Module:Date: Difference between revisions

    From Nonbinary Wiki
    (clean up and some aliases)
    (major refactor with fixes; force Date to be read-only (error on write); list of dates in a month on a particular day of week)
    Line 4: Line 4:
    local MINUS = '−'  -- Unicode U+2212 MINUS SIGN
    local MINUS = '−'  -- Unicode U+2212 MINUS SIGN


    local Date, DateDiff, datemt -- forward declarations
    local Date, DateDiff, diffmt -- forward declarations
    local uniq = { 'unique identifier' }


    local function is_date(t)
    local function is_date(t)
    return type(t) == 'table' and getmetatable(t) == datemt
    -- The system used to make a date read-only means there is no unique
    -- metatable that is conveniently accessible to check.
    return type(t) == 'table' and t._id == uniq
    end
     
    local function is_diff(t)
    return type(t) == 'table' and getmetatable(t) == diffmt
    end
     
    local function _list_join(list, sep)
    return table.concat(list, sep)
    end
    end


    Line 18: Line 29:
    self[self.n] = item
    self[self.n] = item
    end,
    end,
    join = function (self, sep)
    join = _list_join,
    return table.concat(self, sep)
    end,
    }
    }
    end
    end
    Line 93: Line 102:
    local floor = math.floor
    local floor = math.floor
    local calname = date.calname
    local calname = date.calname
    local jd = date.jd
    local limits  -- min/max limits for date ranges −9999-01-01 to 9999-12-31
    local limits  -- min/max limits for date ranges −9999-01-01 to 9999-12-31
    if calname == 'Julian' then
    if calname == 'Julian' then
    Line 100: Line 108:
    limits = { -1930999.5, 5373484.49999 }
    limits = { -1930999.5, 5373484.49999 }
    else
    else
    limits = { 1, 0 }  -- impossible
    return
    end
    end
    if not (limits[1] <= jd and jd <= limits[2]) then
    local jd = date.jd
    if not (type(jd) == 'number' and limits[1] <= jd and jd <= limits[2]) then
    return
    return
    end
    end
    Line 150: Line 159:
    return
    return
    end
    end
    local y = numbers.y or numbers[1]
    local y = numbers.year  or date.year
    local m = numbers.m or numbers[2]
    local m = numbers.month  or date.month
    local d = numbers.d or numbers[3]
    local d = numbers.day    or date.day
    local H = numbers.H or numbers[4]
    local H = numbers.hour
    local M = numbers.M or numbers[5] or 0
    local M = numbers.minute or date.minute or 0
    local S = numbers.S or numbers[6] or 0
    local S = numbers.second or date.second or 0
    if not (y and m and d) then
    if not (y and m and d) or not
    return
    (-9999 <= y and y <= 9999 and
    end
    1 <= m and m <= 12 and
    if not (-9999 <= y and y <= 9999 and 1 <= m and m <= 12 and
    1 <= d and d <= days_in_month(y, m, date.calname)) then
    1 <= d and d <= days_in_month(y, m, date.calname)) then
    return
    return
    end
    end
    Line 166: Line 174:
    date.hastime = true
    date.hastime = true
    else
    else
    H = 0
    H = date.hour or 0
    end
    end
    if not (0 <= H and H <= 23 and
    if not (0 <= H and H <= 23 and
    Line 206: Line 214:
    -- Example: 'am:AM era:BC'
    -- Example: 'am:AM era:BC'
    for item in options1:gmatch('%S+') do
    for item in options1:gmatch('%S+') do
    local lhs, rhs = item:match('^(%w+):(.+)$')
    local lhs, rhs = item:match('^(%w+)[:=](.+)$')
    if lhs then
    if lhs then
    result[lhs] = rhs
    result[lhs] = rhs
    Line 339: Line 347:
    :gsub('%%%%', PERCENT)
    :gsub('%%%%', PERCENT)
    :gsub('(%s*)%%{(%w+)}', replace_property)
    :gsub('(%s*)%%{(%w+)}', replace_property)
    :gsub('(%s*)%%(-?)(%a)', replace_code)
    :gsub('(%s*)%%(%-?)(%a)', replace_code)
    :gsub(PERCENT, '%%')
    :gsub(PERCENT, '%%')
    )
    )
    Line 345: Line 353:


    local function _date_text(date, fmt, options)
    local function _date_text(date, fmt, options)
    -- Return formatted string from given date.
    -- Return a formatted string representing the given date.
    if not is_date(date) then
    if not is_date(date) then
    return 'Need a date (use "date:text()" with a colon).'
    return 'Need a date (use "date:text()" with a colon).'
    Line 410: Line 418:
    { 'Dec', 'December' },
    { 'Dec', 'December' },
    }
    }
    local function name_to_number(text, translate)
    if type(text) == 'string' then
    return translate[text:lower()]
    end
    end
    local function day_number(text)
    return name_to_number(text, {
    sun = 0, sunday = 0,
    mon = 1, monday = 1,
    tue = 2, tuesday = 2,
    wed = 3, wednesday = 3,
    thu = 4, thursday = 4,
    fri = 5, friday = 5,
    sat = 6, saturday = 6,
    })
    end


    local function month_number(text)
    local function month_number(text)
    if type(text) == 'string' then
    return name_to_number(text, {
    local month_names = {
    jan = 1, january = 1,
    jan = 1, january = 1,
    feb = 2, february = 2,
    feb = 2, february = 2,
    mar = 3, march = 3,
    mar = 3, march = 3,
    apr = 4, april = 4,
    apr = 4, april = 4,
    may = 5,
    may = 5,
    jun = 6, june = 6,
    jun = 6, june = 6,
    jul = 7, july = 7,
    jul = 7, july = 7,
    aug = 8, august = 8,
    aug = 8, august = 8,
    sep = 9, september = 9,
    sep = 9, september = 9,
    oct = 10, october = 10,
    oct = 10, october = 10,
    nov = 11, november = 11,
    nov = 11, november = 11,
    dec = 12, december = 12,
    dec = 12, december = 12
    })
    }
    end
    return month_names[text:lower()]
     
    local function _list_text(list, fmt)
    -- Return a list of formatted strings from a list of dates.
    if not type(list) == 'table' then
    return 'Need "list:text()" with a colon.'
    end
    local result = { join = _list_join }
    for i, date in ipairs(list) do
    result[i] = date:text(fmt)
    end
    return result
    end
     
    local function _make_list(date, spec)
    -- Return a possibly empty numbered table of dates meeting the specification.
    -- The spec should be a string like "Tue >=" meaning that the list will
    -- hold dates for all Tuesdays on or after date, and in date's month.
    if not is_date(date) then
    return 'Need a date (use "date:list()" with a colon).'
    end
    local want_dow, op
    local ops = {
    ['>='] = { before = false, include = true  },
    ['>']  = { before = false, include = false },
    ['<='] = { before = true , include = true  },
    ['<']  = { before = true , include = false },
    }
    if spec then
    if type(spec) ~= 'string' then
    return {}
    end
    for item in spec:gmatch('%S+') do
    if ops[item] then
    if op then
    return {}
    end
    op = ops[item]
    else
    local dow = day_number(item)
    if dow then
    if want_dow then
    -- LATER Could handle more than one day, but probably not needed.
    return {}
    end
    want_dow = dow
    else
    return {}
    end
    end
    end
    end
    local offset = want_dow and want_dow - date.dow or 0
    op = op or ops['>=']
    local first, last
    if op.before then
    if offset >= 0 and not (op.include and offset == 0) then
    offset = offset - 7
    end
    last = date.day + offset
    first = last % 7
    if first == 0 then
    first = 7
    end
    else
    if offset < 0 or (not op.include and offset == 0) then
    offset = offset + 7
    end
    first = date.day + offset
    last = date.monthdays
    end
    local list = { text = _list_text }
    local count = math.floor((last - first)/7) + 1
    for i = 1, count do
    list[i] = Date(date, {day = first})
    first = first + 7
    end
    end
    return list
    end
    end


