/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.eclipse.aether.util.repository;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.eclipse.aether.repository.MirrorSelector;
import org.eclipse.aether.repository.RemoteRepository;

import static java.util.Objects.requireNonNull;

/**
 * A simple mirror selector that selects mirrors based on repository identifiers.
 */
public final class DefaultMirrorSelector implements MirrorSelector {

    private static final String WILDCARD = "*";

    private static final String EXTERNAL_WILDCARD = "external:*";

    private static final String EXTERNAL_HTTP_WILDCARD = "external:http:*";

    private final List<MirrorDef> mirrors = new ArrayList<>();

    /**
     * Adds the specified mirror to this selector.
     *
     * @param id the identifier of the mirror, must not be {@code null}
     * @param url the URL of the mirror, must not be {@code null}
     * @param type the content type of the mirror, must not be {@code null}
     * @param repositoryManager a flag whether the mirror is a repository manager or a simple server
     * @param blocked a flag whether the mirror is blocked from performing any download requests
     * @param mirrorOfIds the identifier(s) of remote repositories to mirror, must not be {@code null}. Multiple
     *            identifiers can be separated by comma and additionally the wildcards "*", "external:http:*" and
     *            "external:*" can be used to match all (external) repositories, prefixing a repo id with an
     *            exclamation mark allows to express an exclusion. For example "external:*,!central".
     * @param mirrorOfTypes the content type(s) of remote repositories to mirror, may be {@code null} or empty to match
     *            any content type. Similar to the repo id specification, multiple types can be comma-separated, the
     *            wildcard "*" and the "!" negation syntax are supported. For example "*,!p2".
     * @return this selector for chaining, never {@code null}
     */
    public DefaultMirrorSelector add(
            String id,
            String url,
            String type,
            boolean repositoryManager,
            boolean blocked,
            String mirrorOfIds,
            String mirrorOfTypes) {
        mirrors.add(new MirrorDef(id, url, type, repositoryManager, blocked, mirrorOfIds, mirrorOfTypes));

        return this;
    }

    public RemoteRepository getMirror(RemoteRepository repository) {
        requireNonNull(repository, "repository cannot be null");
        MirrorDef mirror = findMirror(repository);

        if (mirror == null) {
            return null;
        }

        RemoteRepository.Builder builder =
                new RemoteRepository.Builder(mirror.id, repository.getContentType(), mirror.url);

        builder.setRepositoryManager(mirror.repositoryManager);

        builder.setBlocked(mirror.blocked);

        if (mirror.type != null && !mirror.type.isEmpty()) {
            builder.setContentType(mirror.type);
        }

        builder.setSnapshotPolicy(repository.getPolicy(true));
        builder.setReleasePolicy(repository.getPolicy(false));

        builder.setMirroredRepositories(Collections.singletonList(repository));

        return builder.build();
    }

    private MirrorDef findMirror(RemoteRepository repository) {
        String repoId = repository.getId();

        if (repoId != null && !mirrors.isEmpty()) {
            for (MirrorDef mirror : mirrors) {
                if (repoId.equals(mirror.mirrorOfIds)
                        && matchesType(repository.getContentType(), mirror.mirrorOfTypes)) {
                    return mirror;
                }
            }

            for (MirrorDef mirror : mirrors) {
                if (matchPattern(repository, mirror.mirrorOfIds)
                        && matchesType(repository.getContentType(), mirror.mirrorOfTypes)) {
                    return mirror;
                }
            }
        }

        return null;
    }

    /**
     * This method checks if the pattern matches the originalRepository. Valid patterns:
     * <ul>
     * <li>{@code *} = everything,</li>
     * <li>{@code external:*} = everything not on the localhost and not file based,</li>
     * <li>{@code external:http:*} = any repository not on the localhost using HTTP,</li>
     * <li>{@code repo,repo1} = {@code repo} or {@code repo1},</li>
     * <li>{@code *,!repo1} = everything except {@code repo1}.</li>
     * </ul>
     *
     * @param repository to compare for a match
     * @param pattern used for match
     * @return true if the repository is a match to this pattern
     */
    static boolean matchPattern(RemoteRepository repository, String pattern) {
        boolean result = false;
        String originalId = repository.getId();

