baltzo_zoneinfoutil.h

Go to the documentation of this file.

/// @file baltzo_zoneinfoutil.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// baltzo_zoneinfoutil.h                                              -*-C++-*-
#ifndef INCLUDED_BALTZO_ZONEINFOUTIL
#define INCLUDED_BALTZO_ZONEINFOUTIL
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup baltzo_zoneinfoutil baltzo_zoneinfoutil
/// @brief  Provide utility operations on `baltzo::Zoneinfo` objects.
/// @addtogroup bal
/// @{
/// @addtogroup baltzo
/// @{
/// @addtogroup baltzo_zoneinfoutil
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#baltzo_zoneinfoutil-purpose"> Purpose</a>
/// * <a href="#baltzo_zoneinfoutil-classes"> Classes </a>
/// * <a href="#baltzo_zoneinfoutil-description"> Description </a>
///   * <a href="#baltzo_zoneinfoutil-determining-relevant-transitions-with-loadrelevanttransitions"> Determining Relevant Transitions with loadRelevantTransitions </a>
///   * <a href="#baltzo_zoneinfoutil-well-formed-time-zone-information"> Well-Formed Time Zone Information </a>
///     * <a href="#baltzo_zoneinfoutil-overlapping-transitions"> Overlapping Transitions </a>
///   * <a href="#baltzo_zoneinfoutil-usage"> Usage </a>
///     * <a href="#baltzo_zoneinfoutil-prologue-initializing-a-baltzo-zoneinfo-object"> Prologue: Initializing a baltzo::Zoneinfo Object </a>
///     * <a href="#baltzo_zoneinfoutil-example-1-converting-from-a-utc-time-to-a-local-time"> Example 1: Converting from a UTC Time to a Local Time </a>
///     * <a href="#baltzo_zoneinfoutil-example-2-determining-the-type-of-a-local-time"> Example 2: Determining the Type of a Local Time </a>
///
/// # Purpose {#baltzo_zoneinfoutil-purpose}
/// Provide utility operations on `baltzo::Zoneinfo` objects.
///
/// # Classes {#baltzo_zoneinfoutil-classes}
///
/// -  baltzo::ZoneinfoUtil: utility for operations on a `baltzo::Zoneinfo` object
///
/// @see  baltzo_zoneinfo, baltzo_localtimevalidity
///
/// # Description {#baltzo_zoneinfoutil-description}
/// This component provides a suite of pure functions that operate
/// on objects of type `baltzo::Zoneinfo`.  A `baltzo::Zoneinfo` is a value
/// semantic-type providing information about a time zone, mirroring the
/// information found in the Zoneinfo Database, a public-domain distribution of
/// time zone data (see @ref baltzo_zoneinfo  for more information).  The primary
/// functions provided by `baltzo::ZoneinfoUtil` are `convertUtcToLocalTime` and
/// `loadRelevantTransitions`: `convertUtcToLocalTime` converts a UTC time into
/// its corresponding local time in the time zone described by the supplied
/// `baltzo::Zoneinfo` object; `loadRelevantTransitions` returns the transition,
/// from the supplied `baltzo::Zoneinfo` object's list of transitions that
/// describes the attributes of local time in effect at supplied local time;
/// returning two possible transitions in instances where the supplied local
/// time is either invalid or ambiguous (see @ref baltzo_localtimevalidity ).  Note
/// that the time supplied as input to `convertUtcToLocalTime` is a *UTC* time,
/// whereas the time supplied as input to `loadRelevantTransitions` is a *local*
/// time.
///
/// ## Determining Relevant Transitions with loadRelevantTransitions {#baltzo_zoneinfoutil-determining-relevant-transitions-with-loadrelevanttransitions}
///
///
/// The function `loadRelevantTransitions` is used to find the transition in a
/// `baltzo::Zoneinfo` object that describes the properties of a client supplied
/// local time value.  In instances where the client supplied local time is
/// either ambiguous or invalid `loadRelevantTransitions` returns an alternative
/// transition that refers to a second set of properties that could be used to
/// describe the supplied local time.  To understand why multiple transitions
/// might be needed, consider the impact of daylight-saving time transitions on
