Android Open Source - interdroid-vdb Three Way Diff Cursor

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Copyright (c) 2008-2012 Vrije Universiteit, The Netherlands All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the follo...
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Java Source Code

/*
 * Copyright (c) 2008-2012 Vrije Universiteit, The Netherlands All rights
 * reserved./*from  ww w . j a va2 s  . c  o  m*/
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the Vrije Universiteit nor the names of its contributors
 * may be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package interdroid.vdb.persistence.impl;

import interdroid.vdb.persistence.impl.MergeHelper.Database;
import interdroid.vdb.persistence.impl.MergeHelper.DiffResult;
import interdroid.vdb.persistence.impl.MergeHelper.TableMetadata;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

/**
 * A cursor for managing a three way diff.
 *
 * @author nick &lt;palmer@cs.vu.nl&gt;
 *
 */
public class ThreeWayDiffCursor {
  /**
   * The metadata for the table.
   */
  private TableMetadata mTableInfo;
  /**
   * Cursor for theirs vs base.
   */
  private Cursor mTheirs;
  /**
   * Cursor for ours vs base.
   */
  private Cursor mOurs;

  /**
   * This cursor will be used for extracting the row primary key values.
   * If null then there is no current row.
   */
  private Cursor mRow;

  /**
   * If the rowCursor is not null then these will hold the diff result
   * for the current row for our side of the diff.
   */
  private DiffResult mRowStateOurs;
  /**
   * If the rowCursor is not null then these will hold the diff result
   * for the current row for their side of the diff.
   */
  private DiffResult mRowStateTheirs;

  /**
   * Cache the column indexes for the diff result column for our side.
   */
  private int mIndexOursDiffState;
  /**
   * Cache the column indexes for the diff result column for their side.
   */
  private int mIndexTheirsDiffState;

  /**
   * Construct a three way diff cursor.
   * @param helper the merge helper we work inside
   * @param db the database with tables
   * @param table the table we are to merge.
   */
  public ThreeWayDiffCursor(final MergeHelper helper, final SQLiteDatabase db,
      final String table) {
    mTableInfo = helper.getTableMetadata(db, table);
    mTheirs = helper.diff2(db, table, Database.BASE, Database.THEIRS);
    mOurs = helper.diff2(db, table, Database.BASE, Database.OURS);
    mIndexOursDiffState = mOurs.getColumnIndexOrThrow(
        MergeHelper.COL_DIFF_RESULT);
    mIndexTheirsDiffState = mTheirs.getColumnIndexOrThrow(
        MergeHelper.COL_DIFF_RESULT);
  }

  /**
   * Looks for the smallest primary key in the two cursors.
   */
  private void pickSmallestRow() {
    boolean haveTheirs = !mTheirs.isAfterLast()
        && !mTheirs.isBeforeFirst();
    boolean haveOurs   = !mOurs.isAfterLast()
        && !mOurs.isBeforeFirst();
    if (!haveTheirs && !haveOurs) {
      mRow = null;
      return;
    }
    if (haveTheirs && haveOurs) {
      /**
       * Since we are merging, we have to iterate on the pk columns in the
       * same order as the ORDER BY statement in
       * {@link MergeHelper#diff2}.
       **/
      for (int i = 0; i < mTableInfo.mKeyFields.size(); ++i) {
        // TODO: (emilian) rewrite me with strings too
        long ourLong = mOurs.getLong(i);
        long theirLong = mTheirs.getLong(i);

        if (ourLong < theirLong) {
          haveTheirs = false;
          break;
        }
        if (theirLong < ourLong) {
          haveOurs = false;
          break;
        }
      }
    }
    if (haveOurs) {
      mRowStateOurs = DiffResult.SAME;
      mRowStateTheirs = DiffResult.SAME;
    } else {
      mRowStateOurs = DiffResult.valueOf(
          mTheirs.getString(mIndexOursDiffState));
      mRowStateTheirs = DiffResult.valueOf(
          mTheirs.getString(mIndexTheirsDiffState));
    }

  }

  /**
   * Moves both cursors to first and picks the smallest primary key.
   * @return true if the move worked
   */
  public final boolean moveToFirst() {
    mTheirs.moveToFirst();
    mOurs.moveToFirst();
    pickSmallestRow();

    if (mRow != null) {
      return true;
    }
    return false;
  }

  /**
   * Move to the next row.
   * @return true if the move worked.
   */
  public final boolean moveToNext() {
    if (mRow == null) { // already past end
      return false;
    }
    if (!DiffResult.SAME.equals(mRowStateOurs)) {
      mOurs.moveToNext();
    }
    if (!DiffResult.SAME.equals(mRowStateTheirs)) {
      mTheirs.moveToNext();
    }
    if (mRow != null) {
      return true;
    }
    return false;
  }

  /**
   * Checks that we are on a valid row.
   */
  private void checkValidRow() {
    if (mRow == null) {
      throw new IllegalStateException(
          "Do not query the cursor when there are no more rows.");
    }
  }

  /**
   * @return the state of their side.
   */
  public final DiffResult getStateTheirs() {
    checkValidRow();
    return mRowStateTheirs;
  }

  /**
   * @return the state of our side.
   */
  public final DiffResult getStateOurs() {
    checkValidRow();
    return mRowStateOurs;
  }

  /**
   * @return their side cursor
   */
  public final Cursor getTheirsCursor() {
    return mTheirs;
  }

  /**
   * @return our side cursor
   */
  public final Cursor getOursCursor() {
    return mOurs;
  }
}
Java Source Code List