    -- A table to get the current date/time (UTC), but only if needed.
    -- A table to get the current date/time (UTC), but only if needed.
    local current = setmetatable({}, {
    -- A local test can set the global variable to produce fixed results.
    __index = function (self, key)
    local current = setmetatable(
    local d = os.date('!*t')
    set_current_for_test or {}, {
    self.year = d.year
    __index = function (self, key)
    self.month = d.month
    local d = os.date('!*t')
    self.day = d.day
    self.year = d.year
    self.hour = d.hour
    self.month = d.month
    self.minute = d.min
    self.day = d.day
    self.second = d.sec
    self.hour = d.hour
    return rawget(self, key)
    self.minute = d.min
    end
    self.second = d.sec
    })
    return rawget(self, key)
    end })


    local function extract_date(text)
    local function extract_date(text)
    Line 458: Line 560:
    local date, options = {}, {}
    local date, options = {}, {}
    local function extract_ymd(item)
    local function extract_ymd(item)
    local ystr, mstr, dstr = item:match('^(%d%d%d%d)-(%w+)-(%d%d?)$')
    local ystr, mstr, dstr = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$')
    if ystr then
    if ystr then
    local m
    local m
    Line 467: Line 569:
    end
    end
    if m then
    if m then
    date.y = tonumber(ystr)
    date.year = tonumber(ystr)
    date.m = m
    date.month = m
    date.d = tonumber(dstr)
    date.day = tonumber(dstr)
    return true
    return true
    end
    end
    Line 478: Line 580:
    local m = month_number(item)
    local m = month_number(item)
    if m then
    if m then
    date.m = m
    date.month = m
    return true
    return true
    end
    end
    Line 484: Line 586:
    local function extract_time(item)
    local function extract_time(item)
    local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
    local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
    if date.H or not h then
    if date.hour or not h then
    return
    return
    end
    end
    Line 493: Line 595:
    end
    end
    end
    end
    date.H = tonumber(h)
    date.hour = tonumber(h)
    date.M = tonumber(m)
    date.minute = tonumber(m)
    date.S = tonumber(s)  -- nil if empty string
    date.second = tonumber(s)  -- nil if empty string
    return true
    return true
    end
    end
    Line 511: Line 613:
    local index_time
    local index_time
    local function set_ampm(item)
    local function set_ampm(item)
    local H = date.H
    local H = date.hour
    if H and not options.am and index_time + 1 == item_count then
    if H and not options.am and index_time + 1 == item_count then
    options.am = ampm_options[item]
    options.am = ampm_options[item]
    Line 519: Line 621:
    end
    end
    if H == 12 then
    if H == 12 then
    date.H = 0
    date.hour = 0
    end
    end
    else
    else
    Line 526: Line 628:
    end
    end
    if H <= 11 then
    if H <= 11 then
    date.H = H + 12
    date.hour = H + 12
    end
    end
    end
    end
    Line 549: Line 651:
    end
    end
    index_time = item_count
    index_time = item_count
    elseif date.d and date.m then
    elseif date.day and date.month then
    if date.y then
    if date.year then
    return  -- should be nothing more so item is invalid
    return  -- should be nothing more so item is invalid
    end
    end
    Line 556: Line 658:
    return
    return
    end
    end
    date.y = tonumber(item)
    date.year = tonumber(item)
    elseif date.d then
    elseif date.day then
    if not extract_month(item) then
    if not extract_month(item) then
    return
    return
    end
    end
    elseif date.m then
    elseif date.month then
    if not item:match('^(%d%d?)$') then
    if not item:match('^(%d%d?)$') then
    return
    return
    end
    end
    date.d = tonumber(item)
    date.day = tonumber(item)
    elseif not extract_ymd(item) then
    elseif not extract_ymd(item) then
    if item:match('^(%d%d?)$') then
    if item:match('^(%d%d?)$') then
    date.d = tonumber(item)
    date.day = tonumber(item)
    elseif not extract_month(item) then
    elseif not extract_month(item) then
    return
    return
    Line 574: Line 676:
    end
    end
    end
    end
    if not date.y or date.y == 0 then
    if not date.year or date.year == 0 then
    return
    return
    end
    end
    local era = era_text[options.era]
    local era = era_text[options.era]
    if era and era.isbc then
    if era and era.isbc then
    date.y = 1 - date.y
    date.year = 1 - date.year
    end
    end
    return date, options
    return date, options
    Line 587: Line 689:
    -- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
    -- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
    -- or return nothing if invalid.
    -- or return nothing if invalid.
    -- The result is nil if the calculated date exceeds allowable limits.
    -- Caller ensures that lhs is a date; its properties are copied for the new date.
    -- Caller ensures that lhs is a date; its properties are copied for the new date.
    local function is_prefix(text, word, minlen)
    local function is_prefix(text, word, minlen)
    Line 593: Line 696:
    end
    end
    local function do_days(n)
    local function do_days(n)
    if is_sub then
    local forcetime, jd
    n = -n
    if math.floor(n) == n then
    jd = lhs.jd
    else
    forcetime = not lhs.hastime
    jd = lhs.jdz
    end
    end
    return Date(lhs, 'juliandate', lhs.jd + n)
    jd = jd + (is_sub and -n or n)
    if forcetime then
    jd = tostring(jd)
    if not jd:find('.', 1, true) then
    jd = jd .. '.0'
    end
    end
    return Date(lhs, 'juliandate', jd)
    end
    end
    if type(rhs) == 'number' then
    if type(rhs) == 'number' then
    -- Add days, including fractional days.
    -- Add/subtract days, including fractional days.
    return do_days(rhs)
    return do_days(rhs)
    end
    end
    Line 648: Line 762:
    end
    end


    -- Metatable for some operations on dates.
    -- Metatable for a date's calculated fields.
    datemt = {  -- for forward declaration above
    local datemt = {
    __add = function (lhs, rhs)
    if not is_date(lhs) then
    lhs, rhs = rhs, lhs  -- put date on left (it must be a date for this to have been called)
    end
    return date_add_sub(lhs, rhs)
    end,
    __sub = function (lhs, rhs)
    if is_date(lhs) then
    if is_date(rhs) then
    return DateDiff(lhs, rhs)
    end
    return date_add_sub(lhs, rhs, true)
    end
    end,
    __concat = function (lhs, rhs)
    return tostring(lhs) .. tostring(rhs)
    end,
    __tostring = function (self)
    return self:text()
    end,
    __eq = function (lhs, rhs)
    -- Return true if dates identify same date/time where, for example,
    -- Date(-4712, 1, 1, 'Julian') == Date(-4713, 11, 24, 'Gregorian') is true.
    -- This is only called if lhs and rhs have the same metatable.
    return lhs.jdz == rhs.jdz
    end,
    __lt = function (lhs, rhs)
    -- Return true if lhs < rhs, for example,
    -- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.
    -- This is only called if lhs and rhs have the same metatable.
    return lhs.jdz < rhs.jdz
    end,
    __index = function (self, key)
    __index = function (self, key)
    local value
    local value
    Line 689: Line 771:
    value = day_info[self.dow][2]
    value = day_info[self.dow][2]
    elseif key == 'dow' then
    elseif key == 'dow' then
    value = (self.jd + 1) % 7  -- day-of-week 0=Sun to 6=Sat
    value = (self.jdnoon + 1) % 7  -- day-of-week 0=Sun to 6=Sat
    elseif key == 'dayofweek' then
    elseif key == 'dayofweek' then
    value = self.dow
    value = self.dow
    elseif key == 'dowiso' then
    elseif key == 'dowiso' then
    value = (self.jd % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
    value = (self.jdnoon % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
    elseif key == 'dayofweekiso' then
    elseif key == 'dayofweekiso' then
    value = self.dowiso
    value = self.dowiso
    elseif key == 'doy' then
    elseif key == 'doy' then
    local first = Date(self.year, 1, 1, self.calname).jd
    local first = Date(self.year, 1, 1, self.calname).jdnoon
    value = self.jd - first + 1  -- day-of-year 1 to 366
    value = self.jdnoon - first + 1  -- day-of-year 1 to 366
    elseif key == 'dayofyear' then
    elseif key == 'dayofyear' then
    value = self.doy
    value = self.doy
    Line 706: Line 788:
    elseif key == 'gsd' then
    elseif key == 'gsd' then
    -- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
    -- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
    -- which is JDN = 1721426, and is from jd 1721425.5 to 1721426.49999.
    -- which is from jd 1721425.5 to 1721426.49999.
    value = math.floor(self.jd - 1721424.5)
    value = math.floor(self.jd - 1721424.5)
    elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
    elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
    Line 714: Line 796:
    rawset(self, 'jdz', jdz)
    rawset(self, 'jdz', jdz)
    return key == 'jdz' and jdz or jd
    return key == 'jdz' and jdz or jd
    elseif key == 'jdnoon' then
    -- Julian date at noon (an integer) on the calendar day when jd occurs.
    value = math.floor(self.jd + 0.5)
    elseif key == 'isleapyear' then
    elseif key == 'isleapyear' then
    value = is_leap_year(self.year, self.calname)
    value = is_leap_year(self.year, self.calname)
    Line 729: Line 814:
    end,
    end,
    }
    }
    -- Date operators.
    local function mt_date_add(lhs, rhs)
    if not is_date(lhs) then
    lhs, rhs = rhs, lhs  -- put date on left (it must be a date for this to have been called)
    end
    return date_add_sub(lhs, rhs)
    end
    local function mt_date_sub(lhs, rhs)
    if is_date(lhs) then
    if is_date(rhs) then
    return DateDiff(lhs, rhs)
    end
    return date_add_sub(lhs, rhs, true)
    end
    end
    local function mt_date_concat(lhs, rhs)
    return tostring(lhs) .. tostring(rhs)
    end
    local function mt_date_tostring(self)
    return self:text()
    end
    local function mt_date_eq(lhs, rhs)
    -- Return true if dates identify same date/time where, for example,
    -- Date(-4712, 1, 1, 'Julian') == Date(-4713, 11, 24, 'Gregorian') is true.
    -- This is only called if lhs and rhs have the same metatable.
    return lhs.jdz == rhs.jdz
    end
    local function mt_date_lt(lhs, rhs)
    -- Return true if lhs < rhs, for example,
    -- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.
    -- This is only called if lhs and rhs have the same metatable.
    return lhs.jdz < rhs.jdz
    end


