/*-
 *  parsetime.c - parse time for at(1)
 *
 * SPDX-License-Identifier: BSD-2-Clause
 *
 *  Copyright (C) 1993, 1994  Thomas Koenig
 *
 *  modifications for English-language times
 *  Copyright (C) 1993  David Parsons
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. The name of the author(s) may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *  at [NOW] PLUS NUMBER MINUTES|HOURS|DAYS|WEEKS
 *     /NUMBER [DOT NUMBER] [AM|PM]\ /[MONTH NUMBER [NUMBER]]             \
 *     |NOON                       | |[TOMORROW]                          |
 *     |MIDNIGHT                   | |[DAY OF WEEK]                       |
 *     \TEATIME                    / |NUMBER [SLASH NUMBER [SLASH NUMBER]]|
 *                                   \PLUS NUMBER MINUTES|HOURS|DAYS|WEEKS/
 */

#include <sys/cdefs.h>
/* System Headers */

#include <sys/types.h>
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#ifndef __FreeBSD__
#include <getopt.h>
#endif

/* Local headers */

#include "at.h"
#include "panic.h"
#include "parsetime.h"


/* Structures and unions */

enum {  /* symbols */
    MIDNIGHT, NOON, TEATIME,
    PM, AM, TOMORROW, TODAY, NOW,
    MINUTES, HOURS, DAYS, WEEKS, MONTHS, YEARS,
    NUMBER, PLUS, MINUS, DOT, SLASH, ID, JUNK,
    JAN, FEB, MAR, APR, MAY, JUN,
    JUL, AUG, SEP, OCT, NOV, DEC,
    SUN, MON, TUE, WED, THU, FRI, SAT
    };

/* parse translation table - table driven parsers can be your FRIEND!
 */
static const struct {
    const char *name;   /* token name */
    int value;  /* token id */
    int plural; /* is this plural? */
} Specials[] = {
    { "midnight", MIDNIGHT,0 }, /* 00:00:00 of today or tomorrow */
    { "noon", NOON,0 },         /* 12:00:00 of today or tomorrow */
    { "teatime", TEATIME,0 },   /* 16:00:00 of today or tomorrow */
    { "am", AM,0 },             /* morning times for 0-12 clock */
    { "pm", PM,0 },             /* evening times for 0-12 clock */
    { "tomorrow", TOMORROW,0 }, /* execute 24 hours from time */
    { "today", TODAY, 0 },      /* execute today - don't advance time */
    { "now", NOW,0 },           /* opt prefix for PLUS */

    { "minute", MINUTES,0 },    /* minutes multiplier */
    { "minutes", MINUTES,1 },   /* (pluralized) */
    { "hour", HOURS,0 },        /* hours ... */
    { "hours", HOURS,1 },       /* (pluralized) */
    { "day", DAYS,0 },          /* days ... */
    { "days", DAYS,1 },         /* (pluralized) */
    { "week", WEEKS,0 },        /* week ... */
    { "weeks", WEEKS,1 },       /* (pluralized) */
    { "month", MONTHS,0 },      /* month ... */
    { "months", MONTHS,1 },     /* (pluralized) */
    { "year", YEARS,0 },        /* year ... */
    { "years", YEARS,1 },       /* (pluralized) */
    { "jan", JAN,0 },
    { "feb", FEB,0 },
    { "mar", MAR,0 },
    { "apr", APR,0 },
    { "may", MAY,0 },
    { "jun", JUN,0 },
    { "jul", JUL,0 },
    { "aug", AUG,0 },
    { "sep", SEP,0 },
    { "oct", OCT,0 },
    { "nov", NOV,0 },
    { "dec", DEC,0 },
    { "january", JAN,0 },
    { "february", FEB,0 },
    { "march", MAR,0 },
    { "april", APR,0 },
    { "may", MAY,0 },
    { "june", JUN,0 },
    { "july", JUL,0 },
    { "august", AUG,0 },
    { "september", SEP,0 },
    { "october", OCT,0 },
    { "november", NOV,0 },
    { "december", DEC,0 },
    { "sunday", SUN, 0 },
    { "sun", SUN, 0 },
    { "monday", MON, 0 },
    { "mon", MON, 0 },
    { "tuesday", TUE, 0 },
    { "tue", TUE, 0 },
    { "wednesday", WED, 0 },
    { "wed", WED, 0 },
    { "thursday", THU, 0 },
    { "thu", THU, 0 },
    { "friday", FRI, 0 },
    { "fri", FRI, 0 },
    { "saturday", SAT, 0 },
    { "sat", SAT, 0 },
} ;

