Пример #1
0
        public Read GenerateConsensusRead(Read read1, Read read2, StitchingInfo stitchingInfo, bool isOutie)
        {
            var mergedRead = new Read(read1.Chromosome, new BamAlignment
            {
                Name      = read1.Name,
                Bases     = GetSequenceFromArray(stitchingInfo.StitchedBases),
                Position  = Math.Min(read1.Position - 1, read2.Position - 1),
                Qualities = stitchingInfo.StitchedQualities.ToArray(),
                CigarData = stitchingInfo.StitchedCigar
            })
            {
                StitchedCigar = stitchingInfo.StitchedCigar
            };

            return(mergedRead);
        }
Пример #2
0
        public StitchingInfo ReconcileSites(List <StitchedPosition> positions, bool r1IsReverse, out bool success, int prefixProbeClipEnd, int suffixProbeClipStart, bool pairIsOutie, bool leftAlignUnmapped = true)
        {
            var stitchingInfo = new StitchingInfo();

            success = true;

            // Assumption is that exactly one read is forward and one read is reverse, and each component read is only one direction
            var r1DirectionType = r1IsReverse ? DirectionType.Reverse : DirectionType.Forward;
            var r2DirectionType = r1IsReverse ? DirectionType.Forward : DirectionType.Reverse;

            RedistributeSoftclips(positions, true);
            RedistributeSoftclips(positions, false);

            var indexInR1 = -1;
            var indexInR2 = -1;

            for (var i = 0; i < positions.Count; i++)
            {
                StitchedPosition positionBefore = null;
                if (i > 0)
                {
                    positionBefore = positions[i - 1];
                }
                var stitchPosition = positions[i];

                if (stitchPosition.UnmappedPrefix.R1HasInsertion() && !stitchPosition.UnmappedPrefix.R2Ops.Any())
                {
                    if (stitchPosition.MappedSite?.R2Ops.Count(x => x.IsReferenceSpan()) > 0 &&
                        positionBefore?.MappedSite?.R2Ops.Count(x => x.IsReferenceSpan()) > 0)
                    {
                        success = false;
                        return(null);
                    }
                }
                if (stitchPosition.UnmappedPrefix.R2HasInsertion() && !stitchPosition.UnmappedPrefix.R1Ops.Any())
                {
                    if (stitchPosition.MappedSite?.R1Ops.Count(x => x.IsReferenceSpan()) > 0 &&
                        positionBefore?.MappedSite?.R1Ops.Count(x => x.IsReferenceSpan()) > 0)
                    {
                        success = false;
                        return(null);
                    }
                }

                foreach (var stitchSite in new List <StitchedSite>()
                {
                    stitchPosition.UnmappedPrefix, stitchPosition.MappedSite
                })
                {
                    var unmappedSite = stitchSite as UnmappedStretch;
                    var rightAlign   = unmappedSite != null && unmappedSite.IsPrefix; //&& !unmappedSite.IsSuffix;

                    var offset          = Math.Abs(stitchSite.R1Ops.Count - stitchSite.R2Ops.Count);
                    var r1StretchLonger = stitchSite.R1Ops.Count > stitchSite.R2Ops.Count;

                    for (var j = 0; j < Math.Max(stitchSite.R1Ops.Count(), stitchSite.R2Ops.Count()); j++)
                    {
                        int r1StretchIndex;
                        int r2StretchIndex;
                        if (rightAlign)
                        {
                            r1StretchIndex = r1StretchLonger ? j : j - offset;
                            r2StretchIndex = r1StretchLonger ? j - offset : j;
                        }
                        else
                        {
                            r1StretchIndex = j;
                            r2StretchIndex = j;
                        }
                        var r1Op = r1StretchIndex >= 0 && stitchSite.R1Ops.Count > r1StretchIndex ? stitchSite.R1Ops[r1StretchIndex] : null;
                        var r2Op = r2StretchIndex >= 0 && stitchSite.R2Ops.Count > r2StretchIndex ? stitchSite.R2Ops[r2StretchIndex] : null;

