// Time utilities; get the current time (both nanos and millis), sleep, time zones.

// Instants: bare i64 UTC Unix-epoch milliseconds. Durations: i64 milliseconds.
// Monotonic readings are a separate clock domain, for deadlines/elapsed time.

val DateTime = DateTime;
val Timers = Timers;
i64 SECOND = 1000;
i64 MINUTE = 60*SECOND;
i64 HOUR = 60*MINUTE;
i64 DAY = 24*HOUR;
i64 NANOS_PER_MS = 1000*1000;

// Gregorian leap days: every fourth year, except centuries not divisible by 400.
i64 _DAYS_PER_4_YEARS = 4*365+1;
i64 _DAYS_PER_CENTURY = 100*365+100/4-1;
i64 _DAYS_PER_ERA = 4*_DAYS_PER_CENTURY+1;
// Complete years before the Unix epoch and after the last supported date.
i64 _DAYS_BEFORE_EPOCH = 1969*365+1969/4-1969/100+1969/400;
i64 _DAYS_BEFORE_YEAR_10000 = 9999*365+9999/4-9999/100+9999/400;
// The March-based calendar algorithm starts at 0000-03-01, 306 days before 0001-01-01.
i64 _MARCH_EPOCH_DAYS = _DAYS_BEFORE_EPOCH+306;
i64 MIN = -_DAYS_BEFORE_EPOCH*DAY; // 0001-01-01T00:00:00.000Z
i64 MAX = (_DAYS_BEFORE_YEAR_10000-_DAYS_BEFORE_EPOCH)*DAY-1; // 9999-12-31T23:59:59.999Z

// Access to the underlying LIBC functions
int ISO=0, CLOCK12=1, CLOCK24=2, ELAPSED=3, DATE=4, CLOCK24_SECONDS=5;
{ i64 } simple_time_now = "C";
{ i64 } simple_time_mono = "C";
{ i64 } simple_time_nano = "C";
{ i64 i32 -> i32 } simple_time_sleep = "C";
{ i64 i64 -> i32 } simple_time_local = "C";
{ i64 i64 u32 -> i32 } simple_time_zone = "C";
val now       = { -> simple_time_now (); };
val monotonic = { -> simple_time_mono(); };
val nanoTime  = { -> simple_time_nano(); };
val sleep      = { i64 duration_ms -> simple_time_sleep(duration_ms,0); };
val sleepUntil = { i64 deadline_ms -> simple_time_sleep(deadline_ms,1); };

// Signed duration conversions.  Overflow returns -1; reverse conversions truncate
// toward zero.  An exact duration day is 24 hours, independent of DST.
val _scale = { i64 n, i64 unit ->
    if( n>sys.integer.MAX_I64/unit || n<sys.integer.MIN_I64/unit ) return -1;
    return n*unit;
};
val seconds = { i64 n -> _scale(n,SECOND); };
val minutes = { i64 n -> _scale(n,MINUTE); };
val hours   = { i64 n -> _scale(n,HOUR); };
val days    = { i64 n -> _scale(n,DAY); };
val toSeconds = { i64 ms -> ms/SECOND; };
val toMinutes = { i64 ms -> ms/MINUTE; };
val toHours   = { i64 ms -> ms/HOUR; };
val toDays    = { i64 ms -> ms/DAY; };
val fromNanos = { i64 ns -> ns/NANOS_PER_MS; };
val toNanos = { i64 ms -> _scale(ms,NANOS_PER_MS); };

// Clamp to zero once due, and saturate for widely separated i64 readings.
val remaining = { i64 deadline_ms, i64 current_ms ->
    if( deadline_ms<=current_ms ) return 0;
    if( current_ms<0 && deadline_ms>sys.integer.MAX_I64+current_ms ) return sys.integer.MAX_I64;
    return deadline_ms-current_ms;
};

val _mod = { i64 n, i64 unit -> n-n/unit*unit; };
val leap = { int year -> _mod(year,4)==0 && (_mod(year,100)!=0 || _mod(year,400)==0); };
val monthDays = { int year, int month ->
    if( month<1 || month>12 ) return 0;
    return month==2 ? (leap(year) ? 29 : 28) :
        month==4 || month==6 || month==9 || month==11 ? 30 : 31;
};

