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package com.github.obase.spring.transaction;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import javax.sql.DataSource;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.support.TransactionSynchronizationAdapter;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.util.Assert;

public abstract class DataSourceUtils {

	public static final int CONNECTION_SYNCHRONIZATION_ORDER = 1000;

	private static final Log logger = LogFactory.getLog(DataSourceUtils.class);

	public static Connection getConnection(DataSource dataSource) throws SQLException {
		try {
			return doGetConnection(dataSource);
		} catch (SQLException ex) {
			throw new SQLException("Could not get JDBC Connection", ex);
		}
	}

	public static Connection doGetConnection(DataSource dataSource) throws SQLException {
		Assert.notNull(dataSource, "No DataSource specified");

		ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
		if (conHolder != null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
			conHolder.requested();
			if (!conHolder.hasConnection()) {
				logger.debug("Fetching resumed JDBC Connection from DataSource");
				conHolder.setConnection(dataSource.getConnection());
			}
			return conHolder.getConnection();
		}
		// Else we either got no holder or an empty thread-bound holder here.
		logger.debug("Fetching JDBC Connection from DataSource");
		Connection con = dataSource.getConnection();

		if (TransactionSynchronizationManager.isSynchronizationActive()) {
			logger.debug("Registering transaction synchronization for JDBC Connection");
			// Use same Connection for further JDBC actions within the transaction.
			// Thread-bound object will get removed by synchronization at transaction completion.
			ConnectionHolder holderToUse = conHolder;
			if (holderToUse == null) {
				holderToUse = new ConnectionHolder(con);
			} else {
				holderToUse.setConnection(con);
			}
			holderToUse.requested();
			TransactionSynchronizationManager.registerSynchronization(new ConnectionSynchronization(holderToUse, dataSource));
			holderToUse.setSynchronizedWithTransaction(true);
			if (holderToUse != conHolder) {
				TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
			}
		}

		return con;

	}

	public static Integer prepareConnectionForTransaction(Connection con, TransactionDefinition definition) throws SQLException {

		Assert.notNull(con, "No Connection specified");

		// Set read-only flag.
		if (definition != null && definition.isReadOnly()) {
			try {
				if (logger.isDebugEnabled()) {
					logger.debug("Setting JDBC Connection [" + con + "] read-only");
				}
				con.setReadOnly(true);
			} catch (SQLException ex) {
				Throwable exToCheck = ex;
				while (exToCheck != null) {
					if (exToCheck.getClass().getSimpleName().contains("Timeout")) {
						// Assume it's a connection timeout that would otherwise get lost: e.g. from JDBC 4.0
						throw ex;
					}
					exToCheck = exToCheck.getCause();
				}
				// "read-only not supported" SQLException -> ignore, it's just a hint anyway
				logger.debug("Could not set JDBC Connection read-only", ex);
			} catch (RuntimeException ex) {
				Throwable exToCheck = ex;
				while (exToCheck != null) {
					if (exToCheck.getClass().getSimpleName().contains("Timeout")) {
						// Assume it's a connection timeout that would otherwise get lost: e.g. from Hibernate
						throw ex;
					}
					exToCheck = exToCheck.getCause();
				}
				// "read-only not supported" UnsupportedOperationException -> ignore, it's just a hint anyway
				logger.debug("Could not set JDBC Connection read-only", ex);
			}
		}

		// Apply specific isolation level, if any.
		Integer previousIsolationLevel = null;
		if (definition != null && definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
			if (logger.isDebugEnabled()) {
				logger.debug("Changing isolation level of JDBC Connection [" + con + "] to " + definition.getIsolationLevel());
			}
			int currentIsolation = con.getTransactionIsolation();
			if (currentIsolation != definition.getIsolationLevel()) {
				previousIsolationLevel = currentIsolation;
				con.setTransactionIsolation(definition.getIsolationLevel());
			}
		}

		return previousIsolationLevel;
	}

	public static void resetConnectionAfterTransaction(Connection con, Integer previousIsolationLevel) {
		Assert.notNull(con, "No Connection specified");
		try {
			// Reset transaction isolation to previous value, if changed for the transaction.
			if (previousIsolationLevel != null) {
				if (logger.isDebugEnabled()) {
					logger.debug("Resetting isolation level of JDBC Connection [" + con + "] to " + previousIsolationLevel);
				}
				con.setTransactionIsolation(previousIsolationLevel);
			}