/// local time in New York:
/// @code
/// Figure 1: Mapping between UTC Time and New York Local Time
///
///    EST - Eastern Standard Time (UTC-5:00)
///    EDT - Eastern Daylight Time (UTC-4:00)
///
///                                        ,-invalid times    ,- ambiguous times
///                                    T2 /  T3           T4 /   T5
///                                    @-----O            @------O
///
///               T1      EST          T2                 T4        EST
/// New York Time @--------------------O                  @------------------>
///                                    |     T3    EDT    |      T5
///                                    |     @------------|------O
///                                   /   __/            /    __/
///                                 /  __/              /  __/
///                                /__/                /__/
///      UTC Time +---------------+-------------------+---------------------->
///               |               |                   |
///               Transition 1    Transition 2        Transition 3
///               (to EST)        (to EDT)            (to EST)
///
/// @endcode
/// In New York, clocks are set forward an hour in the spring, creating the
/// discontinuity between T2 and T3 in the diagram.  A New York local time value
/// in the range [T2, T3) is considered invalid, because a correctly set clock
/// in New York would never display that value.  Similarly, clocks are set back
/// an hour in the fall, creating the discontinuity between T4 and T5 in the
/// diagram.  A New York local time value in the range [T4, T5) is considered
/// ambiguous, as local times in that range occur twice.  For either invalid or
/// ambiguous times, `loadRelevantTransitions` will return two distinct
/// iterators referring to the adjacent transitions holding the two descriptions
/// that might be applied to that local time.
///
/// For example, consider the returned validity and transitions for the
/// following New York local times:
/// @code
/// New York Local Time  Validity     1st Transition      2nd Transition
/// -------------------  -----------  ------------------  ------------------
/// Jan  1, 2010 2:30am  *_UNIQUE     Nov  1, 2009 (EST)  Nov  1, 2009 (EST)
/// Mar 14, 2010 2:30am  *_INVALID    Nov  1, 2009 (EST)  Mar 14, 2010 (EDT)
/// Nov  7, 2010 1:30am  *_AMBIGUOUS  Mar 14, 2010 (EDT)  Nov  7, 2010 (EST)
/// @endcode
///
/// ## Well-Formed Time Zone Information {#baltzo_zoneinfoutil-well-formed-time-zone-information}
///
///
/// The primary operations provided by this component require the supplied
/// Zoneinfo value meet certain constraints that are not enforced by the
/// `baltzo::Zoneinfo` type itself.  A Zoneinfo meeting these constraints is
/// considered *well-formed*, and `baltzo::ZoneinfoUtil::isWellFormed` will
/// return `true` for such a value.  Specifically, a `baltzo::Zoneinfo` object
/// is considered well-formed only if *all* of the following are true:
///
/// 1. The Zoneinfo provides at least one transition.
/// 2. The first transition in the Zoneinfo is at the first representable
///    `bdlt::Datetime` value, "Jan 01, 0001 00:00" -- i.e.,
///    `bdlt::Datetime(1, 1, 1)`.
/// 3. There is no transition in the ordered sequence of transitions described
///    by the Zoneinfo where local clock time is adjusted (either forwards or
///    backwards) introducing a period of invalid or ambiguous local times,
///    where that range of invalid or ambiguous local times overlaps with the
///    range of invalid or ambiguous local times introduced by subsequent
///    transition.
///
/// Note that `baltzo::ZoneinfoUtil::isWellFormed` has linear complexity with
/// respect to the number of transitions that the Zoneinfo value defines.
///
/// ### Overlapping Transitions {#baltzo_zoneinfoutil-overlapping-transitions}
///
///
