/*
 * Copyright 2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.builder;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import org.gradle.api.Action;
import org.gradle.api.GradleException;
import org.gradle.api.artifacts.ModuleVersionIdentifier;
import org.gradle.api.artifacts.component.ComponentIdentifier;
import org.gradle.api.capabilities.Capability;
import org.gradle.api.internal.artifacts.ComponentSelectorConverter;
import org.gradle.api.internal.artifacts.ResolveContext;
import org.gradle.api.internal.artifacts.dsl.ModuleReplacementsData;
import org.gradle.api.internal.artifacts.ivyservice.dependencysubstitution.DependencySubstitutionApplicator;
import org.gradle.api.internal.artifacts.ivyservice.ivyresolve.strategy.Version;
import org.gradle.api.internal.artifacts.ivyservice.ivyresolve.strategy.VersionParser;
import org.gradle.api.internal.artifacts.ivyservice.ivyresolve.strategy.VersionSelectorScheme;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.excludes.ModuleExclusions;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.DependencyGraphSelector;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.DependencyGraphVisitor;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.conflicts.CapabilitiesConflictHandler;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.conflicts.DefaultCapabilitiesConflictHandler;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.conflicts.ModuleConflictHandler;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.conflicts.PotentialConflict;
import org.gradle.api.internal.artifacts.ivyservice.resolveengine.graph.selectors.SelectorStateResolver;
import org.gradle.api.internal.attributes.AttributesSchemaInternal;
import org.gradle.api.internal.attributes.ImmutableAttributesFactory;
import org.gradle.api.specs.Spec;
import org.gradle.internal.component.external.model.DefaultModuleComponentIdentifier;
import org.gradle.internal.component.model.DependencyMetadata;
import org.gradle.internal.id.IdGenerator;
import org.gradle.internal.id.LongIdGenerator;
import org.gradle.internal.operations.BuildOperationExecutor;
import org.gradle.internal.operations.BuildOperationQueue;
import org.gradle.internal.operations.RunnableBuildOperation;
import org.gradle.internal.resolve.ModuleVersionResolveException;
import org.gradle.internal.resolve.resolver.ComponentMetaDataResolver;
import org.gradle.internal.resolve.resolver.DependencyToComponentIdResolver;
import org.gradle.internal.resolve.resolver.ResolveContextToComponentResolver;
import org.gradle.internal.resolve.result.DefaultBuildableComponentResolveResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;

public class DependencyGraphBuilder {
    private static final Logger LOGGER = LoggerFactory.getLogger(DependencyGraphBuilder.class);
    private final ModuleConflictHandler moduleConflictHandler;
    private final Spec<? super DependencyMetadata> edgeFilter;
    private final ResolveContextToComponentResolver moduleResolver;
    private final DependencyToComponentIdResolver idResolver;
    private final ComponentMetaDataResolver metaDataResolver;
    private final AttributesSchemaInternal attributesSchema;
    private final ModuleExclusions moduleExclusions;
    private final BuildOperationExecutor buildOperationExecutor;
    private final ModuleReplacementsData moduleReplacementsData;
    private final ComponentSelectorConverter componentSelectorConverter;
    private final DependencySubstitutionApplicator dependencySubstitutionApplicator;
    private final ImmutableAttributesFactory attributesFactory;
    private final CapabilitiesConflictHandler capabilitiesConflictHandler;
    private final VersionSelectorScheme versionSelectorScheme;
    private final Comparator<Version> versionComparator;
    private final VersionParser versionParser;

    public DependencyGraphBuilder(DependencyToComponentIdResolver componentIdResolver,
                                  ComponentMetaDataResolver componentMetaDataResolver,
                                  ResolveContextToComponentResolver resolveContextToComponentResolver,
                                  ModuleConflictHandler moduleConflictHandler,
                                  CapabilitiesConflictHandler capabilitiesConflictHandler,
                                  Spec<? super DependencyMetadata> edgeFilter,
                                  AttributesSchemaInternal attributesSchema,
                                  ModuleExclusions moduleExclusions,
                                  BuildOperationExecutor buildOperationExecutor,
                                  ModuleReplacementsData moduleReplacementsData,
                                  DependencySubstitutionApplicator dependencySubstitutionApplicator,
                                  ComponentSelectorConverter componentSelectorConverter,
                                  ImmutableAttributesFactory attributesFactory,
                                  VersionSelectorScheme versionSelectorScheme,
                                  Comparator<Version> versionComparator,
                                  VersionParser versionParser) {
        this.idResolver = componentIdResolver;
        this.metaDataResolver = componentMetaDataResolver;
        this.moduleResolver = resolveContextToComponentResolver;
        this.moduleConflictHandler = moduleConflictHandler;
        this.edgeFilter = edgeFilter;
        this.attributesSchema = attributesSchema;
        this.moduleExclusions = moduleExclusions;
        this.buildOperationExecutor = buildOperationExecutor;
        this.moduleReplacementsData = moduleReplacementsData;
        this.dependencySubstitutionApplicator = dependencySubstitutionApplicator;
        this.componentSelectorConverter = componentSelectorConverter;
        this.attributesFactory = attributesFactory;
        this.capabilitiesConflictHandler = capabilitiesConflictHandler;
        this.versionSelectorScheme = versionSelectorScheme;
        this.versionComparator = versionComparator;
        this.versionParser = versionParser;
    }

