using System;
using System.Collections.Generic;
using System.Text;
using System.Reflection;
using System.Linq;
using System.Linq.Expressions;
using System.Collections;
using System.Data.Linq.SqlClient;
using System.Diagnostics.CodeAnalysis;

namespace System.Data.Linq {
    sealed public class DataLoadOptions {
        bool frozen;
        Dictionary<MetaPosition, MemberInfo> includes = new Dictionary<MetaPosition, MemberInfo>();
        Dictionary<MetaPosition, LambdaExpression> subqueries = new Dictionary<MetaPosition, LambdaExpression>();

        /// <summary>
        /// Describe a property that is automatically loaded when the containing instance is loaded
        /// </summary>
        [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "Microsoft: Generic types are an important part of Linq APIs and they could not exist without nested generic support.")]
        [SuppressMessage("Microsoft.Design", "CA1011:ConsiderPassingBaseTypesAsParameters", Justification = "Microsoft: Need to provide static typing.")]
        public void LoadWith<T>(Expression<Func<T, object>> expression) {
            if (expression == null) {
                throw Error.ArgumentNull("expression");
            }
            MemberInfo mi = GetLoadWithMemberInfo(expression);
            this.Preload(mi);
        }

        /// <summary>
        /// Describe a property that is automatically loaded when the containing instance is loaded
        /// </summary>
        public void LoadWith(LambdaExpression expression) {
            if (expression == null) {
                throw Error.ArgumentNull("expression");
            }
            MemberInfo mi = GetLoadWithMemberInfo(expression);
            this.Preload(mi);
        }

        /// <summary>
        /// Place a subquery on the given association.
        /// </summary>
        [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "Microsoft: Generic types are an important part of Linq APIs and they could not exist without nested generic support.")]
        [SuppressMessage("Microsoft.Design", "CA1011:ConsiderPassingBaseTypesAsParameters", Justification = "Microsoft: Need to provide static typing.")]
        public void AssociateWith<T>(Expression<Func<T, object>> expression) {
            if (expression == null) {
                throw Error.ArgumentNull("expression");
            }
            this.AssociateWithInternal(expression);
        }

        /// <summary>
        /// Place a subquery on the given association.
        /// </summary>
        public void AssociateWith(LambdaExpression expression) {
            if (expression == null) {
                throw Error.ArgumentNull("expression");
            }
            this.AssociateWithInternal(expression);
        }

        private void AssociateWithInternal(LambdaExpression expression) {
            // Strip the cast-to-object.
            Expression op = expression.Body;
            while (op.NodeType == ExpressionType.Convert || op.NodeType == ExpressionType.ConvertChecked) {
                op = ((UnaryExpression)op).Operand;
            }
            LambdaExpression lambda = Expression.Lambda(op, expression.Parameters.ToArray());
            MemberInfo mi = Searcher.MemberInfoOf(lambda);
            this.Subquery(mi, lambda);
        }

        /// <summary>
        /// Determines if the member is automatically loaded with its containing instances.
        /// </summary>
        /// <param name="member">The member this is automatically loaded.</param>
        /// <returns>True if the member is automatically loaded.</returns>
        internal bool IsPreloaded(MemberInfo member) {
            if (member == null) {
                throw Error.ArgumentNull("member");
            }
            return includes.ContainsKey(new MetaPosition(member));
        }

        /// <summary>        
        /// Two shapes are equivalent if any of the following are true:
        ///  (1) They are the same object instance
        ///  (2) They are both null or empty
        ///  (3) They contain the same preloaded members
        /// </summary>
        internal static bool ShapesAreEquivalent(DataLoadOptions ds1, DataLoadOptions ds2) {
            bool shapesAreSameOrEmpty = (ds1 == ds2) || ((ds1 == null || ds1.IsEmpty) && (ds2 == null || ds2.IsEmpty));
            if (!shapesAreSameOrEmpty) {                
                if (ds1 == null || ds2 == null || ds1.includes.Count != ds2.includes.Count) {
                    return false;
                }

                foreach (MetaPosition metaPosition in ds2.includes.Keys) {
                    if (!ds1.includes.ContainsKey(metaPosition)) {
                        return false;
                    }
                }
            }
            return true;
        }

        /// <summary>
        /// Gets the subquery expression associated with the member.
        /// </summary>
        /// <param name="member">The member with the subquery.</param>
        /// <returns></returns>
        internal LambdaExpression GetAssociationSubquery(MemberInfo member) {
            if (member == null) {
                throw Error.ArgumentNull("member");
            }
            LambdaExpression expression = null;
            subqueries.TryGetValue(new MetaPosition(member), out expression);
            return expression;
        }

        /// <summary>
        /// Freeze the shape. Any further attempts to modify the shape will result in 
        /// an exception.
        /// </summary>
        internal void Freeze() {
            this.frozen = true;
        }

        /// <summary>
        /// Describe a property that is automatically loaded when the containing instance is loaded
        /// </summary>
        internal void Preload(MemberInfo association) {
            if (association == null) {
                throw Error.ArgumentNull("association");
            }
            if (this.frozen) {
                throw Error.IncludeNotAllowedAfterFreeze();
            }
            this.includes.Add(new MetaPosition(association), association);
            ValidateTypeGraphAcyclic();
        }

