1 files changed, 82 insertions, 0 deletions
diff --git a/BackEnd/Timeline/Helpers/Cache/DataCacheHelper.cs b/BackEnd/Timeline/Helpers/Cache/DataCacheHelper.cs
new file mode 100644
index 00000000..c26bdddc
--- /dev/null
+++ b/BackEnd/Timeline/Helpers/Cache/DataCacheHelper.cs
@@ -0,0 +1,82 @@
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Net.Http.Headers;
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Timeline.Models;
+using Timeline.Models.Http;
+
+namespace Timeline.Helpers.Cache
+{
+    public static class DataCacheHelper
+    {
+        public static async Task<ActionResult> GenerateActionResult(Controller controller, ICacheableDataProvider provider, TimeSpan? maxAge = null)
+        {
+            const string CacheControlHeaderKey = "Cache-Control";
+            const string IfNonMatchHeaderKey = "If-None-Match";
+            const string IfModifiedSinceHeaderKey = "If-Modified-Since";
+            const string ETagHeaderKey = "ETag";
+            const string LastModifiedHeaderKey = "Last-Modified";
+
+            string GenerateCacheControlHeaderValue()
+            {
+                var cacheControlHeader = new CacheControlHeaderValue()
+                {
+                    NoCache = true,
+                    NoStore = false,
+                    MaxAge = maxAge ?? TimeSpan.FromDays(14),
+                    Private = true,
+                    MustRevalidate = true
+                };
+                return cacheControlHeader.ToString();
+            }
+
+            var digest = await provider.GetDigest();
+            var eTagValue = '"' + digest.ETag + '"';
+            var eTag = new EntityTagHeaderValue(eTagValue);
+
+            ActionResult Generate304Result()
+            {
+                controller.Response.Headers.Add(ETagHeaderKey, eTagValue);
+                controller.Response.Headers.Add(LastModifiedHeaderKey, digest.LastModified.ToString("R"));
+                controller.Response.Headers.Add(CacheControlHeaderKey, GenerateCacheControlHeaderValue());
+                return controller.StatusCode(StatusCodes.Status304NotModified, null);
+            }
+
+            if (controller.Request.Headers.TryGetValue(IfNonMatchHeaderKey, out var ifNonMatchHeaderValue))
+            {
+                if (!EntityTagHeaderValue.TryParseList(ifNonMatchHeaderValue, out var eTagList))
+                {
+                    return controller.BadRequest(ErrorResponse.Common.Header.IfNonMatch_BadFormat());
+                }
+
+                if (eTagList.FirstOrDefault(e => e.Equals(eTag)) != null)
+                {
+                    return Generate304Result();
+                }
+            }
+            else if (controller.Request.Headers.TryGetValue(IfModifiedSinceHeaderKey, out var ifModifiedSinceHeaderValue))
+            {
+                if (!DateTime.TryParse(ifModifiedSinceHeaderValue, out var headerValue))
+                {
+                    return controller.BadRequest(new CommonResponse(ErrorCodes.Common.Header.IfModifiedSince_BadFormat, "Header If-Modified-Since is of bad format."));
+                }
+
+                if (headerValue > digest.LastModified)
+                {
+                    return Generate304Result();
+                }
+            }
+
+            var data = await provider.GetData();
+            controller.Response.Headers.Add(CacheControlHeaderKey, GenerateCacheControlHeaderValue());
+            return controller.File(data.Data, data.ContentType, digest.LastModified, eTag);
+        }
+
+        public static Task<ActionResult> GenerateActionResult(Controller controller, Func<Task<ICacheableDataDigest>> getDigestDelegate, Func<Task<ByteData>> getDataDelegate, TimeSpan? maxAge = null)
+        {
+            return GenerateActionResult(controller, new DelegateCacheableDataProvider(getDigestDelegate, getDataDelegate), maxAge);
+        }
+    }
+}