    public void resolve(final ResolveContext resolveContext, final DependencyGraphVisitor modelVisitor) {

        IdGenerator<Long> idGenerator = new LongIdGenerator();
        DefaultBuildableComponentResolveResult rootModule = new DefaultBuildableComponentResolveResult();
        moduleResolver.resolve(resolveContext, rootModule);

        final ResolveState resolveState = new ResolveState(idGenerator, rootModule, resolveContext.getName(), idResolver, metaDataResolver, edgeFilter, attributesSchema, moduleExclusions, moduleReplacementsData, componentSelectorConverter, attributesFactory, dependencySubstitutionApplicator, versionSelectorScheme, versionComparator, versionParser);

        traverseGraph(resolveState);

        validateGraph(resolveState);

        assembleResult(resolveState, modelVisitor);

    }

    /**
     * Traverses the dependency graph, resolving conflicts and building the paths from the root configuration.
     */
    private void traverseGraph(final ResolveState resolveState) {
        resolveState.onMoreSelected(resolveState.getRoot());
        final List<EdgeState> dependencies = Lists.newArrayList();
        final Map<ModuleVersionIdentifier, ComponentIdentifier> componentIdentifierCache = Maps.newHashMap();

        final PendingDependenciesHandler pendingDependenciesHandler = new DefaultPendingDependenciesHandler();

        while (resolveState.peek() != null || moduleConflictHandler.hasConflicts() || capabilitiesConflictHandler.hasConflicts()) {
            if (resolveState.peek() != null) {
                final NodeState node = resolveState.pop();
                LOGGER.debug("Visiting configuration {}.", node);

                // Register capabilities for this node
                registerCapabilities(resolveState, node.getComponent());

                // Initialize and collect any new outgoing edges of this node
                dependencies.clear();
                node.visitOutgoingDependencies(dependencies, pendingDependenciesHandler);
                resolveEdges(node, dependencies, resolveState, componentIdentifierCache);
            } else {
                // We have some batched up conflicts. Resolve the first, and continue traversing the graph
                if (moduleConflictHandler.hasConflicts()) {
                    moduleConflictHandler.resolveNextConflict(resolveState.getReplaceSelectionWithConflictResultAction());
                } else {
                    capabilitiesConflictHandler.resolveNextConflict(resolveState.getReplaceSelectionWithConflictResultAction());
                }
            }

        }
    }

    private void registerCapabilities(final ResolveState resolveState, final ComponentState moduleRevision) {
        moduleRevision.forEachCapability(new Action<Capability>() {
            @Override
            public void execute(Capability capability) {
                // This is a performance optimization. Most modules do not declare capabilities. So, instead of systematically registering
                // an implicit capability for each module that we see, we only consider modules which _declare_ capabilities. If they do,
                // then we try to find a module which provides the same capability. It that module has been found, then we register it.
                // Otherwise, we have nothing to do. This avoids most of registrations.
                Collection<ComponentState> implicitProvidersForCapability = Collections.emptyList();
                for (ModuleResolveState state : resolveState.getModules()) {
                    if (state.getId().getGroup().equals(capability.getGroup()) && state.getId().getName().equals(capability.getName())) {
                        implicitProvidersForCapability = state.getVersions();
                        break;
                    }
                }
                PotentialConflict c = capabilitiesConflictHandler.registerCandidate(
                    DefaultCapabilitiesConflictHandler.candidate(moduleRevision, capability, implicitProvidersForCapability)
                );
                if (c.conflictExists()) {
                    c.withParticipatingModules(resolveState.getDeselectVersionAction());
                }
            }
        });
    }

    private void resolveEdges(final NodeState node,
                              final List<EdgeState> dependencies,
                              final ResolveState resolveState,
                              final Map<ModuleVersionIdentifier, ComponentIdentifier> componentIdentifierCache) {
        if (dependencies.isEmpty()) {
            return;
        }
        performSelectionSerially(dependencies, resolveState);
        maybeDownloadMetadataInParallel(node, componentIdentifierCache, dependencies);
        attachToTargetRevisionsSerially(dependencies);

