/* date.c:  date parsing for Subversion
 *
 * ====================================================================
 * Copyright (c) 2000-2004 CollabNet.  All rights reserved.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution.  The terms
 * are also available at http://subversion.tigris.org/license-1.html.
 * If newer versions of this license are posted there, you may use a
 * newer version instead, at your option.
 *
 * This software consists of voluntary contributions made by many
 * individuals.  For exact contribution history, see the revision
 * history and logs, available at http://subversion.tigris.org/.
 * ====================================================================
 */

#include <svn_time.h>
#include "svn_error.h"

#include "svn_private_config.h"

/* Valid rule actions */
enum rule_action {
  ACCUM,    /* Accumulate a decimal value */
  MICRO,    /* Accumulate microseconds */
  TZIND,    /* Handle +, -, Z */
  NOOP,     /* Do nothing */
  SKIPFROM, /* If at end-of-value, accept the match.  Otherwise,
               if the next template character matches the current
               value character, continue processing as normal.
               Otherwise, attempt to complete matching starting
               immediately after the first subsequent occurrance of
               ']' in the template. */
  SKIP,     /* Ignore this template character */
  ACCEPT    /* Accept the value */
};

/* How to handle a particular character in a template */
typedef struct
{
  char key;                /* The template char that this rule matches */
  const char *valid;       /* String of valid chars for this rule */
  enum rule_action action; /* What action to take when the rule is matched */
  int offset;              /* Where to store the any results of the action,
                              expressed in terms of bytes relative to the
                              base of a match_state object. */
} rule;

/* The parsed values, before localtime/gmt processing */
typedef struct
{
  apr_time_exp_t base;
  apr_int32_t offhours;
  apr_int32_t offminutes;
} match_state;

#define DIGITS "0123456789"

/* A declarative specification of how each template character
   should be processed, using a rule for each valid symbol. */
static const rule
rules[] =
{
  { 'Y', DIGITS, ACCUM, APR_OFFSETOF (match_state, base.tm_year) },
  { 'M', DIGITS, ACCUM, APR_OFFSETOF (match_state, base.tm_mon) },
  { 'D', DIGITS, ACCUM, APR_OFFSETOF (match_state, base.tm_mday) },
  { 'h', DIGITS, ACCUM, APR_OFFSETOF (match_state, base.tm_hour) },
  { 'm', DIGITS, ACCUM, APR_OFFSETOF (match_state, base.tm_min) },
  { 's', DIGITS, ACCUM, APR_OFFSETOF (match_state, base.tm_sec) },
  { 'u', DIGITS, MICRO, APR_OFFSETOF (match_state, base.tm_usec) },
  { 'O', DIGITS, ACCUM, APR_OFFSETOF (match_state, offhours) },
  { 'o', DIGITS, ACCUM, APR_OFFSETOF (match_state, offminutes) },
  { '+', "-+", TZIND, 0 },
  { 'Z', "Z", TZIND, 0 },
  { ':', ":", NOOP, 0 },
  { '-', "-", NOOP, 0 },
  { 'T', "T", NOOP, 0 },
  { ' ', " ", NOOP, 0 },
  { '.', ".,", NOOP, 0 },
  { '[', NULL, SKIPFROM, 0 },
  { ']', NULL, SKIP, 0 },
  { '\0', NULL, ACCEPT, 0 },
};

/* Return the rule associated with TCHAR, or NULL if there
   is no such rule. */
static const rule *
find_rule (char tchar)
{
  int i = sizeof (rules)/sizeof (rules[0]);
  while (i--)
    if (rules[i].key == tchar)
      return &rules[i];
  return NULL;
}

/* Attempt to match the date-string in VALUE to the provided TEMPLATE,
   using the rules defined above.  Return TRUE on successful match,
   FALSE otherwise.  On successful match, fill in *EXP with the
   matched values and set *LOCALTZ to TRUE if the local time zone
   should be used to interpret the match (i.e. if no time zone
   information was provided), or FALSE if not. */
static svn_boolean_t
template_match (apr_time_exp_t *expt, svn_boolean_t *localtz,
                const char *template, const char *value)
{
  int multiplier = 100000;
  int tzind = 0;
  match_state ms;
  char *base = (char *)&ms;

  memset (&ms, 0, sizeof (ms));

  for (;;)
    {
      const rule *match = find_rule (*template++);
      char vchar = *value++;
      apr_int32_t *place;

      if (!match || (match->valid
                     && (!vchar || !strchr (match->valid, vchar))))
        return FALSE;

      /* Compute the address of memory location affected by this
         rule by adding match->offset bytes to the address of ms.
         Because this is a byte-quantity, it is necessary to cast
         &ms to char *. */
      place = (apr_int32_t *)(base + match->offset);
      switch (match->action)
        {
        case ACCUM:
          *place = *place * 10 + vchar - '0';
          continue;
        case MICRO:
          *place += (vchar - '0') * multiplier;
          multiplier /= 10;
          continue;
        case TZIND:
          tzind = vchar;
          continue;
        case SKIP:
          value--;
          continue;
        case NOOP:
          continue;
        case SKIPFROM:
          if (!vchar)
            break;
          match = find_rule (*template);
          if (!strchr (match->valid, vchar))
            template = strchr (template, ']') + 1;
          value--;
          continue;
        case ACCEPT:
          if (vchar)
            return FALSE;
          break;
        }

      break;
    }

  /* Validate gmt offset here, since we can't reliably do it later. */
  if (ms.offhours > 23 || ms.offminutes > 59)
    return FALSE;