    --[[ Examples of syntax to construct a date:
    --[[ Examples of syntax to construct a date:
    Line 740: Line 864:
    Date('04:30:59 1 April 1995', 'julian')
    Date('04:30:59 1 April 1995', 'julian')
    Date(date)                          copy of an existing date
    Date(date)                          copy of an existing date
    LATER: Following is not yet implemented:
    Date(date, t)                      same, updated with y,m,d,H,M,S fields from table t
    Date('currentdate', H, M, S)       current date with given time
    Date(t)                       date with y,m,d,H,M,S fields from table t
    ]]
    ]]
    function Date(...)  -- for forward declaration above
    function Date(...)  -- for forward declaration above
    Line 747: Line 871:
    -- (proleptic Gregorian calendar or proleptic Julian calendar), or
    -- (proleptic Gregorian calendar or proleptic Julian calendar), or
    -- return nothing if date is invalid.
    -- return nothing if date is invalid.
    local is_copy
    local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
    local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
    local result = {
    local newdate = {
    _id = uniq,
    calname = 'Gregorian',  -- default is Gregorian calendar
    calname = 'Gregorian',  -- default is Gregorian calendar
    hastime = false,  -- true if input sets a time
    hastime = false,  -- true if input sets a time
    Line 756: Line 880:
    second = 0,
    second = 0,
    options = make_option_table(),
    options = make_option_table(),
    list = _make_list,
    text = _date_text,
    text = _date_text,
    }
    }
    local argtype, datetext
    local argtype, datetext, is_copy, jd_number, tnums
    local numbers = collection()
    local numindex = 0
    local numfields = { 'year', 'month', 'day', 'hour', 'minute', 'second' }
    local numbers = {}
    for _, v in ipairs({...}) do
    for _, v in ipairs({...}) do
    v = strip_to_nil(v)
    v = strip_to_nil(v)
    Line 766: Line 893:
    -- Ignore empty arguments after stripping so modules can directly pass template parameters.
    -- Ignore empty arguments after stripping so modules can directly pass template parameters.
    elseif calendars[vlower] then
    elseif calendars[vlower] then
    result.calname = calendars[vlower]
    newdate.calname = calendars[vlower]
    elseif is_date(v) then
    elseif is_date(v) then
    -- Copy existing date (items can be overridden by other arguments).
    -- Copy existing date (items can be overridden by other arguments).
    if is_copy then
    if is_copy or tnums then
    return
    return
    end
    end
    is_copy = true
    is_copy = true
    result.calname = v.calname
    newdate.calname = v.calname
    result.hastime = v.hastime
    newdate.hastime = v.hastime
    result.options = v.options
    newdate.options = v.options
    result.year = v.year
    newdate.year = v.year
    result.month = v.month
    newdate.month = v.month
    result.day = v.day
    newdate.day = v.day
    result.hour = v.hour
    newdate.hour = v.hour
    result.minute = v.minute
    newdate.minute = v.minute
    result.second = v.second
    newdate.second = v.second
    elseif type(v) == 'table' then
    if tnums then
    return
    end
    tnums = {}
    local tfields = { year=1, month=1, day=1, hour=2, minute=2, second=2 }
    for tk, tv in pairs(v) do
    if tfields[tk] then
    tnums[tk] = tonumber(tv)
    end
    if tfields[tk] == 2 then
    newdate.hastime = true
    end
    end
    else
    else
    local num = tonumber(v)
    local num = tonumber(v)
    if not num and argtype == 'setdate' and numbers.n == 1 then
    if not num and argtype == 'setdate' and numindex == 1 then
    num = month_number(v)
    num = month_number(v)
    end
    end
    Line 791: Line 932:
    argtype = 'setdate'
    argtype = 'setdate'
    end
    end
    numbers:add(num)
    if argtype == 'setdate' and numindex < 6 then
    if argtype == 'juliandate' then
    numindex = numindex + 1
    numbers[numfields[numindex]] = num
    elseif argtype == 'juliandate' and not jd_number then
    jd_number = num
    if type(v) == 'string' then
    if type(v) == 'string' then
    if v:find('.', 1, true) then
    if v:find('.', 1, true) then
    result.hastime = true
    newdate.hastime = true
    end
    end
    elseif num ~= math.floor(num) then
    elseif num ~= math.floor(num) then
    -- The given value was a number. The time will be used
    -- The given value was a number. The time will be used
    -- if the fractional part is nonzero.
    -- if the fractional part is nonzero.
    result.hastime = true
    newdate.hastime = true
    end
    end
    else
    return
    end
    end
    elseif argtype then
    elseif argtype then
    Line 818: Line 964:
    end
    end
    if argtype == 'datetext' then
    if argtype == 'datetext' then
    if not (numbers.n == 0 and
    if tnums or not set_date_from_numbers(newdate, extract_date(datetext)) then
    set_date_from_numbers(result,
    extract_date(datetext))) then
    return
    return
    end
    end
    elseif argtype == 'juliandate' then
    elseif argtype == 'juliandate' then
    result.jd = numbers[1]
    newdate.jd = jd_number
    if not (numbers.n == 1 and set_date_from_jd(result)) then
    if not set_date_from_jd(newdate) then
    return
    return
    end
    end
    elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
    elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
    result.year = current.year
    newdate.year = current.year
    result.month = current.month
    newdate.month = current.month
    result.day = current.day
    newdate.day = current.day
    if argtype == 'currentdatetime' then
    if argtype == 'currentdatetime' then
    result.hour = current.hour
    newdate.hour = current.hour
    result.minute = current.minute
    newdate.minute = current.minute
    result.second = current.second
    newdate.second = current.second
    result.hastime = true
    newdate.hastime = true
    end
    end
    result.calname = 'Gregorian'  -- ignore any given calendar name
    newdate.calname = 'Gregorian'  -- ignore any given calendar name
    elseif argtype == 'setdate' then
    elseif argtype == 'setdate' then
    if not set_date_from_numbers(result, numbers) then
    if tnums or not set_date_from_numbers(newdate, numbers) then
    return
    return
    end
    end
    elseif not is_copy then
    elseif not (is_copy or tnums) then
    return
    return
    end
    end
    return setmetatable(result, datemt)
    if tnums then
    newdate.jd = nil  -- force recalculation in case jd was set before changes from tnums
    if not set_date_from_numbers(newdate, tnums) then
    return
    end
    end
    setmetatable(newdate, datemt)
    local readonly = {}
    local mt = {
    __index = newdate,
    __newindex = function(t, k, v) error('Date.' .. tostring(k) .. ' is read-only', 2) end,
    __add = mt_date_add,
    __sub = mt_date_sub,
    __concat = mt_date_concat,
    __tostring = mt_date_tostring,
    __eq = mt_date_eq,
    __lt = mt_date_lt,
    }
    return setmetatable(readonly, mt)
    end
    end
    local function _age_ym(diff)
    -- Return text specifying date difference in years, months.
    local sign = diff.isnegative and MINUS or ''
    local mtext = number_name(diff.months, 'month')
    local result
    if diff.years > 0 then
    local ytext = number_name(diff.years, 'year')
    if diff.months == 0 then
    result = ytext
    else
    result = ytext .. ',&nbsp;' .. mtext
    end
    else
    if diff.months == 0 then
    sign = ''
    end
    result = mtext
    end
    return sign .. result
    end
    -- Metatable for some operations on date differences.
    diffmt = {  -- for forward declaration above
    __concat = function (lhs, rhs)
    return tostring(lhs) .. tostring(rhs)
    end,
    __tostring = function (self)
    return tostring(self.daystotal)
    end,
    __index = function (self, key)
    local value
    if key == 'age_ym' then
    value = _age_ym(self)
    elseif key == 'daystotal' then
    value = self.date1.jdz - self.date2.jdz
    end
    if value ~= nil then
    rawset(self, key, value)
    return value
    end
    end,
    }