        /// <summary>
        /// Place a subquery on the given association.
        /// </summary>
        private void Subquery(MemberInfo association, LambdaExpression subquery) {
            if (this.frozen) {
                throw Error.SubqueryNotAllowedAfterFreeze();
            }
            subquery = (LambdaExpression)System.Data.Linq.SqlClient.Funcletizer.Funcletize(subquery); // Layering violation.
            ValidateSubqueryMember(association);
            ValidateSubqueryExpression(subquery);
            this.subqueries[new MetaPosition(association)] = subquery;
        }

        /// <summary>
        /// If the lambda specified is of the form p.A, where p is the parameter
        /// and A is a member on p, the MemberInfo for A is returned.  If
        /// the expression is not of this form, an exception is thrown.
        /// </summary>
        private static MemberInfo GetLoadWithMemberInfo(LambdaExpression lambda)
        {
            // When the specified member is a value type, there will be a conversion
            // to object that we need to strip
            Expression body = lambda.Body;
            if (body != null && (body.NodeType == ExpressionType.Convert || body.NodeType == ExpressionType.ConvertChecked))
            {
                body = ((UnaryExpression)body).Operand;
            }

            MemberExpression mex = body as MemberExpression;
            if (mex != null && mex.Expression.NodeType == ExpressionType.Parameter)
            {
                return mex.Member;
            }
            else
            {
                throw Error.InvalidLoadOptionsLoadMemberSpecification();
            }
        }

        private static class Searcher {           
            static internal MemberInfo MemberInfoOf(LambdaExpression lambda) {
                Visitor v = new Visitor();
                v.VisitLambda(lambda);
                return v.MemberInfo;
            }
            private class Visitor : System.Data.Linq.SqlClient.ExpressionVisitor { 
                internal MemberInfo MemberInfo;
                internal override Expression VisitMemberAccess(MemberExpression m) {
                    this.MemberInfo = m.Member;
                    return base.VisitMemberAccess(m);
                }

                internal override Expression VisitMethodCall(MethodCallExpression m) {
                    this.Visit(m.Object);
                    foreach (Expression arg in m.Arguments) {
                        this.Visit(arg);
                        break; // Only follow the extension method 'this'
                    }
                    return m;
                }

            }
        }

        private void ValidateTypeGraphAcyclic() {
            IEnumerable<MemberInfo> edges = this.includes.Values;
            int removed = 0;

            for (int loop = 0; loop < this.includes.Count; ++loop) {
                // Build a list of all edge targets.
                HashSet<Type> edgeTargets = new HashSet<Type>();
                foreach (MemberInfo edge in edges) {
                    edgeTargets.Add(GetIncludeTarget(edge));
                }
                // Remove all edges with sources matching no target.
                List<MemberInfo> newEdges = new List<MemberInfo>();
                bool someRemoved = false;
                foreach (MemberInfo edge in edges) {
                    if (edgeTargets.Where(et=>et.IsAssignableFrom(edge.DeclaringType) || edge.DeclaringType.IsAssignableFrom(et)).Any()) {
                        newEdges.Add(edge);
                    }
                    else {
                        ++removed;
                        someRemoved = true;
                        if (removed == this.includes.Count)
                            return;
                    }
                }
                if (!someRemoved) {
                    throw Error.IncludeCycleNotAllowed(); // No edges removed, there must be a loop.
                }
                edges = newEdges;
            }
            throw new InvalidOperationException("Bug in ValidateTypeGraphAcyclic"); // Getting here means a bug.
        }

        private static Type GetIncludeTarget(MemberInfo mi) {
            Type mt = System.Data.Linq.SqlClient.TypeSystem.GetMemberType(mi);
            if (mt.IsGenericType) {
                return mt.GetGenericArguments()[0];
            }
            return mt;
        }

        private static void ValidateSubqueryMember(MemberInfo mi) {
            Type memberType = System.Data.Linq.SqlClient.TypeSystem.GetMemberType(mi);
            if (memberType == null) {
                throw Error.SubqueryNotSupportedOn(mi);
            }
            if (!typeof(IEnumerable).IsAssignableFrom(memberType)) {
                throw Error.SubqueryNotSupportedOnType(mi.Name, mi.DeclaringType);
            }
        }

        private static void ValidateSubqueryExpression(LambdaExpression subquery) {
            if (!typeof(IEnumerable).IsAssignableFrom(subquery.Body.Type)) {
                throw Error.SubqueryMustBeSequence();
            }
            new SubqueryValidator().VisitLambda(subquery);
        }

        /// <summary>
        /// Ensure that the subquery follows the rules for subqueries.
        /// </summary>
        private class SubqueryValidator : System.Data.Linq.SqlClient.ExpressionVisitor { 
            bool isTopLevel = true;
            internal override Expression VisitMethodCall(MethodCallExpression m) {
                bool was = isTopLevel;
                try {
                    if (isTopLevel && !SubqueryRules.IsSupportedTopLevelMethod(m.Method))
                        throw Error.SubqueryDoesNotSupportOperator(m.Method.Name);
                    isTopLevel = false;
                    return base.VisitMethodCall(m);
                }
                finally {
                    isTopLevel = was;
                }
            }
        }

        /// <summary>
        /// Whether there have been LoadOptions specified.
        /// </summary>
        internal bool IsEmpty {
            get { return this.includes.Count == 0 && this.subqueries.Count == 0; }
        }
    }
}