Cursor.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.Generic;
using System.Linq;

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

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

            CursorInfo = cursorInfo;
            State = new CursorState(this);
        }

        ~Cursor() {
            Dispose(false);
        }

        public CursorInfo CursorInfo { get; private set; }

        public CursorStatus Status {
            get { return State.Status; }
        }

        public CursorState State { get; private set; }

        ObjectName IDbObject.FullName {
            get { return new ObjectName(CursorInfo.CursorName); }
        }

        DbObjectType IDbObject.ObjectType {
            get { return DbObjectType.Cursor; }
        }

        public SqlQueryExpression QueryExpression {
            get { return CursorInfo.QueryExpression; }
        }

        private void AssertNotDisposed() {
            if (Status == CursorStatus.Disposed)
                throw new ObjectDisposedException("Cursor");
        }

        private SqlQueryExpression PrepareQuery(SqlExpression[] args) {
            SqlQueryExpression query = CursorInfo.QueryExpression;
            if (CursorInfo.Parameters.Count > 0) {
                var cursorArgs = BuildArgs(CursorInfo.Parameters, args);
                var preparer = new CursorArgumentPreparer(cursorArgs);
                query = query.Prepare(preparer) as SqlQueryExpression;
            }

            return query;
        }

        private Dictionary<string, SqlExpression> BuildArgs(IEnumerable<CursorParameter> parameters, SqlExpression[] args) {
            var orderedParams = parameters.OrderBy(x => x.Offset).ToArray();
            if (args == null || args.Length != orderedParams.Length)
                throw new ArgumentException();

            var result = new Dictionary<string, SqlExpression>();
            for (int i = 0; i < orderedParams.Length; i++) {
                var param = orderedParams[i];
                var arg = args[i];
                result[param.ParameterName] = arg;
            }

            return result;
        }

        private ITable Evaluate(IRequest context, SqlExpression[] args) {
            try {
                var prepared = PrepareQuery(args);
                var queryPlan = context.Query.Context.QueryPlanner().PlanQuery(new QueryInfo(context, prepared));
                return queryPlan.Evaluate(context);
            } catch (Exception) {

                throw;
            }
        }

        public void Open(IRequest context, params SqlExpression[] args) {
            lock (this) {
                AssertNotDisposed();

                ITable result = null;
                if (CursorInfo.IsInsensitive)
                    result = Evaluate(context, args);

                State.Open(result, args);
            }
        }

        public void Close() {
            lock (this) {
                AssertNotDisposed();
                State.Close();
            }
        }

        public void FetchInto(FetchContext context) {
            if (context == null)
                throw new ArgumentNullException("context");

            if (!CursorInfo.IsScroll &&
                context.Direction != FetchDirection.Next)
                throw new ArgumentException(String.Format("Cursor '{0}' is not SCROLL: can fetch only NEXT value.", CursorInfo.CursorName));

            var table = State.Result;
            if (!CursorInfo.IsInsensitive)
                table = Evaluate(context.Request, State.OpenArguments);

            var fetchRow = State.FetchRowFrom(table, context.Direction, context.Offset);

            if (context.IsGlobalReference) {
                var reference = ((SqlReferenceExpression) context.Reference).ReferenceName;
                FetchIntoReference(context.Request, fetchRow, reference);
            } else if (context.IsVariableReference) {
                var varName = ((SqlVariableReferenceExpression) context.Reference).VariableName;
                FetchIntoVatiable(context.Request, fetchRow, varName);
            }
        }

        private void FetchIntoVatiable(IRequest request, Row row, string varName) {
            throw new NotImplementedException();
        }

        private void FetchIntoReference(IRequest request, Row row, ObjectName reference) {
            if (reference == null)
                throw new ArgumentNullException("reference");

            var table = request.Query.GetMutableTable(reference);
            if (table == null)
                throw new ObjectNotFoundException(reference);

            throw new NotImplementedException();
        }

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

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

            State = null;
        }

        #region CursorArgumentPreparer

        class CursorArgumentPreparer : IExpressionPreparer {
            private readonly Dictionary<string, SqlExpression> args;

            public CursorArgumentPreparer(Dictionary<string, SqlExpression> args) {
                this.args = args;
            }

            public bool CanPrepare(SqlExpression expression) {
                return expression is SqlVariableReferenceExpression;
            }

            public SqlExpression Prepare(SqlExpression expression) {
                var varRef = ((SqlVariableReferenceExpression) expression).VariableName;
                SqlExpression exp;
                if (!args.TryGetValue(varRef, out exp))
                    throw new ArgumentException(String.Format("Variable '{0}' was not found in the cursor arguments", varRef));

                return exp;
            }
        }

        #endregion
    }
}