Add overload method to create a page.

* Fix breaking test case

Author: KoditkarVedant

Src/Notion.Client/Api/Databases/RequestParams/DatabasesCreateParameters/ParentPageInput.cs

@@ -2,7 +2,7 @@
 
 namespace Notion.Client
 {
-    public class ParentPageInput
+    public class ParentPageInput : IPageParentInput
     {
         [JsonProperty("page_id")]
         public string PageId { get; set; }

Src/Notion.Client/Api/Pages/IPagesClient.cs

@@ -6,6 +6,18 @@ namespace Notion.Client
     public interface IPagesClient
     {
         Task<Page> CreateAsync(NewPage page);
+
+        /// <summary>
+        /// Creates a new page in the specified database or as a child of an existing page.
+        /// 
+        /// If the parent is a database, the <see href="https://developers.notion.com/reference-link/page#property-value-object">property values</see> of the new page in the properties parameter must conform to the parent <see href="https://developers.notion.com/reference-link/database">database</see>'s property schema.
+        /// 
+        /// If the parent is a page, the only valid property is <strong>title</strong>.
+        /// </summary>
+        /// <param name="pagesCreateParameters">Create page parameters</param>
+        /// <returns>Created page.</returns>
+        Task<Page> CreateAsync(PagesCreateParameters pagesCreateParameters);
+
         Task<Page> RetrieveAsync(string pageId);
 
         Task<Page> UpdatePropertiesAsync(

Src/Notion.Client/Api/Pages/PagesClient.cs

@@ -34,6 +34,37 @@ public async Task<Page> CreateAsync(NewPage page)
             return await _client.PostAsync<Page>(PagesApiUrls.Create(), page);
         }
 
+        /// <summary>
+        /// Creates a new page in the specified database or as a child of an existing page.
+        /// 
+        /// If the parent is a database, the <see href="https://developers.notion.com/reference-link/page#property-value-object">property values</see> of the new page in the properties parameter must conform to the parent <see href="https://developers.notion.com/reference-link/database">database</see>'s property schema.
+        /// 
+        /// If the parent is a page, the only valid property is <strong>title</strong>.
+        /// </summary>
+        /// <param name="pagesCreateParameters">Create page parameters</param>
+        /// <returns>Created page.</returns>
+        public async Task<Page> CreateAsync(PagesCreateParameters pagesCreateParameters)
+        {
+            if (pagesCreateParameters is null)
+            {
+                throw new ArgumentNullException(nameof(pagesCreateParameters));
+            }
+
+            var bodyParameters = (IPagesCreateBodyParameters)pagesCreateParameters;
+
+            if (bodyParameters.Parent == null)
+            {
+                throw new ArgumentNullException(nameof(bodyParameters.Parent), "Parent is required!");
+            }
+
+            if (bodyParameters.Properties == null)
+            {
+                throw new ArgumentNullException(nameof(bodyParameters.Properties), "Properties are required!");
+            }
+
+            return await _client.PostAsync<Page>(PagesApiUrls.Create(), bodyParameters);
+        }
+
         public async Task<Page> RetrieveAsync(string pageId)
         {
             var url = PagesApiUrls.Retrieve(pageId);

Src/Notion.Client/Api/Pages/RequestParams/PagesCreateParameters/DatabaseParentInput.cs

@@ -0,0 +1,10 @@
+using Newtonsoft.Json;
+
+namespace Notion.Client
+{
+    public class DatabaseParentInput : IPageParentInput
+    {
+        [JsonProperty("database_id")]
+        public string DatabaseId { get; set; }
+    }
+}

Src/Notion.Client/Api/Pages/RequestParams/PagesCreateParameters/IPageParentInput.cs

@@ -0,0 +1,6 @@
+namespace Notion.Client
+{
+    public interface IPageParentInput
+    {
+    }
+}

Src/Notion.Client/Api/Pages/RequestParams/PagesCreateParameters/IPagesCreateBodyParameters.cs

@@ -0,0 +1,23 @@
+using System.Collections.Generic;
+using Newtonsoft.Json;
+
+namespace Notion.Client
+{
+    public interface IPagesCreateBodyParameters
+    {
+        [JsonProperty("parent")]
+        IPageParent Parent { get; set; }
+        
+        [JsonProperty("properties")]
+        IDictionary<string, PropertyValue> Properties { get; set; }
+
+        [JsonProperty("children")]
+        IList<Block> Children { get; set; }
+
+        [JsonProperty("icon")]
+        IPageIcon Icon { get; set; }
+
+        [JsonProperty("cover")]
+        FileObject Cover { get; set; }
+    }
+}

Src/Notion.Client/Api/Pages/RequestParams/PagesCreateParameters/IPagesCreateQueryParameters.cs

@@ -0,0 +1,6 @@
+namespace Notion.Client
+{
+    public interface IPagesCreateQueryParameters
+    {
+    }
+}

Src/Notion.Client/Api/Pages/RequestParams/PagesCreateParameters/PagesCreateParameters.cs

@@ -0,0 +1,13 @@
+using System.Collections.Generic;
+
+namespace Notion.Client
+{
+    public class PagesCreateParameters : IPagesCreateBodyParameters, IPagesCreateQueryParameters
+    {
+        public IPageParent Parent { get; set; }
+        public IDictionary<string, PropertyValue> Properties { get; set; }
+        public IList<Block> Children { get; set; }
+        public IPageIcon Icon { get; set; }
+        public FileObject Cover { get; set; }
+    }
+}

Test/Notion.UnitTests/PagesClientTests.cs

@@ -201,7 +201,7 @@ public async Task ArchivePageAsync()
         [Fact]
         public async Task CreateAsync_Throws_ArgumentNullException_When_Parameter_Is_Null()
         {
-            Func<Task> act = async () => await _client.CreateAsync(null);
+            Func<Task> act = async () => await _client.CreateAsync(page: null);
 
             (await act.Should().ThrowAsync<ArgumentNullException>()).And.ParamName.Should().Be("page");
         }