/// In order to better understand the 3rd constraint (above) on a well-formed
/// Zoneinfo object, first, notice that Figure 1 above (showing local time in
/// New York) illustrates a well-formed sequence of transitions.  Both
/// Transition 2 (to EDT) and Transition 3 (to EST) introduce a range of
/// ambiguous or invalid times (ambiguous when clocks are adjusted backwards,
/// invalid when clocks are adjusted forward), but those two ranges of ambiguous
/// and invalid local times do not overlap.
///
/// However, a Zoneinfo object is not well-formed if two transitions occur so
/// close together that the respective ranges of invalid or ambiguous times that
/// those transitions introduce, overlap with one and other, as illustrated in
/// Figure 2.
/// @code
/// Figure 2:  Overlapping Transitions
///
/// Standard Time (STD):        UTC+00:00
/// Daylight-Saving Time (DST): UTC+01:00
///
/// Transition 1 (to DST): At 00:00 UTC (00:00 local)
/// Transition 2 (to STD): At 00:30 UTC (01:30 local)
///
///
///                                  (00:30)    STD
///                   STD   (00:00)    @--------------------------
///   Local Time @------------O        |           DST
///                           |        | (01:00) @------O (01:30)
///                           |        |      __/     _/
///                            \        \  __/     __/
///                             \      __\/     __/
///                              \ ___/   \ __/
///     UTC Time +---------------+---------+----------------------------
///                         Transition 1   Transition 2
///                          (01:00 UTC)   (01:30 UTC)
/// @endcode
/// Notice that between [ 00:30 .. 01:00 ] local time, the range of invalid
/// times introduced by Transition 1, overlaps with the range of ambiguous times
/// introduced by Transition 2.  The above time zone would therefore *not* be
/// well-formed.
///
/// ## Usage {#baltzo_zoneinfoutil-usage}
///
///
/// The following examples demonstrate how to use a `ZoneinfoUtil` to perform
/// common operations on time values using a Zoneinfo description of a time
/// zone.
///
/// ### Prologue: Initializing a baltzo::Zoneinfo Object {#baltzo_zoneinfoutil-prologue-initializing-a-baltzo-zoneinfo-object}
///
///
/// We start by creating a Zoneinfo time zone description for New York, which we
/// will use in subsequent examples.  Note that, in practice, clients should
/// obtain time zone information from a data source (see
/// @ref baltzo_zoneinfocache ).
///
/// First we create a Zoneinfo object for New York, and populate `newYork` with
/// the correct time zone identifier:
/// @code
/// baltzo::Zoneinfo newYork;
/// newYork.setIdentifier("America/New_York");
/// @endcode
/// Next we create two local-time descriptors, one for standard time and one for
/// daylight-saving time:
/// @code
/// baltzo::LocalTimeDescriptor est(-18000, false, "EST");
/// baltzo::LocalTimeDescriptor edt(-14400, true,  "EDT");
/// @endcode
/// Then we set the initial descriptor for `newYork` to Eastern Standard Time.
/// Note that such an initial transition is required for a `baltzo::Zoneinfo`
/// object to be considered Well-Formed (see `isWellFormed`):
/// @code
/// newYork.addTransition(bdlt::EpochUtil::convertToTimeT64(
///                                                   bdlt::Datetime(1, 1, 1)),
///                       est);
/// @endcode
/// Next we create a series of transitions between these local-time descriptors
/// for the years 2007-2011.  Note that the United States transitions to
/// daylight saving time on the second Sunday in March, at 2am local time (07:00
/// UTC), and transitions back to standard time on the first Sunday in November
/// at 2am local time (06:00 UTC), resulting in an even number of transitions:
/// @code
/// static const bdlt::Datetime TRANSITION_TIMES[] = {
///     bdlt::Datetime(2007,  3, 11, 7),
///     bdlt::Datetime(2007, 11,  4, 6),