    function DateDiff(date1, date2)  -- for forward declaration above
    function DateDiff(date1, date2)  -- for forward declaration above
    -- Return a table with the difference between the two dates (date1 - date2).
    -- Return a table with the difference between the two dates (date1 - date2).
    -- The difference is negative if date2 is more recent than date1.
    -- The difference is negative if date1 is older than date2.
    -- Return nothing if invalid.
    -- Return nothing if invalid.
    if not (is_date(date1) and is_date(date2) and date1.calname == date2.calname) then
    if not (is_date(date1) and is_date(date2) and date1.calname == date2.calname) then
    return
    return
    end
    end
    local isnegative
    local isnegative = false
    if date1 < date2 then
    if date1 < date2 then
    isnegative = true
    isnegative = true
    Line 873: Line 1,078:
    years = years - 1
    years = years - 1
    end
    end
    return {
    return setmetatable({
    date1 = date1,
    date2 = date2,
    years = years,
    years = years,
    months = months,
    months = months,
    days = days,
    days = days,
    isnegative = isnegative,
    isnegative = isnegative,
    age_ym = function (self)
    }, diffmt)
    -- Return text specifying difference in years, months.
    local sign = self.isnegative and MINUS or ''
    local mtext = number_name(self.months, 'month')
    local result
    if self.years > 0 then
    local ytext = number_name(self.years, 'year')
    if self.months == 0 then
    result = ytext
    else
    result = ytext .. ',&nbsp;' .. mtext
    end
    else
    if self.months == 0 then
    sign = ''
    end
    result = mtext
    end
    return sign .. result
    end,
    }
    end
    end



    Revision as of 10:31, 20 March 2016

    Documentation for this module may be created at Module:Date/doc

    -- Date functions for use by other modules.
    -- I18N and time zones are not supported.
    
    local MINUS = '−'  -- Unicode U+2212 MINUS SIGN
    
    local Date, DateDiff, diffmt  -- forward declarations
    local uniq = { 'unique identifier' }
    
    local function is_date(t)
    	-- The system used to make a date read-only means there is no unique
    	-- metatable that is conveniently accessible to check.
    	return type(t) == 'table' and t._id == uniq
    end
    
    local function is_diff(t)
    	return type(t) == 'table' and getmetatable(t) == diffmt
    end
    
    local function _list_join(list, sep)
    	return table.concat(list, sep)
    end
    
    local function collection()
    	-- Return a table to hold items.
    	return {
    		n = 0,
    		add = function (self, item)
    			self.n = self.n + 1
    			self[self.n] = item
    		end,
    		join = _list_join,
    	}
    end
    
    local function strip_to_nil(text)
    	-- If text is a string, return its trimmed content, or nil.
    	-- Otherwise return text (convenient when Date fields are provided from
    	-- another module which is able to pass, for example, a number).
    	if type(text) == 'string' then
    		text = text:match('(%S.-)%s*$')
    	end
    	return text
    end
    
    local function number_name(number, singular, plural, sep)
    	-- Return the given number, converted to a string, with the
    	-- separator (default space) and singular or plural name appended.
    	plural = plural or (singular .. 's')
    	sep = sep or ' '
    	return tostring(number) .. sep .. ((number == 1) and singular or plural)
    end
    
    local function is_leap_year(year, calname)
    	-- Return true if year is a leap year.
    	if calname == 'Julian' then
    		return year % 4 == 0
    	end
    	return (year % 4 == 0 and year % 100 ~= 0) or year % 400 == 0
    end
    
    local function days_in_month(year, month, calname)
    	-- Return number of days (1..31) in given month (1..12).
    	if month == 2 and is_leap_year(year, calname) then
    		return 29
    	end
    	return ({ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 })[month]
    end
    
    local function julian_date(date)
    	-- Return jd, jdz from a Julian or Gregorian calendar date where
    	--   jd = Julian date and its fractional part is zero at noon
    	--   jdz = same, but assume time is 00:00:00 if no time given
    	-- http://www.tondering.dk/claus/cal/julperiod.php#formula
    	-- Testing shows this works for all dates from year -9999 to 9999!
    	-- JDN 0 is the 24-hour period starting at noon UTC on Monday
    	--    1 January 4713 BC  = (-4712, 1, 1)   Julian calendar
    	--   24 November 4714 BC = (-4713, 11, 24) Gregorian calendar
    	local floor = math.floor
    	local offset
    	local a = floor((14 - date.month)/12)
    	local y = date.year + 4800 - a
    	if date.calname == 'Julian' then
    		offset = floor(y/4) - 32083
    	else
    		offset = floor(y/4) - floor(y/100) + floor(y/400) - 32045
    	end
    	local m = date.month + 12*a - 3
    	local jd = date.day + floor((153*m + 2)/5) + 365*y + offset
    	if date.hastime then
    		jd = jd + (date.hour + (date.minute + date.second / 60) /60) / 24 - 0.5
    		return jd, jd
    	end
    	return jd, jd - 0.5
    end
    