    }

    private void performSelectionSerially(List<EdgeState> dependencies, ResolveState resolveState) {
        for (EdgeState dependency : dependencies) {
            SelectorState selector = dependency.getSelector();
            ModuleResolveState module = selector.getTargetModule();

            if (!selector.isResolved()) {
                // Have an unprocessed/new selector for this module. Need to re-select the target version.
                performSelection(resolveState, module);
            }

            module.addUnattachedDependency(dependency);
        }
    }

    /**
     * Attempts to resolve a target `ComponentState` for the given dependency.
     * On successful resolve, a `ComponentState` is constructed for the identifier, recorded as {@link ModuleResolveState#selected},
     * and added to the graph.
     * On resolve failure, the failure is recorded and no `ComponentState` is selected.
     */
    private void performSelection(ResolveState resolveState, ModuleResolveState module) {
        ComponentState currentSelection = module.getSelected();

        SelectorStateResolver<ComponentState> selectorStateResolver = new SelectorStateResolver<ComponentState>(moduleConflictHandler.getResolver(), resolveState, resolveState.getRoot().getComponent());
        ComponentState selected;
        try {
            selected = selectorStateResolver.selectBest(module.getId(), module.getSelectors());
        } catch (ModuleVersionResolveException e) {
            // Ignore: All selectors failed, and will have failures recorded
            return;
        }

        // If no current selection for module, just use the candidate.
        if (currentSelection == null) {
            module.select(selected);
            // This is the first time we've seen the module, so register with conflict resolver.
            checkForModuleConflicts(resolveState, module);
            return;
        }

        // If current selection is still the best choice, then only need to point new edge/selector at current selection.
        if (selected == currentSelection) {
            return;
        }

        // New candidate is a preferred choice over current selection. Reset the module state and reselect.
        module.changeSelection(selected);
    }

    private void checkForModuleConflicts(ResolveState resolveState, ModuleResolveState module) {
        // A new module. Check for conflict with capabilities and module replacements.
        PotentialConflict c = moduleConflictHandler.registerCandidate(module);
        if (c.conflictExists()) {
            // We have a conflict
            LOGGER.debug("Found new conflicting module {}", module);

            // For each module participating in the conflict, deselect the currently selection, and remove all outgoing edges from the version.
            // This will propagate through the graph and prune configurations that are no longer required.
            c.withParticipatingModules(resolveState.getDeselectVersionAction());
        }
    }

    /**
     * Prepares the resolution of edges, either serially or concurrently.
     * It uses a simple heuristic to determine if we should perform concurrent resolution, based on the the number of edges, and whether they have unresolved metadata.
     */
    private void maybeDownloadMetadataInParallel(NodeState node, Map<ModuleVersionIdentifier, ComponentIdentifier> componentIdentifierCache, List<EdgeState> dependencies) {
        List<ComponentState> requiringDownload = null;
        for (EdgeState dependency : dependencies) {
            ComponentState targetComponent = dependency.getTargetComponent();
            if (targetComponent != null && targetComponent.isSelected() && !targetComponent.alreadyResolved()) {
                if (!metaDataResolver.isFetchingMetadataCheap(toComponentId(targetComponent.getId(), componentIdentifierCache))) {
                    // Avoid initializing the list if there are no components requiring download (a common case)
                    if (requiringDownload == null) {
                        requiringDownload = Lists.newArrayList();
                    }
                    requiringDownload.add(targetComponent);
                }
            }
        }
        // Only download in parallel if there is more than 1 component to download
        if (requiringDownload != null && requiringDownload.size() > 1) {
            final ImmutableList<ComponentState> toDownloadInParallel = ImmutableList.copyOf(requiringDownload);
            LOGGER.debug("Submitting {} metadata files to resolve in parallel for {}", toDownloadInParallel.size(), node);
            buildOperationExecutor.runAll(new Action<BuildOperationQueue<RunnableBuildOperation>>() {
                @Override
                public void execute(BuildOperationQueue<RunnableBuildOperation> buildOperationQueue) {
                    for (final ComponentState componentState : toDownloadInParallel) {
                        buildOperationQueue.add(new DownloadMetadataOperation(componentState));
                    }
                }
            });
        }
    }

