-- -- Human exchangable identifiers and locators -- -- Copyright © 2011-2014 Operational Dynamics Consulting, Pty Ltd -- -- The code in this file, and the program it is a part of, is -- made available to you by its authors as open source software: -- you can redistribute it and/or modify it under the terms of -- the BSD licence. -- -- This code originally licenced GPLv2. Relicenced BSD3 on 2 Jan 2014. -- {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE ScopedTypeVariables #-} module Data.Locator.Locators ( Locator(..), English16(..), fromLocator16, toLocator16, toLocator16a, hashStringToLocator16a ) where import Prelude hiding (toInteger) import Crypto.Hash.SHA1 as Crypto import Data.ByteString (ByteString) import qualified Data.ByteString as B import qualified Data.ByteString.Char8 as S import Data.List (mapAccumL) import Data.Set (Set) import qualified Data.Set as Set import Data.Word import Numeric (showIntAtBase) -- -- | A symbol set with sixteen uniquely pronounceable digits. -- -- The fact there are sixteen symbols is more an indication of a certain degree -- of bullheaded-ness on the part of the author, and less of any kind of actual -- requirement. We might have a slighly better readback score if we dropped to -- 15 or 14 unique characters. It does mean you can match up with hexidecimal, -- which is not entirely without merit. -- -- The grouping of letters and numbers was the hard part; having come up with -- the set and deconflicted the choices, the ordering is then entirely -- arbitrary. Since there are some numbers, might as well have them at the same -- place they correspond to in base 10; the letters were then allocated in -- alpha order in the remaining slots. -- {- -- 0 Conflicts with @\'O\'@ obviously, and @\'Q\'@ often enough -- -- 2 @\'U\'@, @\'W\'@, and @\'2\'@. @\'W\'@ is disqualifed because of -- the way Australians butcher double-this and triple-that. \"Double -- @\'U\'@\" or \"@\'W\'@\"? -- -- C @\'B\'@, @\'C\'@, @\'D\'@, @\'E\'@, @\'G\'@, @\'P\'@, @\'T\'@, -- @\'V\'@, and @\'3\'@ plus @\'Z\'@ because Americans can't pronounce -- Zed properly. -- -- 4 @\'4\'@ and @\'5\'@ are often confused, and @\'5\'@, definitely -- out due to its collision with @\'I\'@ when spoken and @\'S\'@ in -- writing. -- -- F @\'F\'@ and @\'S\'@ are notoriously confused, making the choice of -- @\'F\'@ borderline, but @\'S\'@ is already disqualified for looking -- like @\'5\'@. -- -- K group of @\'A\'@, @\'J\'@, @\'K\'@. -- -- L @\'L\'@ has good phonetics, and as long as it's upper case (which -- the whole 'English16' symbol set is) there's no conflict with -- @\'1\'@. -- -- M choice from @\'M\'@ and @\'N\'@; the latter is a little too close -- to @\'7\'@. -- -- X choice from @\'X\'@ and @\'6\'@. -- -- Y choice from @\'I\'@, @\'Y\'@, @\'5\'@. @\'I\'@ is out for the -- usual reason of being similar to @\'1\'@. -} data English16 = Zero -- ^ @\'0\'@ /0th/ | One -- ^ @\'1\'@ /1st/ | Two -- ^ @\'2\'@ /2nd/ | Charlie -- ^ @\'C\'@ /3rd/ | Four -- ^ @\'4\'@ /4th/ | Foxtrot -- ^ @\'F\'@ /5th/ | Hotel -- ^ @\'H\'@ /6th/ | Seven -- ^ @\'7\'@ /7th/ | Eight -- ^ @\'8\'@ /8th/ | Nine -- ^ @\'9\'@ /9th/ | Kilo -- ^ @\'K\'@ /10th/ | Lima -- ^ @\'L\'@ /11th/ | Mike -- ^ @\'M\'@ /12th/ | Romeo -- ^ @\'R\'@ /13th/ | XRay -- ^ @\'X\'@ /14th/ | Yankee -- ^ @\'Y\'@ /15th/ deriving (Eq, Ord, Enum, Bounded) class (Ord α, Enum α, Bounded α) => Locator α where locatorToDigit :: α -> Char digitToLocator :: Char -> α instance Locator English16 where -- locatorToDigit :: English16 -> Char locatorToDigit x = case x of Zero -> '0' One -> '1' Two -> '2' Charlie -> 'C' Four -> '4' Foxtrot -> 'F' Hotel -> 'H' Seven -> '7' Eight -> '8' Nine -> '9' Kilo -> 'K' Lima -> 'L' Mike -> 'M' Romeo -> 'R' XRay -> 'X' Yankee -> 'Y' -- digitToLocator :: Char -> English16 digitToLocator c = case c of '0' -> Zero '1' -> One '2' -> Two 'C' -> Charlie '4' -> Four 'F' -> Foxtrot 'H' -> Hotel '7' -> Seven '8' -> Eight '9' -> Nine 'K' -> Kilo 'L' -> Lima 'M' -> Mike 'R' -> Romeo 'X' -> XRay 'Y' -> Yankee _ -> error "Illegal digit" represent :: Int -> Char represent n = locatorToDigit $ (toEnum n :: English16) -- FIXME instance Show English16 where show x = [c] where c = locatorToDigit x value :: Char -> Int value c = fromEnum $ (digitToLocator c :: English16) -- FIXME -- -- | Given a number, convert it to a string in the Locator16 base 16 symbol -- alphabet. You can use this as a replacement for the standard \'0\'-\'9\' -- \'A\'-\'F\' symbols traditionally used to express hexidemimal, though really -- the fact that we came up with 16 total unique symbols was a nice -- co-incidence, not a requirement. -- toLocator16 :: Int -> String toLocator16 x = showIntAtBase 16 represent x "" -- -- | Represent a number in Locator16a format. This uses the Locator16 symbol -- set, and additionally specifies that no symbol can be repeated. The /a/ in -- Locator16a represents that this transformation is done on the cheap; when -- converting if we end up with \'9\' \'9\' we simply pick the subsequent digit -- in the enum, in this case getting you \'9\' \'K\'. -- -- Note that the transformation is /not/ reversible. A number like @4369@ -- (which is @0x1111@, incidentally) encodes as @12C4@. So do @4370@, @4371@, -- and @4372@. The point is not uniqueness, but readibility in adverse -- conditions. So while you can count locators, they don't map continuously to -- base10 integers. -- -- The first argument is the number of digits you'd like in the locator; if the -- number passed in is less than 16^limit, then the result will be padded. -- -- >>> toLocator16a 6 4369 -- 12C40F -- toLocator16a :: Int -> Int -> String toLocator16a limit n = let ls = convert n (replicate limit minBound) :: [English16] (_,us) = mapAccumL uniq Set.empty ls in map locatorToDigit (take limit us) where convert :: Locator α => Int -> [α] -> [α] convert 0 xs = xs convert i xs = let (d,r) = divMod i 16 x = toEnum r in convert d (x:xs) uniq :: Locator α => Set α -> α -> (Set α, α) uniq s x = if Set.member x s then uniq s (subsequent x) else (Set.insert x s, x) subsequent :: Locator α => α -> α subsequent x = if x == maxBound then minBound else succ x multiply :: Int -> Char -> Int multiply acc c = acc * 16 + value c -- -- | Given a number encoded in Locator16, convert it back to an integer. -- fromLocator16 :: String -> Int fromLocator16 ss = foldl multiply 0 ss -- -- Given a string, convert it into a N character hash. -- concatToInteger :: [Word8] -> Int concatToInteger bytes = foldl fn 0 bytes where fn acc b = (acc * 256) + (fromIntegral b) digest :: String -> Int digest ws = i where i = concatToInteger h h = B.unpack h' h' = Crypto.hash x' x' = S.pack ws -- -- | Take an arbitrary sequence of bytes, hash it with SHA1, then format as a -- short @digits@-long Locator16 string. -- -- >>> hashStringToLocator16a 6 "Hello World" -- M48HR0 -- hashStringToLocator16a :: Int -> ByteString -> ByteString hashStringToLocator16a limit s' = let s = S.unpack s' n = digest s -- SHA1 hash r = mod n upperBound -- trim to specified number of base 16 chars x = toLocator16a limit r -- express in locator16 b' = S.pack x in b' where upperBound = 16 ^ limit