/* File scope variables */

static char **scp;      /* scanner - pointer at arglist */
static char scc;        /* scanner - count of remaining arguments */
static char *sct;       /* scanner - next char pointer in current argument */
static int need;        /* scanner - need to advance to next argument */

static char *sc_token;  /* scanner - token buffer */
static size_t sc_len;   /* scanner - length of token buffer */
static int sc_tokid;    /* scanner - token id */
static int sc_tokplur;  /* scanner - is token plural? */

/* Local functions */

/*
 * parse a token, checking if it's something special to us
 */
static int
parse_token(char *arg)
{
    size_t i;

    for (i=0; i<(sizeof Specials/sizeof Specials[0]); i++)
        if (strcasecmp(Specials[i].name, arg) == 0) {
            sc_tokplur = Specials[i].plural;
            return sc_tokid = Specials[i].value;
        }

    /* not special - must be some random id */
    return ID;
} /* parse_token */


/*
 * init_scanner() sets up the scanner to eat arguments
 */
static void
init_scanner(int argc, char **argv)
{
    scp = argv;
    scc = argc;
    need = 1;
    sc_len = 1;
    while (argc-- > 0)
        sc_len += strlen(*argv++);

    if ((sc_token = malloc(sc_len)) == NULL)
        errx(EXIT_FAILURE, "virtual memory exhausted");
} /* init_scanner */

/*
 * token() fetches a token from the input stream
 */
static int
token(void)
{
    int idx;

    while (1) {
        memset(sc_token, 0, sc_len);
        sc_tokid = EOF;
        sc_tokplur = 0;
        idx = 0;

        /* if we need to read another argument, walk along the argument list;
         * when we fall off the arglist, we'll just return EOF forever
         */
        if (need) {
            if (scc < 1)
                return sc_tokid;
            sct = *scp;
            scp++;
            scc--;
            need = 0;
        }
        /* eat whitespace now - if we walk off the end of the argument,
         * we'll continue, which puts us up at the top of the while loop
         * to fetch the next argument in
         */
        while (isspace(*sct))
            ++sct;
        if (!*sct) {
            need = 1;
            continue;
        }

        /* preserve the first character of the new token
         */
        sc_token[0] = *sct++;

        /* then see what it is
         */
        if (isdigit(sc_token[0])) {
            while (isdigit(*sct))
                sc_token[++idx] = *sct++;
            sc_token[++idx] = 0;
            return sc_tokid = NUMBER;
        }
        else if (isalpha(sc_token[0])) {
            while (isalpha(*sct))
                sc_token[++idx] = *sct++;
            sc_token[++idx] = 0;
            return parse_token(sc_token);
        }
        else if (sc_token[0] == ':' || sc_token[0] == '.')
            return sc_tokid = DOT;
        else if (sc_token[0] == '+')
            return sc_tokid = PLUS;
        else if (sc_token[0] == '-')
            return sc_tokid = MINUS;
        else if (sc_token[0] == '/')
            return sc_tokid = SLASH;
        else
            return sc_tokid = JUNK;
    } /* while (1) */
} /* token */


/*
 * plonk() gives an appropriate error message if a token is incorrect
 */
static void
plonk(int tok)
{
    panic((tok == EOF) ? "incomplete time"
                       : "garbled time");
} /* plonk */


/* 
 * expect() gets a token and dies most horribly if it's not the token we want
 */
static void
expect(int desired)
{
    if (token() != desired)
        plonk(sc_tokid);        /* and we die here... */
} /* expect */


/*
 * plus_or_minus() holds functionality common to plus() and minus()
 */
static void
plus_or_minus(struct tm *tm, int delay)
{
    int expectplur;

    expectplur = (delay != 1 && delay != -1) ? 1 : 0;

    switch (token()) {
    case YEARS:
            tm->tm_year += delay;
            break;
    case MONTHS:
            tm->tm_mon += delay;
            break;
    case WEEKS:
            delay *= 7;
    case DAYS:
            tm->tm_mday += delay;
            break;
    case HOURS:
            tm->tm_hour += delay;
            break;
    case MINUTES:
            tm->tm_min += delay;
            break;
    default:
            plonk(sc_tokid);
            break;
    }

    if (expectplur != sc_tokplur)
        warnx("pluralization is wrong");

    tm->tm_isdst = -1;
    if (mktime(tm) < 0)
        plonk(sc_tokid);
} /* plus_or_minus */