    local function set_date_from_jd(date)
    	-- Set the fields of table date from its Julian date field.
    	-- Return true if date is valid.
    	-- http://www.tondering.dk/claus/cal/julperiod.php#formula
    	-- This handles the proleptic Julian and Gregorian calendars.
    	-- Negative Julian dates are not defined but they work.
    	local floor = math.floor
    	local calname = date.calname
    	local limits  -- min/max limits for date ranges −9999-01-01 to 9999-12-31
    	if calname == 'Julian' then
    		limits = { -1931076.5, 5373557.49999 }
    	elseif calname == 'Gregorian' then
    		limits = { -1930999.5, 5373484.49999 }
    	else
    		return
    	end
    	local jd = date.jd
    	if not (type(jd) == 'number' and limits[1] <= jd and jd <= limits[2]) then
    		return
    	end
    	local jdn = floor(jd)
    	if date.hastime then
    		local time = jd - jdn
    		local hour
    		if time >= 0.5 then
    			jdn = jdn + 1
    			time = time - 0.5
    			hour = 0
    		else
    			hour = 12
    		end
    		time = floor(time * 24 * 3600 + 0.5)  -- number of seconds after hour
    		date.second = time % 60
    		time = floor(time / 60)
    		date.minute = time % 60
    		date.hour = hour + floor(time / 60)
    	else
    		date.second = 0
    		date.minute = 0
    		date.hour = 0
    	end
    	local b, c
    	if calname == 'Julian' then
    		b = 0
    		c = jdn + 32082
    	else  -- Gregorian
    		local a = jdn + 32044
    		b = floor((4*a + 3)/146097)
    		c = a - floor(146097*b/4)
    	end
    	local d = floor((4*c + 3)/1461)
    	local e = c - floor(1461*d/4)
    	local m = floor((5*e + 2)/153)
    	date.day = e - floor((153*m + 2)/5) + 1
    	date.month = m + 3 - 12*floor(m/10)
    	date.year = 100*b + d - 4800 + floor(m/10)
    	return true
    end
    
    local function set_date_from_numbers(date, numbers, options)
    	-- Set the fields of table date from numeric values.
    	-- Return true if date is valid.
    	if type(numbers) ~= 'table' then
    		return
    	end
    	local y = numbers.year   or date.year
    	local m = numbers.month  or date.month
    	local d = numbers.day    or date.day
    	local H = numbers.hour
    	local M = numbers.minute or date.minute or 0
    	local S = numbers.second or date.second or 0
    	if not (y and m and d) or not
    		(-9999 <= y and y <= 9999 and
    			1 <= m and m <= 12 and
    			1 <= d and d <= days_in_month(y, m, date.calname)) then
    		return
    	end
    	if H then
    		date.hastime = true
    	else
    		H = date.hour or 0
    	end
    	if not (0 <= H and H <= 23 and
    			0 <= M and M <= 59 and
    			0 <= S and S <= 59) then
    		return
    	end
    	date.year = y    -- -9999 to 9999 ('n BC' → year = 1 - n)
    	date.month = m   -- 1 to 12
    	date.day = d     -- 1 to 31
    	date.hour = H    -- 0 to 59
    	date.minute = M  -- 0 to 59
    	date.second = S  -- 0 to 59
    	if type(options) == 'table' then
    		for _, k in ipairs({ 'am', 'era' }) do
    			if options[k] then
    				date.options[k] = options[k]
    			end
    		end
    	end
    	return true
    end
    
    local function make_option_table(options1, options2)
    	-- If options1 is a string, return a table with its settings, or
    	-- if it is a table, use its settings.
    	-- Missing options are set from options2 or defaults.
    	-- Valid option settings are:
    	-- am: 'am', 'a.m.', 'AM', 'A.M.'
    	-- era: 'BCMINUS', 'BCNEGATIVE', 'BC', 'B.C.', 'BCE', 'B.C.E.', 'AD', 'A.D.', 'CE', 'C.E.'
    	-- Option am = 'am' does not mean the hour is AM; it means 'am' or 'pm' is used, depending on the hour.
    	-- Similarly, era = 'BC' means 'BC' is used if year < 0.
    	-- BCMINUS displays a MINUS if year < 0 and the display format does not include %{era}.
    	-- BCNEGATIVE is similar but displays a hyphen.
    	local result = {}
    	if type(options1) == 'table' then
    		result = options1
    	elseif type(options1) == 'string' then
    		-- Example: 'am:AM era:BC'
    		for item in options1:gmatch('%S+') do
    			local lhs, rhs = item:match('^(%w+)[:=](.+)$')
    			if lhs then
    				result[lhs] = rhs
    			end
    		end
    	end
    	options2 = type(options2) == 'table' and options2 or {}
    	local defaults = { am = 'am', era = 'BC' }
    	for k, v in pairs(defaults) do
    		result[k] = result[k] or options2[k] or v
    	end
    	return result
    end
    
    local era_text = {
    	-- Text for displaying an era with a positive year (after adjusting
    	-- by replacing year with 1 - year if date.year <= 0).
    	-- options.era = { year<=0 , year>0 }
    	['BCMINUS']    = { 'BC'    , ''    , isbc = true, sign = MINUS },
    	['BCNEGATIVE'] = { 'BC'    , ''    , isbc = true, sign = '-'   },
    	['BC']         = { 'BC'    , ''    , isbc = true },
    	['B.C.']       = { 'B.C.'  , ''    , isbc = true },
    	['BCE']        = { 'BCE'   , ''    , isbc = true },
    	['B.C.E.']     = { 'B.C.E.', ''    , isbc = true },
    	['AD']         = { 'BC'    , 'AD'   },
    	['A.D.']       = { 'B.C.'  , 'A.D.' },
    	['CE']         = { 'BCE'   , 'CE'   },
    	['C.E.']       = { 'B.C.E.', 'C.E.' },
    }
    
    local function get_era_for_year(era, year)
    	return (era_text[era or 'BC'] or {})[year > 0 and 2 or 1] or ''
    end
    
    local function strftime(date, format, options)
    	-- Return date formatted as a string using codes similar to those
    	-- in the C strftime library function.
    	local sformat = string.format
    	local shortcuts = {
    		['%c'] = '%-I:%M %p %-d %B %-Y %{era}',  -- date and time: 2:30 pm 1 April 2016
    		['%x'] = '%-d %B %-Y %{era}',            -- date:          1 April 2016
    		['%X'] = '%-I:%M %p',                    -- time:          2:30 pm
    	}
    	if shortcuts[format] then
    		format = shortcuts[format]
    	end
    	local codes = {
    		a = { field = 'dayabbr' },
    		A = { field = 'dayname' },
    		b = { field = 'monthabbr' },
    		B = { field = 'monthname' },
    		u = { fmt = '%d'  , field = 'dowiso' },
    		w = { fmt = '%d'  , field = 'dow' },
    		d = { fmt = '%02d', fmt2 = '%d', field = 'day' },
    		m = { fmt = '%02d', fmt2 = '%d', field = 'month' },
    		Y = { fmt = '%04d', fmt2 = '%d', field = 'year' },
    		H = { fmt = '%02d', fmt2 = '%d', field = 'hour' },
    		M = { fmt = '%02d', fmt2 = '%d', field = 'minute' },
    		S = { fmt = '%02d', fmt2 = '%d', field = 'second' },
    		j = { fmt = '%03d', fmt2 = '%d', field = 'doy' },
    		I = { fmt = '%02d', fmt2 = '%d', field = 'hour', special = 'hour12' },
    		p = { field = 'hour', special = 'am' },
    	}
    	options = make_option_table(options, date.options)
    	local amopt = options.am
    	local eraopt = options.era
    	local function replace_code(spaces, modifier, id)
    		local code = codes[id]
    		if code then
    			local fmt = code.fmt
    			if modifier == '-' and code.fmt2 then
    				fmt = code.fmt2
    			end
    			local value = date[code.field]
    			local special = code.special
    			if special then
    				if special == 'hour12' then
    					value = value % 12
    					value = value == 0 and 12 or value
    				elseif special == 'am' then
    					local ap = ({
    						['a.m.'] = { 'a.m.', 'p.m.' },
    						['AM'] = { 'AM', 'PM' },
    						['A.M.'] = { 'A.M.', 'P.M.' },
    					})[amopt] or { 'am', 'pm' }
    					return (spaces == '' and '' or '&nbsp;') .. (value < 12 and ap[1] or ap[2])
    				end
    			end
    			if code.field == 'year' then
    				local sign = (era_text[eraopt] or {}).sign
    				if not sign or format:find('%{era}', 1, true) then
    					sign = ''
    					if value <= 0 then
    						value = 1 - value
    					end
    				else
    					if value >= 0 then
    						sign = ''
    					else
    						value = -value
    					end
    				end
    				return spaces .. sign .. sformat(fmt, value)
    			end
    			return spaces .. (fmt and sformat(fmt, value) or value)
    		end
    	end
    	local function replace_property(spaces, id)
    		if id == 'era' then
    			-- Special case so can use local era option.
    			local result = get_era_for_year(eraopt, date.year)
    			if result == '' then
    				return ''
    			end
    			return (spaces == '' and '' or '&nbsp;') .. result
    		end
    		local result = date[id]
    		if type(result) == 'string' then
    			return spaces .. result
    		end
    		if type(result) == 'number' then
    			return  spaces .. tostring(result)
    		end
    		if type(result) == 'boolean' then
    			return  spaces .. (result and '1' or '0')
    		end
    		-- This occurs, for example, if id is the name of a function.
    		return nil
    	end
    	local PERCENT = '\127PERCENT\127'
    	return (format
    		:gsub('%%%%', PERCENT)
    		:gsub('(%s*)%%{(%w+)}', replace_property)
    		:gsub('(%s*)%%(%-?)(%a)', replace_code)
    		:gsub(PERCENT, '%%')
    	)
    end
    
