{-|

For date and time values, we use the standard Day and UTCTime types.

A 'SmartDate' is a date which may be partially-specified or relative.
Eg 2008/12/31, but also 2008/12, 12/31, tomorrow, last week, next year.
We represent these as a triple of strings like (\"2008\",\"12\",\"\"),
(\"\",\"\",\"tomorrow\"), (\"\",\"last\",\"week\").

A 'DateSpan' is the span of time between two specific calendar dates, or
an open-ended span where one or both dates are unspecified. (A date span
with both ends unspecified matches all dates.)

An 'Interval' is ledger's "reporting interval" - weekly, monthly,
quarterly, etc.

-}

module Ledger.Dates
where

import Data.Time.Clock
import Data.Time.Format
import Data.Time.Calendar
import Data.Time.Calendar.MonthDay
import Data.Time.Calendar.OrdinalDate
import Data.Time.Calendar.WeekDate
import Data.Time.LocalTime
import System.Locale (defaultTimeLocale)
import Text.Printf
import Data.Maybe
import Text.ParserCombinators.Parsec
import Text.ParserCombinators.Parsec.Char
import Text.ParserCombinators.Parsec.Combinator
import Ledger.Types
import Ledger.Utils


showDate :: Day -> String
showDate d = formatTime defaultTimeLocale "%Y/%m/%d" d

getCurrentDay :: IO Day
getCurrentDay = do
    t <- getZonedTime
    return $ localDay (zonedTimeToLocalTime t)

elapsedSeconds :: Fractional a => UTCTime -> UTCTime -> a
elapsedSeconds t1 t2 = realToFrac $ diffUTCTime t1 t2

-- | Split a DateSpan into one or more consecutive spans at the specified interval.
splitSpan :: Interval -> DateSpan -> [DateSpan]
splitSpan i (DateSpan Nothing Nothing) = [DateSpan Nothing Nothing]
splitSpan NoInterval s = [s]
splitSpan Daily s      = splitspan start next s where (start,next) = (startofday,nextday)
splitSpan Weekly s     = splitspan start next s where (start,next) = (startofweek,nextweek)
splitSpan Monthly s    = splitspan start next s where (start,next) = (startofmonth,nextmonth)
splitSpan Quarterly s  = splitspan start next s where (start,next) = (startofquarter,nextquarter)
splitSpan Yearly s     = splitspan start next s where (start,next) = (startofyear,nextyear)

splitspan _ _ (DateSpan Nothing Nothing) = []
splitspan startof next (DateSpan Nothing (Just e)) = [DateSpan (Just $ startof e) (Just $ next $ startof e)]
splitspan startof next (DateSpan (Just b) Nothing) = [DateSpan (Just $ startof b) (Just $ next $ startof b)]
splitspan startof next s@(DateSpan (Just b) (Just e))
    | b == e = [s]
    | otherwise = splitspan' startof next s
    where splitspan' startof next (DateSpan (Just b) (Just e))
              | b >= e = []
              | otherwise = [DateSpan (Just $ startof b) (Just $ next $ startof b)] 
                            ++ splitspan' startof next (DateSpan (Just $ next $ startof b) (Just e))
    
-- | Parse a period expression to an Interval and overall DateSpan using
-- the provided reference date.
parsePeriodExpr :: Day -> String -> (Interval, DateSpan)
parsePeriodExpr refdate expr = (interval,span)
    where (interval,span) = fromparse $ parsewith (periodexpr refdate) expr
    
-- | Convert a single smart date string to a date span using the provided
-- reference date.
spanFromSmartDateString :: Day -> String -> DateSpan
spanFromSmartDateString refdate s = spanFromSmartDate refdate sdate
    where
      sdate = fromparse $ parsewith smartdate s

