Fixed merge filter and related extension methods.

SharedAssemblyVersion.cs

@@ -1,4 +1,4 @@
 using System.Reflection;
 
 [assembly: AssemblyVersion("7.0.0")]
-[assembly: AssemblyInformationalVersion("7.0.0-pre008")]
+[assembly: AssemblyInformationalVersion("7.0.0-pre009")]

src/OsmSharp/Streams/Filters/OsmStreamFilterMerge.cs

@@ -56,7 +56,20 @@ public override bool CanReset
         {
             get
             {
-                return _source1.CanReset && _source2.CanReset;
+                if (_source1 != null && _source2 != null)
+                {
+                    return _source1.CanReset && _source2.CanReset;
+                }
+                else if (_source1 != null)
+                {
+                    return _source1.CanReset;
+                }
+                else if(_source2 != null)
+                {
+                    return _source2.CanReset;
+                }
+
+                return true; // a stream can be reset when there is no data.
             }
         }
 
@@ -65,8 +78,8 @@ public override bool CanReset
         /// </summary>
         public override void Reset()
         {
-            _source1.Reset();
-            _source2.Reset();
+            _source1?.Reset();
+            _source2?.Reset();
 
             _source1Status = null;
             _source2Status = null;
@@ -115,16 +128,26 @@ public override void RegisterSource(OsmStreamSource source)
         private OsmGeo _current;
         private bool? _source1Status = null; // false when finished, true when there is data, null when unintialized.
         private bool? _source2Status = null; // false when finished, true when there is data, null when unintialized.
-        private ConflictResolutionType _resolutionType = ConflictResolutionType.None;
+        private readonly ConflictResolutionType _resolutionType;
 
         /// <summary>
         /// Move to the next object.
         /// </summary>
         public override bool MoveNext(bool ignoreNodes, bool ignoreWays, bool ignoreRelations)
         {
+            if (_source1 != null && _source2 == null)
+            {
+                return _source1.MoveNext(ignoreNodes, ignoreWays, ignoreRelations);
+            }
+
+            if (_source1 == null && _source2 != null)
+            {
+                return _source2.MoveNext(ignoreNodes, ignoreWays, ignoreRelations);
+            }
+
             OsmGeo source1Current = null;
             OsmGeo source2Current = null;
-
+            
             // get currents or move to first.
             if (_source1Status == null)
             {

src/OsmSharp/Streams/OsmStreamExtensions.cs

@@ -84,25 +84,122 @@ public static OsmStreamSource Progress(this OsmStreamSource source)
             return progress;
         }
 
+        /// <summary>
+        /// Merges a stream with the given other stream.
+        /// </summary>
+        public static OsmStreamSource Merge(this IEnumerable<OsmGeo> source, ConflictResolutionType resolutionType, OsmStreamSource other)
+        {
+            var merged = new OsmStreamFilterMerge(resolutionType);
+            merged.RegisterSource(source);
+            merged.RegisterSource(other);
+            return merged;
+        }
+
         /// <summary>
         /// Merges the given sources into this source.
         /// </summary>
         public static OsmStreamSource Merge(this IEnumerable<OsmGeo> source, params OsmStreamSource[] sources)
         {
-            return source.Merge(ConflictResolutionType.FirstStream, new OsmEnumerableStreamSource(source));
+            return source.Merge(ConflictResolutionType.FirstStream, sources);
+        }
+
+        /// <summary>
+        /// Merges the given sources into this source.
+        /// </summary>
+        public static OsmStreamSource Merge(this IEnumerable<OsmGeo> source, ConflictResolutionType resolutionType, params OsmStreamSource[] sources)
+        {
+            if (sources.Length == 0)
+            {
+                return new OsmEnumerableStreamSource(source);
+            }
+
+            var merged = new OsmStreamFilterMerge(resolutionType);
+            merged.RegisterSource(source);
+            merged.RegisterSource(sources[0]);
+            for (var s = 1; s < sources.Length; s++)
+            {
+                var next = new OsmStreamFilterMerge(resolutionType);
+                next.RegisterSource(merged);
+                next.RegisterSource(sources[s]);
+
+                merged = next;
+            }
+
+            return merged;
+        }
+
+        /// <summary>
+        /// Merges all the given sources.
+        /// </summary>
+        /// <param name="sources">The sources.</param>
+        /// <param name="resolutionType">The resolution type.</param>
+        /// <returns>A merged stream.</returns>
+        public static OsmStreamSource Merge(this IEnumerable<IEnumerable<OsmGeo>> sources, 
+            ConflictResolutionType resolutionType = ConflictResolutionType.FirstStream)
+        {
+            OsmStreamSource previous = null;
+            foreach (var source in sources)
+            {
+                var osmSource = new OsmEnumerableStreamSource(source);
+
+                if (previous == null)
+                {
+                    previous = osmSource;
+                }
+                else
+                {
+                    var next = new OsmStreamFilterMerge(resolutionType);
+                    next.RegisterSource(previous);
+                    next.RegisterSource(osmSource);
+
+                    previous = next;
+                }
+            }
+
+            return previous;
+        }
+
+        /// <summary>
+        /// Merges all the given sources.
+        /// </summary>
+        /// <param name="sources">The sources.</param>
+        /// <param name="resolutionType">The resolution type.</param>
+        /// <returns>A merged stream.</returns>
+        public static OsmStreamSource Merge(this IEnumerable<OsmStreamSource> sources, 
+            ConflictResolutionType resolutionType = ConflictResolutionType.FirstStream)
+        {
+            OsmStreamSource previous = null;
+            foreach (var osmSource in sources)
+            {
+                if (previous == null)
+                {
+                    previous = osmSource;
+                }
+                else
+                {
+                    var next = new OsmStreamFilterMerge(resolutionType);
+                    next.RegisterSource(previous);
+                    next.RegisterSource(osmSource);
+
+                    previous = next;
+                }
+            }
+
+            return previous;
         }
 
         /// <summary>
         /// Merges the given sources into this source.
         /// </summary>
         public static OsmStreamSource Merge(this IEnumerable<OsmGeo> source, ConflictResolutionType resolutionType, params IEnumerable<OsmGeo>[] sources)
         {
-            var merge = new OsmStreamFilterMerge(resolutionType);
-            for(var i = 0; i < sources.Length; i++)
+            var osmSources = new OsmStreamSource[sources.Length];
+            for (var s = 0; s < sources.Length; s++)
             {
-                merge.RegisterSource(sources[i]);
+                osmSources[s] = new OsmEnumerableStreamSource(sources[s]);
             }
-            return merge;
+
+            return source.Merge(resolutionType, osmSources);
         }
 
         /// <summary>