    local function _date_text(date, fmt, options)
    	-- Return a formatted string representing the given date.
    	if not is_date(date) then
    		return 'Need a date (use "date:text()" with a colon).'
    	end
    	if type(fmt) ~= 'string' then
    		fmt = '%-d %B %-Y %{era}'
    		if date.hastime then
    			if date.second > 0 then
    				fmt = '%H:%M:%S ' .. fmt
    			else
    				fmt = '%H:%M ' .. fmt
    			end
    		end
    		return strftime(date, fmt, options)
    	end
    	if fmt:find('%', 1, true) then
    		return strftime(date, fmt, options)
    	end
    	local t = collection()
    	for item in fmt:gmatch('%S+') do
    		local f
    		if item == 'hm' then
    			f = '%H:%M'
    		elseif item == 'hms' then
    			f = '%H:%M:%S'
    		elseif item == 'ymd' then
    			f = '%Y-%m-%d %{era}'
    		elseif item == 'mdy' then
    			f = '%B %-d, %-Y %{era}'
    		elseif item == 'dmy' then
    			f = '%-d %B %-Y %{era}'
    		else
    			return '(invalid format)'
    		end
    		t:add(f)
    	end
    	return strftime(date, t:join(' '), options)
    end
    
    local day_info = {
    	-- 0=Sun to 6=Sat
    	[0] = { 'Sun', 'Sunday' },
    	{ 'Mon', 'Monday' },
    	{ 'Tue', 'Tuesday' },
    	{ 'Wed', 'Wednesday' },
    	{ 'Thu', 'Thursday' },
    	{ 'Fri', 'Friday' },
    	{ 'Sat', 'Saturday' },
    }
    
    local month_info = {
    	-- 1=Jan to 12=Dec
    	{ 'Jan', 'January' },
    	{ 'Feb', 'February' },
    	{ 'Mar', 'March' },
    	{ 'Apr', 'April' },
    	{ 'May', 'May' },
    	{ 'Jun', 'June' },
    	{ 'Jul', 'July' },
    	{ 'Aug', 'August' },
    	{ 'Sep', 'September' },
    	{ 'Oct', 'October' },
    	{ 'Nov', 'November' },
    	{ 'Dec', 'December' },
    }
    
    local function name_to_number(text, translate)
    	if type(text) == 'string' then
    		return translate[text:lower()]
    	end
    end
    
    local function day_number(text)
    	return name_to_number(text, {
    		sun = 0, sunday = 0,
    		mon = 1, monday = 1,
    		tue = 2, tuesday = 2,
    		wed = 3, wednesday = 3,
    		thu = 4, thursday = 4,
    		fri = 5, friday = 5,
    		sat = 6, saturday = 6,
    	})
    end
    
    local function month_number(text)
    	return name_to_number(text, {
    		jan = 1, january = 1,
    		feb = 2, february = 2,
    		mar = 3, march = 3,
    		apr = 4, april = 4,
    		may = 5,
    		jun = 6, june = 6,
    		jul = 7, july = 7,
    		aug = 8, august = 8,
    		sep = 9, september = 9,
    		oct = 10, october = 10,
    		nov = 11, november = 11,
    		dec = 12, december = 12,
    	})
    end
    
    local function _list_text(list, fmt)
    	-- Return a list of formatted strings from a list of dates.
    	if not type(list) == 'table' then
    		return 'Need "list:text()" with a colon.'
    	end
    	local result = { join = _list_join }
    	for i, date in ipairs(list) do
    		result[i] = date:text(fmt)
    	end
    	return result
    end
    
    local function _make_list(date, spec)
    	-- Return a possibly empty numbered table of dates meeting the specification.
    	-- The spec should be a string like "Tue >=" meaning that the list will
    	-- hold dates for all Tuesdays on or after date, and in date's month.
    	if not is_date(date) then
    		return 'Need a date (use "date:list()" with a colon).'
    	end
    	local want_dow, op
    	local ops = {
    		['>='] = { before = false, include = true  },
    		['>']  = { before = false, include = false },
    		['<='] = { before = true , include = true  },
    		['<']  = { before = true , include = false },
    	}
    	if spec then
    		if type(spec) ~= 'string' then
    			return {}
    		end
    		for item in spec:gmatch('%S+') do
    			if ops[item] then
    				if op then
    					return {}
    				end
    				op = ops[item]
    			else
    				local dow = day_number(item)
    				if dow then
    					if want_dow then
    						-- LATER Could handle more than one day, but probably not needed.
    						return {}
    					end
    					want_dow = dow
    				else
    					return {}
    				end
    			end
    		end
    	end
    	local offset = want_dow and want_dow - date.dow or 0
    	op = op or ops['>=']
    	local first, last
    	if op.before then
    		if offset >= 0 and not (op.include and offset == 0) then
    			offset = offset - 7
    		end
    		last = date.day + offset
    		first = last % 7
    		if first == 0 then
    			first = 7
    		end
    	else
    		if offset < 0 or (not op.include and offset == 0) then
    			offset = offset + 7
    		end
    		first = date.day + offset
    		last = date.monthdays
    	end
    	local list = { text = _list_text }
    	local count = math.floor((last - first)/7) + 1
    	for i = 1, count do
    		list[i] = Date(date, {day = first})
    		first = first + 7
    	end
    	return list
    end
    
    -- A table to get the current date/time (UTC), but only if needed.
    -- A local test can set the global variable to produce fixed results.
    local current = setmetatable(
    	set_current_for_test or {}, {
    	__index = function (self, key)
    		local d = os.date('!*t')
    		self.year = d.year
    		self.month = d.month
    		self.day = d.day
    		self.hour = d.hour
    		self.minute = d.min
    		self.second = d.sec
    		return rawget(self, key)
    	end })
    
