/*
    * 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 de.softwareforge.testing.postgres.embedded;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  import static com.google.common.base.Preconditions.checkState;
  import static de.softwareforge.testing.postgres.embedded.DatabaseInfo.PG_DEFAULT_USER;
  import static java.lang.String.format;
  
  import jakarta.annotation.Nonnull;
  import java.io.IOException;
  import java.sql.Connection;
  import java.sql.SQLException;
  import java.sql.Statement;
  import java.util.Set;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.SynchronousQueue;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.function.Supplier;
  import javax.sql.DataSource;
  
  import com.google.common.collect.ImmutableSet;
  import com.google.common.util.concurrent.ThreadFactoryBuilder;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Controls database instances on a PostgreSQL server instances.
   */
  public final class DatabaseManager implements AutoCloseable {
  
      private static final String PG_DEFAULT_ENCODING = "utf8";
  
      private static final Logger LOG = LoggerFactory.getLogger(DatabaseManager.class);
  
      private final AtomicBoolean closed = new AtomicBoolean();
      private final AtomicBoolean started = new AtomicBoolean();
  
      private final Set<EmbeddedPostgresPreparer<DataSource>> databasePreparers;
      private final Set<EmbeddedPostgresPreparer<EmbeddedPostgres.Builder>> instancePreparers;
      private final boolean multiMode;
  
      private volatile InstanceProvider instanceProvider = null;
      private volatile EmbeddedPostgres pg = null;
  
      private DatabaseManager(Set<EmbeddedPostgresPreparer<DataSource>> databasePreparers,
              Set<EmbeddedPostgresPreparer<EmbeddedPostgres.Builder>> instancePreparers,
              boolean multiMode) {
          this.databasePreparers = checkNotNull(databasePreparers, "databasePreparers is null");
          this.instancePreparers = checkNotNull(instancePreparers, "instancePreparers is null");
          this.multiMode = multiMode;
      }
  
      /**
       * Creates a new {@link Builder<DatabaseManager>} instance that will create a new database on each call to {@link DatabaseManager#getDatabaseInfo()}.
       *
       * @return A builder instance.
       */
      @Nonnull
      public static Builder<DatabaseManager> multiDatabases() {
          return new DatabaseManagerBuilder(true);
      }
  
      /**
       * Creates a new {@link Builder<DatabaseManager>} instance that will return a connection to the same database on each call to
       * {@link DatabaseManager#getDatabaseInfo()}.
       *
       * @return A builder instance.
       */
      @Nonnull
      public static Builder<DatabaseManager> singleDatabase() {
          return new DatabaseManagerBuilder(false);
      }
  
      /**
       * Start the database server and the machinery that will provide new database instances.
       *
       * @return This object.
       * @throws IOException  The server could not be started.
       * @throws SQLException A SQL problem occured while trying to initialize the database.
       */
      @Nonnull
      public DatabaseManager start() throws IOException, SQLException {
          if (!started.getAndSet(true)) {
  
              // bring up the embedded postgres server and call all instance preparer instances on it.
             EmbeddedPostgres.Builder builder = EmbeddedPostgres.builder();
 
             for (EmbeddedPostgresPreparer<EmbeddedPostgres.Builder> instancePreparer : instancePreparers) {
                 instancePreparer.prepare(builder);
             }
 
             this.pg = builder.build();
 
             final DataSource dataSource;
 
             if (multiMode) {
                 // apply database setup to the template database.
                 dataSource = pg.createTemplateDataSource();
 
                 // the provider pipeline will create new instances based on the template database.
                 this.instanceProvider = new InstanceProviderPipeline();
             } else {
                 // apply database setup to the default database.
                 dataSource = pg.createDefaultDataSource();
 
