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Packages/com.tivadar.best.http/Runtime/Shared/Database/MetadataService.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+
+using Best.HTTP.Shared.Databases.MetadataIndexFinders;
+
+namespace Best.HTTP.Shared.Databases
+{
+    public struct MetadataStats
+    {
+        public int min;
+        public int max;
+        public int count;
+        public int sum;
+    }
+
+    public abstract class MetadataService<MetadataType, ContentType> where MetadataType : Metadata, new()
+    {
+        public List<MetadataType> Metadatas { get; protected set; }
+        public IndexingService<ContentType, MetadataType> IndexingService { get; protected set; }
+        public IEmptyMetadataIndexFinder<MetadataType> EmptyMetadataIndexFinder { get; protected set; }
+
+        protected MetadataService(IndexingService<ContentType, MetadataType> indexingService, IEmptyMetadataIndexFinder<MetadataType> emptyMetadataIndexFinder)
+        {
+            this.IndexingService = indexingService;
+            this.EmptyMetadataIndexFinder = emptyMetadataIndexFinder;
+
+            this.Metadatas = new List<MetadataType>();
+        }
+
+        /// <summary>
+        /// Called when metadata loaded from file
+        /// </summary>
+        public virtual MetadataType CreateFrom(Stream stream)
+        {
+            var metadata = new MetadataType();
+
+            metadata.Index = this.Metadatas.Count;
+            metadata.LoadFrom(stream);
+
+            this.Metadatas.Add(metadata);
+
+            this.IndexingService.Index(metadata);
+
+            return metadata;
+        }
+
+        /// <summary>
+        /// Called by a concrete MetadataService implementation to create a new metadata
+        /// </summary>
+        protected MetadataType CreateDefault(ContentType content, int filePos, int length, Action<ContentType, MetadataType> setupCallback)
+        {
+            var metadata = new MetadataType();
+            metadata.FilePosition = filePos;
+            metadata.Length = length;
+
+            metadata.Index = this.EmptyMetadataIndexFinder.FindFreeIndex(this.Metadatas);
+
+            if (setupCallback != null)
+                setupCallback(content, metadata);
+
+            if (metadata.Index == this.Metadatas.Count)
+                this.Metadatas.Add(metadata);
+            else
+                this.Metadatas[metadata.Index] = metadata;
+
+            this.IndexingService.Index(metadata);
+
+            return metadata;
+        }
+
+        public void Remove(MetadataType metadata)
+        {
+            this.IndexingService.Remove(metadata);
+
+            // Mark metadata for deletion. Next time we save, it's not going to written out to disk.
+            metadata.MarkForDelete();
+        }
+
+        public void SaveTo(Stream stream)
+        {
+            stream.SetLength(0);
+
+            var optimizedIndexes = this.IndexingService.GetOptimizedIndexes();
+
+            if (optimizedIndexes != null)
+            {
+                foreach (var index in optimizedIndexes)
+                {
+                    var metadata = this.Metadatas[index];
+
+                    if (metadata.IsDeleted)
+                        continue;
+
+                    metadata.SaveTo(stream);
+                }
+            }
+            else
+            {
+            for (int i = 0; i < this.Metadatas.Count; ++i)
+            {
+                var metadata = this.Metadatas[i];
+
+                if (metadata.IsDeleted)
+                    continue;
+
+                metadata.SaveTo(stream);
+            }
+        }
+        }
+
+        public void LoadFrom(Stream stream)
+        {
+            while (stream.Position < stream.Length)
+                CreateFrom(stream);
+        }
+
+        public virtual void Clear()
+        {
+            this.Metadatas.Clear();
+            this.IndexingService.Clear();
+        }
+
+        public MetadataStats GetStats()
+        {
+            int min = int.MaxValue;
+            int max = 0;
+            int sum = 0;
+            int count = 0;
+            foreach (var metadata in this.Metadatas)
+            {
+                if (metadata.IsDeleted)
+                    continue;
+
+                if (metadata.Length > max)
+                    max = metadata.Length;
+                if (metadata.Length < min)
+                    min = metadata.Length;
+                sum += metadata.Length;
+                count++;
+            }
+
+            return new MetadataStats
+            {
+                count = count,
+                min = min,
+                max = max,
+                sum = sum
+            };
+        }
+    }
+}