                        var combinedOp = GetCombinedOp(r1Op, r2Op);

                        if (combinedOp == null)
                        {
                            success = false;
                            if (_debug)
                            {
                                Logger.WriteToLog(string.Format("Could not stitch operations {0} and {1}.", r1Op?.Type,
                                                                r2Op?.Type));
                            }
                            _statusCounter.AddDebugStatusCount("Could not stitch operations");
                            return(null);
                        }

                        stitchingInfo.StitchedCigar.Add(combinedOp);
                        var r1opUsed = r1Op != null;
                        var r2opUsed = r2Op != null;

                        if (combinedOp.Type != 'S')
                        {
                            if (!_useSoftclippedBases && r2Op?.Type == 'S')
                            {
                                r2opUsed = false;
                            }
                            if (!_useSoftclippedBases && r1Op?.Type == 'S')
                            {
                                r1opUsed = false;
                            }
                        }

                        if (r1opUsed && r1Op.IsReadSpan())
                        {
                            indexInR1++;
                        }
                        if (r2opUsed && r2Op.IsReadSpan())
                        {
                            indexInR2++;
                        }

                        if (_ignoreProbeSoftclips)
                        {
                            if (r1opUsed && r1Op.Type == 'S')
                            {
                                var isProbeSoftclip = (pairIsOutie && indexInR1 >= suffixProbeClipStart) ||
                                                      (!pairIsOutie && indexInR1 < prefixProbeClipEnd);

                                // If this is a probe softclip, don't stitch it
                                if (isProbeSoftclip && r2opUsed)
                                {
                                    r1opUsed = false;
                                    if (pairIsOutie)
                                    {
                                        stitchingInfo.IgnoredProbeSuffixBases++;
                                    }
                                    else
                                    {
                                        stitchingInfo.IgnoredProbePrefixBases++;
                                    }
                                }
                            }
                            if (r2opUsed && r2Op.Type == 'S')
                            {
                                var isProbeSoftclip = (pairIsOutie && indexInR2 < prefixProbeClipEnd) ||
                                                      (!pairIsOutie && indexInR2 >= suffixProbeClipStart);
                                if (isProbeSoftclip && r1opUsed)
                                {
                                    r2opUsed = false;
                                    if (pairIsOutie)
                                    {
                                        stitchingInfo.IgnoredProbePrefixBases++;
                                    }
                                    else
                                    {
                                        stitchingInfo.IgnoredProbeSuffixBases++;
                                    }
                                }
                            }
                            // TODO support scenarios where R1 and R2 are both in probe softclips, if necessary. Otherwise, if this is really never going to happen, throw an exception if we see it.
                            if (!r1opUsed && !r2opUsed)
                            {
                                throw new Exception("Stitching exception: Both R1 and R2 are in probe softclip regions at overlapping position.");
                            }
                        }
                        var stitched = r1opUsed && r2opUsed;
                        stitchingInfo.StitchedDirections.Directions.Add(new DirectionOp()
                        {
                            Direction =
                                stitched
                                    ? DirectionType.Stitched
                                    : (r1opUsed ? r1DirectionType : r2DirectionType),
                            Length = 1
                        });
                    }
                }
            }

            stitchingInfo.StitchedCigar.Compress();
            stitchingInfo.StitchedDirections.Compress();

