LimitedTable.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 System.Collections;
using System.Collections.Generic;

namespace Deveel.Data.Sql.Tables {
    class LimitedTable : FilterTable {
        public long Offset { get; private set; }

        public long Total { get; private set; }

        public LimitedTable(ITable parent, long offset, long total) 
            : base(parent) {
            if (offset < 0)
                offset = 0;

            Offset = offset;
            Total = total;
        }

        private long NormalizeRow(long rowNumber) {
            rowNumber += Offset;
            return rowNumber;
        }

        private int NormalizeCount(long count) {
            count -= Offset;
            return (int) System.Math.Min(count, Total);
        }

        public override int RowCount {
            get { return NormalizeCount(base.RowCount); }
        }

        public override DataObject GetValue(long rowNumber, int columnOffset) {
            if (rowNumber >= RowCount)
                throw new ArgumentOutOfRangeException("rowNumber");

            return base.GetValue(NormalizeRow(rowNumber), columnOffset);
        }

        public override IEnumerator<Row> GetEnumerator() {
            return new Enumerator(this);
        }

        #region Enumerator

        class Enumerator : IEnumerator<Row> {
            private int offset = -1;
            private LimitedTable table;

            public Enumerator(LimitedTable table) {
                this.table = table;
            }

            public void Dispose() {
                table = null;
            }

            public bool MoveNext() {
                return ++offset < table.RowCount;
            }

            public void Reset() {
                offset = -1;
            }

            public Row Current {
                get { return table.GetRow(offset); }
            }

            object IEnumerator.Current {
                get { return Current; }
            }
        }

        #endregion
    }
}