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-- | Parser for Ogma specs stored in JSON files.
module Language.JSONSpec.Parser where

-- External imports
import           Data.Aeson            (FromJSON (..), Value (..), decode, (.:))
import           Data.Aeson.Key        (toString)
import qualified Data.Aeson.KeyMap     as M
import           Data.Aeson.Types      (prependFailure, typeMismatch)
import           Data.Bifunctor        (first)
import           Data.ByteString.Lazy  (fromStrict)
import           Data.JSONPath.Execute
import           Data.JSONPath.Parser
import           Data.JSONPath.Types
import           Data.Text             (pack, unpack)
import qualified Data.Text             as T
import qualified Data.Text.Encoding    as T
import qualified Data.Text.IO          as T
import           Text.Megaparsec       (eof, errorBundlePretty, parse)

-- External imports: ogma-spec
import Data.OgmaSpec

data JSONFormat = JSONFormat
  { specInternalVars    :: String
  , specInternalVarId   :: String
  , specInternalVarExpr :: String
  , specInternalVarType :: String
  , specExternalVars    :: String
  , specExternalVarId   :: String
  , specExternalVarType :: String
  , specRequirements    :: String
  , specRequirementId   :: String
  , specRequirementDesc :: String
  , specRequirementExpr :: String
  }

data JSONFormatInternal = JSONFormatInternal
  { jfiInternalVars    :: [JSONPathElement]
  , jfiInternalVarId   :: [JSONPathElement]
  , jfiInternalVarExpr :: [JSONPathElement]
  , jfiInternalVarType :: [JSONPathElement]
  , jfiExternalVars    :: [JSONPathElement]
  , jfiExternalVarId   :: [JSONPathElement]
  , jfiExternalVarType :: [JSONPathElement]
  , jfiRequirements    :: [JSONPathElement]
  , jfiRequirementId   :: [JSONPathElement]
  , jfiRequirementDesc :: [JSONPathElement]
  , jfiRequirementExpr :: [JSONPathElement]
  }

parseJSONFormat :: JSONFormat -> Either String JSONFormatInternal
parseJSONFormat jsonFormat = do
  jfi2  <- showErrors $ parseJSONPath (pack (specInternalVars    jsonFormat))
  jfi3  <- showErrors $ parseJSONPath (pack (specInternalVarId   jsonFormat))
  jfi4  <- showErrors $ parseJSONPath (pack (specInternalVarExpr jsonFormat))
  jfi5  <- showErrors $ parseJSONPath (pack (specInternalVarType jsonFormat))
  jfi6  <- showErrors $ parseJSONPath (pack (specExternalVars    jsonFormat))
  jfi7  <- showErrors $ parseJSONPath (pack (specExternalVarId   jsonFormat))
  jfi8  <- showErrors $ parseJSONPath (pack (specExternalVarType jsonFormat))
  jfi9  <- showErrors $ parseJSONPath (pack (specRequirements    jsonFormat))
  jfi10 <- showErrors $ parseJSONPath (pack (specRequirementId   jsonFormat))
  jfi11 <- showErrors $ parseJSONPath (pack (specRequirementDesc jsonFormat))
  jfi12 <- showErrors $ parseJSONPath (pack (specRequirementExpr jsonFormat))
  return $ JSONFormatInternal
             { jfiInternalVars    = jfi2
             , jfiInternalVarId   = jfi3
             , jfiInternalVarExpr = jfi4
             , jfiInternalVarType = jfi5
             , jfiExternalVars    = jfi6
             , jfiExternalVarId   = jfi7
             , jfiExternalVarType = jfi8
             , jfiRequirements    = jfi9
             , jfiRequirementId   = jfi10
             , jfiRequirementDesc = jfi11
             , jfiRequirementExpr = jfi12
             }

parseJSONSpec :: (String -> Either String a) -> JSONFormat -> Value -> Either String (Spec a)
parseJSONSpec parseExpr jsonFormat value = do
  jsonFormatInternal <- parseJSONFormat jsonFormat

  let values :: [Value]
      values = executeJSONPath (jfiInternalVars jsonFormatInternal) value

      internalVarDef :: Value -> Either String InternalVariableDef
      internalVarDef value = do
        let msg = "internal variable name"
        varId   <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiInternalVarId jsonFormatInternal) value))

        let msg = "internal variable type"
        varType <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiInternalVarType jsonFormatInternal) value))

        let msg = "internal variable expr"
        varExpr <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiInternalVarExpr jsonFormatInternal) value))

        return $ InternalVariableDef
                   { internalVariableName    = varId
                   , internalVariableType    = varType
                   , internalVariableExpr    = varExpr
                   }

  internalVariableDefs <- mapM internalVarDef values

  let values :: [Value]
      values = executeJSONPath (jfiExternalVars jsonFormatInternal) value

      externalVarDef :: Value -> Either String ExternalVariableDef
      externalVarDef value = do

        let msg = "external variable name"
        varId   <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiExternalVarId jsonFormatInternal) value))

        let msg = "external variable type"
        varType <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiExternalVarType jsonFormatInternal) value))

        return $ ExternalVariableDef
                   { externalVariableName    = varId
                   , externalVariableType    = varType
                   }

  externalVariableDefs <- mapM externalVarDef values

  let values :: [Value]
      values = executeJSONPath (jfiRequirements jsonFormatInternal) value

      -- requirementDef :: Value -> Either String (Requirement a)
      requirementDef value = do
        let msg = "Requirement name"
        reqId <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiRequirementId jsonFormatInternal) value))

        let msg = "Requirement expression"
        reqExpr <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiRequirementExpr jsonFormatInternal) value))
        reqExpr' <- parseExpr reqExpr

        let msg = "Requirement description"
        reqDesc <- valueToString msg =<< (listToEither msg (executeJSONPath (jfiRequirementDesc jsonFormatInternal) value))

        return $ Requirement
                   { requirementName        = reqId
                   , requirementExpr        = reqExpr'
                   , requirementDescription = reqDesc
                   }

  requirements <- mapM requirementDef values

  return $ Spec internalVariableDefs externalVariableDefs requirements

valueToString :: String -> Value -> Either String String
valueToString msg (String x) = Right $ unpack x
valueToString msg _          = Left $ "The JSON value provided for " ++ msg ++ " does not contain a string"

listToEither :: String -> [a] -> Either String a
listToEither _   [x] = Right x
listToEither msg []  = Left $ "Failed to find a value for " ++ msg
listToEither msg _   = Left $ "Unexpectedly found multiple values for " ++ msg

-- | Parse a JSONPath expression, returning its element components.
parseJSONPath :: T.Text -> Either String [JSONPathElement]
parseJSONPath = first errorBundlePretty . parse (jsonPath eof) ""

showErrors :: Show a => Either a b -> Either String b
showErrors (Left s)  = Left (show s)
showErrors (Right x) = Right x