http_last_modified.hpp

//
// Copyright (C) 2019 Jack.
//
// Author: jack
// Email:  jack.wgm at gmail dot com
//

#pragma once
#include <ctime>
#include <string>

#include <boost/filesystem.hpp>

namespace avhttp {
	namespace detail {
		static const char* const my_curl_wkday[] =
		{ "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun" };

		static const char* const my_weekday[] =
		{ "Monday", "Tuesday", "Wednesday", "Thursday",
		"Friday", "Saturday", "Sunday" };

		static const char* const my_curl_month[] =
		{ "Jan", "Feb", "Mar", "Apr", "May", "Jun",
		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };

		using tzinfo = struct
		{
			char name[5];
			int offset; /* +/- in minutes */
		};

		enum {
			PARSEDATE_FAIL = -1,
			PARSEDATE_OK = 0,
			PARSEDATE_LATER = 1,
			PARSEDATE_SOONER = 2,
		};

		static const tzinfo tz[] = {
		  {"GMT", 0},              /* Greenwich Mean */
		  {"UTC", 0},              /* Universal (Coordinated) */
		  {"WET", 0},              /* Western European */
		  {"BST", 0 -60},     /* British Summer */
		  {"WAT", 60},             /* West Africa */
		  {"AST", 240},            /* Atlantic Standard */
		  {"ADT", 240 -60},   /* Atlantic Daylight */
		  {"EST", 300},            /* Eastern Standard */
		  {"EDT", 300 -60},   /* Eastern Daylight */
		  {"CST", 360},            /* Central Standard */
		  {"CDT", 360 -60},   /* Central Daylight */
		  {"MST", 420},            /* Mountain Standard */
		  {"MDT", 420 -60},   /* Mountain Daylight */
		  {"PST", 480},            /* Pacific Standard */
		  {"PDT", 480 -60},   /* Pacific Daylight */
		  {"YST", 540},            /* Yukon Standard */
		  {"YDT", 540 -60},   /* Yukon Daylight */
		  {"HST", 600},            /* Hawaii Standard */
		  {"HDT", 600 -60},   /* Hawaii Daylight */
		  {"CAT", 600},            /* Central Alaska */
		  {"AHST", 600},           /* Alaska-Hawaii Standard */
		  {"NT",  660},            /* Nome */
		  {"IDLW", 720},           /* International Date Line West */
		  {"CET", -60},            /* Central European */
		  {"MET", -60},            /* Middle European */
		  {"MEWT", -60},           /* Middle European Winter */
		  {"MEST", -60 -60},  /* Middle European Summer */
		  {"CEST", -60 -60},  /* Central European Summer */
		  {"MESZ", -60 -60},  /* Middle European Summer */
		  {"FWT", -60},            /* French Winter */
		  {"FST", -60 -60},   /* French Summer */
		  {"EET", -120},           /* Eastern Europe, USSR Zone 1 */
		  {"WAST", -420},          /* West Australian Standard */
		  {"WADT", -420 -60}, /* West Australian Daylight */
		  {"CCT", -480},           /* China Coast, USSR Zone 7 */
		  {"JST", -540},           /* Japan Standard, USSR Zone 8 */
		  {"EAST", -600},          /* Eastern Australian Standard */
		  {"EADT", -600 -60}, /* Eastern Australian Daylight */
		  {"GST", -600},           /* Guam Standard, USSR Zone 9 */
		  {"NZT", -720},           /* New Zealand */
		  {"NZST", -720},          /* New Zealand Standard */
		  {"NZDT", -720 -60}, /* New Zealand Daylight */
		  {"IDLE", -720},          /* International Date Line East */
		  /* Next up: Military timezone names. RFC822 allowed these, but (as noted in
			 RFC 1123) had their signs wrong. Here we use the correct signs to match
			 actual military usage.
		   */
		  {"A",  +1 * 60},         /* Alpha */
		  {"B",  +2 * 60},         /* Bravo */
		  {"C",  +3 * 60},         /* Charlie */
		  {"D",  +4 * 60},         /* Delta */
		  {"E",  +5 * 60},         /* Echo */
		  {"F",  +6 * 60},         /* Foxtrot */
		  {"G",  +7 * 60},         /* Golf */
		  {"H",  +8 * 60},         /* Hotel */
		  {"I",  +9 * 60},         /* India */
		  /* "J", Juliet is not used as a timezone, to indicate the observer's local
			 time */
		  {"K", +10 * 60},         /* Kilo */
		  {"L", +11 * 60},         /* Lima */
		  {"M", +12 * 60},         /* Mike */
		  {"N",  -1 * 60},         /* November */
		  {"O",  -2 * 60},         /* Oscar */
		  {"P",  -3 * 60},         /* Papa */
		  {"Q",  -4 * 60},         /* Quebec */
		  {"R",  -5 * 60},         /* Romeo */
		  {"S",  -6 * 60},         /* Sierra */
		  {"T",  -7 * 60},         /* Tango */
		  {"U",  -8 * 60},         /* Uniform */
		  {"V",  -9 * 60},         /* Victor */
		  {"W", -10 * 60},         /* Whiskey */
		  {"X", -11 * 60},         /* X-ray */
		  {"Y", -12 * 60},         /* Yankee */
		  {"Z", 0},                /* Zulu, zero meridian, a.k.a. UTC */
		};



