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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/basictypes.h"
#include "base/strings/string16.h"
#include "ui/base/ui_base_export.h"
namespace base {
class Time;
class TimeDelta;
namespace ui {
// Methods to format time values as strings.
class UI_BASE_EXPORT TimeFormat {
enum Format {
FORMAT_DURATION, // Plain duration, e.g. in English: "2 minutes".
FORMAT_REMAINING, // Remaining time, e.g. in English: "2 minutes left".
FORMAT_ELAPSED, // Elapsed time, e.g. in English: "2 minutes ago".
FORMAT_COUNT // Enum size counter, not a format. Must be last.
enum Length {
LENGTH_SHORT, // Short format, e.g. in English: sec/min/hour/day.
LENGTH_LONG, // Long format, e.g. in English: second/minute/hour/day.
LENGTH_COUNT // Enum size counter, not a length. Must be last.
// Return a localized string of approximate time duration, formatted as a
// single number, e.g. in English "2 hours ago". Currently, all combinations
// of format and length except (FORMAT_ELAPSED, LENGTH_LONG) are implemented
// but it's easy to add this, if required.
static base::string16 Simple(Format format,
Length length,
const base::TimeDelta& delta);
// Return a localized string of more precise time duration, either formatted
// as a single value or as two values: for a time delta of e.g. 2h19m either
// "2 hours" or "2 hours and 19 minutes" could be returned in English.
// Two-value output can be forced by setting |cutoff| to -1. Single-value
// output can be forced by using Simple() or setting |cutoff| to 0.
// Otherwise, choice of format happens automatically and the value of |cutoff|
// determines the largest numeric value that may appear in a single-value
// format -- for lower numeric values, a second unit is added to increase
// precision. (Applied to the examples above, a |cutoff| of 2 or smaller
// would yield the first string and a |cutoff| of 3 or larger would return the
// second string.)
// The aim of this logic is to reduce rounding errors (that in single-value
// representation can amount up to 33% of the true time duration) while at the
// same time avoiding over-precise time outputs such as e.g. "56 minutes 29
// seconds". The relative rounding error is guaranteed to be less than 0.5 /
// |cutoff| (e.g. 5% for a |cutoff| of 10) and a second unit is only used when
// necessary to achieve the precision guarantee.
// Currently, the only combination of format and length that is implemented is
// (FORMAT_DURATION, LENGTH_LONG), but it's easy to add others if required.
// Note: To allow pre-, post- and infixes which can be inflected depending on
// either the first or the second value, two separate translation strings
// (IDS_TIME_*_1ST and IDS_TIME_*_2ND) are used per [plurality] times [pair of
// units] and are concatenated after having been formatted individually. The
// separator between first unit and second unit (a blank in English) is
// included in IDS_TIME_*_1ST.
static base::string16 Detailed(Format format,
Length length,
int cutoff,
const base::TimeDelta& delta);
// For displaying a relative time in the past. This method returns either
// "Today", "Yesterday", or an empty string if it's older than that. Returns
// the empty string for days in the future.
// TODO(brettw): This should be able to handle days in the future like
// "Tomorrow".
// TODO(tc): This should be able to do things like "Last week". This
// requires handling singluar/plural for all languages.
// The second parameter is optional, it is midnight of "Now" for relative day
// computations: Time::Now().LocalMidnight()
// If NULL, the current day's midnight will be retrieved, which can be
// slow. If many items are being processed, it is best to get the current
// time once at the beginning and pass it for each computation.
static base::string16 RelativeDate(const base::Time& time,
const base::Time* optional_midnight_today);
} // namespace ui