CursorState.cs

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// 
//  Copyright 2010-2015 Deveel
// 
//    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.
//

using System;

using Deveel.Data.Sql.Expressions;
using Deveel.Data.Sql.Tables;

namespace Deveel.Data.Sql.Cursors {
    public sealed class CursorState : IDisposable {
        internal CursorState(Cursor cursor) {
            if (cursor == null)
                throw new ArgumentNullException("cursor");

            Cursor = cursor;
        }

        ~CursorState() {
            Dispose(false);
        }

        public Cursor Cursor { get; private set; }

        public CursorStatus Status { get; private set; }

        public SqlExpression[] OpenArguments { get; private set; }

        internal ITable Result { get; private set; }

        private int CurrentOffset { get; set; }

        internal void Open(ITable result, SqlExpression[] args) {
            Status = CursorStatus.Open;
            Result = result;
            OpenArguments = args;
        }

        internal void Close() {
            Status = CursorStatus.Closed;
            OpenArguments = null;
        }

        internal Row FetchRowFrom(ITable table, FetchDirection direction, int offset) {
            int rowOffset;
            if (direction == FetchDirection.Next) {
                rowOffset = CurrentOffset + 1;
            } else if (direction == FetchDirection.Prior) {
                rowOffset = CurrentOffset - 1;
            } else if (direction == FetchDirection.First) {
                rowOffset = CurrentOffset = 0;
            } else if (direction == FetchDirection.Last) {
                rowOffset = table.RowCount;
            } else if (direction == FetchDirection.Absolute) {
                rowOffset = offset;
            } else if (direction == FetchDirection.Relative) {
                rowOffset = CurrentOffset + offset;
            } else {
                // Should never happen
                throw new InvalidOperationException();
            }

            if (rowOffset < 0 || rowOffset >= table.RowCount)
                throw new IndexOutOfRangeException(
                    String.Format("The fetch offset '{0}' is smaller than zero or greater than the result set ({1}).", rowOffset,
                        table.RowCount));

            CurrentOffset = rowOffset;
            Status = CursorStatus.Fetching;

            return table.GetRow(rowOffset);
        }

        public void Dispose() {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        private void Dispose(bool disposing) {
            if (disposing) {
                if (Result != null)
                    Result.Dispose();
            }

            Result = null;
            Cursor = null;
            Status = CursorStatus.Disposed;
        }
    }
}