///     bdlt::Datetime(2008,  3,  9, 7),
///     bdlt::Datetime(2008, 11,  2, 6),
///     bdlt::Datetime(2009,  3,  8, 7),
///     bdlt::Datetime(2009, 11,  1, 6),
///     bdlt::Datetime(2010,  3, 14, 7),
///     bdlt::Datetime(2010, 11,  7, 6),
///     bdlt::Datetime(2011,  3, 13, 7),
///     bdlt::Datetime(2011, 11,  6, 6),
/// };
/// const int NUM_TRANSITION_TIMES =
///                         sizeof TRANSITION_TIMES / sizeof *TRANSITION_TIMES;
/// assert(0 == NUM_TRANSITION_TIMES % 2);
///
/// for (int i = 0; i < NUM_TRANSITION_TIMES; i += 2) {
///     newYork.addTransition(bdlt::EpochUtil::convertToTimeT64(
///                                                       TRANSITION_TIMES[i]),
///                           edt);
///     newYork.addTransition(bdlt::EpochUtil::convertToTimeT64(
///                                                   TRANSITION_TIMES[i + 1]),
///                           est);
/// }
/// @endcode
/// Finally we verify that the time zone information we've created is considered
/// well-formed (as discussed above):
/// @code
/// assert(true == baltzo::ZoneinfoUtil::isWellFormed(newYork));
/// @endcode
///
/// ### Example 1: Converting from a UTC Time to a Local Time {#baltzo_zoneinfoutil-example-1-converting-from-a-utc-time-to-a-local-time}
///
///
/// In this example we demonstrate how to convert a UTC time to the
/// corresponding local time using the `convertUtcToLocalTime` class method.
///
/// We start by creating a `bdlt::Datetime` representing the UTC time "Dec 12,
/// 2010 15:00":
/// @code
/// bdlt::Datetime utcTime(2010, 12, 12, 15, 0, 0);
/// @endcode
/// Now, we call `convertUtcToLocalTime` and supply as input both `utcTime` and
/// the Zoneinfo description for `newYork` (which we initialized in the prologue
/// above):
/// @code
/// bdlt::DatetimeTz                          localNYTime;
/// baltzo::Zoneinfo::TransitionConstIterator iterator;
/// baltzo::ZoneinfoUtil::convertUtcToLocalTime(&localNYTime,
///                                             &iterator,
///                                             utcTime,
///                                             newYork);
/// @endcode
/// Then we verify that `localNYTime` is "Dec 12, 2010 10:00+5:00", the time in
/// New York corresponding to the UTC time "Dec 12, 2010 15:00".
/// @code
/// assert(utcTime                          == localNYTime.utcDatetime());
/// assert(bdlt::Datetime(2010, 12, 12, 10) == localNYTime.localDatetime());
/// assert(-5 * 60                          == localNYTime.offset());
/// @endcode
/// Finally, we verify that the returned `iterator` refers to the local-time
/// transition immediately before `utcTime`, and that that transition refers to
/// a local-time descriptor characterizing standard-time in New York:
/// @code
/// baltzo::Zoneinfo::TransitionConstIterator transitionIter     = iterator;
/// baltzo::Zoneinfo::TransitionConstIterator nextTransitionIter = ++iterator;
///
/// const bdlt::EpochUtil::TimeT64 utcTimeT =
///                                  bdlt::EpochUtil::converToTimeT64(utcTime);
/// assert(utcTimeT >= transitionIter->transition());
/// assert(utcTimeT <  nextTransitionIter->transition());
///
/// assert(false        == transitionIter->descriptor().dstInEffectFlag());
/// assert(-5 * 60 * 60 == transitionIter->descriptor().utcOffsetInSeconds());
/// assert("EST"        == transitionIter->descriptor().description());
/// @endcode
///
/// ### Example 2: Determining the Type of a Local Time {#baltzo_zoneinfoutil-example-2-determining-the-type-of-a-local-time}
///
///
/// In this next example we use `loadRelevantTransitions` to determine the
/// local-time descriptor (see @ref baltzo_localtimedescriptor ) that applies to a
/// local time value, represented using a `bdlt::Datetime` object.
///
/// We start by defining a `bdlt::Datetime` object for "Jan 1, 2011 12:00" in
/// New York:
/// @code