            // Don't allow stitching that creates internal softclip
            if (stitchingInfo.StitchedCigar.HasInternalSoftclip())
            {
                success = false;
                return(null);
            }

            return(stitchingInfo);
        }
Пример #3
0
        public Read GenerateConsensusRead(Read read1, Read read2, StitchingInfo stitchingInfo, bool isOutie)
        {
            var stitchedBases     = new List <char>();
            var stitchedQualities = new List <byte>();

            var expandedDirections = stitchingInfo.StitchedDirections.Expand();
            var expandedCigar      = stitchingInfo.StitchedCigar.Expand();

            var startIndexInR1 = 0;
            var startIndexInR2 = 0;

            if (!_useSoftclippedBases)
            {
                // If we're not using softclipped bases to count toward stitching-ness, we need to fast-forward ahead of the sofctclip bases in R2
                // That way, we essentially ignore the R2 softclipped bases and start from the "real" calls once we get to the Reverse-only region
                startIndexInR2 += (int)read2.CigarData.GetPrefixClip();
            }

            if (_ignoreProbeSoftclips)
            {
                if (isOutie)
                {
                    startIndexInR2 += stitchingInfo.IgnoredProbePrefixBases;
                }
                else
                {
                    startIndexInR1 += stitchingInfo.IgnoredProbePrefixBases;
                }
            }

            var r1Indexer = new ReadIndexer(startIndexInR1);
            var r2Indexer = new ReadIndexer(startIndexInR2);

            ReadIndexer forwardReadIndexer;
            ReadIndexer reverseReadIndexer;

            // Assumption is that exactly one read is forward and one read is reverse, and each component read is only one direction
            if (read1.SequencedBaseDirectionMap.First() == DirectionType.Forward)
            {
                forwardReadIndexer = r1Indexer;
                reverseReadIndexer = r2Indexer;
            }
            else
            {
                forwardReadIndexer = r2Indexer;
                reverseReadIndexer = r1Indexer;
            }

            for (var i = 0; i < expandedCigar.Count; i++)
            {
                var cigarOp   = expandedCigar[i];
                var direction = expandedDirections[i];

                if (cigarOp.Type == 'D')
                {
                    continue;
                }

                var r1Index = r1Indexer.Index;
                var r2Index = r2Indexer.Index;

                if (r1Index >= 0 && r1Index < read1.BamAlignment.Bases.Length)
                {
                    r1Indexer.BaseAtIndex    = read1.BamAlignment.Bases[r1Index];
                    r1Indexer.QualityAtIndex = read1.Qualities[r1Index];
                }
                else
                {
                    r1Indexer.BaseAtIndex    = null;
                    r1Indexer.QualityAtIndex = null;
                }
                if (r2Index >= 0 && r2Index < read2.BamAlignment.Bases.Length)
                {
                    r2Indexer.BaseAtIndex    = read2.BamAlignment.Bases[r2Index];
                    r2Indexer.QualityAtIndex = read2.Qualities[r2Index];
                }
                else
                {
                    r2Indexer.BaseAtIndex    = null;
                    r2Indexer.QualityAtIndex = null;
                }

                switch (direction)
                {
                case DirectionType.Forward:
                    if (forwardReadIndexer.BaseAtIndex == null)
                    {
                        throw new Exception("Forward base at index " + forwardReadIndexer.Index + " is null.");
                    }
                    stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);
                    stitchedQualities.Add((byte)forwardReadIndexer.QualityAtIndex);
                    forwardReadIndexer.Increment();
                    break;

                case DirectionType.Reverse:
                    if (reverseReadIndexer.BaseAtIndex == null)
                    {
                        throw new Exception("Reverse base at index " + reverseReadIndexer.Index + " is null.");
                    }
                    stitchedBases.Add((char)reverseReadIndexer.BaseAtIndex);     // TODO - stringbuilder instead?
                    stitchedQualities.Add((byte)reverseReadIndexer.QualityAtIndex);
                    reverseReadIndexer.Increment();
                    break;

                case DirectionType.Stitched:
                    if (forwardReadIndexer.BaseAtIndex != null && reverseReadIndexer.BaseAtIndex != null)
                    {
                        if (forwardReadIndexer.BaseAtIndex == reverseReadIndexer.BaseAtIndex)
                        {
                            stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);
                            var sticheredQuality = Convert.ToInt32((byte)forwardReadIndexer.QualityAtIndex) +
                                                   Convert.ToInt32((byte)reverseReadIndexer.QualityAtIndex);