		/* Portable, consistent toupper (remember EBCDIC). Do not use toupper() because
		   its behavior is altered by the current locale. */
		static char url_raw_toupper(char in)
		{
			switch (in) {
			case 'a':
				return 'A';
			case 'b':
				return 'B';
			case 'c':
				return 'C';
			case 'd':
				return 'D';
			case 'e':
				return 'E';
			case 'f':
				return 'F';
			case 'g':
				return 'G';
			case 'h':
				return 'H';
			case 'i':
				return 'I';
			case 'j':
				return 'J';
			case 'k':
				return 'K';
			case 'l':
				return 'L';
			case 'm':
				return 'M';
			case 'n':
				return 'N';
			case 'o':
				return 'O';
			case 'p':
				return 'P';
			case 'q':
				return 'Q';
			case 'r':
				return 'R';
			case 's':
				return 'S';
			case 't':
				return 'T';
			case 'u':
				return 'U';
			case 'v':
				return 'V';
			case 'w':
				return 'W';
			case 'x':
				return 'X';
			case 'y':
				return 'Y';
			case 'z':
				return 'Z';
			}
			return in;
		}

		static int url_raw_equal(const char* first, const char* second)
		{
			while (*first && *second) {
				if (url_raw_toupper(*first) != url_raw_toupper(*second))
					/* get out of the loop as soon as they don't match */
					break;
				first++;
				second++;
			}
			/* we do the comparison here (possibly again), just to make sure that if the
			   loop above is skipped because one of the strings reached zero, we must not
			   return this as a successful match */
			return (url_raw_toupper(*first) == url_raw_toupper(*second));
		}

		int url_raw_nequal(const char* first, const char* second, size_t max)
		{
			while (*first && *second && max) {
				if (url_raw_toupper(*first) != url_raw_toupper(*second)) {
					break;
				}
				max--;
				first++;
				second++;
			}
			if (0 == max)
				return 1; /* they are equal this far */

			return url_raw_toupper(*first) == url_raw_toupper(*second);
		}

		/* returns:
		   -1 no day
		   0 monday - 6 sunday
		*/

		static int checkday(const char* check, size_t len)
		{
			int i;
			const char* const* what;
			bool found = false;
			if (len > 3)
				what = &my_weekday[0];
			else
				what = &my_curl_wkday[0];
			for (i = 0; i < 7; i++) {
				if (url_raw_equal(check, what[0])) {
					found = true;
					break;
				}
				what++;
			}
			return found ? i : -1;
		}

		static int checkmonth(const char* check)
		{
			int i;
			const char* const* what;
			bool found = false;

			what = &my_curl_month[0];
			for (i = 0; i < 12; i++) {
				if (url_raw_equal(check, what[0])) {
					found = true;
					break;
				}
				what++;
			}
			return found ? i : -1; /* return the offset or -1, no real offset is -1 */
		}