    local function extract_date(text)
    	-- Parse the date/time in text and return n, o where
    	--   n = table of numbers with date/time fields
    	--   o = table of options for AM/PM or AD/BC, if any
    	-- or return nothing if date is known to be invalid.
    	-- Caller determines if the values in n are valid.
    	-- A year must be positive ('1' to '9999'); use 'BC' for BC.
    	-- In a y-m-d string, the year must be four digits to avoid ambiguity
    	-- ('0001' to '9999'). The only way to enter year <= 0 is by specifying
    	-- the date as three numeric parameters like ymd Date(-1, 1, 1).
    	-- Dates of form d/m/y, m/d/y, y/m/d are rejected as ambiguous.
    	local date, options = {}, {}
    	local function extract_ymd(item)
    		local ystr, mstr, dstr = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$')
    		if ystr then
    			local m
    			if mstr:match('^%d%d?$') then
    				m = tonumber(mstr)
    			else
    				m = month_number(mstr)
    			end
    			if m then
    				date.year = tonumber(ystr)
    				date.month = m
    				date.day = tonumber(dstr)
    				return true
    			end
    		end
    	end
    	local function extract_month(item)
    		-- A month must be given as a name or abbreviation; a number would be ambiguous.
    		local m = month_number(item)
    		if m then
    			date.month = m
    			return true
    		end
    	end
    	local function extract_time(item)
    		local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
    		if date.hour or not h then
    			return
    		end
    		if s ~= '' then
    			s = s:match('^:(%d%d)$')
    			if not s then
    				return
    			end
    		end
    		date.hour = tonumber(h)
    		date.minute = tonumber(m)
    		date.second = tonumber(s)  -- nil if empty string
    		return true
    	end
    	local ampm_options = {
    		['am']   = 'am',
    		['AM']   = 'AM',
    		['a.m.'] = 'a.m.',
    		['A.M.'] = 'A.M.',
    		['pm']   = 'am',  -- same as am
    		['PM']   = 'AM',
    		['p.m.'] = 'a.m.',
    		['P.M.'] = 'A.M.',
    	}
    	local item_count = 0
    	local index_time
    	local function set_ampm(item)
    		local H = date.hour
    		if H and not options.am and index_time + 1 == item_count then
    			options.am = ampm_options[item]
    			if item:match('^[Aa]') then
    				if not (1 <= H and H <= 12) then
    					return
    				end
    				if H == 12 then
    					date.hour = 0
    				end
    			else
    				if not (1 <= H and H <= 23) then
    					return
    				end
    				if H <= 11 then
    					date.hour = H + 12
    				end
    			end
    			return true
    		end
    	end
    	for item in text:gsub(',', ' '):gmatch('%S+') do
    		item_count = item_count + 1
    		if era_text[item] then
    			-- Era is accepted in peculiar places.
    			if options.era then
    				return
    			end
    			options.era = item
    		elseif ampm_options[item] then
    			if not set_ampm(item) then
    				return
    			end
    		elseif item:find(':', 1, true) then
    			if not extract_time(item) then
    				return
    			end
    			index_time = item_count
    		elseif date.day and date.month then
    			if date.year then
    				return  -- should be nothing more so item is invalid
    			end
    			if not item:match('^(%d%d?%d?%d?)$') then
    				return
    			end
    			date.year = tonumber(item)
    		elseif date.day then
    			if not extract_month(item) then
    				return
    			end
    		elseif date.month then
    			if not item:match('^(%d%d?)$') then
    				return
    			end
    			date.day = tonumber(item)
    		elseif not extract_ymd(item) then
    			if item:match('^(%d%d?)$') then
    				date.day = tonumber(item)
    			elseif not extract_month(item) then
    				return
    			end
    		end
    	end
    	if not date.year or date.year == 0 then
    		return
    	end
    	local era = era_text[options.era]
    	if era and era.isbc then
    		date.year = 1 - date.year
    	end
    	return date, options
    end
    
    local function date_add_sub(lhs, rhs, is_sub)
    	-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
    	-- or return nothing if invalid.
    	-- The result is nil if the calculated date exceeds allowable limits.
    	-- Caller ensures that lhs is a date; its properties are copied for the new date.
    	local function is_prefix(text, word, minlen)
    		local n = #text
    		return (minlen or 1) <= n and n <= #word and text == word:sub(1, n)
    	end
    	local function do_days(n)
    		local forcetime, jd
    		if math.floor(n) == n then
    			jd = lhs.jd
    		else
    			forcetime = not lhs.hastime
    			jd = lhs.jdz
    		end
    		jd = jd + (is_sub and -n or n)
    		if forcetime then
    			jd = tostring(jd)
    			if not jd:find('.', 1, true) then
    				jd = jd .. '.0'
    			end
    		end
    		return Date(lhs, 'juliandate', jd)
    	end
    	if type(rhs) == 'number' then
    		-- Add/subtract days, including fractional days.
    		return do_days(rhs)
    	end
    	if type(rhs) == 'string' then
    		-- rhs is a single component like '26m' or '26 months' (unsigned integer only).
    		local num, id = rhs:match('^%s*(%d+)%s*(%a+)$')
    		if num then
    			local y, m
    			num = tonumber(num)
    			id = id:lower()
    			if is_prefix(id, 'years') then
    				y = num
    				m = 0
    			elseif is_prefix(id, 'months') then
    				y = math.floor(num / 12)
    				m = num % 12
    			elseif is_prefix(id, 'weeks') then
    				return do_days(num * 7)
    			elseif is_prefix(id, 'days') then
    				return do_days(num)
    			elseif is_prefix(id, 'hours') then
    				return do_days(num / 24)
    			elseif is_prefix(id, 'minutes', 3) then
    				return do_days(num / (24 * 60))
    			elseif is_prefix(id, 'seconds') then
    				return do_days(num / (24 * 3600))
    			else
    				return
    			end
    			if is_sub then
    				y = -y
    				m = -m
    			end
    			assert(-11 <= m and m <= 11)
    			y = lhs.year + y
    			m = lhs.month + m
    			if m > 12 then
    				y = y + 1
    				m = m - 12
    			elseif m < 1 then
    				y = y - 1
    				m = m + 12
    			end
    			local d = math.min(lhs.day, days_in_month(y, m, lhs.calname))
    			return Date(lhs, y, m, d)
    		end
    	end
    end
    
    -- Metatable for a date's calculated fields.
    local datemt = {
    	__index = function (self, key)
    		local value
    		if key == 'dayabbr' then
    			value = day_info[self.dow][1]
    		elseif key == 'dayname' then
    			value = day_info[self.dow][2]
    		elseif key == 'dow' then
    			value = (self.jdnoon + 1) % 7  -- day-of-week 0=Sun to 6=Sat
    		elseif key == 'dayofweek' then
    			value = self.dow
    		elseif key == 'dowiso' then
    			value = (self.jdnoon % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
    		elseif key == 'dayofweekiso' then
    			value = self.dowiso
    		elseif key == 'doy' then
    			local first = Date(self.year, 1, 1, self.calname).jdnoon
    			value = self.jdnoon - first + 1  -- day-of-year 1 to 366
    		elseif key == 'dayofyear' then
    			value = self.doy
    		elseif key == 'era' then
    			-- Era text (never a negative sign) from year and options.
    			value = get_era_for_year(self.options.era, self.year)
    		elseif key == 'gsd' then
    			-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
    			-- which is from jd 1721425.5 to 1721426.49999.
    			value = math.floor(self.jd - 1721424.5)
    		elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
    			local jd, jdz = julian_date(self)
    			rawset(self, 'juliandate', jd)
    			rawset(self, 'jd', jd)
    			rawset(self, 'jdz', jdz)
    			return key == 'jdz' and jdz or jd
    		elseif key == 'jdnoon' then
    			-- Julian date at noon (an integer) on the calendar day when jd occurs.
    			value = math.floor(self.jd + 0.5)
    		elseif key == 'isleapyear' then
    			value = is_leap_year(self.year, self.calname)
    		elseif key == 'monthabbr' then
    			value = month_info[self.month][1]
    		elseif key == 'monthdays' then
    			value = days_in_month(self.year, self.month, self.calname)
    		elseif key == 'monthname' then
    			value = month_info[self.month][2]
    		end
    		if value ~= nil then
    			rawset(self, key, value)
    			return value
    		end
    	end,
    }
    
    -- Date operators.
    local function mt_date_add(lhs, rhs)
    	if not is_date(lhs) then
    		lhs, rhs = rhs, lhs  -- put date on left (it must be a date for this to have been called)
    	end
    	return date_add_sub(lhs, rhs)
    end
    
    local function mt_date_sub(lhs, rhs)
    	if is_date(lhs) then
    		if is_date(rhs) then
    			return DateDiff(lhs, rhs)
    		end
    		return date_add_sub(lhs, rhs, true)
    	end
    end
    
    local function mt_date_concat(lhs, rhs)
    	return tostring(lhs) .. tostring(rhs)
    end
    
    local function mt_date_tostring(self)
    	return self:text()
    end
    
    local function mt_date_eq(lhs, rhs)
    	-- Return true if dates identify same date/time where, for example,
    	-- Date(-4712, 1, 1, 'Julian') == Date(-4713, 11, 24, 'Gregorian') is true.
    	-- This is only called if lhs and rhs have the same metatable.
    	return lhs.jdz == rhs.jdz
    end
    
    local function mt_date_lt(lhs, rhs)
    	-- Return true if lhs < rhs, for example,
    	-- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.
    	-- This is only called if lhs and rhs have the same metatable.
    	return lhs.jdz < rhs.jdz
    end
    
