/*
 * 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.apache.jena.dboe.transaction.txn;

import java.util.Objects;

import org.apache.jena.atlas.lib.Lib;
import org.apache.jena.atlas.logging.Log;
import org.apache.jena.dboe.transaction.Transactional;
import org.apache.jena.query.ReadWrite;
import org.apache.jena.query.TxnType;

/**
 * Framework for implementing a {@link Transactional} via {@link TransactionalSystem}.
 * This base class provides the "per thread" aspect - the {@link TransactionCoordinator} itself
 * is not thread aware.
 */
public class TransactionalBase implements TransactionalSystem {
    // Optional labelling - development/debugging aid.
    private final String label;
    protected boolean isShutdown = false;
    protected final TransactionCoordinator txnMgr;

    // Per thread transaction.
    private final ThreadLocal<Transaction> theTxn = new ThreadLocal<>();

    public TransactionalBase(String label, TransactionCoordinator txnMgr) {
        this.label = label;
        this.txnMgr = txnMgr;
    }

    public TransactionalBase(TransactionCoordinator txnMgr) {
        this(null, txnMgr);
    }

    @Override
    public TransactionCoordinator getTxnMgr() {
        return txnMgr;
    }

    // Development
    private static final boolean trackAttachDetach = false;

    @Override
    public TransactionCoordinatorState detach() {
        if ( trackAttachDetach )
            Log.info(this,  ">> detach");
        checkRunning();
        // Not if it just commited but before end.
        //checkActive();
        Transaction txn = theTxn.get();
        TransactionCoordinatorState coordinatorState = null;
        if ( txn != null )
            // We are not ending.
            coordinatorState = txnMgr.detach(txn);
        if ( trackAttachDetach )
            Log.info(this,  "  theTxn = "+txn);
        theTxn.remove(); ///??????
        if ( trackAttachDetach )
            Log.info(this,  "<< detach");
        if ( coordinatorState == null )
            throw new TransactionException("Not attached");
        return coordinatorState;
    }

    @Override
    public void attach(TransactionCoordinatorState coordinatorState) {
        if ( trackAttachDetach )
            Log.info(this,  ">> attach");
        Objects.nonNull(coordinatorState);
        checkRunning();
        checkNotActive();
        TxnState txnState = coordinatorState.transaction.getState();
        if ( txnState != TxnState.DETACHED )
            throw new TransactionException("Not a detached transaction");
        txnMgr.attach(coordinatorState);
        if ( trackAttachDetach )
            Log.info(this,  "  theTxn = "+coordinatorState.transaction);
        theTxn.set(coordinatorState.transaction);
        if ( trackAttachDetach )
            Log.info(this,  "<< attach");
    }

    @Override
    public final void begin(ReadWrite readWrite) {
        begin(TxnType.convert(readWrite));
    }

    @Override
    public final void begin(TxnType txnType) {
        Objects.nonNull(txnType);
        checkRunning();
        checkNotActive();
        Transaction transaction = txnMgr.begin(txnType);
        theTxn.set(transaction);
    }

    @Override
    public final boolean promote() {
        checkActive();
        return TransactionalSystem.super.promote();
    }

    @Override
    public final boolean promote(Promote promoteMode) {
        checkActive();
        boolean readCommitted = (promoteMode == Promote.READ_COMMITTED);
        Transaction txn = getValidTransaction();
        return txn.promote(readCommitted);
    }

    @Override
    public final void commit() {
        checkRunning();
        TransactionalSystem.super.commit();
    }

    @Override
    public void commitPrepare() {
        Transaction txn = getValidTransaction();
        txn.prepare();
    }

    @Override
    public void commitExec() {
        Transaction txn = getValidTransaction();
        try { txn.commit(); }
        finally { _end(); }
    }

//    /** Signal end of commit phase */
//    @Override
//    public void commitEnd() {
//        _end();
//    }

    @Override
    public final void abort() {
        checkRunning();
        checkActive();
        Transaction txn = getValidTransaction();
        try { txn.abort(); }
        finally { _end(); }
    }

    @Override
    public final void end() {
        checkRunning();
        // Don't check if active or if any thread locals exist
        // because this may have already been called.
        // txn.get(); -- may be null -- test repeat calls.
        _end();
    }

    @Override
    public ReadWrite transactionMode() {
        checkRunning();
        Transaction txn = Lib.readThreadLocal(theTxn);
        if ( txn != null )
            return txn.getMode();
        return null;
    }

    @Override
    public TxnType transactionType() {
        checkRunning();
        Transaction txn = Lib.readThreadLocal(theTxn);
        if ( txn != null )
            return txn.getTxnType();
        return null;
    }

    @Override
    public boolean isInTransaction() {
        return Lib.readThreadLocal(theTxn) != null;
    }

    @Override
    final
    public TransactionInfo getTransactionInfo() {
        return getThreadTransaction();
    }

    @Override
    final
    public Transaction getThreadTransaction() {
        return  Lib.readThreadLocal(theTxn);
    }

    /** Get the transaction, checking there is one */
    private Transaction getValidTransaction() {
        Transaction txn = theTxn.get();
        if ( txn == null )
            throw new TransactionException("Not in a transaction");
        return txn;
    }

    private void checkRunning() {
//        if ( ! hasStarted )
//            throw new TransactionException("Not started");

        if ( isShutdown )
            throw new TransactionException("Shutdown");
    }

    /**
     * Shutdown component, aborting any in-progress transactions. This operation
     * is not guaranteed to be called.
     */
    public void shutdown() {
        txnMgr.shutdown();
        isShutdown = true;
    }

    protected String label(String msg) {
        if ( label == null )
            return msg;
        return label+": "+msg;
    }

    final
    protected void checkActive() {
        checkNotShutdown();
        if ( ! isInTransaction() )
            throw new TransactionException(label("Not in an active transaction"));
    }

    final
    protected void checkNotActive() {
        checkNotShutdown();
        if ( isInTransaction() )
            throw new TransactionException(label("Currently in an active transaction"));
    }

    final
    protected void checkNotShutdown() {
        if ( isShutdown )
            throw new TransactionException(label("Already shutdown"));
    }

    private final void _end() {
        Transaction txn = theTxn.get();
        if ( txn != null ) {
            try {
                // Can throw an exception on begin(W)...end().
                txn.end();
            } finally {
                // Makes this "call txn.end" once-only.
                theTxn.set(null);
                theTxn.remove();
            }
        }
    }
}

