ContextExtensions.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.Services;
using Deveel.Data.Sql.Expressions;
using Deveel.Data.Types;

namespace Deveel.Data.Sql.Variables {
    public static class ContextExtensions {
        public static Variable FindVariable(this IContext context, string variableName) {
            var currentContext = context;
            while (currentContext != null) {
                if (currentContext is IVariableScope) {
                    var scope = (IVariableScope) currentContext;
                    var variable = scope.GetVariable(variableName);
                    if (variable != null)
                        return variable;
                }

                currentContext = currentContext.Parent;
            }


            // not found in the hierarchy
            return null;
        }

        public static bool VariableExists(this IContext context, string variableName) {
            var currentContext = context;
            while (currentContext != null) {
                if (currentContext is IVariableScope) {
                    var scope = (IVariableScope)currentContext;
                    if (scope.HasVariable(variableName))
                        return true;
                }

                currentContext = currentContext.Parent;
            }


            // not found in the hierarchy
            return false;
        }

        public static bool DropVariable(this IContext context, string variableName) {
            var currentContext = context;
            while (currentContext != null) {
                if (currentContext is IVariableScope) {
                    var scope = (IVariableScope)currentContext;
                    if (scope.HasVariable(variableName))
                        return scope.DropVariable(variableName);
                }

                currentContext = currentContext.Parent;
            }


            // not found in the hierarchy
            return false;
        }

        public static Variable DeclareVariable(this IContext context, VariableInfo variableInfo) {
            if (context.VariableExists(variableInfo.VariableName))
                throw new InvalidOperationException(String.Format("Variable '{0}' already defined in the context hierarchy.", variableInfo.VariableName));

            var currentContext = context;
            while (currentContext != null) {
                if (currentContext is IVariableScope) {
                    var scope = (IVariableScope)currentContext;
                    return scope.DefineVariable(variableInfo);
                }

                currentContext = currentContext.Parent;
            }

            // not found in the hierarchy
            return null;
        }

        public static Variable DeclareVariable(this IContext context, string variableName, SqlType variableType) {
            return DeclareVariable(context, variableName, variableType, false);
        }

        public static Variable DeclareVariable(this IContext context, string variableName, SqlType variableType, bool constant) {
            return context.DeclareVariable(new VariableInfo(variableName, variableType, constant));
        }

        public static Variable SetVariable(this IContext context, string variableName, SqlExpression value) {
            var currentContext = context;
            while (currentContext != null) {
                if (currentContext is IVariableScope) {
                    var scope = (IVariableScope) currentContext;
                    if (scope.HasVariable(variableName)) {
                        // TODO: support also in-context evaluation
                        var constantValue = value.EvaluateToConstant(null, context.VariableResolver());
                        return scope.SetVariable(variableName, constantValue);
                    }
                }

                currentContext = currentContext.Parent;
            }

            currentContext = context;
            while (currentContext != null) {
                if (currentContext is IVariableScope) {
                    var scope = (IVariableScope)currentContext;
                        // TODO: support also in-context evaluation
                    var constantValue = value.EvaluateToConstant(null, context.VariableResolver());
                    return scope.SetVariable(variableName, constantValue);
                }

                currentContext = currentContext.Parent;
            }

            // not found in the hierarchy
            return null;
        }

        public static IVariableResolver VariableResolver(this IContext context) {
            return new ContextVariableResolver(context);
        }

        #region ContextVariableResolver

        class ContextVariableResolver : IVariableResolver, IDisposable {
            private IContext context;

            public ContextVariableResolver(IContext context) {
                this.context = context;
            }

            public DataObject Resolve(ObjectName variableName) {
                var variable = context.FindVariable(variableName.Name);
                if (variable == null)
                    return null;

                return variable.Value;
            }

            public SqlType ReturnType(ObjectName variableName) {
                var variable = context.FindVariable(variableName.Name);
                if (variable == null)
                    return null;

                return variable.Type;
            }

            public void Dispose() {
                context = null;
            }
        }

        #endregion
    }
}