// Gregorian civil dates, expressed using 400-year eras; no per-year loops.
val _days = { i64 year, i64 month, i64 day ->
    year -= month<=2 ? 1 : 0;
    i64 era=year/400, y=year-era*400;
    i64 mp=month+(month>2 ? -3 : 9);
    return era*_DAYS_PER_ERA+y*365+y/4-y/100+(153*mp+2)/5+day-1-_MARCH_EPOCH_DAYS;
};

val valid = { int year, int month, int day, int hour, int minute, int second, int millisecond ->
    return year>=1 && year<=9999 && month>=1 && month<=12 && day>=1 && day<=monthDays(year,month) &&
        hour>=0 && hour<=23 && minute>=0 && minute<=59 && second>=0 && second<=59 &&
        millisecond>=0 && millisecond<=999;
};

val makeUTC = { int year, int month, int day, int hour, int minute, int second, int millisecond ->
    if( !valid(year,month,day,hour,minute,second,millisecond) ) return -1;
    return _days(year,month,day)*DAY+hour*HOUR+minute*MINUTE+second*SECOND+millisecond;
};

val utc = { i64 instant ->
    val d=DateTime.empty();
    if( instant<MIN || instant>MAX ) return d;
    i64 day=instant/DAY, rest=_mod(instant,DAY);
    if( rest<0 ) { rest+=DAY; day--; }
    i64 z=day+_MARCH_EPOCH_DAYS, era=z/_DAYS_PER_ERA, doe=z-era*_DAYS_PER_ERA;
    i64 y=(doe-doe/(_DAYS_PER_4_YEARS-1)+doe/_DAYS_PER_CENTURY-doe/(_DAYS_PER_ERA-1))/365;
    i64 doy=doe-(365*y+y/4-y/100), mp=(5*doy+2)/153;
    d.day=doy-(153*mp+2)/5+1;
    d.month=mp+(mp<10 ? 3 : -9);
    d.year=y+era*400+(d.month<=2 ? 1 : 0);
    d.hour=rest/HOUR; d.minute=_mod(rest/MINUTE,60);
    d.second=_mod(rest/SECOND,60); d.millisecond=_mod(rest,SECOND);
    d.weekday=_mod(day+4,7);
    if( d.weekday<0 ) d.weekday+=7;
    return d;
};

val local = { i64 instant ->
    val d=DateTime.empty();
    val f=new i64[10];
    i64 ptr=f;
    if( simple_time_local(instant,ptr)!=0 ) return d;
    d.year=f[0]; d.month=f[1]; d.day=f[2];
    d.hour=f[3]; d.minute=f[4]; d.second=f[5]; d.millisecond=f[6];
    d.weekday=f[7]; d.offsetSeconds=f[8]; d.daylight=f[9]!=0;
    return d;
};

val zoneName = { i64 instant ->
    val bytes=new u8[128];
    i64 ptr=bytes;
    int n=simple_time_zone(instant,ptr,bytes#);
    if( n<0 ) return "";
    val b=new aryu8();
    for( int i=0; i<n; i++ ) b.add(bytes[i]);
    return text.end(b);
};

val _digits = { !aryu8 b, i64 n, int width ->
    text.integer(b,n,'d'|4096,width,-1);
};