                 // always return a reference to the default database.
                 this.instanceProvider = pg::createDefaultDatabaseInfo;
             }
 
             for (EmbeddedPostgresPreparer<DataSource> databasePreparer : databasePreparers) {
                 databasePreparer.prepare(dataSource);
             }
 
             this.instanceProvider.start();
         }
 
         return this;
     }
 
     @Override
     public void close() throws Exception {
         checkState(started.get(), "not yet started!");
         if (!closed.getAndSet(true)) {
 
             if (instanceProvider != null) {
                 instanceProvider.close();
             }
 
             if (pg != null) {
                 pg.close();
             }
         }
     }
 
     /**
      * Returns a {@link DatabaseInfo} instance that describes a database. If this database provider is in multi mode, every call to this method will return a
      * new database instance. If it is in single mode, it will always return the same database instance.
      *
      * @return A {@link DatabaseInfo} instance. This is never null.
      * @throws SQLException Any error that happened during the database creation is thrown here.
      */
     @Nonnull
     public DatabaseInfo getDatabaseInfo() throws SQLException {
         checkState(started.get(), "not yet started!");
 
         DatabaseInfo databaseInfo = instanceProvider.get();
         if (databaseInfo.exception().isPresent()) {
             throw databaseInfo.exception().get();
         }
 
         return databaseInfo;
     }
 
     /**
      * Return the {@link EmbeddedPostgres} instance that manages the database server which holds all of the databases managed by this database manager.
      *
      * @return An {@link EmbeddedPostgres} instance. Never null.
      */
     @Nonnull
     public EmbeddedPostgres getEmbeddedPostgres() {
         checkState(started.get(), "not yet started!");
         return pg;
     }
 
     private interface InstanceProvider extends Supplier<DatabaseInfo>, AutoCloseable {
 
         default void start() {
         }
 
         @Override
         default void close() {
         }
 
         @Override
         DatabaseInfo get();
     }
 
     private final class InstanceProviderPipeline implements InstanceProvider, Runnable {
 
         private final ExecutorService executor;
         private final SynchronousQueue<DatabaseInfo> nextDatabase = new SynchronousQueue<>();
 
         private final AtomicBoolean closed = new AtomicBoolean();
 
         InstanceProviderPipeline() {
             this.executor = Executors.newSingleThreadExecutor(
                     new ThreadFactoryBuilder()
                             .setDaemon(true)
                             .setNameFormat("instance-creator-" + pg.instanceId() + "-%d")
                             .build());
 
         }
 
         @Override
         public void start() {
             this.executor.submit(this);
         }
 
         @Override
         public void close() {
             if (!this.closed.getAndSet(true)) {
                 executor.shutdownNow();
             }
         }
 
         @Override
         public void run() {
             while (!closed.get()) {
                 try {
                     final String newDbName = EmbeddedUtil.randomLowercase(12);
                     try {
                         createDatabase(pg.createDefaultDataSource(), newDbName);
                         nextDatabase.put(DatabaseInfo.builder()
                                 .dbName(newDbName)
                                 .port(pg.getPort())
                                 .connectionProperties(pg.getConnectionProperties())
                                 .build());
                     } catch (SQLException e) {
                         // https://www.postgresql.org/docs/13/errcodes-appendix.html - 57P01 admin_shutdown
                         if (!e.getSQLState().equals("57P01")) {
                             LOG.warn("Caught SQL Exception (" + e.getSQLState() + "):", e);
                             nextDatabase.put(DatabaseInfo.forException(e));
                         }
                     }
                 } catch (InterruptedException e) {
                     Thread.currentThread().interrupt();
                     return;
                 } catch (Exception e) {
                     LOG.warn("Caught exception in instance provider loop:", e);
                 }
             }
         }
 
         @Override
         public DatabaseInfo get() {
             try {
                 return nextDatabase.take();
             } catch (final InterruptedException e) {
                 Thread.currentThread().interrupt();
                 throw new IllegalStateException(e);
             }
         }
     }
 
     private static void createDatabase(final DataSource dataSource, final String databaseName) throws SQLException {
         try (Connection c = dataSource.getConnection();
                 Statement stmt = c.createStatement()) {
             stmt.executeUpdate(format("CREATE DATABASE %s OWNER %s ENCODING = '%s'", databaseName, PG_DEFAULT_USER, PG_DEFAULT_ENCODING));
         }
     }
 
     /**
      * Builder template.
      *
      * @param <T> Object to create.
      */
     public abstract static class Builder<T> {
 
         protected ImmutableSet.Builder<EmbeddedPostgresPreparer<DataSource>> databasePreparers = ImmutableSet.builder();
         protected ImmutableSet.Builder<EmbeddedPostgresPreparer<EmbeddedPostgres.Builder>> instancePreparers = ImmutableSet.builder();
         protected final boolean multiMode;
 
