More helpers for collections

src/DotNetStac/Extensions/AssignableStacExtension.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Reflection;
 using Newtonsoft.Json.Linq;
 using Stac.Item;
 
@@ -54,7 +55,9 @@ protected T GetField<T>(string fieldName)
             if (@object == null) return default(T);
             if (@object is JToken)
                 return (@object as JToken).ToObject<T>();
-            return (T)@object;
+            if (typeof(T).GetTypeInfo().IsEnum)
+                return (T)Enum.Parse(typeof(T), @object.ToString());
+            return (T)Convert.ChangeType(@object, typeof(T));
         }
 
     }

src/DotNetStac/Item/StacItem.Helper.cs

@@ -117,7 +117,7 @@ public Itenso.TimePeriod.ITimePeriod DateTime
                         }
                     }
                 }
-                return null;
+                return Itenso.TimePeriod.TimeInterval.Anytime;
             }
             set
             {

src/DotNetStac/Item/StacItem.Model.cs

@@ -44,6 +44,7 @@ public StacItem(StacItem stacItem) : this(stacItem.Geometry, stacItem.Properties
             this.assets = stacItem.assets;
             this.collection = stacItem.collection;
             this.sourceUri = stacItem.sourceUri;
+            this.extensions = stacItem.extensions;
         }
 
         [JsonProperty("stac_extensions")]

src/DotNetStac/StacExtent.cs

@@ -1,4 +1,8 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using Newtonsoft.Json;
+using Stac.Item;
 
 namespace Stac
 {
@@ -10,5 +14,17 @@ public class StacExtent
 
         [JsonProperty("temporal")]
         public StacTemporalExtent Temporal { get; set; }
+
+        public static StacExtent Create(IEnumerable<StacItem> items)
+        {
+            return new StacExtent()
+            {
+                Spatial = new StacSpatialExtent(items.Min(i => i.GetBoundingBoxFromGeometryExtent()[0]),
+                                                items.Min(i => i.GetBoundingBoxFromGeometryExtent()[1]),
+                                                items.Max(i => i.GetBoundingBoxFromGeometryExtent()[2]),
+                                                items.Max(i => i.GetBoundingBoxFromGeometryExtent()[3])),
+                Temporal = new StacTemporalExtent(items.Min(i => i.DateTime.Start), items.Max(i => i.DateTime.End))
+            };
+        }
     }
 }