors.conversionTypeError(stringValue, source, type, matchingConverter, converted).toException();
            }

            return new ConvertedConstantBindingImpl<>(this, key, converted, stringBinding);
        } catch (RuntimeException e) {
            throw errors.conversionError(stringValue, source, type, matchingConverter, e).toException();
        }
    }

    private static class ConvertedConstantBindingImpl<T> extends BindingImpl<T> implements ConvertedConstantBinding<T> {
        final T value;
        final Provider<T> provider;
        final Binding<String> originalBinding;

        ConvertedConstantBindingImpl(Injector injector, Key<T> key, T value, Binding<String> originalBinding) {
            super(injector, key, originalBinding.getSource(), new ConstantFactory<>(Initializables.of(value)), Scoping.UNSCOPED);
            this.value = value;
            provider = Providers.of(value);
            this.originalBinding = originalBinding;
        }

        @Override
        public Provider<T> getProvider() {
            return provider;
        }

        @Override
        public <V> void acceptTargetVisitor(BindingTargetVisitor<? super T, V> visitor) {
            visitor.visit();
        }

        @Override
        public String toString() {
            return new ToStringBuilder(ConvertedConstantBinding.class).add("key", getKey())
                .add("sourceKey", originalBinding.getKey())
                .add("value", value)
                .toString();
        }
    }

    <T> void initializeBinding(BindingImpl<T> binding, Errors errors) throws ErrorsException {
        // Put the partially constructed binding in the map a little early. This enables us to handle
        // circular dependencies. Example: FooImpl -> BarImpl -> FooImpl.
        // Note: We don't need to synchronize on state.lock() during injector creation.
        // TODO: for the above example, remove the binding for BarImpl if the binding for FooImpl fails
        if (binding instanceof ConstructorBindingImpl<?>) {
            Key<T> key = binding.getKey();
            jitBindings.put(key, binding);
            boolean successful = false;
            try {
                ((ConstructorBindingImpl<?>) binding).initialize(this, errors);
                successful = true;
            } finally {
                if (successful == false) {
                    jitBindings.remove(key);
                }
            }
        }
    }

    /**
     * Creates a binding for an injectable type with the given scope. Looks for a scope on the type if
     * none is specified.
     */
    <T> BindingImpl<T> createUnitializedBinding(Key<T> key, Scoping scoping, Object source, Errors errors) throws ErrorsException {
        Class<?> rawType = key.getTypeLiteral().getRawType();

        // Don't try to inject arrays, or enums.
        if (rawType.isArray() || rawType.isEnum()) {
            throw errors.missingImplementation(key).toException();
        }

        // Handle TypeLiteral<T> by binding the inner type
        if (rawType == TypeLiteral.class) {
            @SuppressWarnings("unchecked") // we have to fudge the inner type as Object
            BindingImpl<T> binding = (BindingImpl<T>) createTypeLiteralBinding((Key<TypeLiteral<Object>>) key, errors);
            return binding;
        }

        // We can't inject abstract classes.
        // TODO: Method interceptors could actually enable us to implement
        // abstract types. Should we remove this restriction?
        if (Modifier.isAbstract(rawType.getModifiers())) {
            throw errors.missingImplementation(key).toException();
        }

        // Error: Inner class.
        if (Classes.isInnerClass(rawType)) {
            throw errors.cannotInjectInnerClass(rawType).toException();
        }

        return ConstructorBindingImpl.create(this, key, source, scoping);
    }

    /**
     * Converts a binding for a {@code Key<TypeLiteral<T>>} to the value {@code TypeLiteral<T>}. It's
     * a bit awkward because we have to pull out the inner type in the type literal.
     */
    private <T> BindingImpl<TypeLiteral<T>> createTypeLiteralBinding(Key<TypeLiteral<T>> key, Errors errors) throws ErrorsException {
        Type typeLiteralType = key.getTypeLiteral().getType();
        if ((typeLiteralType instanceof ParameterizedType) == false) {
            throw errors.cannotInjectRawTypeLiteral().toException();
        }

        ParameterizedType parameterizedType = (ParameterizedType) typeLiteralType;
        Type innerType = parameterizedType.getActualTypeArguments()[0];

        // this is unfortunate. We don't support building TypeLiterals for type variable like 'T'. If
        // this proves problematic, we can probably fix TypeLiteral to support type variables
        if ((innerType instanceof Class) == false
            && (innerType instanceof GenericArrayType) == false
            && (innerType instanceof ParameterizedType) == false) {
            throw errors.cannotInjectTypeLiteralOf(innerType).toException();
        }

