// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

/*============================================================
**
** Class: CurrentTimeZone
**
**
** Purpose: 
** This class represents the current system timezone.  It is
** the only meaningful implementation of the TimeZone class 
** available in this version.
**
** The only TimeZone that we support in version 1 is the 
** CurrentTimeZone as determined by the system timezone.
**
**
============================================================*/
namespace System {
    using System;
    using System.Diagnostics.Contracts;
    using System.Text;
    using System.Threading;
    using System.Collections;
    using System.Globalization;
    using System.Runtime.CompilerServices;
    using System.Runtime.Versioning;

    //
    // Currently, this is the only supported timezone.
    // The values of the timezone is from the current system timezone setting in the
    // control panel.
    //
#if FEATURE_CORECLR
    [Obsolete("System.CurrentSystemTimeZone has been deprecated.  Please investigate the use of System.TimeZoneInfo.Local instead.")]
#endif
    [Serializable]
    internal class CurrentSystemTimeZone : TimeZone {
        // <BUGBUG>BUGBUG :
        // One problem is when user changes the current timezone.  We 
        // are not able to update currentStandardName/currentDaylightName/
        // currentDaylightChanges.
        // We need WM_TIMECHANGE to do this or use
        // RegNotifyChangeKeyValue() to monitor </BUGBUG>
        //    
        private const long TicksPerMillisecond = 10000;
        private const long TicksPerSecond = TicksPerMillisecond * 1000;
        private const long TicksPerMinute = TicksPerSecond * 60;

        // The per-year information is cached in in this instance value. As a result it can
        // be cleaned up by CultureInfo.ClearCachedData, which will clear the instance of this object
        private Hashtable m_CachedDaylightChanges = new Hashtable();

        // Standard offset in ticks to the Universal time if
        // no daylight saving is in used.
        // E.g. the offset for PST (Pacific Standard time) should be -8 * 60 * 60 * 1000 * 10000.
        // (1 millisecond = 10000 ticks)
        private long   m_ticksOffset;
        private String m_standardName;
        private String m_daylightName;
             
        [System.Security.SecuritySafeCritical]  // auto-generated
        internal CurrentSystemTimeZone() {
            m_ticksOffset = nativeGetTimeZoneMinuteOffset() * TicksPerMinute;
            m_standardName = null;
            m_daylightName = null;
        }
    
        public override String StandardName {
            [System.Security.SecuritySafeCritical]  // auto-generated
            get {
                if (m_standardName == null) {
                    m_standardName = nativeGetStandardName();
                }
                return (m_standardName);
            }    
        }

        public override String DaylightName {
            [System.Security.SecuritySafeCritical]  // auto-generated
            get {
                if (m_daylightName == null) {
                    m_daylightName = nativeGetDaylightName(); 
                    if (m_daylightName == null) {
                        m_daylightName = this.StandardName;
                    }
                }
                return (m_daylightName);
            }
        }

        internal long GetUtcOffsetFromUniversalTime(DateTime time, ref Boolean isAmbiguousLocalDst) {
            // Get the daylight changes for the year of the specified time.
            TimeSpan offset = new TimeSpan(m_ticksOffset);
            DaylightTime daylightTime = GetDaylightChanges(time.Year);  
            isAmbiguousLocalDst= false;
                     
            if (daylightTime == null || daylightTime.Delta.Ticks == 0) {
                return offset.Ticks;
            }
            
            // The start and end times represent the range of universal times that are in DST for that year.                
            // Within that there is an ambiguous hour, usually right at the end, but at the beginning in
            // the unusual case of a negative daylight savings delta.
            DateTime startTime = daylightTime.Start - offset;
            DateTime endTime = daylightTime.End - offset - daylightTime.Delta;
            DateTime ambiguousStart;
            DateTime ambiguousEnd;
            if (daylightTime.Delta.Ticks > 0) {
                ambiguousStart = endTime - daylightTime.Delta;
                ambiguousEnd = endTime;
            } else {
                ambiguousStart = startTime;
                ambiguousEnd = startTime - daylightTime.Delta;
            }

            Boolean isDst = false;
            if (startTime > endTime) {
                // In southern hemisphere, the daylight saving time starts later in the year, and ends in the beginning of next year.
                // Note, the summer in the southern hemisphere begins late in the year.
                isDst = (time < endTime || time >= startTime);
            }
            else {
                // In northern hemisphere, the daylight saving time starts in the middle of the year.
                isDst = (time>=startTime && time<endTime);
            }
            if (isDst) {
                offset += daylightTime.Delta;
                
                // See if the resulting local time becomes ambiguous. This must be captured here or the
                // DateTime will not be able to round-trip back to UTC accurately.
                if (time >= ambiguousStart && time < ambiguousEnd ) {
                    isAmbiguousLocalDst = true;
                }
            }
            return offset.Ticks;
        }
        
        public override DateTime ToLocalTime(DateTime time) {
            if (time.Kind == DateTimeKind.Local) {
                return time;
            }
            Boolean isAmbiguousLocalDst = false;
            Int64 offset = GetUtcOffsetFromUniversalTime(time, ref isAmbiguousLocalDst);
            long tick = time.Ticks + offset;
            if (tick>DateTime.MaxTicks) {
                return new DateTime(DateTime.MaxTicks, DateTimeKind.Local);
            }
            if (tick<DateTime.MinTicks) {
                return new DateTime(DateTime.MinTicks, DateTimeKind.Local);
            }
            return new DateTime(tick, DateTimeKind.Local, isAmbiguousLocalDst);            
        }