/// bdlt::Datetime nyLocalTime(2011, 1, 1, 12);
/// @endcode
/// Then, we call `loadRelevantTransitions`, and supply, as input, both
/// `nyLocalTime` and the Zoneinfo description for `newYork` (which we
/// initialized in the prologue above):
/// @code
/// baltzo::LocalTimeValidity::Enum           validity;
/// baltzo::Zoneinfo::TransitionConstIterator firstTransition;
/// baltzo::Zoneinfo::TransitionConstIterator secondTransition;
/// baltzo::ZoneinfoUtil::loadRelevantTransitions(&firstTransition,
///                                               &secondTransition,
///                                               &validity,
///                                               nyLocalTime,
///                                               newYork);
/// @endcode
/// "Jan 1, 2011 12:00" in New York, is not near a daylight-saving time
/// transition, so it uniquely describes a valid time (in New York) which falls
/// during Eastern Standard Time, and whose local time offset from UTC is -5:00.
/// Because "Jan 1, 2011 12:00" is both a valid and unique local time, the
/// returned validity will be `baltzo::LocalTimeValidity::e_VALID_UNIQUE` and
/// the two returned transition iterators will be equal:
/// @code
/// assert(baltzo::LocalTimeValidity::e_VALID_UNIQUE == validity);
/// assert(firstTransition == secondTransition);
///
/// assert(false    == firstTransition->descriptor().dstInEffectFlag());
/// assert(-5*60*60 == firstTransition->descriptor().utcOffsetInSeconds());
/// assert("EST"    == firstTransition->descriptor().description());
/// @endcode
/// Next, we create a second `bdlt::Datetime` object to represent "Nov 7, 2010
/// 1:30" in New York.  Note that the clock time "Nov 7, 2010 1:30" occurred
/// twice in New York, as clocks were set back by an hour an instant before the
/// local clock would have reached "Nov 7, 2010 02:00 EDT", and it is therefore
/// ambiguous which of those two values that local time is meant to refer.
/// @code
/// bdlt::Datetime ambiguousLocalTime(2010, 11, 7, 1, 30);
/// @endcode
/// Now, we call `loadRelevantTransitions`, this time supplying
/// `ambiguousLocalTime`:
/// @code
/// baltzo::ZoneinfoUtil::loadRelevantTransitions(&firstTransition,
///                                               &secondTransition,
///                                               &validity,
///                                               ambiguousLocalTime,
///                                               newYork);
/// @endcode
/// Finally we observe that the local time was ambiguous and that the returned
/// transitions are distinct:
/// @code
/// assert(baltzo::LocalTimeValidity::e_VALID_AMBIGUOUS == validity);
/// assert(firstTransition != secondTransition);
/// @endcode
/// Because `ambiguousLocalTime` may refer to either the standard or the
/// daylight-saving time value "Nov 7, 2010 01:30", the returned validity will
/// be `e_VALID_AMBIGUOUS`, and the `first` and `second` iterators will differ.
/// `first` will refer to a description of the local time before the transition
/// (daylight-saving time) and `second` will refer to a description of local
/// time after the transition (standard-time):
/// @code
/// assert(true      == firstTransition->descriptor().dstInEffectFlag());
/// assert(-4*60*60  == firstTransition->descriptor().utcOffsetInSeconds());
/// assert("EDT"     == firstTransition->descriptor().description());
///
/// assert(false     == secondTransition->descriptor().dstInEffectFlag());
/// assert(-5*60*60  == secondTransition->descriptor().utcOffsetInSeconds());
/// assert("EST"     == secondTransition->descriptor().description());
/// @endcode
/// Note that the two transitions returned are adjacent:
/// @code
/// ++firstTransition;
/// assert(firstTransition == secondTransition);
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bal
 * @{
 */
/** @addtogroup baltzo
 * @{
 */
/** @addtogroup baltzo_zoneinfoutil
 * @{
 */
 