                            stitchedQualities.Add((byte)sticheredQuality);
                        }
                        else     //the bases disagree...
                        {
                            if (_nifyDisagreements)
                            {
                                // we have disagreeing bases AND we chose to always Nify them
                                stitchedBases.Add('N');
                                stitchedQualities.Add(0);
                            }
                            else
                            {
                                if ((byte)forwardReadIndexer.QualityAtIndex >= reverseReadIndexer.QualityAtIndex)
                                // Original stitching implementation -- TODO, reconcile this with new reqs.
                                {
                                    stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);

                                    if (reverseReadIndexer.QualityAtIndex < _minBasecallQuality)
                                    {
                                        stitchedQualities.Add((byte)forwardReadIndexer.QualityAtIndex);
                                    }
                                    else
                                    {
                                        stitchedQualities.Add(0);
                                    }
                                    //this was a high Q disagreement, and dangerous! we will filter this base.
                                }
                                else
                                //if ((byte)forwardReadIndexer.QualityAtIndex < reverseReadIndexer.QualityAtIndex) // Original stitching implementation
                                {
                                    stitchedBases.Add((char)reverseReadIndexer.BaseAtIndex);
                                    if (forwardReadIndexer.QualityAtIndex < _minBasecallQuality)
                                    {
                                        stitchedQualities.Add((byte)reverseReadIndexer.QualityAtIndex);
                                    }
                                    else
                                    {
                                        stitchedQualities.Add(0);
                                    }
                                    //this was a high Q disagreement, and dangerous! we will filter this base.
                                }
                            }
                        }
                    }
                    forwardReadIndexer.Increment();
                    reverseReadIndexer.Increment();
                    break;

                default:
                    throw new ArgumentOutOfRangeException();
                }
            }

            // Validate stitched cigar
            var r2CigarLength = read2.CigarData.Cast <CigarOp>().Sum(op => (int)op.Length);
            var r1CigarLength = read1.CigarData.Cast <CigarOp>().Sum(op => (int)op.Length);

            var stitchedCigarLength = stitchingInfo.StitchedCigar.Cast <CigarOp>().Sum(op => (int)op.Length);
            var earliestStart       = Math.Min(read1.ClipAdjustedPosition, read2.ClipAdjustedPosition);
            var latestEnd           = Math.Max(read1.ClipAdjustedPosition + r1CigarLength, read2.ClipAdjustedPosition + r2CigarLength);

            //var latestEnd = Math.Max(read1.ClipAdjustedPosition + read1.CigarData.GetReadSpan(), read2.ClipAdjustedPosition + read2.CigarData+ stitchingInfo.InsertionAdjustment);

            if (stitchedCigarLength != (latestEnd - earliestStart))
            {
                // TODO what is really the point of this???
                if (_debug)
                {
                    Logger.WriteToLog(string.Format(
                                          "Attempted stitched cigar {0} is not consistent with component reads {1}:{2} and {3}:{4}",
                                          stitchingInfo.StitchedCigar, read1.Position, read1.CigarData, read2.Position,
                                          read2.CigarData));
                }
                _statusCounter.AddDebugStatusCount("Attempted stitched cigar not consistent with component reads");
                //return null;
            }

            // TODO investigate if these are ever worth handling
            if (stitchingInfo.StitchedCigar.Count > 0 && stitchingInfo.StitchedCigar.GetReadSpan() != stitchedBases.Count)
            {
                if (_debug)
                {
                    Logger.WriteToLog(string.Format("Invalid cigar '{0}': does not match length {1} of read ({2})", stitchingInfo.StitchedCigar,
                                                    stitchedBases.Count, read1.Name));
                }

                _statusCounter.AddDebugStatusCount("Invalid cigar does not match length of read");
                return(null);
            }

            var mergedRead = new Read(read1.Chromosome, new BamAlignment
            {
                Name      = read1.Name,
                Bases     = string.Join("", stitchedBases),
                Position  = Math.Min(read1.Position - 1, read2.Position - 1),
                Qualities = stitchedQualities.ToArray(),
                CigarData = stitchingInfo.StitchedCigar
            })
            {
                StitchedCigar   = stitchingInfo.StitchedCigar,
                CigarDirections = new CigarDirection(stitchingInfo.StitchedDirections.ToString())
            };



            return(mergedRead);
        }
Пример #4
0
        public Read GenerateConsensusReadForSimple(Read read1, Read read2, StitchingInfo stitchingInfo, bool isOutie)
        {
            _stitchedBases.Clear();
            _stitchedQualities.Clear();

            var startIndexInR1 = 0;
            var startIndexInR2 = 0;

            var r1PrefixClip = (int)read1.CigarData.GetPrefixClip();
            var r2PrefixClip = (int)read2.CigarData.GetPrefixClip();

            var r1SuffixClipEnd = (int)read1.CigarData.GetReadSpan();
            var r2SuffixClipEnd = (int)read2.CigarData.GetReadSpan();

            var r1SuffixClipBegin = r1SuffixClipEnd - read1.CigarData.GetSuffixClip();
            var r2SuffixClipBegin = r2SuffixClipEnd - read2.CigarData.GetSuffixClip();


            if (!_useSoftclippedBases)
            {
                if (r2PrefixClip == 0)
                {
                    // If we're not using softclipped bases to count toward stitching-ness, we need to fast-forward ahead of the sofctclip bases in R2
                    // That way, we essentially ignore the R2 softclipped bases and start from the "real" calls once we get to the Reverse-only region
                    startIndexInR2 += (int)read2.CigarData.GetPrefixClip();
                }
            }

            if (_ignoreProbeSoftclips)
            {
                if (isOutie)
                {
                    startIndexInR2 += stitchingInfo.IgnoredProbePrefixBases;
                }
                else if (r2PrefixClip == 0)
                {
                    startIndexInR1 += stitchingInfo.IgnoredProbePrefixBases;
                }
            }

            var r1Indexer = new ReadIndexer(startIndexInR1);
            var r2Indexer = new ReadIndexer(startIndexInR2);

            ReadIndexer forwardReadIndexer;
            ReadIndexer reverseReadIndexer;

            var read1Reverse = false;

            // Assumption is that exactly one read is forward and one read is reverse, and each component read is only one direction
            if (read1.SequencedBaseDirectionMap.First() == DirectionType.Forward)
            {
                forwardReadIndexer = r1Indexer;
                reverseReadIndexer = r2Indexer;
            }
            else
            {
                read1Reverse       = true;
                forwardReadIndexer = r2Indexer;
                reverseReadIndexer = r1Indexer;
            }

            var r1SoftclipBeforeR2 = read2.ClipAdjustedPosition - read1.ClipAdjustedPosition;
            var r2SoftclipBeforeR1 = read1.ClipAdjustedPosition - read2.ClipAdjustedPosition;


            var expandedDirections = stitchingInfo.StitchedDirections.Expand();
            var expandedCigar      = stitchingInfo.StitchedCigar.ExpandToChars();

