ExpressionEvaluatorVisitor.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;
using Deveel.Data.Routines;
using Deveel.Data.Sql.Objects;
using Deveel.Data.Sql.Query;
using Deveel.Data.Sql.Variables;
using Deveel.Data.Types;

namespace Deveel.Data.Sql.Expressions {
    class ExpressionEvaluatorVisitor : SqlExpressionVisitor {
        private readonly EvaluateContext context;

        public ExpressionEvaluatorVisitor(EvaluateContext context) {
            this.context = context;
        }

        public override SqlExpression Visit(SqlExpression expression) {
            if (expression is QueryReferenceExpression)
                return VisitQueryReference((QueryReferenceExpression) expression);

            return base.Visit(expression);
        }

        private SqlExpression VisitQueryReference(QueryReferenceExpression expression) {
            var reference = expression.QueryReference;
            var value = reference.Evaluate(context.VariableResolver);
            return SqlExpression.Constant(value);
        }

        private SqlExpression[] EvaluateSides(SqlBinaryExpression binary) {
            var info = new List<BinaryEvaluateInfo> {
                new BinaryEvaluateInfo {Expression = binary.Left, Offset = 0},
                new BinaryEvaluateInfo {Expression = binary.Right, Offset = 1}
            }.OrderByDescending(x => x.Precedence);

            foreach (var evaluateInfo in info) {
                evaluateInfo.Expression = Visit(evaluateInfo.Expression);
            }

            return info.OrderBy(x => x.Offset)
                .Select(x => x.Expression)
                .ToArray();
        }

        private SqlExpression EvaluateBinary(SqlExpression left, SqlExpressionType binaryType, SqlExpression right) {
            if (left.ExpressionType != SqlExpressionType.Constant)
                throw new ExpressionEvaluateException("The evaluated left side of a binary expression is not constant");
            if (right.ExpressionType != SqlExpressionType.Constant)
                throw new ExpressionEvaluateException("The evaluated right side of a binary expression is not constant.");

            var value1 = ((SqlConstantExpression) left).Value;
            var value2 = ((SqlConstantExpression) right).Value;

            var result = EvaluateBinary(value1, binaryType, value2);

            return SqlExpression.Constant(result);
        }

        private DataObject EvaluateBinary(DataObject left, SqlExpressionType binaryType, DataObject right) {
            if (binaryType.IsAll())
                return left.Any(binaryType.SubQueryPlainType(), right, context);
            if (binaryType.IsAny())
                return left.All(binaryType.SubQueryPlainType(), right, context);

            switch (binaryType) {
                case SqlExpressionType.Add:
                    return left.Add(right);
                case SqlExpressionType.Subtract:
                    return left.Subtract(right);
                case SqlExpressionType.Multiply:
                    return left.Multiply(right);
                case SqlExpressionType.Divide:
                    return left.Divide(right);
                case SqlExpressionType.Modulo:
                    return left.Modulus(right);
                case SqlExpressionType.GreaterThan:
                    return left.IsGreaterThan(right);
                case SqlExpressionType.GreaterOrEqualThan:
                    return left.IsGreterOrEqualThan(right);
                case SqlExpressionType.SmallerThan:
                    return left.IsSmallerThan(right);
                case SqlExpressionType.SmallerOrEqualThan:
                    return left.IsSmallerOrEqualThan(right);
                case SqlExpressionType.Equal:
                    return left.IsEqualTo(right);
                case SqlExpressionType.NotEqual:
                    return left.IsNotEqualTo(right);
                case SqlExpressionType.Is:
                    return left.Is(right);
                case SqlExpressionType.IsNot:
                    return left.IsNot(right);
                case SqlExpressionType.Like:
                    return left.IsLike(right);
                case SqlExpressionType.NotLike:
                    return left.IsNotLike(right);
                case SqlExpressionType.And:
                    return left.And(right);
                case SqlExpressionType.Or:
                    return left.Or(right);
                case SqlExpressionType.XOr:
                    return left.XOr(right);
                // TODO: ANY and ALL
                default:
                    throw new ExpressionEvaluateException(String.Format("The type {0} is not a binary expression or is not supported.", binaryType));
            }
        }

