{-# LANGUAGE GeneralizedNewtypeDeriving, MultiParamTypeClasses #-}

{- Copyright 2016 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

module Cost (
	module Cost,
	module Types.Cost
) where

import Types.Cost

-- | Cost in seconds, with the type of hardware needed.
totalCost :: Cost op -> (Seconds, [UsingHardware])
totalCost (CPUCost s) = (s, [UsingCPU])
totalCost (GPUCost s) = (s, [UsingGPU])
totalCost (CombinedCost a b) = 
	let (s1, h1) = totalCost a
	    (s2, h2) = totalCost b
	in (s1+s2, h1++h2)

raiseCostPower :: Cost c -> Entropy e -> Cost c
raiseCostPower c (Entropy e) = adjustCost c (* 2^e)

adjustCost :: Cost c -> (Seconds -> Seconds) -> Cost c
adjustCost (CPUCost s) f = CPUCost (f s)
adjustCost (GPUCost s) f = GPUCost (f s)
adjustCost (CombinedCost a b) f = CombinedCost (adjustCost a f) (adjustCost b f)

castCost :: Cost a -> Cost b
castCost (CPUCost s) = CPUCost s
castCost (GPUCost s) = GPUCost s
castCost (CombinedCost a b) = CombinedCost (castCost a) (castCost b)

-- | CostCalc for a brute force linear search through an entropy space
-- in which each step entails paying a cost.
--
-- On average, the solution will be found half way through.
-- This is equivilant to one bit less of entropy.
bruteForceLinearSearch :: Cost step -> CostCalc BruteForceOp t
bruteForceLinearSearch stepcost e = 
	castCost stepcost `raiseCostPower` reduceEntropy e 1

-- | Estimate of cost of a brute force attack.
estimateBruteforceOf :: Bruteforceable t a => t -> Entropy a -> Cost BruteForceOp
estimateBruteforceOf t e = getBruteCostCalc t e

data DataCenterPrice = DataCenterPrice
	{ instanceCpuCores :: Integer
	, instanceCostPerHour :: Cents
	}

-- August 2016 spot pricing: 36 CPU core c4.8xlarge at 33c/hour
spotAWS :: DataCenterPrice
spotAWS = DataCenterPrice
	{ instanceCpuCores = 36
	, instanceCostPerHour = Cents 33
	}

-- | Estimate of cost of brute force attack using a datacenter.
--
-- Note that this assumes that CPU cores and GPU cores are of equal number,
-- which is unlikely to be the case; typically there will be many more
-- cores than GPUs. So, this underestimates the price to brute force
-- operations which run faster on GPUs.
estimateAttack :: DataCenterPrice -> Cost BruteForceOp -> Dollars
estimateAttack dc opcost = centsToDollars $ costcents
  where
	(Seconds cpuseconds) = fst (totalCost opcost)
	cpuyears = cpuseconds `div` (60*60*24*365)
	costpercpuyear = Cents $
		fromIntegral (instanceCostPerHour dc) * 24 * 365
			`div` instanceCpuCores dc
	costcents = Cents cpuyears * costpercpuyear

newtype Cents = Cents Integer
	deriving (Num, Integral, Enum, Real, Ord, Eq, Show)

newtype Dollars = Dollars Integer
	deriving (Num, Integral, Enum, Real, Ord, Eq, Show)

centsToDollars :: Cents -> Dollars
centsToDollars (Cents c) = Dollars (c `div` 100)