// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Runtime.CompilerServices;
using System.ComponentModel;
using System.Globalization;
 
namespace System.Windows.Markup
{
    /// <summary>
    /// This class converts DateTime values to/from string.
    /// We don't use the DateTimeConverter because it doesn't support
    /// custom cultures, and in Xaml we require the converter to
    /// support en-us culture.
    /// </summary>
    [TypeForwardedFrom("WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")]
    public class DateTimeValueSerializer : ValueSerializer
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="DateTimeConverter" /> class.
        /// </summary>
        public DateTimeValueSerializer() { }
 
        /// <summary>
        /// Indicate that we do convert DateTime's from string.
        /// </summary>
        public override bool CanConvertFromString(string? value, IValueSerializerContext? context) => true;
 
        /// <summary>
        /// Indicate that we do convert a DateTime to string.
        /// </summary>
        public override bool CanConvertToString(object? value, IValueSerializerContext? context) => value is DateTime;
 
        /// <summary>
        /// Converts the given value object to a <see cref="DateTime" />.
        /// </summary>
        public override object ConvertFromString(string value, IValueSerializerContext? context)
        {
            if (value is null)
            {
                throw GetConvertFromException(value);
            }
 
            if (value.Length == 0)
            {
                return DateTime.MinValue;
            }
 
            // Set the formatting style for round-tripping and to trim the string.
            const DateTimeStyles DateTimeStyles = DateTimeStyles.RoundtripKind
                                                | DateTimeStyles.NoCurrentDateDefault
                                                | DateTimeStyles.AllowLeadingWhite
                                                | DateTimeStyles.AllowTrailingWhite;
            return DateTime.Parse(value, DateTimeFormatInfo.InvariantInfo, DateTimeStyles);
        }
 
        /// <summary>
        /// Converts the given value object to a <see cref="DateTime" /> using the arguments.
        /// </summary>
        public override string ConvertToString(object? value, IValueSerializerContext? context)
        {
            if (value is not DateTime dateTime)
            {
                throw GetConvertToException(value, typeof(string));
            }
 
            // We always append format specifier that indicates we want the DateTimeKind
            // to be included in the output formulation -- UTC gets written out with a "Z",
            // and Local gets written out with e.g. "-08:00" for Pacific Standard Time.
            const string YearMonthDay = "yyyy-MM-ddK";
            const string DateWithHoursMinutes = "yyyy-MM-dd'T'HH':'mmK";
            const string FullDateTime = "yyyy-MM-dd'T'HH':'mm':'ssK";
            const string FullDateTimeWithFraction = "yyyy-MM-dd'T'HH':'mm':'ss'.'FFFFFFFK";
 
            string formatString = YearMonthDay;
            if (dateTime.TimeOfDay == TimeSpan.Zero)
            {
                // The time portion of this DateTime is exactly at midnight.
                // We don't include the time component if the Kind is unspecified.
                // Otherwise, we're going to be including the time zone info, so'll
                // we'll have to include the time.
                if (dateTime.Kind != DateTimeKind.Unspecified)
                {
                    formatString = DateWithHoursMinutes;
                }
            }
            else
            {
                long digitsAfterSecond = dateTime.Ticks % 10000000;
                int second = dateTime.Second;
 
                // We're going to write out at least the hours/minutes
                formatString = DateWithHoursMinutes;
                if (second != 0 || digitsAfterSecond != 0)
                {
                    // Need to write out seconds
                    formatString = FullDateTime;
                    if (digitsAfterSecond != 0)
                    {
                        // need to write out digits after seconds
                        formatString = FullDateTimeWithFraction;
                    }
                }
            }
 
            return dateTime.ToString(formatString, DateTimeFormatInfo.InvariantInfo);
        }
    }
}