/*
 * Copyright 2015-2022 Transmogrify LLC, 2022-2023 Revetware LLC.
 *
 * 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 com.pyranid;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Savepoint;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.logging.Logger;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;

/**
 * Represents a database transaction.
 * <p>
 * Note that commit and rollback operations are controlled internally by {@link Database}.
 *
 * @author <a href="https://www.revetkn.com">Mark Allen</a>
 * @since 1.0.0
 */
@ThreadSafe
public class Transaction {
        @Nonnull
        private static final AtomicLong ID_GENERATOR;

        static {
                ID_GENERATOR = new AtomicLong(0);
        }

        @Nonnull
        private final Long id;
        @Nonnull
        private final DataSource dataSource;
        @Nonnull
        private final TransactionIsolation transactionIsolation;
        @Nonnull
        private final List<Consumer<TransactionResult>> postTransactionOperations;
        @Nonnull
        private final ReentrantLock connectionLock;
        @Nonnull
        private final Logger logger;

        @Nullable
        private Connection connection;
        @Nonnull
        private Boolean rollbackOnly;
        @Nullable
        private Boolean initialAutoCommit;

        Transaction(@Nonnull DataSource dataSource,
                                                        @Nonnull TransactionIsolation transactionIsolation) {
                requireNonNull(dataSource);
                requireNonNull(transactionIsolation);

                this.id = generateId();
                this.dataSource = dataSource;
                this.transactionIsolation = transactionIsolation;
                this.connection = null;
                this.rollbackOnly = false;
                this.initialAutoCommit = null;
                this.postTransactionOperations = new CopyOnWriteArrayList();
                this.connectionLock = new ReentrantLock();
                this.logger = Logger.getLogger(Transaction.class.getName());
        }

        @Override
        @Nonnull
        public String toString() {
                return format("%s{id=%s, transactionIsolation=%s, hasConnection=%s, isRollbackOnly=%s}",
                                getClass().getSimpleName(), id(), getTransactionIsolation(), hasConnection(), isRollbackOnly());
        }

        /**
         * Creates a transaction savepoint that can be rolled back to via {@link #rollback(Savepoint)}.
         *
         * @return a transaction savepoint
         */
        @Nonnull
        public Savepoint createSavepoint() {
                try {
                        return getConnection().setSavepoint();
                } catch (SQLException e) {
                        throw new DatabaseException("Unable to create savepoint", e);
                }
        }

        /**
         * Rolls back to the provided transaction savepoint.
         *
         * @param savepoint the savepoint to roll back to
         */
        public void rollback(@Nonnull Savepoint savepoint) {
                requireNonNull(savepoint);

                try {
                        getConnection().rollback(savepoint);
                } catch (SQLException e) {
                        throw new DatabaseException("Unable to roll back to savepoint", e);
                }
        }

        /**
         * Should this transaction be rolled back upon completion?
         * <p>
         * Default value is {@code false}.
         *
         * @return {@code true} if this transaction should be rolled back, {@code false} otherwise
         */
        @Nonnull
        public Boolean isRollbackOnly() {
                return this.rollbackOnly;
        }

        /**
         * Sets whether this transaction should be rolled back upon completion.
         *
         * @param rollbackOnly whether to set this transaction to be rollback-only
         */
        public void setRollbackOnly(@Nonnull Boolean rollbackOnly) {
                requireNonNull(rollbackOnly);
                this.rollbackOnly = rollbackOnly;
        }

        /**
         * Adds an operation to the list of operations to be executed when the transaction completes.
         *
         * @param postTransactionOperation the post-transaction operation to add
         */
        public void addPostTransactionOperation(@Nonnull Consumer<TransactionResult> postTransactionOperation) {
                requireNonNull(postTransactionOperation);
                this.postTransactionOperations.add(postTransactionOperation);
        }

        /**
         * Removes an operation from the list of operations to be executed when the transaction completes.
         *
         * @param postTransactionOperation the post-transaction operation to remove
         * @return {@code true} if the post-transaction operation was removed, {@code false} otherwise
         */
        @Nonnull
        public Boolean removePostTransactionOperation(@Nonnull Consumer<TransactionResult> postTransactionOperation) {
                requireNonNull(postTransactionOperation);
                return this.postTransactionOperations.remove(postTransactionOperation);
        }