        @SuppressWarnings("unchecked") // by definition, innerType == T, so this is safe
        TypeLiteral<T> value = (TypeLiteral<T>) TypeLiteral.get(innerType);
        InternalFactory<TypeLiteral<T>> factory = new ConstantFactory<>(Initializables.of(value));
        return new InstanceBindingImpl<>(this, key, SourceProvider.UNKNOWN_SOURCE, factory, emptySet(), value);
    }

    /**
     * Attempts to create a just-in-time binding for {@code key} in the root injector, falling back to
     * other ancestor injectors until this injector is tried.
     */
    private <T> BindingImpl<T> createJustInTimeBindingRecursive(Key<T> key, Errors errors) throws ErrorsException {
        if (state.isBlacklisted(key)) {
            throw errors.childBindingAlreadySet(key).toException();
        }

        BindingImpl<T> binding = createJustInTimeBinding(key, errors);
        state.parent().blacklist(key);
        jitBindings.put(key, binding);
        return binding;
    }

    /**
     * Returns a new just-in-time binding created by resolving {@code key}. The strategies used to
     * create just-in-time bindings are:
     * <ol>
     * <li>Internalizing Providers. If the requested binding is for {@code Provider<T>}, we delegate
     * to the binding for {@code T}.
     * <li>Converting constants.
     * <li>ImplementedBy and ProvidedBy annotations. Only for unannotated keys.
     * <li>The constructor of the raw type. Only for unannotated keys.
     * </ol>
     *
     * @throws ErrorsException
     *          if the binding cannot be created.
     */
    <T> BindingImpl<T> createJustInTimeBinding(Key<T> key, Errors errors) throws ErrorsException {
        if (state.isBlacklisted(key)) {
            throw errors.childBindingAlreadySet(key).toException();
        }

        // Handle cases where T is a Provider<?>.
        if (isProvider(key)) {
            // These casts are safe. We know T extends Provider<X> and that given Key<Provider<X>>,
            // createProviderBinding() will return BindingImpl<Provider<X>>.
            @SuppressWarnings("unchecked")
            BindingImpl<T> binding = (BindingImpl<T>) createProviderBinding((Key<Provider<T>>) key, errors);
            return binding;
        }

        // Handle cases where T is a MembersInjector<?>
        if (isMembersInjector(key)) {
            // These casts are safe. T extends MembersInjector<X> and that given Key<MembersInjector<X>>,
            // createMembersInjectorBinding() will return BindingImpl<MembersInjector<X>>.
            @SuppressWarnings("unchecked")
            BindingImpl<T> binding = (BindingImpl<T>) createMembersInjectorBinding((Key<MembersInjector<T>>) key, errors);
            return binding;
        }

        // Try to convert a constant string binding to the requested type.
        BindingImpl<T> convertedBinding = convertConstantStringBinding(key, errors);
        if (convertedBinding != null) {
            return convertedBinding;
        }

        // If the key has an annotation...
        if (key.hasAnnotationType()) {
            // Look for a binding without annotation attributes or return null.
            if (key.hasAttributes()) {
                try {
                    Errors ignored = new Errors();
                    return getBindingOrThrow(key.withoutAttributes(), ignored);
                } catch (ErrorsException ignored) {
                    // throw with a more appropriate message below
                }
            }
            throw errors.missingImplementation(key).toException();
        }

        Object source = key.getTypeLiteral().getRawType();
        BindingImpl<T> binding = createUnitializedBinding(key, Scoping.UNSCOPED, source, errors);
        initializeBinding(binding, errors);
        return binding;
    }

    <T> InternalFactory<? extends T> getInternalFactory(Key<T> key, Errors errors) throws ErrorsException {
        return getBindingOrThrow(key, errors).getInternalFactory();
    }

    private static class BindingsMultimap {
        final Map<TypeLiteral<?>, List<Binding<?>>> multimap = new HashMap<>();

        <T> void put(TypeLiteral<T> type, Binding<T> binding) {
            multimap.computeIfAbsent(type, k -> new ArrayList<>()).add(binding);
        }

        @SuppressWarnings("unchecked")
        // safe because we only put matching entries into the map
        <T> List<Binding<T>> getAll(TypeLiteral<T> type) {
            List<Binding<?>> bindings = multimap.get(type);
            return bindings != null ? Collections.<Binding<T>>unmodifiableList((List) multimap.get(type)) : Collections.emptyList();
        }
    }