            //CigarDirectionExpander cigarDirectionExpander = new CigarDirectionExpander(stitchingInfo.StitchedDirections);
            //for (CigarExtensions.CigarOpExpander cigarExpander = new CigarExtensions.CigarOpExpander(stitchingInfo.StitchedCigar);
            //    cigarExpander.IsNotEnd() && cigarDirectionExpander.IsNotEnd();
            //    cigarExpander.MoveNext(), cigarDirectionExpander.MoveNext())
            for (int i = 0; i < expandedCigar.Count; i++)
            {
                var cigarType = expandedCigar[i];
                var direction = expandedDirections[i];

                if (cigarType == 'D')
                {
                    continue;
                }

                var r1Index = r1Indexer.Index;
                var r2Index = r2Indexer.Index;

                if (r1SoftclipBeforeR2 > 0)
                {
                    if (r1Index == r1SoftclipBeforeR2 && !r2Indexer.StartedIndexing)
                    {
                        r2Indexer.StartIndexing();
                    }
                }
                else if (r2SoftclipBeforeR1 > 0)
                {
                    if (r2Index == r2SoftclipBeforeR1 && !r1Indexer.StartedIndexing)
                    {
                        r1Indexer.StartIndexing();
                    }
                }
                else
                {
                    r1Indexer.StartIndexing();
                    r2Indexer.StartIndexing();
                }

                // Start moving in read if needed
                switch (direction)
                {
                case DirectionType.Forward:
                    if (!forwardReadIndexer.StartedIndexing)
                    {
                        forwardReadIndexer.StartIndexing();
                    }
                    break;

                case DirectionType.Reverse:
                    if (!reverseReadIndexer.StartedIndexing)
                    {
                        reverseReadIndexer.StartIndexing();
                    }
                    break;

                case DirectionType.Stitched:
                    if (!forwardReadIndexer.StartedIndexing)
                    {
                        forwardReadIndexer.StartIndexing();
                    }
                    if (!reverseReadIndexer.StartedIndexing)
                    {
                        reverseReadIndexer.StartIndexing();
                    }
                    break;
                }

                var forwardIndex           = read1Reverse ? r2Index : r1Index;
                var reverseIndex           = read1Reverse ? r1Index : r2Index;
                var forwardPrefixClip      = read1Reverse ? r2PrefixClip : r1PrefixClip;
                var reversePrefixClip      = read1Reverse ? r1PrefixClip : r2PrefixClip;
                var reverseSuffixClipEnd   = read1Reverse ? r1SuffixClipEnd : r2SuffixClipEnd;
                var forwardSuffixClipEnd   = read1Reverse ? r2SuffixClipEnd : r1SuffixClipEnd;
                var forwardSuffixClipBegin = read1Reverse ? r2SuffixClipBegin : r1SuffixClipBegin;
                var reverseSuffixClipBegin = read1Reverse ? r1SuffixClipBegin : r2SuffixClipBegin;

                // If R1 & R2 are both in prefix softclips, favor R2 as more "real" and skip over the R1 base
                if (forwardReadIndexer.StartedIndexing && forwardIndex >= 0 && forwardIndex < forwardPrefixClip)
                {
                    if (reverseReadIndexer.StartedIndexing && reverseIndex >= 0 && reverseIndex < reversePrefixClip)
                    {
                        direction = DirectionType.Reverse;
                        forwardReadIndexer.Increment();
                    }
                }

                // If R1 & R2 are both in suffix softclips, favor R1 as more "real" and skip over the R2 base
                if (reverseReadIndexer.StartedIndexing && reverseIndex >= reverseSuffixClipBegin && reverseIndex < reverseSuffixClipEnd)
                {
                    if (forwardReadIndexer.StartedIndexing && forwardIndex >= forwardSuffixClipBegin && forwardIndex < forwardSuffixClipEnd)
                    {
                        direction = DirectionType.Forward;
                        reverseReadIndexer.Increment();
                    }
                }


                if (r1Index >= 0 && r1Index < read1.BamAlignment.Bases.Length)
                {
                    r1Indexer.BaseAtIndex    = read1.BamAlignment.Bases[r1Index];
                    r1Indexer.QualityAtIndex = read1.Qualities[r1Index];
                }
                else
                {
                    r1Indexer.BaseAtIndex    = null;
                    r1Indexer.QualityAtIndex = null;
                }
                if (r2Index >= 0 && r2Index < read2.BamAlignment.Bases.Length)
                {
                    r2Indexer.BaseAtIndex    = read2.BamAlignment.Bases[r2Index];
                    r2Indexer.QualityAtIndex = read2.Qualities[r2Index];
                }
                else
                {
                    r2Indexer.BaseAtIndex    = null;
                    r2Indexer.QualityAtIndex = null;
                }