    private ComponentIdentifier toComponentId(ModuleVersionIdentifier id, Map<ModuleVersionIdentifier, ComponentIdentifier> componentIdentifierCache) {
        ComponentIdentifier identifier = componentIdentifierCache.get(id);
        if (identifier == null) {
            identifier = DefaultModuleComponentIdentifier.newId(id);
            componentIdentifierCache.put(id, identifier);
        }
        return identifier;
    }

    private void attachToTargetRevisionsSerially(List<EdgeState> dependencies) {
        // the following only needs to be done serially to preserve ordering of dependencies in the graph: we have visited the edges
        // but we still didn't add the result to the queue. Doing it from resolve threads would result in non-reproducible graphs, where
        // edges could be added in different order. To avoid this, the addition of new edges is done serially.
        for (EdgeState dependency : dependencies) {
            dependency.attachToTargetConfigurations();
        }
    }

    private void validateGraph(ResolveState resolveState) {
        for (ModuleResolveState module : resolveState.getModules()) {
            if (module.getSelected() != null && module.getSelected().isRejected()) {
                GradleException error = new GradleException(new RejectedModuleMessageBuilder().buildFailureMessage(module));
                attachFailureToEdges(error, module.getIncomingEdges());
                // We need to attach failures on unattached dependencies too, in case a node wasn't selected
                // at all, but we still want to see an error message for it.
                attachFailureToEdges(error, module.getUnattachedDependencies());
            }
        }
    }

    /**
     * Attaches errors late in the process. This is useful whenever we have built a graph, and that
     * validation is going to cause a failure (the error is not in the graph itself, but in the way
     * we handle it: do we use failOnVersionConflict?). This method therefore needs to be called
     * before the graph is handed over, so that we can properly fail resolution.
     */
    private void attachFailureToEdges(GradleException error, Collection<EdgeState> incomingEdges) {
        for (EdgeState edge : incomingEdges) {
            edge.failWith(error);
        }
    }

    /**
     * Populates the result from the graph traversal state.
     */
    private void assembleResult(ResolveState resolveState, DependencyGraphVisitor visitor) {
        visitor.start(resolveState.getRoot());

        // Visit the selectors
        for (DependencyGraphSelector selector : resolveState.getSelectors()) {
            visitor.visitSelector(selector);
        }

        // Visit the nodes prior to visiting the edges
        for (NodeState nodeState : resolveState.getNodes()) {
            if (nodeState.isSelected()) {
                visitor.visitNode(nodeState);
            }
        }

        // Collect the components to sort in consumer-first order
        List<ComponentState> queue = Lists.newArrayListWithExpectedSize(resolveState.getNodeCount());
        for (ModuleResolveState module : resolveState.getModules()) {
            if (module.getSelected() != null) {
                queue.add(module.getSelected());
            }
        }

        // Visit the edges after sorting the components in consumer-first order
        while (!queue.isEmpty()) {
            ComponentState component = queue.get(0);
            if (component.getVisitState() == VisitState.NotSeen) {
                component.setVisitState(VisitState.Visiting);
                int pos = 0;
                for (NodeState node : component.getNodes()) {
                    if (!node.isSelected()) {
                        continue;
                    }
                    for (EdgeState edge : node.getIncomingEdges()) {
                        ComponentState owner = edge.getFrom().getOwner();
                        if (owner.getVisitState() == VisitState.NotSeen) {
                            queue.add(pos, owner);
                            pos++;
                        } // else, already visited or currently visiting (which means a cycle), skip
                    }
                }
                if (pos == 0) {
                    // have visited all consumers, so visit this node
                    component.setVisitState(VisitState.Visited);
                    queue.remove(0);
                    for (NodeState node : component.getNodes()) {
                        if (node.isSelected()) {
                            visitor.visitEdges(node);
                        }
                    }
                }
            } else if (component.getVisitState() == VisitState.Visiting) {
                // have visited all consumers, so visit this node
                component.setVisitState(VisitState.Visited);
                queue.remove(0);
                for (NodeState node : component.getNodes()) {
                    if (node.isSelected()) {
                        visitor.visitEdges(node);
                    }
                }
            } else {
                // else, already visited previously, skip
                queue.remove(0);
            }
        }

        visitor.finish(resolveState.getRoot());
    }

    enum VisitState {
        NotSeen, Visiting, Visited
    }

}