/*
 * plus() parses a now + time
 *
 *  at [NOW] PLUS NUMBER [MINUTES|HOURS|DAYS|WEEKS|MONTHS|YEARS]
 *
 */
static void
plus(struct tm *tm)
{
    int delay;

    expect(NUMBER);

    delay = atoi(sc_token);
    plus_or_minus(tm, delay);
} /* plus */


/*
 * minus() is like plus but can not be used with NOW
 */
static void
minus(struct tm *tm)
{
    int delay;

    expect(NUMBER);

    delay = -atoi(sc_token);
    plus_or_minus(tm, delay);
} /* minus */


/*
 * tod() computes the time of day
 *     [NUMBER [DOT NUMBER] [AM|PM]]
 */
static void
tod(struct tm *tm)
{
    int hour, minute = 0;
    int tlen;

    hour = atoi(sc_token);
    tlen = strlen(sc_token);

    /* first pick out the time of day - if it's 4 digits, we assume
     * a HHMM time, otherwise it's HH DOT MM time
     */
    if (token() == DOT) {
        expect(NUMBER);
        minute = atoi(sc_token);
        if (minute > 59)
            panic("garbled time");
        token();
    }
    else if (tlen == 4) {
        minute = hour%100;
        if (minute > 59)
            panic("garbled time");
        hour = hour/100;
    }

    /* check if an AM or PM specifier was given
     */
    if (sc_tokid == AM || sc_tokid == PM) {
        if (hour > 12)
            panic("garbled time");

        if (sc_tokid == PM) {
            if (hour != 12)     /* 12:xx PM is 12:xx, not 24:xx */
                        hour += 12;
        } else {
            if (hour == 12)     /* 12:xx AM is 00:xx, not 12:xx */
                        hour = 0;
        }
        token();
    }
    else if (hour > 23)
        panic("garbled time");

    /* if we specify an absolute time, we don't want to bump the day even
     * if we've gone past that time - but if we're specifying a time plus
     * a relative offset, it's okay to bump things
     */
    if ((sc_tokid == EOF || sc_tokid == PLUS || sc_tokid == MINUS) && 
        tm->tm_hour > hour) {
        tm->tm_mday++;
        tm->tm_wday++;
    }

    tm->tm_hour = hour;
    tm->tm_min = minute;
    if (tm->tm_hour == 24) {
        tm->tm_hour = 0;
        tm->tm_mday++;
    }
} /* tod */


/*
 * assign_date() assigns a date, wrapping to next year if needed
 */
static void
assign_date(struct tm *tm, long mday, long mon, long year)
{

   /*
    * Convert year into tm_year format (year - 1900).
    * We may be given the year in 2 digit, 4 digit, or tm_year format.
    */
    if (year != -1) {
        if (year >= 1900)
                year -= 1900;   /* convert from 4 digit year */
        else if (year < 100) {
                /* convert from 2 digit year */
                struct tm *lt;
                time_t now;

                time(&now);
                lt = localtime(&now);

                /* Convert to tm_year assuming current century */
                year += (lt->tm_year / 100) * 100;

                if (year == lt->tm_year - 1) year++;
                else if (year < lt->tm_year)
                        year += 100;    /* must be in next century */
        }
    }

    if (year < 0 &&
        (tm->tm_mon > mon ||(tm->tm_mon == mon && tm->tm_mday > mday)))
        year = tm->tm_year + 1;

    tm->tm_mday = mday;
    tm->tm_mon = mon;

    if (year >= 0)
        tm->tm_year = year;
} /* assign_date */


/* 
 * month() picks apart a month specification
 *
 *  /[<month> NUMBER [NUMBER]]           \
 *  |[TOMORROW]                          |
 *  |[DAY OF WEEK]                       |
 *  |NUMBER [SLASH NUMBER [SLASH NUMBER]]|
 *  \PLUS NUMBER MINUTES|HOURS|DAYS|WEEKS/
 */
static void
month(struct tm *tm)
{
    long year= (-1);
    long mday = 0, wday, mon;
    int tlen;

    switch (sc_tokid) {
    case PLUS:
            plus(tm);
            break;
    case MINUS:
            minus(tm);
            break;

    case TOMORROW:
            /* do something tomorrow */
            tm->tm_mday ++;
            tm->tm_wday ++;
    case TODAY: /* force ourselves to stay in today - no further processing */
            token();
            break;