         /**
          * Creates a new builder.
          *
          * @param multiMode True if the resulting object should be in multi mode (create multiple database instances) or single mode (use only one instance).
          */
         protected Builder(boolean multiMode) {
             this.multiMode = multiMode;
         }
 
         /**
          * Add a preparer for the template database. Each preparer is called once when the database manager starts to prepare the template database. This can be
          * used to create tables, sequences etc. or preload the databases with information. In multi database mode, the template database is used and each
          * created database will have this information cloned.
          *
          * @param databasePreparer A {@link EmbeddedPostgresPreparer<DataSource>} instance. Must not be null.
          * @return This object instance.
          * @since 3.0
          */
         @Nonnull
         public Builder<T> withDatabasePreparer(@Nonnull EmbeddedPostgresPreparer<DataSource> databasePreparer) {
             this.databasePreparers.add(checkNotNull(databasePreparer, "databasePreparer is null"));
             return this;
         }
 
         /**
          * Add preparers for the template database. Each preparer is called once when the database manager starts to prepare the template database. This can be
          * used to create tables, sequences etc. or preload the databases with information. In multi database mode, the template database is used and each
          * created database will have this information cloned.
          *
          * @param databasePreparers A set of {@link EmbeddedPostgresPreparer<DataSource>} instances. Must not be null.
          * @return This object instance.
          * @since 3.0
          */
         @Nonnull
         public Builder<T> withDatabasePreparers(@Nonnull Set<EmbeddedPostgresPreparer<DataSource>> databasePreparers) {
             this.databasePreparers.addAll(checkNotNull(databasePreparers, "databasePreparers is null"));
             return this;
         }
 
         /**
          * Add a preparer for the {@link EmbeddedPostgres.Builder} object. Each preparer is called once when the {@link EmbeddedPostgres} instance that manages
          * the server is created.
          *
          * @param instancePreparer A {@link EmbeddedPostgresPreparer<EmbeddedPostgres.Builder>} instance. Must not be null.
          * @return This object instance.
          * @since 3.0
          */
         @Nonnull
         public Builder<T> withInstancePreparer(@Nonnull EmbeddedPostgresPreparer<EmbeddedPostgres.Builder> instancePreparer) {
             this.instancePreparers.add(checkNotNull(instancePreparer, "instancePreparer is null"));
             return this;
         }
 
         /**
          * Add preparers for the {@link EmbeddedPostgres.Builder} object. Each preparer is called once when the {@link EmbeddedPostgres} instance that manages
          * the server is created.
          *
          * @param instancePreparers A set of {@link EmbeddedPostgresPreparer<EmbeddedPostgres.Builder>} instances. Must not be null.
          * @return This object instance.
          * @since 3.0
          */
         @Nonnull
         public Builder<T> withInstancePreparers(@Nonnull Set<EmbeddedPostgresPreparer<EmbeddedPostgres.Builder>> instancePreparers) {
             this.instancePreparers.addAll(checkNotNull(instancePreparers, "instancePreparers is null"));
             return this;
         }
 
         /**
          * Creates a new instance.
          *
          * @return The instance to create.
          */
         @Nonnull
         public abstract T build();
     }
 
     /**
      * Create new {@link DatabaseManager} instances.
      */
     public static final class DatabaseManagerBuilder extends Builder<DatabaseManager> {
 
         /**
          * Creates a new builder for {@link DatabaseManager} instances.
          *
          * @param multiMode True if the database manager should return a new database instance for every {@link DatabaseManager#getDatabaseInfo()}} call, false
          *                  if it should return the same database instance.
          */
         public DatabaseManagerBuilder(boolean multiMode) {
             super(multiMode);
         }
 
         /**
          * Creates a new {@link DatabaseManager} instance from the builder.
          *
          * @return A database manager. Never null.
          */
         @Override
         @Nonnull
         public DatabaseManager build() {
             return new DatabaseManager(databasePreparers.build(), instancePreparers.build(), multiMode);
         }
     }
 }