(#801) Add genconf subcommand to the expression fuzzer

Author: rexim

HyperNerd.cabal

@@ -165,6 +165,7 @@ executable Fuzzy
                      , text
                      , random
                      , aeson
+                     , bytestring
 
   hs-source-dirs:      src
 

src/FuzzyMain.hs

@@ -12,6 +12,7 @@ import qualified Data.Text as T
 import System.Environment
 import System.Random
 import Text.Printf
+import qualified Data.ByteString.Lazy as BS
 
 data FuzzParams = FuzzParams
   { fpFuzzCount :: Int
@@ -42,6 +43,9 @@ instance FromJSON FuzzParams where
 readFuzzParams :: FilePath -> IO FuzzParams
 readFuzzParams = fmap (either error id) . eitherDecodeFileStrict
 
+saveFuzzParams :: FuzzParams -> FilePath -> IO ()
+saveFuzzParams params filePath = BS.writeFile filePath $ encode params
+
 defaultFuzzParams :: FuzzParams
 defaultFuzzParams =
   FuzzParams
@@ -132,8 +136,15 @@ fuzz params = do
   printf "Successes: %d\n" $ length $ filter id report
 
 mainWithArgs :: [String] -> IO ()
-mainWithArgs (fuzzParamsPath:_) = readFuzzParams fuzzParamsPath >>= fuzz
-mainWithArgs _ = error "Usage: Fuzz <fuzz.json>"
+mainWithArgs ("genconf":configFilePath:_) = do
+  saveFuzzParams defaultFuzzParams configFilePath
+  printf "Generated default configuration at %s" configFilePath
+mainWithArgs ("runconf":fuzzParamsPath:_) = readFuzzParams fuzzParamsPath >>= fuzz
+mainWithArgs _ =
+  error
+    "Usage: \n\
+    \       Fuzz genconf <fuzz.json>\n\
+    \       Fuzz runconf <fuzz.json>"
 
 main :: IO ()
 main = getArgs >>= mainWithArgs