feat(*): add page manager to hold pagination details

Author: jaredcnance

src/JsonApiDotNetCore/Builders/DocumentBuilder.cs

@@ -68,7 +68,7 @@ private Dictionary<string, object> _getMeta(IIdentifiable entity)
                 meta = metaEntity.GetMeta(_jsonApiContext);
 
             if(_jsonApiContext.Options.IncludeTotalRecordCount)
-                meta["total-records"] = _jsonApiContext.TotalRecords;
+                meta["total-records"] = _jsonApiContext.PageManager.TotalRecords;
 
             if(meta.Count > 0) return meta;
             return null;

src/JsonApiDotNetCore/Controllers/JsonApiController.cs

@@ -66,7 +66,7 @@ public virtual async Task<IActionResult> GetAsync()
                 entities = IncludeRelationships(entities, _jsonApiContext.QuerySet.IncludedRelationships);
 
             if (_jsonApiContext.Options.IncludeTotalRecordCount)
-                _jsonApiContext.TotalRecords = await entities.CountAsync();
+                _jsonApiContext.PageManager.TotalRecords = await entities.CountAsync();
 
             // pagination should be done last since it will execute the query
             var pagedEntities = await ApplyPageQueryAsync(entities);
@@ -188,17 +188,15 @@ private IQueryable<T> ApplySortAndFilterQuery(IQueryable<T> entities)
 
         private async Task<IEnumerable<T>> ApplyPageQueryAsync(IQueryable<T> entities)
         {
-            if(_jsonApiContext.Options.DefaultPageSize == 0 && (_jsonApiContext.QuerySet == null || _jsonApiContext.QuerySet.PageQuery.PageSize == 0))
+            var pageManager = _jsonApiContext.PageManager;
+            if(!pageManager.IsPaginated)
                 return entities;
 
             var query = _jsonApiContext.QuerySet?.PageQuery ?? new PageQuery();
-            
-            var pageNumber = query.PageOffset > 0 ? query.PageOffset : 1;
-            var pageSize = query.PageSize > 0 ? query.PageSize : _jsonApiContext.Options.DefaultPageSize;
 
-            _logger?.LogInformation($"Applying paging query. Fetching page {pageNumber} with {pageSize} entities");
+            _logger?.LogInformation($"Applying paging query. Fetching page {pageManager.CurrentPage} with {pageManager.PageSize} entities");
 
-            return await _entities.PageAsync(entities, pageSize, pageNumber);
+            return await _entities.PageAsync(entities, pageManager.PageSize, pageManager.CurrentPage);
         }
 
         private IQueryable<T> IncludeRelationships(IQueryable<T> entities, List<string> relationships)

src/JsonApiDotNetCore/Internal/PageManager.cs

@@ -0,0 +1,10 @@
+namespace JsonApiDotNetCore.Internal
+{
+    public class PageManager
+    {
+        public int TotalRecords { get; set; }
+        public int PageSize { get; set; }
+        public int CurrentPage { get; set; }
+        public bool IsPaginated { get { return PageSize > 0; } }
+    }
+}

src/JsonApiDotNetCore/Services/IJsonApiContext.cs

@@ -15,6 +15,6 @@ public interface IJsonApiContext
         QuerySet QuerySet { get; set; }
         bool IsRelationshipData { get; set; }
         List<string> IncludedRelationships { get; set; }
-        int TotalRecords { get; set; }
+        PageManager PageManager { get; set; }
     }
 }

src/JsonApiDotNetCore/Services/JsonApiContext.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using JsonApiDotNetCore.Builders;
@@ -28,7 +29,7 @@ public JsonApiContext(
         public QuerySet QuerySet { get; set; }
         public bool IsRelationshipData { get; set; }
         public List<string> IncludedRelationships { get; set; }
-        public int TotalRecords { get; set; }
+        public PageManager PageManager { get; set; }
 
         public IJsonApiContext ApplyContext<T>()
         {
@@ -40,12 +41,26 @@ public IJsonApiContext ApplyContext<T>()
             {
                 QuerySet = new QuerySet(this, context.Request.Query);
                 IncludedRelationships = QuerySet.IncludedRelationships;
-            }                
+            }
 
             var linkBuilder = new LinkBuilder(this);
             BasePath = linkBuilder.GetBasePath(context, RequestEntity.EntityName);
+            PageManager = GetPageManager();
 
             return this;
         }
+
+        private PageManager GetPageManager()
+        {
+            if(Options.DefaultPageSize == 0 && (QuerySet == null || QuerySet.PageQuery.PageSize == 0))
+                return new PageManager();
+            
+            var query = QuerySet?.PageQuery ?? new PageQuery(); 
+
+            return new PageManager {
+                CurrentPage = query.PageOffset > 0 ? query.PageOffset : 1,
+                PageSize = query.PageSize > 0 ? query.PageSize : Options.DefaultPageSize
+            };
+        }
     }
 }