        // simple checks first to short circuit processing below.
        if (WILDCARD.equals(pattern) || pattern.equals(originalId)) {
            result = true;
        } else {
            // process the list
            String[] repos = pattern.split(",");
            for (String repo : repos) {
                // see if this is a negative match
                if (repo.length() > 1 && repo.startsWith("!")) {
                    if (repo.substring(1).equals(originalId)) {
                        // explicitly exclude. Set result and stop processing.
                        result = false;
                        break;
                    }
                }
                // check for exact match
                else if (repo.equals(originalId)) {
                    result = true;
                    break;
                }
                // check for external:*
                else if (EXTERNAL_WILDCARD.equals(repo) && isExternalRepo(repository)) {
                    result = true;
                    // don't stop processing in case a future segment explicitly excludes this repo
                }
                // check for external:http:*
                else if (EXTERNAL_HTTP_WILDCARD.equals(repo) && isExternalHttpRepo(repository)) {
                    result = true;
                    // don't stop processing in case a future segment explicitly excludes this repo
                } else if (WILDCARD.equals(repo)) {
                    result = true;
                    // don't stop processing in case a future segment explicitly excludes this repo
                }
            }
        }
        return result;
    }

    /**
     * Checks the URL to see if this repository refers to an external repository.
     *
     * @param repository the repository to check, must not be {@code null}
     * @return {@code true} if external, {@code false} otherwise
     */
    static boolean isExternalRepo(RemoteRepository repository) {
        boolean local = isLocal(repository.getHost()) || "file".equalsIgnoreCase(repository.getProtocol());
        return !local;
    }

    private static boolean isLocal(String host) {
        return "localhost".equals(host) || "127.0.0.1".equals(host);
    }

    /**
     * Checks the URL to see if this repository refers to a non-localhost repository using HTTP.
     *
     * @param repository the repository to check, must not be {@code null}
     * @return {@code true} if external, {@code false} otherwise
     */
    static boolean isExternalHttpRepo(RemoteRepository repository) {
        return ("http".equalsIgnoreCase(repository.getProtocol())
                        || "dav".equalsIgnoreCase(repository.getProtocol())
                        || "dav:http".equalsIgnoreCase(repository.getProtocol())
                        || "dav+http".equalsIgnoreCase(repository.getProtocol()))
                && !isLocal(repository.getHost());
    }

    /**
     * Checks whether the types configured for a mirror match with the type of the repository.
     *
     * @param repoType the type of the repository, may be {@code null}
     * @param mirrorType the types supported by the mirror, may be {@code null}
     * @return {@code true} if the types associated with the mirror match the type of the original repository,
     *         {@code false} otherwise
     */
    static boolean matchesType(String repoType, String mirrorType) {
        boolean result = false;

        // simple checks first to short circuit processing below.
        if (mirrorType == null || mirrorType.isEmpty() || WILDCARD.equals(mirrorType)) {
            result = true;
        } else if (mirrorType.equals(repoType)) {
            result = true;
        } else {
            // process the list
            String[] layouts = mirrorType.split(",");
            for (String layout : layouts) {
                // see if this is a negative match
                if (layout.length() > 1 && layout.startsWith("!")) {
                    if (layout.substring(1).equals(repoType)) {
                        // explicitly exclude. Set result and stop processing.
                        result = false;
                        break;
                    }
                }
                // check for exact match
                else if (layout.equals(repoType)) {
                    result = true;
                    break;
                } else if (WILDCARD.equals(layout)) {
                    result = true;
                    // don't stop processing in case a future segment explicitly excludes this repo
                }
            }
        }

        return result;
    }

    static class MirrorDef {

        final String id;

        final String url;

        final String type;

        final boolean repositoryManager;

        final boolean blocked;

        final String mirrorOfIds;

        final String mirrorOfTypes;

        MirrorDef(
                String id,
                String url,
                String type,
                boolean repositoryManager,
                boolean blocked,
                String mirrorOfIds,
                String mirrorOfTypes) {
            this.id = id;
            this.url = url;
            this.type = type;
            this.repositoryManager = repositoryManager;
            this.blocked = blocked;
            this.mirrorOfIds = mirrorOfIds;
            this.mirrorOfTypes = mirrorOfTypes;
        }
    }
}
