Random.hs

-- | Random value library for arduino-copilot.
--
-- Here's an example that flashes the LED randomly.
--
-- > main :: IO ()
-- > main = arduino $ do
-- >	if firstIteration
-- > 		then randomSeedPin a0
-- > 		else do
-- > 			n <- input (random 10) :: Sketch (Behavior Word32)
-- > 			led =: (n >= 5)
--
-- The use of `firstIteration` makes the RNG be seeded in the first
-- iteration, and then random numbers are generated in subsequent
-- iterations. That's a typical pattern when using this module.

{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE RebindableSyntax #-}
{-# LANGUAGE TypeApplications #-}

module Copilot.Arduino.Library.Random (
	randomSeed,
	randomSeedPin,
	RandomSeed,
	RandomInput,
	random,
	randomR,
) where

import Copilot.Arduino hiding (show)
import Copilot.Arduino.Internals
import Control.Monad.Writer
import Data.Proxy
import Prelude ()
import qualified Prelude

-- | Use this to seed the RNG.
--
-- > randomSeed =: constant (1 :: Word8)
randomSeed :: RandomSeed
randomSeed = RandomSeed

data RandomSeed = RandomSeed

instance Output PinId RandomSeed (Event () (Stream Word8)) where
	RandomSeed =: e = randomSeedWith e

-- Seeds with the first 8 bits read from the ADC, discarding the rest.
instance Output PinId RandomSeed (Event () (Stream ADC)) where
	RandomSeed =: e = randomSeedWith e

randomSeedWith :: Typed a => Event p (Stream a) -> Sketch ()
randomSeedWith (Event n c) = do
		(f, triggername) <- defineTriggerAlias "randomSeed" mempty
		tell [(go triggername, \_ -> f)]
	  where
		go triggername tl = 
			let c' = addTriggerLimit tl c
			in trigger triggername c' [arg n]

-- | Seed the RNG by reading from an analog input pin.
--
-- If the pin is left unconnected, noise will be read from it.
randomSeedPin :: IsAnalogInputPin t => Pin t -> Sketch ()
randomSeedPin p = do
	seed <- input p :: Sketch (Behavior ADC)
	randomSeed =: seed

data RandomInput = RandomInput Word32 Word32

-- | Generate a random number, up to but exclusive of an upper bound.
--
-- > n <- input (random 10)
random :: Word32 -> RandomInput
random hi = RandomInput 0 hi

-- | Generate a random number in the range (lo, hi). The number will be 
-- @>= lo@ and @< hi@
--
-- > n <- input (randomR 5 10) :: Sketch (Behavior Word32)
randomR :: (Word32, Word32) -> RandomInput
randomR (lo, hi) = RandomInput lo hi

instance Input PinId RandomInput Word32 where
	input' (RandomInput lo hi) interpretvalues = do
		i <- getUniqueId "random"
		let varname = uniqueName "randomval" i
		let word32 = showCType (Proxy @Word32)
		mkInput $ InputSource
			{ setupInput = []
			, defineVar = mkCChunk
				[ CLine $ word32 <> " " <> varname <> ";"
				]
			, inputPinmode = mempty
			, readInput = mkCChunk
				[ CLine $ varname <> " = random"
					<> "("
						<> Prelude.show lo
						<> ", " 
						<> Prelude.show hi
					<> ");"]
			, inputStream = extern varname interpretvalues'
			}
  	  where
		interpretvalues'
			| null interpretvalues = Nothing
			| otherwise = Just interpretvalues