                switch (direction)
                {
                case DirectionType.Forward:
                    if (forwardReadIndexer.BaseAtIndex == null)
                    {
                        throw new InvalidDataException("Forward base at index " + forwardReadIndexer.Index + " is null.");
                    }
                    _stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);
                    _stitchedQualities.Add((byte)forwardReadIndexer.QualityAtIndex);
                    forwardReadIndexer.Increment();
                    break;

                case DirectionType.Reverse:
                    if (reverseReadIndexer.BaseAtIndex == null)
                    {
                        throw new InvalidDataException("Reverse base at index " + reverseReadIndexer.Index + " is null.");
                    }
                    _stitchedBases.Add((char)reverseReadIndexer.BaseAtIndex);     // TODO - stringbuilder instead?
                    _stitchedQualities.Add((byte)reverseReadIndexer.QualityAtIndex);
                    reverseReadIndexer.Increment();
                    break;

                case DirectionType.Stitched:
                    if (forwardReadIndexer.BaseAtIndex != null && reverseReadIndexer.BaseAtIndex != null)
                    {
                        if (forwardReadIndexer.BaseAtIndex == reverseReadIndexer.BaseAtIndex)
                        {
                            _stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);
                            var sumQuality = Convert.ToInt32((byte)forwardReadIndexer.QualityAtIndex) +
                                             Convert.ToInt32((byte)reverseReadIndexer.QualityAtIndex);

                            var stitchedQuality = sumQuality > MaxBaseQuality ? MaxBaseQuality : sumQuality;
                            stitchingInfo.NumAgreements++;

                            _stitchedQualities.Add((byte)stitchedQuality);
                        }
                        else if (!_treatNasDisagreement && (reverseReadIndexer.BaseAtIndex == 'N' || reverseReadIndexer.QualityAtIndex == 0))
                        {
                            _stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);
                            var sumQuality = Convert.ToInt32((byte)forwardReadIndexer.QualityAtIndex);

                            var stitchedQuality = sumQuality > MaxBaseQuality ? MaxBaseQuality : sumQuality;
                            stitchingInfo.NumNDisagreements++;

                            _stitchedQualities.Add((byte)stitchedQuality);
                        }
                        else if (!_treatNasDisagreement && (forwardReadIndexer.BaseAtIndex == 'N' || forwardReadIndexer.QualityAtIndex == 0))
                        {
                            _stitchedBases.Add((char)reverseReadIndexer.BaseAtIndex);
                            var sumQuality = Convert.ToInt32((byte)reverseReadIndexer.QualityAtIndex);

                            var stitchedQuality = sumQuality > MaxBaseQuality ? MaxBaseQuality : sumQuality;
                            stitchingInfo.NumNDisagreements++;

                            _stitchedQualities.Add((byte)stitchedQuality);
                        }
                        else     //the bases disagree...
                        {
                            stitchingInfo.NumDisagreeingBases++;
                            if (_nifyDisagreements)
                            {
                                // we have disagreeing bases AND we chose to always Nify them
                                _stitchedBases.Add('N');
                                _stitchedQualities.Add(0);
                            }
                            else
                            {
                                if ((byte)forwardReadIndexer.QualityAtIndex >= reverseReadIndexer.QualityAtIndex)
                                // Original stitching implementation -- TODO, reconcile this with new reqs.
                                {
                                    _stitchedBases.Add((char)forwardReadIndexer.BaseAtIndex);

