```{-|
An 'Amount' is some quantity of money, shares, or anything else.

A simple amount is a 'Commodity', quantity pair:

@
\$1
£-50
EUR 3.44
GOOG 500
1.5h
90apples
0
@

A 'MixedAmount' is zero or more simple amounts:

@
\$50, EUR 3, AAPL 500
16h, \$13.55, oranges 6
@

Not implemented:
Commodities may be convertible or not. A mixed amount containing only
convertible commodities can be converted to a simple amount. Arithmetic
examples:

@
\$1 - \$5 = \$-4
\$1 + EUR 0.76 = \$2
EUR0.76 + \$1 = EUR 1.52
EUR0.76 - \$1 = 0
(\$5, 2h) + \$1 = (\$6, 2h)
(\$50, EUR 3, AAPL 500) + (\$13.55, oranges 6) = \$67.51, AAPL 500, oranges 6
(\$50, EUR 3) * \$-1 = \$-53.96
(\$50, AAPL 500) * \$-1 = error
@
-}

module Ledger.Amount
where
import qualified Data.Map as Map
import Ledger.Utils
import Ledger.Types
import Ledger.Commodity

instance Show Amount where show = showAmount
instance Show MixedAmount where show = showMixedAmount

instance Num Amount where
abs (Amount c q p) = Amount c (abs q) p
signum (Amount c q p) = Amount c (signum q) p
fromInteger i = Amount (comm "") (fromInteger i) Nothing
(+) = amountop (+)
(-) = amountop (-)
(*) = amountop (*)

instance Ord Amount where
compare (Amount ac aq ap) (Amount bc bq bp) = compare (ac,aq,ap) (bc,bq,bp)

instance Num MixedAmount where
fromInteger i = Mixed [Amount (comm "") (fromInteger i) Nothing]
negate (Mixed as) = Mixed \$ map negateAmountPreservingPrice as
(+) (Mixed as) (Mixed bs) = normaliseMixedAmount \$ Mixed \$ as ++ bs
(*)    = error "programming error, mixed amounts do not support multiplication"
abs    = error "programming error, mixed amounts do not support abs"
signum = error "programming error, mixed amounts do not support signum"

instance Ord MixedAmount where
compare (Mixed as) (Mixed bs) = compare as bs

negateAmountPreservingPrice a = (-a){price=price a}

-- | Apply a binary arithmetic operator to two amounts - converting to the
-- any price information. (Using the second commodity is best since sum
amountop :: (Double -> Double -> Double) -> Amount -> Amount -> Amount
amountop op a@(Amount ac aq ap) b@(Amount bc bq bp) =
Amount bc ((quantity \$ convertAmountTo bc a) `op` bq) Nothing

-- | Convert an amount to the commodity of its saved price, if any.
costOfAmount :: Amount -> Amount
costOfAmount a@(Amount _ _ Nothing) = a
costOfAmount a@(Amount _ q (Just price))
| isZeroMixedAmount price = nullamt
| otherwise = Amount pc (pq*q) Nothing
where (Amount pc pq _) = head \$ amounts price

-- | Convert an amount to the specified commodity using the appropriate
-- exchange rate (which is currently always 1).
convertAmountTo :: Commodity -> Amount -> Amount
convertAmountTo c2 (Amount c1 q p) = Amount c2 (q * conversionRate c1 c2) Nothing

-- | Get the string representation of an amount, based on its commodity's
-- display settings.
showAmount :: Amount -> String
showAmount a@(Amount (Commodity {symbol=sym,side=side,spaced=spaced}) q pri)
| sym=="AUTO" = "" -- can display one of these in an error message
| side==L = printf "%s%s%s%s" sym space quantity price
| side==R = printf "%s%s%s%s" quantity space sym price
where
space = if spaced then " " else ""
quantity = showAmount' a
price = case pri of (Just pamt) -> " @ " ++ showMixedAmount pamt
Nothing -> ""

-- | Get the string representation (of the number part of) of an amount
showAmount' :: Amount -> String
showAmount' (Amount (Commodity {comma=comma,precision=p}) q _) = quantity
where
quantity = commad \$ printf ("%."++show p++"f") q
commad = if comma then punctuatethousands else id

-- | Add thousands-separating commas to a decimal number string
punctuatethousands :: String -> String
punctuatethousands s =
sign ++ (addcommas int) ++ frac
where
(sign,num) = break isDigit s
(int,frac) = break (=='.') num
addcommas = reverse . concat . intersperse "," . triples . reverse
triples [] = []
triples l  = [take 3 l] ++ (triples \$ drop 3 l)

-- | Does this amount appear to be zero when displayed with its given precision ?