spanFromSmartDate :: Day -> SmartDate -> DateSpan
spanFromSmartDate refdate sdate = DateSpan (Just b) (Just e)
    where
      (ry,rm,rd) = toGregorian refdate
      (b,e) = span sdate
      span :: SmartDate -> (Day,Day)
      span ("","","today")       = (refdate, nextday refdate)
      span ("","this","day")     = (refdate, nextday refdate)
      span ("","","yesterday")   = (prevday refdate, refdate)
      span ("","last","day")     = (prevday refdate, refdate)
      span ("","","tomorrow")    = (nextday refdate, addDays 2 refdate)
      span ("","next","day")     = (nextday refdate, addDays 2 refdate)
      span ("","last","week")    = (prevweek refdate, thisweek refdate)
      span ("","this","week")    = (thisweek refdate, nextweek refdate)
      span ("","next","week")    = (nextweek refdate, startofweek $ addDays 14 refdate)
      span ("","last","month")   = (prevmonth refdate, thismonth refdate)
      span ("","this","month")   = (thismonth refdate, nextmonth refdate)
      span ("","next","month")   = (nextmonth refdate, startofmonth $ addGregorianMonthsClip 2 refdate)
      span ("","last","quarter") = (prevquarter refdate, thisquarter refdate)
      span ("","this","quarter") = (thisquarter refdate, nextquarter refdate)
      span ("","next","quarter") = (nextquarter refdate, startofquarter $ addGregorianMonthsClip 6 refdate)
      span ("","last","year")    = (prevyear refdate, thisyear refdate)
      span ("","this","year")    = (thisyear refdate, nextyear refdate)
      span ("","next","year")    = (nextyear refdate, startofyear $ addGregorianYearsClip 2 refdate)
      span ("","",d)             = (day, nextday day) where day = fromGregorian ry rm (read d)
      span ("",m,"")             = (startofmonth day, nextmonth day) where day = fromGregorian ry (read m) 1
      span ("",m,d)              = (day, nextday day) where day = fromGregorian ry (read m) (read d)
      span (y,"","")             = (startofyear day, nextyear day) where day = fromGregorian (read y) 1 1
      span (y,m,"")              = (startofmonth day, nextmonth day) where day = fromGregorian (read y) (read m) 1
      span (y,m,d)               = (day, nextday day) where day = fromGregorian (read y) (read m) (read d)

-- | Convert a smart date string to an explicit yyyy/mm/dd string using
-- the provided reference date.
fixSmartDateStr :: Day -> String -> String
fixSmartDateStr t s = printf "%04d/%02d/%02d" y m d
    where
      (y,m,d) = toGregorian $ fixSmartDate t sdate
      sdate = fromparse $ parsewith smartdate $ lowercase s

-- | Convert a SmartDate to an absolute date using the provided reference date.
fixSmartDate :: Day -> SmartDate -> Day
fixSmartDate refdate sdate = fix sdate
    where
      fix :: SmartDate -> Day
      fix ("","","today")       = fromGregorian ry rm rd
      fix ("","this","day")     = fromGregorian ry rm rd
      fix ("","","yesterday")   = prevday refdate
      fix ("","last","day")     = prevday refdate
      fix ("","","tomorrow")    = nextday refdate
      fix ("","next","day")     = nextday refdate
      fix ("","last","week")    = prevweek refdate
      fix ("","this","week")    = thisweek refdate
      fix ("","next","week")    = nextweek refdate
      fix ("","last","month")   = prevmonth refdate
      fix ("","this","month")   = thismonth refdate
      fix ("","next","month")   = nextmonth refdate
      fix ("","last","quarter") = prevquarter refdate
      fix ("","this","quarter") = thisquarter refdate
      fix ("","next","quarter") = nextquarter refdate
      fix ("","last","year")    = prevyear refdate
      fix ("","this","year")    = thisyear refdate
      fix ("","next","year")    = nextyear refdate
      fix ("","",d)             = fromGregorian ry rm (read d)
      fix ("",m,"")             = fromGregorian ry (read m) 1
      fix ("",m,d)              = fromGregorian ry (read m) (read d)
      fix (y,"","")             = fromGregorian (read y) 1 1
      fix (y,m,"")              = fromGregorian (read y) (read m) 1
      fix (y,m,d)               = fromGregorian (read y) (read m) (read d)
      (ry,rm,rd) = toGregorian refdate

prevday :: Day -> Day
prevday = addDays (-1)
nextday = addDays 1
startofday = id

thisweek = startofweek
prevweek = startofweek . addDays (-7)
nextweek = startofweek . addDays 7
startofweek day = fromMondayStartWeek y w 1
    where
      (y,_,_) = toGregorian day
      (w,_) = mondayStartWeek day

thismonth = startofmonth
prevmonth = startofmonth . addGregorianMonthsClip (-1)
nextmonth = startofmonth . addGregorianMonthsClip 1
startofmonth day = fromGregorian y m 1 where (y,m,_) = toGregorian day