		/* return the time zone offset between GMT and the input one, in number
		   of seconds or -1 if the timezone wasn't found/legal */

		static int checktz(const char* check)
		{
			unsigned int i;
			const tzinfo* what;
			bool found = false;

			what = tz;
			for (i = 0; i < sizeof(tz) / sizeof(tz[0]); i++) {
				if (url_raw_equal(check, what->name)) {
					found = true;
					break;
				}
				what++;
			}
			return found ? what->offset * 60 : -1;
		}

		static bool my_isdigit(const char c) noexcept
		{
			return c >= '0' && c <= '9';
		}

		static bool my_isalpha(const char c) noexcept
		{
			return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
		}

		static bool my_isalnum(const char c) noexcept
		{
			return my_isdigit(c) || my_isalpha(c);
		}

		static int my_curlx_sltosi(long slnum)
		{
			return (int)(slnum & (long)0x7FFFFFFF);
		}

		static void skip(const char** date)
		{
			/* skip everything that aren't letters or digits */
			while (**date && !my_isalnum(**date))
				(*date)++;
		}

		using assume = enum {
			DATE_MDAY,
			DATE_YEAR,
			DATE_TIME
		};

		/* this is a clone of 'struct tm' but with all fields we don't need or use
		   cut out */
		using my_tm = struct {
			int tm_sec;
			int tm_min;
			int tm_hour;
			int tm_mday;
			int tm_mon;
			int tm_year;
		};

		/* struct tm to time since epoch in GMT time zone.
		 * This is similar to the standard mktime function but for GMT only, and
		 * doesn't suffer from the various bugs and portability problems that
		 * some systems' implementations have.
		 */
		static time_t my_timegm(my_tm* tm)
		{
			static const int month_days_cumulative[12] =
			{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
			int month, year, leap_days;

			if (tm->tm_year < 70)
				/* we don't support years before 1970 as they will cause this function
				   to return a negative value */
				return -1;

			year = tm->tm_year + 1900;
			month = tm->tm_mon;
			if (month < 0) {
				year += (11 - month) / 12;
				month = 11 - (11 - month) % 12;
			}
			else if (month >= 12) {
				year -= month / 12;
				month = month % 12;
			}

			leap_days = year - (tm->tm_mon <= 1);
			leap_days = ((leap_days / 4) - (leap_days / 100) + (leap_days / 400)
				- (1969 / 4) + (1969 / 100) - (1969 / 400));

			return ((((time_t)(year - 1970) * 365
				+ leap_days + month_days_cumulative[month] + tm->tm_mday - 1) * 24
				+ tm->tm_hour) * 60 + tm->tm_min) * 60 + tm->tm_sec;
		}

		static int parsedate(const char* date, time_t* output)
		{
			time_t t = 0;
			int wdaynum = -1;  /* day of the week number, 0-6 (mon-sun) */
			int monnum = -1;   /* month of the year number, 0-11 */
			int mdaynum = -1; /* day of month, 1 - 31 */
			int hournum = -1;
			int minnum = -1;
			int secnum = -1;
			int yearnum = -1;
			int tzoff = -1;
			my_tm tm;
			assume dignext = DATE_MDAY;
			const char* indate = date; /* save the original pointer */
			int part = 0; /* max 6 parts */

			while (*date && (part < 6)) {
				bool found = false;

				skip(&date);

				if (my_isalpha(*date)) {
					/* a name coming up */
					char buf[32] = "";
					size_t len;
					sscanf(date, "%31[ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz]",
						buf);
					len = strlen(buf);

					if (wdaynum == -1) {
						wdaynum = checkday(buf, len);
						if (wdaynum != -1)
							found = true;
					}
					if (!found && (monnum == -1)) {
						monnum = checkmonth(buf);
						if (monnum != -1)
							found = true;
					}

					if (!found && (tzoff == -1)) {
						/* this just must be a time zone string */
						tzoff = checktz(buf);
						if (tzoff != -1)
							found = true;
					}

					if (!found)
						return PARSEDATE_FAIL; /* bad string */

					date += len;
				}
				else if (my_isdigit(*date)) {
					/* a digit */
					int val;
					char* end;
					if ((secnum == -1) &&
						(3 == sscanf(date, "%02d:%02d:%02d", &hournum, &minnum, &secnum))) {
						/* time stamp! */
						date += 8;
					}
					else if ((secnum == -1) &&
						(2 == sscanf(date, "%02d:%02d", &hournum, &minnum))) {
						/* time stamp without seconds */
						date += 5;
						secnum = 0;
					}
					else {
						val = my_curlx_sltosi(strtol(date, &end, 10));

						if ((tzoff == -1) &&
							((end - date) == 4) &&
							(val <= 1400) &&
							(indate < date) &&
							((date[-1] == '+' || date[-1] == '-'))) {
							/* four digits and a value less than or equal to 1400 (to take into
							   account all sorts of funny time zone diffs) and it is preceded
							   with a plus or minus. This is a time zone indication.  1400 is
							   picked since +1300 is frequently used and +1400 is mentioned as
							   an edge number in the document "ISO C 200X Proposal: Timezone
							   Functions" at http://david.tribble.com/text/c0xtimezone.html If
							   anyone has a more authoritative source for the exact maximum time
							   zone offsets, please speak up! */
							found = true;
							tzoff = (val / 100 * 60 + val % 100) * 60;