        public override SqlExpression VisitBinary(SqlBinaryExpression binaryEpression) {
            var sides = EvaluateSides(binaryEpression);

            var newLeft = sides[0];
            var newRight = sides[1];

            return EvaluateBinary(newLeft, binaryEpression.ExpressionType, newRight);
        }

        public override SqlExpression VisitCast(SqlCastExpression castExpression) {
            var valueExp = Visit(castExpression.Value);
            if (valueExp.ExpressionType != SqlExpressionType.Constant)
                throw new ExpressionEvaluateException(String.Format("Cannot CAST an expression of type {0}.", valueExp.ExpressionType));

            var value = ((SqlConstantExpression) valueExp).Value;
            var casted = value.CastTo(castExpression.SqlType);
            return SqlExpression.Constant(casted);
        }

        //public override SqlExpression VisitConstant(SqlConstantExpression constant) {
        //  var value = constant.Value;
        //  if (value.IsNull)
        //      return constant;

        //  var obj = value.Value;
        //  if (obj is SqlQueryObject) {
        //      return EvaluateQueryPlan((SqlQueryObject) obj);
        //  }

        //  return base.VisitConstant(constant);
        //}

        //private SqlConstantExpression EvaluateQueryPlan(SqlQueryObject obj) {
        //  if (context.QueryContext == null)
        //      throw new ExpressionEvaluateException("A query context is required to evaluate a query.");

        //  try {
        //      var plan = obj.QueryPlan;
        //      var result = plan.Evaluate(context.QueryContext);

        //      return SqlExpression.Constant(new DataObject(new TabularType(), SqlTabular.From(result)));
        //  } catch (ExpressionEvaluateException) {
        //      throw;
        //  } catch (Exception ex) {
        //      throw new ExpressionEvaluateException("Could not evaluate a query.", ex);
        //  }
        //}

        public override SqlExpression VisitFunctionCall(SqlFunctionCallExpression expression) {
            try {
                var invoke = new Invoke(expression.FunctioName, expression.Arguments);
                IRequest request = null;
                IVariableResolver variableResolver = null;
                IGroupResolver groupResolver = null;
                if (context != null) {
                    request = context.Request;
                    variableResolver = context.VariableResolver;
                    groupResolver = context.GroupResolver;
                }

                // TODO: if we don't have a return value (PROCEDURES) what should w return?
                var result = invoke.Execute(request, variableResolver, groupResolver);
                if (!result.HasReturnValue)
                    return SqlExpression.Constant(DataObject.Null());

                return SqlExpression.Constant(result.ReturnValue);
            } catch (ExpressionEvaluateException) {
                throw;
            } catch (Exception ex) {
                throw new ExpressionEvaluateException(String.Format("Could not evaluate function expression '{0}' because of an error.", expression), ex);
            }
        }

        public override SqlExpression VisitQuery(SqlQueryExpression query) {
            if (context.Request == null)
                throw new ExpressionEvaluateException("A query expression is required to evaluate a query.");

            try {
                var planner = context.Request.Context.QueryPlanner();
                var plan = planner.PlanQuery(new QueryInfo(context.Request, query));
                return SqlExpression.Constant(new DataObject(new QueryType(), new SqlQueryObject(plan)));
            } catch (ExpressionEvaluateException) {
                throw;
            } catch (Exception ex) {
                throw new ExpressionEvaluateException("Evaluation of a QUERY expression could not generate a plan.", ex);
            }
        }

        public override SqlExpression VisitReference(SqlReferenceExpression reference) {
            var refName = reference.ReferenceName;

            if (context.VariableResolver == null)
                throw new ExpressionEvaluateException(String.Format("A resolver is required to dereference variable '{0}'.", refName));

            try {
                var value = context.VariableResolver.Resolve(refName);
                return SqlExpression.Constant(value);
            } catch (ExpressionEvaluateException) {
                throw;
            } catch (Exception ex) {
                throw new ExpressionEvaluateException(String.Format("An error occurred while trying to dereference '{0}' to a constant value", refName), ex);
            }
        }

        public override SqlExpression VisitUnary(SqlUnaryExpression unary) {
            var operand = Visit(unary.Operand);
            if (operand.ExpressionType != SqlExpressionType.Constant)
                throw new ExpressionEvaluateException("Operand of a unary operator could not be evaluated to a constant.");