thisquarter = startofquarter
prevquarter = startofquarter . addGregorianMonthsClip (-3)
nextquarter = startofquarter . addGregorianMonthsClip 3
startofquarter day = fromGregorian y (firstmonthofquarter m) 1
    where
      (y,m,_) = toGregorian day
      firstmonthofquarter m = ((m-1) `div` 3) * 3 + 1

thisyear = startofyear
prevyear = startofyear . addGregorianYearsClip (-1)
nextyear = startofyear . addGregorianYearsClip 1
startofyear day = fromGregorian y 1 1 where (y,_,_) = toGregorian day

----------------------------------------------------------------------
-- parsing

firstJust ms = case dropWhile (==Nothing) ms of
    [] -> Nothing
    (md:_) -> md

parsedatetimeM :: String -> Maybe LocalTime
parsedatetimeM s = firstJust [
    parseTime defaultTimeLocale "%Y/%m/%d %H:%M:%S" s,
    parseTime defaultTimeLocale "%Y-%m-%d %H:%M:%S" s
    ]

-- | Parse a date-time string to a time type, or raise an error.
parsedatetime :: String -> LocalTime
parsedatetime s = fromMaybe (error $ "could not parse timestamp \"" ++ s ++ "\"")
                            (parsedatetimeM s)

-- | Parse a date string to a time type, or raise an error.
parsedateM :: String -> Maybe Day
parsedateM s = firstJust [ 
     parseTime defaultTimeLocale "%Y/%m/%d" s,
     parseTime defaultTimeLocale "%Y-%m-%d" s 
     ]

-- | Parse a date string to a time type, or raise an error.
parsedate :: String -> Day
parsedate s =  fromMaybe (error $ "could not parse date \"" ++ s ++ "\"")
                         (parsedateM s)

-- | Parse a time string to a time type using the provided pattern, or
-- return the default.
parsetimewith :: ParseTime t => String -> String -> t -> t
parsetimewith pat s def = fromMaybe def $ parseTime defaultTimeLocale pat s

{-| 
Parse a date in any of the formats allowed in ledger's period expressions,
and maybe some others:

> 2004
> 2004/10
> 2004/10/1
> 10/1
> 21
> october, oct
> yesterday, today, tomorrow
> (not yet) this/next/last week/day/month/quarter/year

Returns a SmartDate, to be converted to a full date later (see fixSmartDate).
Assumes any text in the parse stream has been lowercased.
-}
smartdate :: GenParser Char st SmartDate
smartdate = do
  let dateparsers = [yyyymmdd, ymd, ym, md, y, d, month, mon, today, yesterday, tomorrow,
                     lastthisnextthing
                    ]
  (y,m,d) <- choice $ map try dateparsers
  return $ (y,m,d)

datesepchar = oneOf "/-."

yyyymmdd :: GenParser Char st SmartDate
yyyymmdd = do
  y <- count 4 digit
  m <- count 2 digit
  guard (read m <= 12)
  d <- count 2 digit
  guard (read d <= 31)
  return (y,m,d)

ymd :: GenParser Char st SmartDate
ymd = do
  y <- many1 digit
  datesepchar
  m <- many1 digit
  guard (read m <= 12)
  datesepchar
  d <- many1 digit
  guard (read d <= 31)
  return (y,m,d)

ym :: GenParser Char st SmartDate
ym = do
  y <- many1 digit
  guard (read y > 12)
  datesepchar
  m <- many1 digit
  guard (read m <= 12)
  return (y,m,"")

y :: GenParser Char st SmartDate
y = do
  y <- many1 digit
  guard (read y >= 1000)
  return (y,"","")

d :: GenParser Char st SmartDate
d = do
  d <- many1 digit
  guard (read d <= 31)
  return ("","",d)

md :: GenParser Char st SmartDate
md = do
  m <- many1 digit
  guard (read m <= 12)
  datesepchar
  d <- many1 digit
  guard (read d <= 31)
  return ("",m,d)

months         = ["january","february","march","april","may","june",
                  "july","august","september","october","november","december"]
monthabbrevs   = ["jan","feb","mar","apr","may","jun","jul","aug","sep","oct","nov","dec"]
weekdays       = ["monday","tuesday","wednesday","thursday","friday","saturday","sunday"]
weekdayabbrevs = ["mon","tue","wed","thu","fri","sat","sun"]