							/* the + and - prefix indicates the local time compared to GMT,
							   this we need ther reversed math to get what we want */
							tzoff = date[-1] == '+' ? -tzoff : tzoff;
						}

						if (((end - date) == 8) &&
							(yearnum == -1) &&
							(monnum == -1) &&
							(mdaynum == -1)) {
							/* 8 digits, no year, month or day yet. This is YYYYMMDD */
							found = true;
							yearnum = val / 10000;
							monnum = (val % 10000) / 100 - 1; /* month is 0 - 11 */
							mdaynum = val % 100;
						}

						if (!found && (dignext == DATE_MDAY) && (mdaynum == -1)) {
							if ((val > 0) && (val < 32)) {
								mdaynum = val;
								found = true;
							}
							dignext = DATE_YEAR;
						}

						if (!found && (dignext == DATE_YEAR) && (yearnum == -1)) {
							yearnum = val;
							found = true;
							if (yearnum < 1900) {
								if (yearnum > 70)
									yearnum += 1900;
								else
									yearnum += 2000;
							}
							if (mdaynum == -1)
								dignext = DATE_MDAY;
						}

						if (!found)
							return PARSEDATE_FAIL;

						date = end;
					}
				}

				part++;
			}

			if (-1 == secnum)
				secnum = minnum = hournum = 0; /* no time, make it zero */

			if ((-1 == mdaynum) ||
				(-1 == monnum) ||
				(-1 == yearnum))
				/* lacks vital info, fail */
				return PARSEDATE_FAIL;

		#if defined(_USE_32BIT_TIME_T) && defined(_MSC_VER)
			/* 32 bit time_t can only hold dates to the beginning of 2038 */
			if (yearnum > 2037) {
				*output = 0x7fffffff;
				return PARSEDATE_LATER;
			}
		#endif

			if (yearnum < 1970) {
				*output = 0;
				return PARSEDATE_SOONER;
			}

			tm.tm_sec = secnum;
			tm.tm_min = minnum;
			tm.tm_hour = hournum;
			tm.tm_mday = mdaynum;
			tm.tm_mon = monnum;
			tm.tm_year = yearnum - 1900;

			/* my_timegm() returns a time_t. time_t is often 32 bits, even on many
			   architectures that feature 64 bit 'long'.

			   Some systems have 64 bit time_t and deal with years beyond 2038. However,
			   even on some of the systems with 64 bit time_t mktime() returns -1 for
			   dates beyond 03:14:07 UTC, January 19, 2038. (Such as AIX 5100-06)
			*/
			t = my_timegm(&tm);

			/* time zone adjust (cast t to int to compare to negative one) */
			if (-1 != (int)t) {

				/* Add the time zone diff between local time zone and GMT. */
				long delta = (long)(tzoff != -1 ? tzoff : 0);

				if ((delta > 0) && (t + delta < t))
					return -1; /* time_t overflow */

				t += delta;
			}

			*output = t;

			return PARSEDATE_OK;
		}
	}

	inline std::string http_last_modified(const std::string& file)
	{
		std::string str;
		boost::filesystem::path p(file);
		if (boost::filesystem::exists(p))
		{
			std::time_t t = boost::filesystem::last_write_time(p);
			tm* gmt = gmtime((const time_t*)&t);
			char time_buf[512] = { 0 };
			strftime(time_buf, 200, "%a, %d %b %Y %H:%M:%S GMT", gmt);
			str = time_buf;
		}

		return str;
	}

	inline std::time_t http_parse_last_modified(const std::string& gmttime)
	{
		std::time_t out;
		if (detail::parsedate(gmttime.c_str(), &out) != 0)
			return -1;
		return out;
	}
}