        /**
         * Gets an unmodifiable list of post-transaction operations.
         * <p>
         * To manipulate the list, use {@link #addPostTransactionOperation(Consumer)} and
         * {@link #removePostTransactionOperation(Consumer)}.
         *
         * @return the list of post-transaction operations
         */
        @Nonnull
        public List<Consumer<TransactionResult>> getPostTransactionOperations() {
                return Collections.unmodifiableList(this.postTransactionOperations);
        }

        /**
         * Get the isolation level for this transaction.
         *
         * @return the isolation level
         */
        @Nonnull
        public TransactionIsolation getTransactionIsolation() {
                return this.transactionIsolation;
        }

        @Nonnull
        Long id() {
                return this.id;
        }

        @Nonnull
        Boolean hasConnection() {
                getConnectionLock().lock();

                try {
                        return this.connection != null;
                } finally {
                        getConnectionLock().unlock();
                }
        }

        void commit() {
                getConnectionLock().lock();

                try {
                        if (!hasConnection()) {
                                logger.finer("Transaction has no connection, so nothing to commit");
                                return;
                        }

                        logger.finer("Committing transaction...");

                        try {
                                getConnection().commit();
                                logger.finer("Transaction committed.");
                        } catch (SQLException e) {
                                throw new DatabaseException("Unable to commit transaction", e);
                        }
                } finally {
                        getConnectionLock().unlock();
                }
        }

        void rollback() {
                getConnectionLock().lock();

                try {
                        if (!hasConnection()) {
                                logger.finer("Transaction has no connection, so nothing to roll back");
                                return;
                        }

                        logger.finer("Rolling back transaction...");

                        try {
                                getConnection().rollback();
                                logger.finer("Transaction rolled back.");
                        } catch (SQLException e) {
                                throw new DatabaseException("Unable to roll back transaction", e);
                        }
                } finally {
                        getConnectionLock().unlock();
                }
        }

        /**
         * The connection associated with this transaction.
         * <p>
         * If no connection is associated yet, we ask the {@link DataSource} for one.
         *
         * @return The connection associated with this transaction.
         * @throws DatabaseException if unable to acquire a connection.
         */
        @Nonnull
        Connection getConnection() {
                getConnectionLock().lock();

                try {
                        if (hasConnection())
                                return this.connection;

                        try {
                                this.connection = getDataSource().getConnection();
                        } catch (SQLException e) {
                                throw new DatabaseException("Unable to acquire database connection", e);
                        }

                        // Keep track of the initial setting for autocommit since it might need to get changed from "true" to "false" for
                        // the duration of the transaction and then back to "true" post-transaction.
                        try {
                                this.initialAutoCommit = this.connection.getAutoCommit();
                        } catch (SQLException e) {
                                throw new DatabaseException("Unable to determine database connection autocommit setting", e);
                        }

                        // Immediately flip autocommit to false if needed...if initially true, it will get set back to true by Database at
                        // the end of the transaction
                        if (this.initialAutoCommit)
                                setAutoCommit(false);

                        return this.connection;
                } finally {
                        getConnectionLock().unlock();
                }
        }

        void setAutoCommit(@Nonnull Boolean autoCommit) {
                requireNonNull(autoCommit);

                try {
                        getConnection().setAutoCommit(autoCommit);
                } catch (SQLException e) {
                        throw new DatabaseException(format("Unable to set database connection autocommit value to '%s'", autoCommit), e);
                }
        }

        @Nonnull
        Long generateId() {
                return ID_GENERATOR.incrementAndGet();
        }

        @Nonnull
        Optional<Boolean> getInitialAutoCommit() {
                return Optional.ofNullable(this.initialAutoCommit);
        }

        @Nonnull
        DataSource getDataSource() {
                return this.dataSource;
        }

        @Nonnull
        protected ReentrantLock getConnectionLock() {
                return this.connectionLock;
        }
}