monthIndex s = maybe 0 (+1) $ (lowercase s) `elemIndex` months
monIndex s   = maybe 0 (+1) $ (lowercase s) `elemIndex` monthabbrevs

month :: GenParser Char st SmartDate
month = do
  m <- choice $ map (try . string) months
  let i = monthIndex m
  return $ ("",show i,"")

mon :: GenParser Char st SmartDate
mon = do
  m <- choice $ map (try . string) monthabbrevs
  let i = monIndex m
  return ("",show i,"")

today,yesterday,tomorrow :: GenParser Char st SmartDate
today     = string "today"     >> return ("","","today")
yesterday = string "yesterday" >> return ("","","yesterday")
tomorrow  = string "tomorrow"  >> return ("","","tomorrow")

lastthisnextthing :: GenParser Char st SmartDate
lastthisnextthing = do
  r <- choice [
        string "last"
       ,string "this"
       ,string "next"
      ]
  many spacenonewline  -- make the space optional for easier scripting
  p <- choice $ [
        string "day"
       ,string "week"
       ,string "month"
       ,string "quarter"
       ,string "year"
      ]
-- XXX support these in fixSmartDate
--       ++ (map string $ months ++ monthabbrevs ++ weekdays ++ weekdayabbrevs)
            
  return ("",r,p)

periodexpr :: Day -> GenParser Char st (Interval, DateSpan)
periodexpr rdate = choice $ map try [
                    intervalanddateperiodexpr rdate,
                    intervalperiodexpr,
                    dateperiodexpr rdate,
                    (return $ (NoInterval,DateSpan Nothing Nothing))
                   ]

intervalanddateperiodexpr :: Day -> GenParser Char st (Interval, DateSpan)
intervalanddateperiodexpr rdate = do
  many spacenonewline
  i <- periodexprinterval
  many spacenonewline
  s <- periodexprdatespan rdate
  return (i,s)

intervalperiodexpr :: GenParser Char st (Interval, DateSpan)
intervalperiodexpr = do
  many spacenonewline
  i <- periodexprinterval
  return (i, DateSpan Nothing Nothing)

dateperiodexpr :: Day -> GenParser Char st (Interval, DateSpan)
dateperiodexpr rdate = do
  many spacenonewline
  s <- periodexprdatespan rdate
  return (NoInterval, s)

periodexprinterval :: GenParser Char st Interval
periodexprinterval = 
    choice $ map try [
                tryinterval "day" "daily" Daily,
                tryinterval "week" "weekly" Weekly,
                tryinterval "month" "monthly" Monthly,
                tryinterval "quarter" "quarterly" Quarterly,
                tryinterval "year" "yearly" Yearly
               ]
    where
      tryinterval s1 s2 v = 
          choice [try (string $ "every "++s1), try (string s2)] >> return v

periodexprdatespan :: Day -> GenParser Char st DateSpan
periodexprdatespan rdate = choice $ map try [
                            doubledatespan rdate,
                            fromdatespan rdate,
                            todatespan rdate,
                            justdatespan rdate
                           ]

doubledatespan :: Day -> GenParser Char st DateSpan
doubledatespan rdate = do
  optional (string "from" >> many spacenonewline)
  b <- smartdate
  many spacenonewline
  optional (string "to" >> many spacenonewline)
  e <- smartdate
  return $ DateSpan (Just $ fixSmartDate rdate b) (Just $ fixSmartDate rdate e)

fromdatespan :: Day -> GenParser Char st DateSpan
fromdatespan rdate = do
  string "from" >> many spacenonewline
  b <- smartdate
  return $ DateSpan (Just $ fixSmartDate rdate b) Nothing

todatespan :: Day -> GenParser Char st DateSpan
todatespan rdate = do
  string "to" >> many spacenonewline
  e <- smartdate
  return $ DateSpan Nothing (Just $ fixSmartDate rdate e)

justdatespan :: Day -> GenParser Char st DateSpan
justdatespan rdate = do
  optional (string "in" >> many spacenonewline)
  d <- smartdate
  return $ spanFromSmartDate rdate d

nulldatespan = DateSpan Nothing Nothing

mkdatespan b e = DateSpan (Just $ parsedate b) (Just $ parsedate e)