isZeroAmount :: Amount -> Bool
isZeroAmount a = nonzerodigits == ""
where nonzerodigits = filter (`elem` "123456789") \$ showAmount a

-- | Access a mixed amount's components.
amounts :: MixedAmount -> [Amount]
amounts (Mixed as) = as

-- | Does this mixed amount appear to be zero - empty, or
-- containing only simple amounts which appear to be zero ?
isZeroMixedAmount :: MixedAmount -> Bool
isZeroMixedAmount = all isZeroAmount . amounts . normaliseMixedAmount

-- | MixedAmount derives Eq in Types.hs, but that doesn't know that we
-- want \$0 = EUR0 = 0. Yet we don't want to drag all this code in there.
-- When zero equality is important, use this, for now; should be used
-- everywhere.
mixedAmountEquals :: MixedAmount -> MixedAmount -> Bool
mixedAmountEquals a b = amounts a' == amounts b' || (isZeroMixedAmount a' && isZeroMixedAmount b')
where a' = normaliseMixedAmount a
b' = normaliseMixedAmount b

-- | Get the string representation of a mixed amount, showing each of
-- its component amounts. NB a mixed amount can have an empty amounts
-- list in which case it shows as \"\".
showMixedAmount :: MixedAmount -> String
showMixedAmount m = concat \$ intersperse "\n" \$ map showfixedwidth as
where
(Mixed as) = normaliseMixedAmount m
width = maximum \$ map (length . show) \$ as
showfixedwidth = printf (printf "%%%ds" width) . show

-- | Get the string representation of a mixed amount, and if it
-- appears to be all zero just show a bare 0, ledger-style.
showMixedAmountOrZero :: MixedAmount -> String
showMixedAmountOrZero a
| isZeroMixedAmount a = "0"
| otherwise = showMixedAmount a

-- | Simplify a mixed amount by combining any component amounts which have
-- the same commodity and the same price. Also removes redundant zero amounts
-- and adds a single zero amount if there are no amounts at all.
normaliseMixedAmount :: MixedAmount -> MixedAmount
normaliseMixedAmount (Mixed as) = Mixed as''
where
as'' = map sumAmountsPreservingPrice \$ group \$ sort as'
sort = sortBy cmpsymbolandprice
cmpsymbolandprice a1 a2 = compare (sym a1,price a1) (sym a2,price a2)
group = groupBy samesymbolandprice
samesymbolandprice a1 a2 = (sym a1 == sym a2) && (price a1 == price a2)
sym = symbol . commodity
as' | null nonzeros = [head \$ zeros ++ [nullamt]]
| otherwise = nonzeros
(zeros,nonzeros) = partition isZeroAmount as

sumAmountsPreservingPrice [] = nullamt
sumAmountsPreservingPrice as = (sum as){price=price \$ head as}

-- | Convert a mixed amount's component amounts to the commodity of their
-- saved price, if any.
costOfMixedAmount :: MixedAmount -> MixedAmount
costOfMixedAmount (Mixed as) = Mixed \$ map costOfAmount as

-- | The empty simple amount.
nullamt :: Amount
nullamt = Amount unknown 0 Nothing

-- | The empty mixed amount.
nullmixedamt :: MixedAmount
nullmixedamt = Mixed []

-- | A temporary value for parsed transactions which had no amount specified.
missingamt :: MixedAmount
missingamt = Mixed [Amount (Commodity {symbol="AUTO",side=L,spaced=False,comma=False,precision=0}) 0 Nothing]

```