        // Private object for locking instead of locking on a public type for SQL reliability work.
        private static Object s_InternalSyncObject;
        private static Object InternalSyncObject {
            get {
                if (s_InternalSyncObject == null) {
                    Object o = new Object();
                    Interlocked.CompareExchange<Object>(ref s_InternalSyncObject, o, null);
                }
                return s_InternalSyncObject;
            }
        }


        [System.Security.SecuritySafeCritical]  // auto-generated
        public override DaylightTime GetDaylightChanges(int year) {
            if (year < 1 || year > 9999) {
                throw new ArgumentOutOfRangeException("year", Environment.GetResourceString("ArgumentOutOfRange_Range", 1, 9999));
            }
            Contract.EndContractBlock();

            Object objYear = (Object)year;

            if (!m_CachedDaylightChanges.Contains(objYear)) {
                lock (InternalSyncObject) {

                    if (!m_CachedDaylightChanges.Contains(objYear)) {

                        //
                        // rawData is an array of 17 short (16 bit) numbers.
                        // The first 8 numbers contains the 
                        // year/month/day/dayOfWeek/hour/minute/second/millisecond for the starting time of daylight saving time.
                        // The next 8 numbers contains the
                        // year/month/day/dayOfWeek/hour/minute/second/millisecond for the ending time of daylight saving time.
                        // The last short number is the delta to the standard offset in minutes.
                        //
                        short[] rawData = nativeGetDaylightChanges(year);

                        if (rawData == null) {
                            //
                            // If rawData is null, it means that daylight saving time is not used
                            // in this timezone. So keep currentDaylightChanges as the empty array.
                            //
                            m_CachedDaylightChanges.Add(objYear, new DaylightTime(DateTime.MinValue, DateTime.MinValue, TimeSpan.Zero));
                        } else {
                            DateTime start;
                            DateTime end;
                            TimeSpan delta;

                            //
                            // Store the start of daylight saving time.
                            //

                            start = GetDayOfWeek(year, (rawData[0] != 0), rawData[1], rawData[2],
                                                  rawData[3],
                                                  rawData[4], rawData[5], rawData[6], rawData[7]);

                            //
                            // Store the end of daylight saving time.
                            //
                            end = GetDayOfWeek(year, (rawData[8] != 0), rawData[9], rawData[10],
                                                rawData[11],
                                                rawData[12], rawData[13], rawData[14], rawData[15]);

                            delta = new TimeSpan(rawData[16] * TicksPerMinute);
                            DaylightTime currentDaylightChanges = new DaylightTime(start, end, delta);
                            m_CachedDaylightChanges.Add(objYear, currentDaylightChanges);
                        }
                    }
                }
            }        

            DaylightTime result = (DaylightTime)m_CachedDaylightChanges[objYear];

            return result;
        }

        public override TimeSpan GetUtcOffset(DateTime time) {
            if (time.Kind == DateTimeKind.Utc) {
                return TimeSpan.Zero;
            }
            else {
                return new TimeSpan(TimeZone.CalculateUtcOffset(time, GetDaylightChanges(time.Year)).Ticks + m_ticksOffset);                    
            }
        }

        //
        // Return the (numberOfSunday)th day of week in a particular year/month.
        //
        private static DateTime GetDayOfWeek(int year, bool fixedDate, int month, int targetDayOfWeek, int numberOfSunday, int hour, int minute, int second, int millisecond) {
            DateTime time;
            
            if (fixedDate) {
                //
                // Create a Fixed-Date transition time based on the supplied parameters
                // For Fixed-Dated transition times, the 'numberOfSunday' parameter actually
                // represents the day of the month.
                //

                // if the day is out of range for the month then use the last day of the month
                int day = DateTime.DaysInMonth(year, month);

                time = new DateTime(year, month, (day < numberOfSunday) ? day : numberOfSunday,
                                  hour, minute, second, millisecond, DateTimeKind.Local);
            }
            else if (numberOfSunday <= 4) {
                //
                // Get the (numberOfSunday)th Sunday.
                //
                
                time = new DateTime(year, month, 1, hour, minute, second, millisecond, DateTimeKind.Local);
    
                int dayOfWeek = (int)time.DayOfWeek;
                int delta = targetDayOfWeek - dayOfWeek;
                if (delta < 0) {
                    delta += 7;
                }
                delta += 7 * (numberOfSunday - 1);
    
                if (delta > 0) {
                    time = time.AddDays(delta);
                }
            } else {
                //
                // If numberOfSunday is greater than 4, we will get the last sunday.
                //
                Calendar cal = GregorianCalendar.GetDefaultInstance();            
                time = new DateTime(year, month, cal.GetDaysInMonth(year, month), hour, minute, second, millisecond, DateTimeKind.Local);
                // This is the day of week for the last day of the month.
                int dayOfWeek = (int)time.DayOfWeek;
                int delta = dayOfWeek - targetDayOfWeek;
                if (delta < 0) {
                    delta += 7;
                }
                
                if (delta > 0) {
                    time = time.AddDays(-delta);
                }
            }
            return (time);
        }

        [System.Security.SecurityCritical]  // auto-generated
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal extern static int nativeGetTimeZoneMinuteOffset();
        [System.Security.SecurityCritical]  // auto-generated
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal extern static String nativeGetDaylightName();
        [System.Security.SecurityCritical]  // auto-generated
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal extern static String nativeGetStandardName();
        [System.Security.SecurityCritical]  // auto-generated
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal extern static short[] nativeGetDaylightChanges(int year);
    } // class CurrentSystemTimeZone
}