/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * 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 android.database;

A convenience class that lets you present an array of Cursors as a single linear Cursor.
The schema of the cursors presented is entirely up to the creator of the MergeCursor, and
may be different if that is desired. Calls to getColumns, getColumnIndex, etc will return the
value for the row that the MergeCursor is currently pointing at.
/**
 * A convenience class that lets you present an array of Cursors as a single linear Cursor.
 * The schema of the cursors presented is entirely up to the creator of the MergeCursor, and
 * may be different if that is desired. Calls to getColumns, getColumnIndex, etc will return the
 * value for the row that the MergeCursor is currently pointing at.
 */
public class MergeCursor extends AbstractCursor
{
    private DataSetObserver mObserver = new DataSetObserver() {

        @Override
        public void onChanged() {
            // Reset our position so the optimizations in move-related code
            // don't screw us over
            mPos = -1;
        }

        @Override
        public void onInvalidated() {
            mPos = -1;
        }
    };
    
    public MergeCursor(Cursor[] cursors)
    {
        mCursors = cursors;
        mCursor = cursors[0];
        
        for (int i = 0; i < mCursors.length; i++) {
            if (mCursors[i] == null) continue;
            
            mCursors[i].registerDataSetObserver(mObserver);
        }
    }
    
    @Override
    public int getCount()
    {
        int count = 0;
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                count += mCursors[i].getCount();
            }
        }
        return count;
    }

    @Override
    public boolean onMove(int oldPosition, int newPosition)
    {
        /* Find the right cursor */
        mCursor = null;
        int cursorStartPos = 0;
        int length = mCursors.length;
        for (int i = 0 ; i < length; i++) {
            if (mCursors[i] == null) {
                continue;
            }
            
            if (newPosition < (cursorStartPos + mCursors[i].getCount())) {
                mCursor = mCursors[i];
                break;
            }

            cursorStartPos += mCursors[i].getCount();
        }

        /* Move it to the right position */
        if (mCursor != null) {
            boolean ret = mCursor.moveToPosition(newPosition - cursorStartPos);
            return ret;
        }
        return false;
    }

    @Override
    public String getString(int column)
    {
        return mCursor.getString(column);
    }

    @Override
    public short getShort(int column)
    {
        return mCursor.getShort(column);
    }

    @Override
    public int getInt(int column)
    {
        return mCursor.getInt(column);
    }

    @Override
    public long getLong(int column)
    {
        return mCursor.getLong(column);
    }

    @Override
    public float getFloat(int column)
    {
        return mCursor.getFloat(column);
    }

    @Override
    public double getDouble(int column)
    {
        return mCursor.getDouble(column);
    }

    @Override
    public int getType(int column) {
        return mCursor.getType(column);
    }

    @Override
    public boolean isNull(int column)
    {
        return mCursor.isNull(column);
    }

    @Override
    public byte[] getBlob(int column)
    {
        return mCursor.getBlob(column);   
    }

    @Override
    public String[] getColumnNames()
    {
        if (mCursor != null) {
            return mCursor.getColumnNames();
        } else {
            return new String[0];
        }
    }
    
    @Override
    public void deactivate()
    {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].deactivate();
            }
        }
        super.deactivate();
    }

    @Override
    public void close() {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] == null) continue;
            mCursors[i].close();
        }
        super.close();
    }

    @Override
    public void registerContentObserver(ContentObserver observer) {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].registerContentObserver(observer);
            }
        }
    }
    @Override
    public void unregisterContentObserver(ContentObserver observer) {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].unregisterContentObserver(observer);
            }
        }
    }
    
    @Override
    public void registerDataSetObserver(DataSetObserver observer) {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].registerDataSetObserver(observer);
            }
        }
    }
    
    @Override
    public void unregisterDataSetObserver(DataSetObserver observer) {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].unregisterDataSetObserver(observer);
            }
        }
    }

    @Override
    public boolean requery()
    {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] == null) {
                continue;
            }

            if (mCursors[i].requery() == false) {
                return false;
            }
        }

        return true;
    }

    private Cursor mCursor; // updated in onMove
    private Cursor[] mCursors;
}