  /* tzind will be '+' or '-' for an explicit time zone, 'Z' to
     indicate UTC, or 0 to indicate local time. */
  switch (tzind)
    {
    case '+':
      ms.base.tm_gmtoff = ms.offhours * 3600 + ms.offminutes * 60;
      break;
    case '-':
      ms.base.tm_gmtoff = -(ms.offhours * 3600 + ms.offminutes * 60);
      break;
    }

  *expt = ms.base;
  *localtz = (tzind == 0);
  return TRUE;
}

static int
valid_days_by_month[] = {
  31, 29, 31, 30,
  31, 30, 31, 31,
  30, 31, 30, 31
};

svn_error_t *
svn_parse_date (svn_boolean_t *matched, apr_time_t *result, const char *text,
                apr_time_t now, apr_pool_t *pool)
{
  apr_time_exp_t expt, expnow;
  apr_status_t apr_err;
  svn_boolean_t localtz;

  *matched = FALSE;

  apr_err = apr_time_exp_lt (&expnow, now);
  if (apr_err != APR_SUCCESS)
    return svn_error_wrap_apr (apr_err, _("Can't manipulate current date"));

  if (template_match (&expt, &localtz, /* ISO-8601 extended, date only */
                      "YYYY-M[M]-D[D]",
                      text)
      || template_match (&expt, &localtz, /* ISO-8601 extended, UTC */
                         "YYYY-M[M]-D[D]Th[h]:mm[:ss[.u[u[u[u[u[u][Z]",
                         text)
      || template_match (&expt, &localtz, /* ISO-8601 extended, with offset */
                         "YYYY-M[M]-D[D]Th[h]:mm[:ss[.u[u[u[u[u[u]+OO[:oo]",
                         text)
      || template_match (&expt, &localtz, /* ISO-8601 basic, date only */
                         "YYYYMMDD",
                         text)
      || template_match (&expt, &localtz, /* ISO-8601 basic, UTC */
                         "YYYYMMDDThhmm[ss[.u[u[u[u[u[u][Z]",
                         text)
      || template_match (&expt, &localtz, /* ISO-8601 basic, with offset */
                         "YYYYMMDDThhmm[ss[.u[u[u[u[u[u]+OO[oo]",
                         text)
      || template_match (&expt, &localtz, /* "svn log" format */
                         "YYYY-M[M]-D[D] h[h]:mm[:ss[.u[u[u[u[u[u][ +OO[oo]",
                         text)
      || template_match (&expt, &localtz, /* GNU date's iso-8601 */
                         "YYYY-M[M]-D[D]Th[h]:mm[:ss[.u[u[u[u[u[u]+OO[oo]",
                         text))
    {
      expt.tm_year -= 1900;
      expt.tm_mon -= 1;
    }
  else if (template_match (&expt, &localtz, /* Just a time */
                           "h[h]:mm[:ss[.u[u[u[u[u[u]",
                           text))
    {
      expt.tm_year = expnow.tm_year;
      expt.tm_mon = expnow.tm_mon;
      expt.tm_mday = expnow.tm_mday;
    }
  else
    return SVN_NO_ERROR;

  /* Range validation, allowing for leap seconds */
  if (expt.tm_mon < 0 || expt.tm_mon > 11
      || expt.tm_mday > valid_days_by_month[expt.tm_mon]
      || expt.tm_mday < 1
      || expt.tm_hour > 23
      || expt.tm_min > 59
      || expt.tm_sec > 60)
    return SVN_NO_ERROR;

  /* february/leap-year day checking.  tm_year is bias-1900, so centuries
     that equal 100 (mod 400) are multiples of 400. */
  if (expt.tm_mon == 1
      && expt.tm_mday == 29
      && (expt.tm_year % 4 != 0
          || (expt.tm_year % 100 == 0 && expt.tm_year % 400 != 100)))
    return SVN_NO_ERROR;

  if (localtz)
    {
      apr_time_t candidate;
      apr_time_exp_t expthen;

      /* We need to know the GMT offset of the requested time, not the
         current time.  In some cases, that quantity is ambiguous,
         since at the end of daylight saving's time, an hour's worth
         of local time happens twice.  For those cases, we should
         prefer DST if we are currently in DST, and standard time if
         not.  So, calculate the time value using the current time's
         GMT offset and use the GMT offset of the resulting time. */
      expt.tm_gmtoff = expnow.tm_gmtoff;
      apr_err = apr_time_exp_gmt_get (&candidate, &expt);
      if (apr_err != APR_SUCCESS)
        return svn_error_wrap_apr (apr_err,
                                   _("Can't calculate requested date"));
      apr_err = apr_time_exp_lt (&expthen, candidate);
      if (apr_err != APR_SUCCESS)
        return svn_error_wrap_apr (apr_err, _("Can't expand time"));
      expt.tm_gmtoff = expthen.tm_gmtoff;
    }
  apr_err = apr_time_exp_gmt_get (result, &expt);
  if (apr_err != APR_SUCCESS)
    return svn_error_wrap_apr (apr_err, _("Can't calculate requested date"));

  *matched = TRUE;
  return SVN_NO_ERROR;
}