                                    if (reverseReadIndexer.QualityAtIndex < _minBasecallQuality)
                                    {
                                        _stitchedQualities.Add((byte)forwardReadIndexer.QualityAtIndex);
                                    }
                                    else
                                    {
                                        _stitchedQualities.Add(0);
                                    }
                                    //this was a high Q disagreement, and dangerous! we will filter this base.
                                }
                                else
                                //if ((byte)forwardReadIndexer.QualityAtIndex < reverseReadIndexer.QualityAtIndex) // Original stitching implementation
                                {
                                    _stitchedBases.Add((char)reverseReadIndexer.BaseAtIndex);
                                    if (forwardReadIndexer.QualityAtIndex < _minBasecallQuality)
                                    {
                                        _stitchedQualities.Add((byte)reverseReadIndexer.QualityAtIndex);
                                    }
                                    else
                                    {
                                        _stitchedQualities.Add(0);
                                    }
                                    //this was a high Q disagreement, and dangerous! we will filter this base.
                                }
                            }
                        }
                    }

                    forwardReadIndexer.Increment();
                    reverseReadIndexer.Increment();
                    break;

                default:
                    throw new ArgumentOutOfRangeException();
                }
            }

            // Validate stitched cigar
            //var r2CigarLength = read2.CigarData.Cast<CigarOp>().Sum(op => (int)op.Length);
            //var r1CigarLength = read1.CigarData.Cast<CigarOp>().Sum(op => (int)op.Length);
            var r2CigarLength = read2.CigarData.GetCigarSpan();
            var r1CigarLength = read1.CigarData.GetCigarSpan();

            //var stitchedCigarLength = stitchingInfo.StitchedCigar.Cast<CigarOp>().Sum(op => (int)op.Length);
            var stitchedCigarLength = stitchingInfo.StitchedCigar.GetCigarSpan();
            var earliestStart       = Math.Min(read1.ClipAdjustedPosition, read2.ClipAdjustedPosition);
            var latestEnd           = Math.Max(read1.ClipAdjustedPosition + r1CigarLength, read2.ClipAdjustedPosition + r2CigarLength);

            //var latestEnd = Math.Max(read1.ClipAdjustedPosition + read1.CigarData.GetReadSpan(), read2.ClipAdjustedPosition + read2.CigarData+ stitchingInfo.InsertionAdjustment);

            if (stitchedCigarLength != (latestEnd - earliestStart))
            {
                // TODO what is really the point of this???
                if (_debug)
                {
                    Logger.WriteToLog(string.Format(
                                          "Attempted stitched cigar {0} is not consistent with component reads {1}:{2} and {3}:{4}",
                                          stitchingInfo.StitchedCigar, read1.Position, read1.CigarData, read2.Position,
                                          read2.CigarData));
                }
                _statusCounter.AddDebugStatusCount("Attempted stitched cigar not consistent with component reads");
                //return null;
            }

            // TODO investigate if these are ever worth handling
            if (stitchingInfo.StitchedCigar.Count > 0 && stitchingInfo.StitchedCigar.GetReadSpan() != _stitchedBases.Count)
            {
                if (_debug)
                {
                    Logger.WriteToLog(string.Format("Invalid cigar '{0}': does not match length {1} of read ({2})", stitchingInfo.StitchedCigar,
                                                    _stitchedBases.Count, read1.Name));
                }

                _statusCounter.AddDebugStatusCount("Invalid cigar does not match length of read");
                return(null);
            }

            var mergedRead = new Read(read1.Chromosome, new BamAlignment
            {
                Name      = read1.Name,
                Bases     = GetSequenceFromArray(_stitchedBases),
                Position  = Math.Min(read1.Position - 1, read2.Position - 1),
                Qualities = _stitchedQualities.ToArray(),
                CigarData = stitchingInfo.StitchedCigar
            })
            {
                StitchedCigar = stitchingInfo.StitchedCigar
            };

            return(mergedRead);
        }