/*
 * Copyright 2004-2014 H2 Group. Multiple-Licensed under the MPL 2.0,
 * and the EPL 1.0 (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */
package org.h2.schema;

import java.math.BigInteger;
import org.h2.api.ErrorCode;
import org.h2.engine.DbObject;
import org.h2.engine.Session;
import org.h2.message.DbException;
import org.h2.message.Trace;
import org.h2.table.Table;

/**
 * A sequence is created using the statement
 * CREATE SEQUENCE
 */
public class Sequence extends SchemaObjectBase {

    /**
     * The default cache size for sequences.
     */
    public static final int DEFAULT_CACHE_SIZE = 32;

    private long value;
    private long valueWithMargin;
    private long increment;
    private long cacheSize;
    private long minValue;
    private long maxValue;
    private boolean cycle;
    private boolean belongsToTable;
    private final Object flushSync = new Object();
    private boolean writeWithMargin;

    /**
     * Creates a new sequence for an auto-increment column.
     *
     * @param schema the schema
     * @param id the object id
     * @param name the sequence name
     * @param startValue the first value to return
     * @param increment the increment count
     */
    public Sequence(Schema schema, int id, String name, long startValue,
            long increment) {
        this(schema, id, name, startValue, increment, null, null, null, false,
                true);
    }

    /**
     * Creates a new sequence.
     *
     * @param schema the schema
     * @param id the object id
     * @param name the sequence name
     * @param startValue the first value to return
     * @param increment the increment count
     * @param cacheSize the number of entries to pre-fetch
     * @param minValue the minimum value
     * @param maxValue the maximum value
     * @param cycle whether to jump back to the min value if needed
     * @param belongsToTable whether this sequence belongs to a table (for
     *            auto-increment columns)
     */
    public Sequence(Schema schema, int id, String name, Long startValue,
            Long increment, Long cacheSize, Long minValue, Long maxValue,
            boolean cycle, boolean belongsToTable) {
        initSchemaObjectBase(schema, id, name, Trace.SEQUENCE);
        this.increment = increment != null ?
                increment : 1;
        this.minValue = minValue != null ?
                minValue : getDefaultMinValue(startValue, this.increment);
        this.maxValue = maxValue != null ?
                maxValue : getDefaultMaxValue(startValue, this.increment);
        this.value = startValue != null ?
                startValue : getDefaultStartValue(this.increment);
        this.valueWithMargin = value;
        this.cacheSize = cacheSize != null ?
                Math.max(1, cacheSize) : DEFAULT_CACHE_SIZE;
        this.cycle = cycle;
        this.belongsToTable = belongsToTable;
        if (!isValid(this.value, this.minValue, this.maxValue, this.increment)) {
            throw DbException.get(ErrorCode.SEQUENCE_ATTRIBUTES_INVALID, name,
                    String.valueOf(this.value), String.valueOf(this.minValue),
                    String.valueOf(this.maxValue),
                    String.valueOf(this.increment));
        }
    }

    /**
     * Allows the start value, increment, min value and max value to be updated
     * atomically, including atomic validation. Useful because setting these
     * attributes one after the other could otherwise result in an invalid
     * sequence state (e.g. min value > max value, start value < min value,
     * etc).
     *
     * @param startValue the new start value (<code>null</code> if no change)
     * @param minValue the new min value (<code>null</code> if no change)
     * @param maxValue the new max value (<code>null</code> if no change)
     * @param increment the new increment (<code>null</code> if no change)
     */
    public synchronized void modify(Long startValue, Long minValue,
            Long maxValue, Long increment) {
        if (startValue == null) {
            startValue = this.value;
        }
        if (minValue == null) {
            minValue = this.minValue;
        }
        if (maxValue == null) {
            maxValue = this.maxValue;
        }
        if (increment == null) {
            increment = this.increment;
        }
        if (!isValid(startValue, minValue, maxValue, increment)) {
            throw DbException.get(ErrorCode.SEQUENCE_ATTRIBUTES_INVALID,
                    getName(), String.valueOf(startValue),
                    String.valueOf(minValue),
                    String.valueOf(maxValue),
                    String.valueOf(increment));
        }
        this.value = startValue;
        this.valueWithMargin = startValue;
        this.minValue = minValue;
        this.maxValue = maxValue;
        this.increment = increment;
    }

    /**
     * Validates the specified prospective start value, min value, max value and
     * increment relative to each other, since each of their respective
     * validities are contingent on the values of the other parameters.
     *
     * @param value the prospective start value
     * @param minValue the prospective min value
     * @param maxValue the prospective max value
     * @param increment the prospective increment
     */
    private static boolean isValid(long value, long minValue, long maxValue,
            long increment) {
        return minValue <= value &&
            maxValue >= value &&
            maxValue > minValue &&
            increment != 0 &&
            // Math.abs(increment) < maxValue - minValue
            // use BigInteger to avoid overflows when maxValue and minValue
            // are really big
            BigInteger.valueOf(increment).abs().compareTo(
                    BigInteger.valueOf(maxValue).subtract(BigInteger.valueOf(minValue))) < 0;
    }