#include <balscm_version.h>
 
#include <baltzo_localtimevalidity.h>
#include <baltzo_zoneinfo.h>
 
#include <bdlt_datetime.h>
#include <bdlt_datetimetz.h>
 
#include <bsl_iosfwd.h>
 
 
namespace baltzo {
                             // ==================
                             // class ZoneinfoUtil
                             // ==================
 
/// This `struct` provides a namespace for utility operations using a
/// `Zoneinfo` object.
struct ZoneinfoUtil {
 
    // CLASS METHODS
 
    /// Load, into the specified `resultTime`, the local date-time value, in
    /// the specified `timeZone`, corresponding to the specified `utcTime`,
    /// and load, into the specified `resultTransition`, an iterator
    /// referring to the first transition in `timeZone` whose
    /// transition-time is before `utcTime`.  Return 0 on success, and
    /// `baltzo::ErrorCode::k_OUT_OF_RANGE` if `resultTime` would be outside
    /// of the legal range that a `bdlt::DatetimeTz` can represent.  The
    /// behavior is undefined unless `isWellFormed(timeZone)` is `true`.
    static int convertUtcToLocalTime(
                           bdlt::DatetimeTz                  *resultTime,
                           Zoneinfo::TransitionConstIterator *resultTransition,
                           const bdlt::Datetime&              utcTime,
                           const Zoneinfo&                    timeZone);
 
    /// Load, into the specified `firstResultTransition`, an iterator
    /// referring to the transition describing the characteristics of local
    /// time in effect at the specified `localTime` in the specified
    /// `timeZone`; in instances where `localTime` is not both a unique and
    /// valid local time in `timeZone`, load, into the specified
    /// `secondResultTransition`, an iterator referring to a subsequent
    /// transition describing the alternative characteristics of local time
    /// that could also apply to `localTime`; finally load, into the
    /// specified `resultValidity`, the validity of `localTime` as being
    /// unique, ambiguous but valid, or invalid.  If `resultValidity` is
    /// `e_VALID_UNIQUE`, then `firstResultTransition` and
    /// `secondResultTransition` will be loaded with the same transition,
    /// otherwise the returned transitions will be distinct with
    /// `secondResultTransition` referring to the transition immediately
    /// after `firstResultTransition`.  The behavior is undefined unless
    /// `isWellFormed(timeZone)` is `true`, and
    /// `firstResultTransition != secondResultTransition`.
    static void loadRelevantTransitions(
                     Zoneinfo::TransitionConstIterator *firstResultTransition,
                     Zoneinfo::TransitionConstIterator *secondResultTransition,
                     LocalTimeValidity::Enum           *resultValidity,
                     const bdlt::Datetime&              localTime,
                     const Zoneinfo&                    timeZone);
 
    /// Return `true` if the specified `timeZone` is a well-formed Zoneinfo
    /// object (which can be used by other methods on this utility), and
    /// `false` otherwise.  For a Zoneinfo to be considered well-formed
    /// *all* of the following must be true:
    ///
    /// 1. `timeZone.numTransitions() > 0`
    /// 2. The first transition in `timeZone` is at the first representable
    ///    `bdlt::Datetime` value, "Jan 01, 0001 00 00.000" -- i.e.,
    ///    `bdlt::Datetime(1, 1, 1)`.
    /// 3. There is no transition in the ordered sequence of transitions
    ///    described by `timeZone` where the local clock time is adjusted
    ///    (either forwards or backwards) introducing a period of invalid or
    ///    ambiguous local times, where that range of invalid or ambiguous
    ///    local times overlaps with a range of invalid or or ambiguous
    ///    local times introduced by the subsequent transition (see
    ///    component documentation for an illustration).
    ///
    /// Note that this method has linear worst-case time complexity with
    /// respect to `timeZone.numTransitions()`.
    static bool isWellFormed(const Zoneinfo& timeZone);
};
 
}  // close package namespace
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2015 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */