FullOuterJoinedSource.cs

using System.Collections.Generic;
using System.Threading.Tasks;
using Waher.Persistence.Serialization;
using Waher.Script.Model;
using Waher.Script.Persistence.SQL.Enumerators;
 
namespace Waher.Script.Persistence.SQL.Sources
{
    public class FullOuterJoinedSource : JoinedSource
    {
        public FullOuterJoinedSource(IDataSource Left, IDataSource Right, 
            ScriptNode Conditions)
            : base(Left, Right, Conditions)
        {
        }
 
        public override async Task<IResultSetEnumerator> Find(int Offset, int Top, bool Generic, ScriptNode Where, Variables Variables,
            KeyValuePair<VariableReference, bool>[] Order, ScriptNode Node)
        {
            ScriptNode LeftWhere = await Reduce(this.Left, Where);
            KeyValuePair<VariableReference, bool>[] LeftOrder = await Reduce(this.Left, Order);
 
            IResultSetEnumerator LeftEnum = await this.Left.Find(0, int.MaxValue, Generic, LeftWhere, Variables, LeftOrder, Node);
 
            ScriptNode RightWhere = await Reduce(this.Right, this.Left, Where);
 
            LeftEnum = new LeftOuterJoinedSource.LeftOuterJoinEnumerator(LeftEnum, this.Left.Name, this.Right, this.Right.Name, Generic,
                this.Combine(RightWhere, this.Conditions), Variables, false);
 
            ScriptNode RightWhere2 = await Reduce(this.Right, Where);
            KeyValuePair<VariableReference, bool>[] RightOrder2 = await Reduce(this.Right, Order);
 
            IResultSetEnumerator RightEnum = await this.Right.Find(0, int.MaxValue, Generic, RightWhere2, Variables, RightOrder2, Node);
 
            ScriptNode LeftWhere2 = await Reduce(this.Left, this.Right, Where);
 
            RightEnum = new LeftOuterJoinedSource.LeftOuterJoinEnumerator(RightEnum, this.Right.Name, this.Left, this.Left.Name, Generic,
                this.Combine(LeftWhere2, this.Conditions), Variables, true);
 
            IResultSetEnumerator e = new FullOuterJoinEnumerator(LeftEnum, RightEnum);
 
            if (!(Where is null))
                e = new ConditionalEnumerator(e, Variables, Where);
 
            if (Offset > 0)
                e = new OffsetEnumerator(e, Offset);
 
            if (Top != int.MaxValue)
                e = new MaxCountEnumerator(e, Top);
 
            return e;
        }
 
        private class FullOuterJoinEnumerator : IResultSetEnumerator
        {
            private readonly Dictionary<object, bool> reportedLeft = new Dictionary<object, bool>();
            private readonly IResultSetEnumerator leftEnum;
            private readonly IResultSetEnumerator rightEnum;
            private object current;
            private bool leftMode;
 
            public FullOuterJoinEnumerator(IResultSetEnumerator Left, IResultSetEnumerator Right)
            {
                this.leftEnum = Left;
                this.rightEnum = Right;
                this.leftMode = true;
                this.current = null;
            }
 
            public object Current => this.current;
 
            public bool MoveNext()
            {
                return this.MoveNextAsync().Result;
            }
 
            public async Task<bool> MoveNextAsync()
            {
                if (this.leftMode)
                {
                    if (await this.leftEnum.MoveNextAsync())
                    {
                        this.current = this.leftEnum.Current;
                        this.reportedLeft[this.current] = true;
                        return true;
                    }
                    else
                        this.leftMode = false;
                }
 
                do
                {
                    if (await this.rightEnum.MoveNextAsync())
                        this.current = this.rightEnum.Current;
                    else
                        return false;
                }
                while (this.reportedLeft.ContainsKey(this.current));
 
                return true;
            }
 
            public void Reset()
            {
                this.reportedLeft.Clear();
                this.current = null;
                this.leftMode = true;
                this.leftEnum.Reset();
                this.rightEnum.Reset();
            }
        }
    
    }
}