			// Reset read-only flag.
			if (con.isReadOnly()) {
				if (logger.isDebugEnabled()) {
					logger.debug("Resetting read-only flag of JDBC Connection [" + con + "]");
				}
				con.setReadOnly(false);
			}
		} catch (Throwable ex) {
			logger.debug("Could not reset JDBC Connection after transaction", ex);
		}
	}

	public static boolean isConnectionTransactional(Connection con, DataSource dataSource) {
		if (dataSource == null) {
			return false;
		}
		ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
		return (conHolder != null && connectionEquals(conHolder, con));
	}

	public static void applyTransactionTimeout(Statement stmt, DataSource dataSource) throws SQLException {
		applyTimeout(stmt, dataSource, -1);
	}

	public static void applyTimeout(Statement stmt, DataSource dataSource, int timeout) throws SQLException {
		Assert.notNull(stmt, "No Statement specified");
		Assert.notNull(dataSource, "No DataSource specified");
		ConnectionHolder holder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
		if (holder != null && holder.hasTimeout()) {
			// Remaining transaction timeout overrides specified value.
			stmt.setQueryTimeout(holder.getTimeToLiveInSeconds());
		} else if (timeout >= 0) {
			// No current transaction timeout -> apply specified value.
			stmt.setQueryTimeout(timeout);
		}
	}

	public static void releaseConnection(Connection con, DataSource dataSource) {
		try {
			doReleaseConnection(con, dataSource);
		} catch (SQLException ex) {
			logger.debug("Could not close JDBC Connection", ex);
		} catch (Throwable ex) {
			logger.debug("Unexpected exception on closing JDBC Connection", ex);
		}
	}

	public static void doReleaseConnection(Connection con, DataSource dataSource) throws SQLException {
		if (con == null) {
			return;
		}
		if (dataSource != null) {
			ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
			if (conHolder != null && connectionEquals(conHolder, con)) {
				// It's the transactional Connection: Don't close it.
				conHolder.released();
				return;
			}
		}
		logger.debug("Returning JDBC Connection to DataSource");
		con.close();
	}

	private static boolean connectionEquals(ConnectionHolder conHolder, Connection passedInCon) {
		if (!conHolder.hasConnection()) {
			return false;
		}
		Connection heldCon = conHolder.getConnection();
		// Explicitly check for identity too: for Connection handles that do not implement
		// "equals" properly, such as the ones Commons DBCP exposes).
		return (heldCon == passedInCon || heldCon.equals(passedInCon));
	}

	private static class ConnectionSynchronization extends TransactionSynchronizationAdapter {

		private final ConnectionHolder connectionHolder;

		private final DataSource dataSource;

		private int order;

		private boolean holderActive = true;

		public ConnectionSynchronization(ConnectionHolder connectionHolder, DataSource dataSource) {
			this.connectionHolder = connectionHolder;
			this.dataSource = dataSource;
			this.order = CONNECTION_SYNCHRONIZATION_ORDER;
		}

		@Override
		public int getOrder() {
			return this.order;
		}

		@Override
		public void suspend() {
			if (this.holderActive) {
				TransactionSynchronizationManager.unbindResource(this.dataSource);
				if (this.connectionHolder.hasConnection() && !this.connectionHolder.isOpen()) {
					// Release Connection on suspend if the application doesn't keep
					// a handle to it anymore. We will fetch a fresh Connection if the
					// application accesses the ConnectionHolder again after resume,
					// assuming that it will participate in the same transaction.
					releaseConnection(this.connectionHolder.getConnection(), this.dataSource);
					this.connectionHolder.setConnection(null);
				}
			}
		}

		@Override
		public void resume() {
			if (this.holderActive) {
				TransactionSynchronizationManager.bindResource(this.dataSource, this.connectionHolder);
			}
		}

		@Override
		public void beforeCompletion() {
			// Release Connection early if the holder is not open anymore
			// (that is, not used by another resource like a Hibernate Session
			// that has its own cleanup via transaction synchronization),
			// to avoid issues with strict JTA implementations that expect
			// the close call before transaction completion.
			if (!this.connectionHolder.isOpen()) {
				TransactionSynchronizationManager.unbindResource(this.dataSource);
				this.holderActive = false;
				if (this.connectionHolder.hasConnection()) {
					releaseConnection(this.connectionHolder.getConnection(), this.dataSource);
				}
			}
		}

		@Override
		public void afterCompletion(int status) {
			// If we haven't closed the Connection in beforeCompletion,
			// close it now. The holder might have been used for other
			// cleanup in the meantime, for example by a Hibernate Session.
			if (this.holderActive) {
				// The thread-bound ConnectionHolder might not be available anymore,
				// since afterCompletion might get called from a different thread.
				TransactionSynchronizationManager.unbindResourceIfPossible(this.dataSource);
				this.holderActive = false;
				if (this.connectionHolder.hasConnection()) {
					releaseConnection(this.connectionHolder.getConnection(), this.dataSource);
					// Reset the ConnectionHolder: It might remain bound to the thread.
					this.connectionHolder.setConnection(null);
				}
			}
			this.connectionHolder.reset();
		}
	}

}