    /**
     * Returns parameter injectors, or {@code null} if there are no parameters.
     */
    SingleParameterInjector<?>[] getParametersInjectors(List<Dependency<?>> parameters, Errors errors) throws ErrorsException {
        if (parameters.isEmpty()) {
            return null;
        }

        int numErrorsBefore = errors.size();
        SingleParameterInjector<?>[] result = new SingleParameterInjector<?>[parameters.size()];
        int i = 0;
        for (Dependency<?> parameter : parameters) {
            try {
                result[i++] = createParameterInjector(parameter, errors.withSource(parameter));
            } catch (ErrorsException rethrownBelow) {
                // rethrown below
            }
        }

        errors.throwIfNewErrors(numErrorsBefore);
        return result;
    }

    <T> SingleParameterInjector<T> createParameterInjector(final Dependency<T> dependency, final Errors errors) throws ErrorsException {
        InternalFactory<? extends T> factory = getInternalFactory(dependency.getKey(), errors);
        return new SingleParameterInjector<>(dependency, factory);
    }

    /**
     * Cached constructor injectors for each type
     */
    ConstructorInjectorStore constructors = new ConstructorInjectorStore(this);

    /**
     * Cached field and method injectors for each type.
     */
    MembersInjectorStore membersInjectorStore;

    private <T> Provider<T> getProvider(Class<T> type) {
        return getProvider(Key.get(type));
    }

    <T> Provider<T> getProviderOrThrow(final Key<T> key, Errors errors) throws ErrorsException {
        final InternalFactory<? extends T> factory = getInternalFactory(key, errors);
        // ES: optimize for a common case of read only instance getting from the parent...
        if (factory instanceof InternalFactory.Instance) {
            return () -> {
                try {
                    return factory.get(null, null, null);
                } catch (ErrorsException e) {
                    // ignore
                }
                // should never happen...
                assert false;
                return null;
            };
        }

        final Dependency<T> dependency = Dependency.get(key);
        return new Provider<>() {
            @Override
            public T get() {
                final Errors errors = new Errors(dependency);
                try {
                    T t = callInContext((ContextualCallable<T>) context -> {
                        context.setDependency(dependency);
                        try {
                            return factory.get(errors, context, dependency);
                        } finally {
                            context.setDependency(null);
                        }
                    });
                    errors.throwIfNewErrors(0);
                    return t;
                } catch (ErrorsException e) {
                    throw new ProvisionException(errors.merge(e.getErrors()).getMessages());
                }
            }

            @Override
            public String toString() {
                return factory.toString();
            }
        };
    }

    @Override
    public <T> Provider<T> getProvider(final Key<T> key) {
        Errors errors = new Errors(key);
        try {
            Provider<T> result = getProviderOrThrow(key, errors);
            errors.throwIfNewErrors(0);
            return result;
        } catch (ErrorsException e) {
            throw new ConfigurationException(errors.merge(e.getErrors()).getMessages());
        }
    }

    @Override
    public <T> T getInstance(Key<T> key) {
        return getProvider(key).get();
    }

    @Override
    public <T> T getInstance(Class<T> type) {
        return getProvider(type).get();
    }

    private final ThreadLocal<Object[]> localContext;

    /**
     * Looks up thread local context. Creates (and removes) a new context if necessary.
     */
    <T> T callInContext(ContextualCallable<T> callable) throws ErrorsException {
        Object[] reference = localContext.get();
        if (reference == null) {
            reference = new Object[1];
            localContext.set(reference);
        }
        if (reference[0] == null) {
            reference[0] = new InternalContext();
            try {
                return callable.call((InternalContext) reference[0]);
            } finally {
                // Only clear the context if this call created it.
                reference[0] = null;
            }
        } else {
            // Someone else will clean up this context.
            return callable.call((InternalContext) reference[0]);
        }
    }

    @Override
    public String toString() {
        return new ToStringBuilder(Injector.class).add("bindings", state.getExplicitBindingsThisLevel().values()).toString();
    }

    // ES_GUICE: clear caches
    public void clearCache() {
        state.clearBlacklisted();
        constructors = new ConstructorInjectorStore(this);
        membersInjectorStore = new MembersInjectorStore(this);
        jitBindings = new HashMap<>();
    }

    // ES_GUICE: make all registered bindings act as eager singletons
    public void readOnlyAllSingletons() {
        state.makeAllBindingsToEagerSingletons(this);
        bindingsMultimap = new BindingsMultimap();
        // reindex the bindings
        index();
    }
}