    case JAN: case FEB: case MAR: case APR: case MAY: case JUN:
    case JUL: case AUG: case SEP: case OCT: case NOV: case DEC:
            /* do month mday [year]
             */
            mon = (sc_tokid-JAN);
            expect(NUMBER);
            mday = atol(sc_token);
            if (token() == NUMBER) {
                year = atol(sc_token);
                token();
            }
            assign_date(tm, mday, mon, year);
            break;

    case SUN: case MON: case TUE:
    case WED: case THU: case FRI:
    case SAT:
            /* do a particular day of the week
             */
            wday = (sc_tokid-SUN);

            mday = tm->tm_mday;

            /* if this day is < today, then roll to next week
             */
            if (wday < tm->tm_wday)
                mday += 7 - (tm->tm_wday - wday);
            else
                mday += (wday - tm->tm_wday);

            tm->tm_wday = wday;

            assign_date(tm, mday, tm->tm_mon, tm->tm_year);
            break;

    case NUMBER:
            /* get numeric MMDDYY, mm/dd/yy, or dd.mm.yy
             */
            tlen = strlen(sc_token);
            mon = atol(sc_token);
            token();

            if (sc_tokid == SLASH || sc_tokid == DOT) {
                int sep;

                sep = sc_tokid;
                expect(NUMBER);
                mday = atol(sc_token);
                if (token() == sep) {
                    expect(NUMBER);
                    year = atol(sc_token);
                    token();
                }

                /* flip months and days for European timing
                 */
                if (sep == DOT) {
                    int x = mday;
                    mday = mon;
                    mon = x;
                }
            }
            else if (tlen == 6 || tlen == 8) {
                if (tlen == 8) {
                    year = (mon % 10000) - 1900;
                    mon /= 10000;
                }
                else {
                    year = mon % 100;
                    mon /= 100;
                }
                mday = mon % 100;
                mon /= 100;
            }
            else
                panic("garbled time");

            mon--;
            if (mon < 0 || mon > 11 || mday < 1 || mday > 31)
                panic("garbled time");

            assign_date(tm, mday, mon, year);
            break;
    } /* case */
} /* month */


/* Global functions */

time_t
parsetime(int argc, char **argv)
{
/* Do the argument parsing, die if necessary, and return the time the job
 * should be run.
 */
    time_t nowtimer, runtimer;
    struct tm nowtime, runtime;
    int hr = 0;
    /* this MUST be initialized to zero for midnight/noon/teatime */

    nowtimer = time(NULL);
    nowtime = *localtime(&nowtimer);

    runtime = nowtime;
    runtime.tm_sec = 0;
    runtime.tm_isdst = 0;

    if (argc <= optind)
        usage();

    init_scanner(argc-optind, argv+optind);

    switch (token()) {
    case NOW:   
            if (scc < 1) {
                return nowtimer;
            }
            /* now is optional prefix for PLUS tree */
            expect(PLUS);
            /* FALLTHROUGH */
    case PLUS:
            plus(&runtime);
            break;

            /* MINUS is different from PLUS in that NOW is not
             * an optional prefix for it
             */
    case MINUS:
            minus(&runtime);
            break;
    case NUMBER:
            tod(&runtime);
            month(&runtime);
            break;

            /* evil coding for TEATIME|NOON|MIDNIGHT - we've initialised
             * hr to zero up above, then fall into this case in such a
             * way so we add +12 +4 hours to it for teatime, +12 hours
             * to it for noon, and nothing at all for midnight, then
             * set our runtime to that hour before leaping into the
             * month scanner
             */
    case TEATIME:
            hr += 4;
            /* FALLTHROUGH */
    case NOON:
            hr += 12;
            /* FALLTHROUGH */
    case MIDNIGHT:
            if (runtime.tm_hour >= hr) {
                runtime.tm_mday++;
                runtime.tm_wday++;
            }
            runtime.tm_hour = hr;
            runtime.tm_min = 0;
            token();
            /* FALLTHROUGH to month setting */
    default:
            month(&runtime);
            break;
    } /* ugly case statement */
    expect(EOF);

    /* convert back to time_t
     */
    runtime.tm_isdst = -1;
    runtimer = mktime(&runtime);

    if (runtimer < 0)
        panic("garbled time");

    if (nowtimer > runtimer)
        panic("trying to travel back in time");

    return runtimer;
} /* parsetime */