    --[[ Examples of syntax to construct a date:
    Date(y, m, d, 'julian')             default calendar is 'gregorian'
    Date(y, m, d, H, M, S, 'julian')
    Date('juliandate', jd, 'julian')    if jd contains "." text output includes H:M:S
    Date('currentdate')
    Date('currentdatetime')
    Date('1 April 1995', 'julian')      parse date from text
    Date('1 April 1995 AD', 'julian')   using an era sets a flag to do the same for output
    Date('04:30:59 1 April 1995', 'julian')
    Date(date)                          copy of an existing date
    Date(date, t)                       same, updated with y,m,d,H,M,S fields from table t
    Date(t)                       		date with y,m,d,H,M,S fields from table t
    ]]
    function Date(...)  -- for forward declaration above
    	-- Return a table holding a date assuming a uniform calendar always applies
    	-- (proleptic Gregorian calendar or proleptic Julian calendar), or
    	-- return nothing if date is invalid.
    	local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
    	local newdate = {
    		_id = uniq,
    		calname = 'Gregorian',  -- default is Gregorian calendar
    		hastime = false,  -- true if input sets a time
    		hour = 0,  -- always set hour/minute/second so don't have to handle nil
    		minute = 0,
    		second = 0,
    		options = make_option_table(),
    		list = _make_list,
    		text = _date_text,
    	}
    	local argtype, datetext, is_copy, jd_number, tnums
    	local numindex = 0
    	local numfields = { 'year', 'month', 'day', 'hour', 'minute', 'second' }
    	local numbers = {}
    	for _, v in ipairs({...}) do
    		v = strip_to_nil(v)
    		local vlower = type(v) == 'string' and v:lower() or nil
    		if v == nil then
    			-- Ignore empty arguments after stripping so modules can directly pass template parameters.
    		elseif calendars[vlower] then
    			newdate.calname = calendars[vlower]
    		elseif is_date(v) then
    			-- Copy existing date (items can be overridden by other arguments).
    			if is_copy or tnums then
    				return
    			end
    			is_copy = true
    			newdate.calname = v.calname
    			newdate.hastime = v.hastime
    			newdate.options = v.options
    			newdate.year = v.year
    			newdate.month = v.month
    			newdate.day = v.day
    			newdate.hour = v.hour
    			newdate.minute = v.minute
    			newdate.second = v.second
    		elseif type(v) == 'table' then
    			if tnums then
    				return
    			end
    			tnums = {}
    			local tfields = { year=1, month=1, day=1, hour=2, minute=2, second=2 }
    			for tk, tv in pairs(v) do
    				if tfields[tk] then
    					tnums[tk] = tonumber(tv)
    				end
    				if tfields[tk] == 2 then
    					newdate.hastime = true
    				end
    			end
    		else
    			local num = tonumber(v)
    			if not num and argtype == 'setdate' and numindex == 1 then
    				num = month_number(v)
    			end
    			if num then
    				if not argtype then
    					argtype = 'setdate'
    				end
    				if argtype == 'setdate' and numindex < 6 then
    					numindex = numindex + 1
    					numbers[numfields[numindex]] = num
    				elseif argtype == 'juliandate' and not jd_number then
    					jd_number = num
    					if type(v) == 'string' then
    						if v:find('.', 1, true) then
    							newdate.hastime = true
    						end
    					elseif num ~= math.floor(num) then
    						-- The given value was a number. The time will be used
    						-- if the fractional part is nonzero.
    						newdate.hastime = true
    					end
    				else
    					return
    				end
    			elseif argtype then
    				return
    			elseif type(v) == 'string' then
    				if v == 'currentdate' or v == 'currentdatetime' or v == 'juliandate' then
    					argtype = v
    				else
    					argtype = 'datetext'
    					datetext = v
    				end
    			else
    				return
    			end
    		end
    	end
    	if argtype == 'datetext' then
    		if tnums or not set_date_from_numbers(newdate, extract_date(datetext)) then
    			return
    		end
    	elseif argtype == 'juliandate' then
    		newdate.jd = jd_number
    		if not set_date_from_jd(newdate) then
    			return
    		end
    	elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
    		newdate.year = current.year
    		newdate.month = current.month
    		newdate.day = current.day
    		if argtype == 'currentdatetime' then
    			newdate.hour = current.hour
    			newdate.minute = current.minute
    			newdate.second = current.second
    			newdate.hastime = true
    		end
    		newdate.calname = 'Gregorian'  -- ignore any given calendar name
    	elseif argtype == 'setdate' then
    		if tnums or not set_date_from_numbers(newdate, numbers) then
    			return
    		end
    	elseif not (is_copy or tnums) then
    		return
    	end
    	if tnums then
    		newdate.jd = nil  -- force recalculation in case jd was set before changes from tnums
    		if not set_date_from_numbers(newdate, tnums) then
    			return
    		end
    	end
    	setmetatable(newdate, datemt)
    	local readonly = {}
    	local mt = {
    		__index = newdate,
    		__newindex = function(t, k, v) error('Date.' .. tostring(k) .. ' is read-only', 2) end,
    		__add = mt_date_add,
    		__sub = mt_date_sub,
    		__concat = mt_date_concat,
    		__tostring = mt_date_tostring,
    		__eq = mt_date_eq,
    		__lt = mt_date_lt,
    	}
    	return setmetatable(readonly, mt)
    end
    
    local function _age_ym(diff)
    	-- Return text specifying date difference in years, months.
    	local sign = diff.isnegative and MINUS or ''
    	local mtext = number_name(diff.months, 'month')
    	local result
    	if diff.years > 0 then
    		local ytext = number_name(diff.years, 'year')
    		if diff.months == 0 then
    			result = ytext
    		else
    			result = ytext .. ',&nbsp;' .. mtext
    		end
    	else
    		if diff.months == 0 then
    			sign = ''
    		end
    		result = mtext
    	end
    	return sign .. result
    end
    
    -- Metatable for some operations on date differences.
    diffmt = {  -- for forward declaration above
    	__concat = function (lhs, rhs)
    		return tostring(lhs) .. tostring(rhs)
    	end,
    	__tostring = function (self)
    		return tostring(self.daystotal)
    	end,
    	__index = function (self, key)
    		local value
    		if key == 'age_ym' then
    			value = _age_ym(self)
    		elseif key == 'daystotal' then
    			value = self.date1.jdz - self.date2.jdz
    		end
    		if value ~= nil then
    			rawset(self, key, value)
    			return value
    		end
    	end,
    }
    
    function DateDiff(date1, date2)  -- for forward declaration above
    	-- Return a table with the difference between the two dates (date1 - date2).
    	-- The difference is negative if date1 is older than date2.
    	-- Return nothing if invalid.
    	if not (is_date(date1) and is_date(date2) and date1.calname == date2.calname) then
    		return
    	end
    	local isnegative = false
    	if date1 < date2 then
    		isnegative = true
    		date1, date2 = date2, date1
    	end
    	-- It is known that date1 >= date2.
    	local y1, m1 = date1.year, date1.month
    	local y2, m2 = date2.year, date2.month
    	local years, months, days = y1 - y2, m1 - m2, date1.day - date2.day
    	if days < 0 then
    		days = days + days_in_month(y2, m2, date2.calname)
    		months = months - 1
    	end
    	if months < 0 then
    		months = months + 12
    		years = years - 1
    	end
    	return setmetatable({
    		date1 = date1,
    		date2 = date2,
    		years = years,
    		months = months,
    		days = days,
    		isnegative = isnegative,
    	}, diffmt)
    end
    
    return {
    	_current = current,
    	_Date = Date,
    	_days_in_month = days_in_month,
    }