Fix: date custom converter to serialize and deserialize ISO 8601 date and time

Src/Notion.Client/Models/PropertyValue/DateCustomConverter.cs

@@ -5,6 +5,9 @@ namespace Notion.Client
 {
     public class DateCustomConverter : JsonConverter<Date>
     {
+        private const string DateFormat = "yyyy-MM-dd";
+        private const string DateTimeFormat = "yyyy-MM-ddTHH:mm:ssZ";
+
         public override Date ReadJson(JsonReader reader, Type objectType, Date existingValue, bool hasExistingValue,
             JsonSerializer serializer)
         {
@@ -39,14 +42,14 @@ public override void WriteJson(JsonWriter writer, Date value, JsonSerializer ser
 
             if (value.Start.HasValue)
             {
-                string startFormat = value.IncludeTime ? "yyyy-MM-ddTHH:mm:ss" : "yyyy-MM-dd";
+                string startFormat = value.IncludeTime ? DateTimeFormat : DateFormat;
                 writer.WritePropertyName("start");
                 writer.WriteValue(value.Start.Value.ToString(startFormat));
             }
 
             if (value.End.HasValue)
             {
-                string endFormat = value.IncludeTime ? "yyyy-MM-ddTHH:mm:ss" : "yyyy-MM-dd";
+                string endFormat = value.IncludeTime ? DateTimeFormat : DateFormat;
                 writer.WritePropertyName("end");
                 writer.WriteValue(value.End.Value.ToString(endFormat));
             }
@@ -71,7 +74,7 @@ public override void WriteJson(JsonWriter writer, Date value, JsonSerializer ser
 
             includeTime = dateTimeString.Contains("T") || dateTimeString.Contains(" ");
 
-            return DateTimeOffset.Parse(dateTimeString).UtcDateTime;
+            return DateTimeOffset.Parse(dateTimeString, null, System.Globalization.DateTimeStyles.AssumeUniversal).UtcDateTime;
         }
     }
 }

Src/Notion.Client/Models/PropertyValue/DatePropertyValue.cs

@@ -48,6 +48,7 @@ public class Date
         /// <summary>
         ///     Whether to include time
         /// </summary>
+        [JsonIgnore]
         public bool IncludeTime { get; set; } = true;
     }
 }

Test/Notion.UnitTests/DatabasesClientTests.cs

@@ -500,7 +500,7 @@ var jsonData
                 });
 
             //var formulaPropertyValue = (FormulaPropertyValue)page.Properties["FormulaProp"];
-            formulaPropertyValue.Formula.Date.Start.Should().Be(DateTime.Parse("2021-06-28"));
+            formulaPropertyValue.Formula.Date.Start.Should().Be(DateTimeOffset.Parse("2021-06-28", null, System.Globalization.DateTimeStyles.AssumeUniversal).UtcDateTime);
             formulaPropertyValue.Formula.Date.End.Should().BeNull();
         }
     }