    private static long getDefaultMinValue(Long startValue, long increment) {
        long v = increment >= 0 ? 1 : Long.MIN_VALUE;
        if (startValue != null && increment >= 0 && startValue < v) {
            v = startValue;
        }
        return v;
    }

    private static long getDefaultMaxValue(Long startValue, long increment) {
        long v = increment >= 0 ? Long.MAX_VALUE : -1;
        if (startValue != null && increment < 0 && startValue > v) {
            v = startValue;
        }
        return v;
    }

    private long getDefaultStartValue(long increment) {
        return increment >= 0 ? minValue : maxValue;
    }

    public boolean getBelongsToTable() {
        return belongsToTable;
    }

    public long getIncrement() {
        return increment;
    }

    public long getMinValue() {
        return minValue;
    }

    public long getMaxValue() {
        return maxValue;
    }

    public boolean getCycle() {
        return cycle;
    }

    public void setCycle(boolean cycle) {
        this.cycle = cycle;
    }

    @Override
    public String getDropSQL() {
        if (getBelongsToTable()) {
            return null;
        }
        return "DROP SEQUENCE IF EXISTS " + getSQL();
    }

    @Override
    public String getCreateSQLForCopy(Table table, String quotedName) {
        throw DbException.throwInternalError(toString());
    }

    @Override
    public synchronized String getCreateSQL() {
        long v = writeWithMargin ? valueWithMargin : value;
        StringBuilder buff = new StringBuilder("CREATE SEQUENCE ");
        buff.append(getSQL()).append(" START WITH ").append(v);
        if (increment != 1) {
            buff.append(" INCREMENT BY ").append(increment);
        }
        if (minValue != getDefaultMinValue(v, increment)) {
            buff.append(" MINVALUE ").append(minValue);
        }
        if (maxValue != getDefaultMaxValue(v, increment)) {
            buff.append(" MAXVALUE ").append(maxValue);
        }
        if (cycle) {
            buff.append(" CYCLE");
        }
        if (cacheSize != DEFAULT_CACHE_SIZE) {
            buff.append(" CACHE ").append(cacheSize);
        }
        if (belongsToTable) {
            buff.append(" BELONGS_TO_TABLE");
        }
        return buff.toString();
    }

    /**
     * Get the next value for this sequence.
     *
     * @param session the session
     * @return the next value
     */
    public long getNext(Session session) {
        boolean needsFlush = false;
        long result;
        synchronized (this) {
            if ((increment > 0 && value >= valueWithMargin) ||
                    (increment < 0 && value <= valueWithMargin)) {
                valueWithMargin += increment * cacheSize;
                needsFlush = true;
            }
            if ((increment > 0 && value > maxValue) ||
                    (increment < 0 && value < minValue)) {
                if (cycle) {
                    value = increment > 0 ? minValue : maxValue;
                    valueWithMargin = value + (increment * cacheSize);
                    needsFlush = true;
                } else {
                    throw DbException.get(ErrorCode.SEQUENCE_EXHAUSTED, getName());
                }
            }
            result = value;
            value += increment;
        }
        if (needsFlush) {
            flush(session);
        }
        return result;
    }

    /**
     * Flush the current value to disk.
     */
    public void flushWithoutMargin() {
        if (valueWithMargin != value) {
            valueWithMargin = value;
            flush(null);
        }
    }

    /**
     * Flush the current value, including the margin, to disk.
     *
     * @param session the session
     */
    public void flush(Session session) {
        if (isTemporary()) {
            return;
        }
        if (session == null || !database.isSysTableLockedBy(session)) {
            // This session may not lock the sys table (except if it has already
            // locked it) because it must be committed immediately, otherwise
            // other threads can not access the sys table.
            Session sysSession = database.getSystemSession();
            synchronized (database.isMultiThreaded() ?  sysSession : database) {
                flushInternal(sysSession);
                sysSession.commit(false);
            }
        } else {
            synchronized (database.isMultiThreaded() ? session : database) {
                flushInternal(session);
            }
        }
    }

    private void flushInternal(Session session) {
        synchronized (flushSync) {
            final boolean metaWasLocked = database.lockMeta(session);
            // just for this case, use the value with the margin
            try {
                writeWithMargin = true;
                database.updateMeta(session, this);
            } finally {
                writeWithMargin = false;
            }
            if (!metaWasLocked) {
                database.unlockMeta(session);
            }
        }
    }

    /**
     * Flush the current value to disk and close this object.
     */
    public void close() {
        flushWithoutMargin();
    }

    @Override
    public int getType() {
        return DbObject.SEQUENCE;
    }

    @Override
    public void removeChildrenAndResources(Session session) {
        database.removeMeta(session, getId());
        invalidate();
    }

    @Override
    public void checkRename() {
        // nothing to do
    }

    public synchronized long getCurrentValue() {
        return value - increment;
    }

    public void setBelongsToTable(boolean b) {
        this.belongsToTable = b;
    }

    public void setCacheSize(long cacheSize) {
        this.cacheSize = Math.max(1, cacheSize);
    }

    public long getCacheSize() {
        return cacheSize;
    }

}