val _format = { i64 instant, int style, bool localZone ->
    val d = localZone ? local(instant) : utc(instant);
    if( d.year==0 || style<0 || style>5 || style==3 ) return "<invalid time>";
    val b = new aryu8();
    if( style==4 ) {
        _digits(b,d.day,2).add('/'); _digits(b,d.month,2).add('/'); _digits(b,_mod(d.year,100),2);
    } else {
        if( style==0 ) {
            _digits(b,d.year,4).add('-'); _digits(b,d.month,2).add('-'); _digits(b,d.day,2).add('T');
        }
        int hour=d.hour;
        if( style==1 ) { hour=_mod(hour,12); if( hour==0 ) hour=12; }
        _digits(b,hour,style==1 ? 1 : 2).add(':'); _digits(b,d.minute,2);
        if( style==0 || style==5 ) { b.add(':'); _digits(b,d.second,2); }
        if( style==1 ) b.addAry(d.hour<12 ? "am" : "pm");
        if( style==0 ) {
            b.add('.'); _digits(b,d.millisecond,3);
            if( d.offsetSeconds==0 ) b.add('Z');
            else {
                i64 offset=d.offsetSeconds;
                b.add(offset<0 ? '-' : '+');
                if( offset<0 ) offset=-offset;
                _digits(b,offset/3600,2).add(':'); _digits(b,_mod(offset/60,60),2);
                if( _mod(offset,60)!=0 ) { b.add(':'); _digits(b,_mod(offset,60),2); }
            }
        }
    }
    return text.end(b);
};

val elapsed = { i64 ms ->
    val b=new aryu8();
    // Nonpositive arithmetic handles the minimum i64 without negating it.
    if( ms<0 ) b.add('-'); else ms=-ms;
    _digits(b,-(ms/MINUTE),2).add(':');
    _digits(b,-_mod(ms/SECOND,60),2).add('.'); _digits(b,-_mod(ms,SECOND),3);
    return text.end(b);
};
val format = { i64 instant, int style ->
    if( style==ELAPSED ) return elapsed(instant);
    return _format(instant,style,false);
};
val formatLocal = { i64 instant, int style ->
    if( style==ELAPSED ) return elapsed(instant);
    return _format(instant,style,true);
};

val _number = { u8[~] s, i64 at, int count ->
    if( at<0 || count<1 || at+count>s# ) return -1;
    int n=0;
    for( int i=0; i<count; i++ ) {
        int c=s[at+i];
        if( c<'0' || c>'9' ) return -1;
        n=n*10+c-'0';
    }
    return n;
};

// Keep suffix validation separate from calendar construction.
val _parseZone = { u8[~] s, int at, i64 instant ->
    if( at<0 || at>=s# ) return -1;
    i64 offset=0;
    if( s[at]=='Z' ) { if( at+1!=s# ) return -1; }
    else {
        int sign=s[at]=='+' ? 1 : s[at]=='-' ? -1 : 0;
        if( !sign || (s#!=at+6 && s#!=at+9) || s[at+3]!=':' ) return -1;
        int oh=_number(s,at+1,2), om=_number(s,at+4,2), os=0;
        if( s#==at+9 ) { if( s[at+6]!=':' ) return -1; os=_number(s,at+7,2); }
        if( oh<0 || oh>23 || om<0 || om>59 || os<0 || os>59 ) return -1;
        offset=sign*(oh*HOUR+om*MINUTE+os*SECOND);
    }
    instant-=offset;
    return instant<MIN || instant>MAX ? -1 : instant;
};

// Strict ISO absolute instants only. -1 is reserved for failure (and therefore
// cannot distinguish the valid instant one millisecond before Unix epoch).
val parse = { u8[~] s ->
    if( s#<20 || s[4]!='-' || s[7]!='-' || s[10]!='T' || s[13]!=':' || s[16]!=':' ) return -1;
    int y=_number(s, 0,4), m  =_number(s, 5,2), d  =_number(s, 8,2);
    int h=_number(s,11,2), min=_number(s,14,2), sec=_number(s,17,2);
    bool fraction=s[19]=='.';
    int ms=fraction ? _number(s,20,3) : 0;
    if( !valid(y,m,d,h,min,sec,ms) ) return -1;
    return _parseZone(s,fraction ? 23 : 19,makeUTC(y,m,d,h,min,sec,ms));
};