Test/Notion.UnitTests/DateCustomConverterTests.cs

@@ -0,0 +1,219 @@
+using System;
+using System.IO;
+using Newtonsoft.Json;
+using Notion.Client;
+using Xunit;
+
+namespace NotionUnitTests.PropertyValue;
+
+public class DateCustomConverterTests
+{
+    private readonly DateCustomConverter _converter = new();
+    private readonly JsonSerializer _serializer = new();
+
+    [Fact]
+    public void Serialize_null_writes_null()
+    {
+        // Arrange
+        Date date = null;
+        var stringWriter = new StringWriter();
+        var jsonWriter = new JsonTextWriter(stringWriter);
+
+        // Act
+        _converter.WriteJson(jsonWriter, date, _serializer);
+        jsonWriter.Flush();
+
+        // Assert
+        Assert.Equal("null", stringWriter.ToString());
+    }
+
+    [Fact]
+    public void Serialize_start_date_only_produces_correct_json()
+    {
+        // Arrange
+        var date = new Date
+        {
+            Start = new DateTimeOffset(2023, 5, 15, 0, 0, 0, TimeSpan.Zero),
+            IncludeTime = false
+        };
+
+        // Act
+        var json = JsonConvert.SerializeObject(date);
+
+        // Assert
+        Assert.Contains("\"start\":\"2023-05-15\"", json);
+        Assert.DoesNotContain("\"end\":", json);
+        Assert.DoesNotContain("\"time_zone\":", json);
+    }
+
+    [Fact]
+    public void Serialize_start_and_end_dates_produces_correct_json()
+    {
+        // Arrange
+        var date = new Date
+        {
+            Start = new DateTimeOffset(2023, 5, 15, 0, 0, 0, TimeSpan.Zero),
+            End = new DateTimeOffset(2023, 5, 20, 0, 0, 0, TimeSpan.Zero),
+            IncludeTime = false
+        };
+
+        // Act
+        var json = JsonConvert.SerializeObject(date);
+
+        // Assert
+        Assert.Contains("\"start\":\"2023-05-15\"", json);
+        Assert.Contains("\"end\":\"2023-05-20\"", json);
+        Assert.DoesNotContain("\"time_zone\":", json);
+    }
+
+    [Fact]
+    public void Serialize_with_time_included_formats_time_correctly()
+    {
+        // Arrange
+        var date = new Date
+        {
+            Start = new DateTimeOffset(2023, 5, 15, 14, 30, 45, TimeSpan.Zero),
+            IncludeTime = true
+        };
+
+        // Act
+        var json = JsonConvert.SerializeObject(date);
+
+        // Assert
+        Assert.Contains("\"start\":\"2023-05-15T14:30:45Z\"", json);
+    }
+
+    [Fact]
+    public void Serialize_with_time_zone_includes_time_zone()
+    {
+        // Arrange
+        var date = new Date
+        {
+            Start = new DateTimeOffset(2023, 5, 15, 14, 30, 45, TimeSpan.Zero),
+            TimeZone = "Europe/London",
+            IncludeTime = true
+        };
+
+        // Act
+        var json = JsonConvert.SerializeObject(date);
+
+        // Assert
+        Assert.Contains("\"start\":\"2023-05-15T14:30:45Z\"", json);
+        Assert.Contains("\"time_zone\":\"Europe/London\"", json);
+    }
+
+    [Fact]
+    public void Deserialize_null_returns_null()
+    {
+        // Arrange
+        const string Json = "null";
+
+        // Act
+        var result = JsonConvert.DeserializeObject<Date>(Json);
+
+        // Assert
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Deserialize_start_date_only_returns_correct_date()
+    {
+        // Arrange
+        const string Json = "{\"start\":\"2023-05-15\"}";
+
+        // Act
+        var result = JsonConvert.DeserializeObject<Date>(Json);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(new DateTimeOffset(2023, 5, 15, 0, 0, 0, TimeSpan.Zero), result.Start);
+        Assert.Null(result.End);
+        Assert.Null(result.TimeZone);
+        Assert.False(result.IncludeTime);
+    }
+
+    [Fact]
+    public void Deserialize_with_time_sets_include_time_flag()
+    {
+        // Arrange
+        const string Json = "{\"start\":\"2023-05-15T14:30:45\"}";
+
+        // Act
+        var result = JsonConvert.DeserializeObject<Date>(Json);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(new DateTimeOffset(2023, 5, 15, 14, 30, 45, TimeSpan.Zero), result.Start);
+        Assert.True(result.IncludeTime);
+    }
+
+    [Fact]
+    public void Deserialize_with_start_end_and_time_zone_returns_complete_date()
+    {
+        // Arrange
+        const string Json = "{\"start\":\"2023-05-15T14:30:45\",\"end\":\"2023-05-20T16:45:00\",\"time_zone\":\"America/New_York\"}";
+
+        // Act
+        var result = JsonConvert.DeserializeObject<Date>(Json);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(new DateTimeOffset(2023, 5, 15, 14, 30, 45, TimeSpan.Zero), result.Start);
+        Assert.Equal(new DateTimeOffset(2023, 5, 20, 16, 45, 0, TimeSpan.Zero), result.End);
+        Assert.Equal("America/New_York", result.TimeZone);
+        Assert.True(result.IncludeTime);
+    }
+
+    [Fact]
+    public void Date_property_value_serialize_deserialize_maintains_data()
+    {
+        // Arrange
+        var datePropertyValue = new DatePropertyValue
+        {
+            Date = new Date
+            {
+                Start = new DateTimeOffset(2023, 5, 15, 14, 30, 45, TimeSpan.Zero),
+                End = new DateTimeOffset(2023, 5, 20, 16, 45, 0, TimeSpan.Zero),
+                TimeZone = "Europe/Berlin",
+                IncludeTime = true
+            }
+        };
+
+        // Act
+        var json = JsonConvert.SerializeObject(datePropertyValue);
+        var result = JsonConvert.DeserializeObject<DatePropertyValue>(json);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(PropertyValueType.Date, result.Type);
+        Assert.NotNull(result.Date);
+        Assert.Equal(datePropertyValue.Date.Start, result.Date.Start);
+        Assert.Equal(datePropertyValue.Date.End, result.Date.End);
+        Assert.Equal(datePropertyValue.Date.TimeZone, result.Date.TimeZone);
+        Assert.Equal(datePropertyValue.Date.IncludeTime, result.Date.IncludeTime);
+    }
+
+    [Fact]
+    public void Round_trip_preserves_data()
+    {
+        // Arrange
+        var originalDate = new Date
+        {
+            Start = new DateTimeOffset(2023, 5, 15, 14, 30, 45, TimeSpan.Zero),
+            End = new DateTimeOffset(2023, 5, 20, 16, 45, 0, TimeSpan.Zero),
+            TimeZone = "Europe/Berlin",
+            IncludeTime = true
+        };
+
+        // Act
+        var json = JsonConvert.SerializeObject(originalDate);
+        var deserializedDate = JsonConvert.DeserializeObject<Date>(json);
+
+        // Assert
+        Assert.NotNull(deserializedDate);
+        Assert.Equal(originalDate.Start, deserializedDate.Start);
+        Assert.Equal(originalDate.End, deserializedDate.End);
+        Assert.Equal(originalDate.TimeZone, deserializedDate.TimeZone);
+        Assert.True(deserializedDate.IncludeTime);
+    }
+}