            var result = EvaluateUnary(((SqlConstantExpression)operand).Value, unary.ExpressionType);
            return SqlExpression.Constant(result);
        }

        private DataObject EvaluateUnary(DataObject operand, SqlExpressionType unaryType) {
            switch (unaryType) {
                case SqlExpressionType.UnaryPlus:
                    return operand.Plus();
                case SqlExpressionType.Negate:
                case SqlExpressionType.Not:
                    return operand.Negate();
                default:
                    throw new ExpressionEvaluateException(String.Format("Expression of type '{0}' is not unary.", unaryType));
            }
        }

        public override SqlExpression VisitAssign(SqlAssignExpression assign) {
            if (context.Request == null)
                throw new ExpressionEvaluateException("Cannot assign a variable outside a query context.");

            var valueExpression = Visit(assign.ValueExpression);

            if (valueExpression.ExpressionType != SqlExpressionType.Constant)
                throw new ExpressionEvaluateException("Cannot assign a variable from a non constant value.");

            var reference = assign.ReferenceExpression;
            var value = ((SqlConstantExpression)valueExpression).Value;

            string variableName;

            if (reference is SqlVariableReferenceExpression) {
                variableName = ((SqlVariableReferenceExpression) reference).VariableName;
            } else if (reference is SqlReferenceExpression) {
                var refName = ((SqlReferenceExpression) reference).ReferenceName;
                if (refName.Parent != null)  // This might be the assignment to a complex type attribute
                    throw new NotSupportedException(string.Format("Reference to '{0}' is not supported.", refName));

                variableName = refName.Name;
            } else {
                throw new NotSupportedException();
            }

            try {
                context.Request.SetVariable(variableName, valueExpression);
            } catch (Exception ex) {
                throw new ExpressionEvaluateException(String.Format("Could not assign value to variable '{0}'", reference), ex);
            }


            return SqlExpression.Constant(value);
        }

        public override SqlExpression VisitTuple(SqlTupleExpression expression) {
            var list = expression.Expressions;
            if (list != null) {
                list = VisitExpressionList(list);
            }

            if (list == null)
                return SqlExpression.Constant(new DataObject(new ArrayType(-1), SqlArray.Null));

            // This is not an array, but a subquery
            if (list.Length == 1 &&
                list[0].ExpressionType == SqlExpressionType.Constant &&
                ((SqlConstantExpression)list[0]).Value.Type is QueryType)
                return list[0];

            return SqlExpression.Constant(new DataObject(new ArrayType(list.Length), new SqlArray(list)));
        }

        public override SqlExpression VisitVariableReference(SqlVariableReferenceExpression reference) {
            var refName = reference.VariableName;

            if (context.Request == null)
                throw new ExpressionEvaluateException(String.Format("Cannot dereference variable {0} outside a query context", refName));
            if (context.VariableResolver == null)
                throw new ExpressionEvaluateException("The query context does not handle variables.");

            
            var variable = context.Request.FindVariable(refName);
            if (variable == null)
                return SqlExpression.Constant(DataObject.Null());

            return SqlExpression.Constant(variable.Value);
        }

        public override SqlExpression VisitConditional(SqlConditionalExpression conditional) {
            var evalTest = Visit(conditional.TestExpression);
            if (evalTest.ExpressionType != SqlExpressionType.Constant)
                throw new ExpressionEvaluateException("The test expression of a conditional must evaluate to a constant value.");

            var evalTestValue = ((SqlConstantExpression) evalTest).Value;
            if (!(evalTestValue.Type is BooleanType))
                throw new ExpressionEvaluateException("The test expression of a conditional must be a boolean value.");

            if (evalTestValue)
                return Visit(conditional.TrueExpression);

            if (conditional.FalseExpression != null)
                return Visit(conditional.FalseExpression);

            return SqlExpression.Constant(PrimitiveTypes.Null());
        }

        #region BinaryEvaluateInfo

        class BinaryEvaluateInfo {
            public SqlExpression Expression { get; set; }
            public int Offset { get; set; }

            public int Precedence {
                get { return Expression.EvaluatePrecedence; }
            }
        }

        #endregion
    }
}

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