{-# LANGUAGE NoImplicitPrelude, FlexibleInstances, OverloadedStrings #-}

module IHaskell.Eval.Hoogle (
    search,
    document,
    render,
    OutputFormat(..),
    HoogleResult,
    ) where

import           ClassyPrelude hiding (last, span, div)
import           Text.Printf
import           Network.HTTP.Client
import           Network.HTTP.Client.TLS
import           Data.Aeson
import           Data.String.Utils
import           Data.List (elemIndex, (!!), last)
import           Data.Char (isAscii, isAlphaNum)
import qualified Data.ByteString.Lazy.Char8 as Char
import qualified Prelude as P


import           IHaskell.IPython

-- | Types of formats to render output to.
data OutputFormat = Plain      -- ^ Render to plain text.
                  | HTML       -- ^ Render to HTML.

data HoogleResponse = HoogleResponse { location :: String, self :: String, docs :: String }
  deriving (Eq, Show)

data HoogleResult = SearchResult HoogleResponse
                  | DocResult HoogleResponse
                  | NoResult String
  deriving Show

instance FromJSON [HoogleResponse] where
  parseJSON (Object obj) = do
    results <- obj .: "results"
    mapM parseJSON results

  parseJSON _ = fail "Expected object with 'results' field."

instance FromJSON HoogleResponse where
  parseJSON (Object obj) =
    HoogleResponse <$> obj .: "location" <*> obj .: "self" <*> obj .: "docs"

  parseJSON _ = fail "Expected object with fields: location, self, docs"

-- | Query Hoogle for the given string. This searches Hoogle using the internet. It returns either
-- an error message or the successful JSON result.
query :: String -> IO (Either String String)
query str = do
  request <- parseUrl $ queryUrl $ urlEncode str
  response <- try $ withManager tlsManagerSettings $ httpLbs request
  return $
    case response of
      Left err   -> Left $ show (err :: SomeException)
      Right resp -> Right $ Char.unpack $ responseBody resp

  where
    queryUrl :: String -> String
    queryUrl = printf "https://www.haskell.org/hoogle/?hoogle=%s&mode=json"

-- | Copied from the HTTP package.
urlEncode :: String -> String
urlEncode [] = []
urlEncode (ch:t)
  | (isAscii ch && isAlphaNum ch) || ch `P.elem` "-_.~" = ch : urlEncode t
  | not (isAscii ch) = P.foldr escape (urlEncode t) (eightBs [] (P.fromEnum ch))
  | otherwise = escape (P.fromEnum ch) (urlEncode t)
  where
    escape :: Int -> String -> String
    escape b rs = '%' : showH (b `P.div` 16) (showH (b `mod` 16) rs)

    showH :: Int -> String -> String
    showH x xs
      | x <= 9 = toEnum (o_0 + x) : xs
      | otherwise = toEnum (o_A + (x - 10)) : xs
      where
        o_0 = P.fromEnum '0'
        o_A = P.fromEnum 'A'

    eightBs :: [Int] -> Int -> [Int]
    eightBs acc x
      | x <= 255 = x : acc
      | otherwise = eightBs ((x `mod` 256) : acc) (x `P.div` 256)

-- | Search for a query on Hoogle. Return all search results.
search :: String -> IO [HoogleResult]
search string = do
  response <- query string
  return $
    case response of
      Left err -> [NoResult err]
      Right json ->
        case eitherDecode $ Char.pack json of
          Left err -> [NoResult err]
          Right results ->
            case map SearchResult results of
              []  -> [NoResult "no matching identifiers found."]
              res -> res

-- | Look up an identifier on Hoogle. Return documentation for that identifier. If there are many
-- identifiers, include documentation for all of them.
document :: String -> IO [HoogleResult]
document string = do
  matchingResults <- filter matches <$> search string
  let results = map toDocResult matchingResults
  return $
    case results of
      []  -> [NoResult "no matching identifiers found."]
      res -> res

  where
    matches (SearchResult resp) =
      case split " " $ self resp of
        name:_ -> strip string == strip name
        _      -> False
    matches _ = False

    toDocResult (SearchResult resp) = DocResult resp

-- | Render a Hoogle search result into an output format.
render :: OutputFormat -> HoogleResult -> String
render Plain = renderPlain
render HTML = renderHtml

-- | Render a Hoogle result to plain text.
renderPlain :: HoogleResult -> String
renderPlain (NoResult res) =
  "No response available: " ++ res

renderPlain (SearchResult resp) =
  printf "%s\nURL: %s\n%s" (self resp) (location resp) (docs resp)

renderPlain (DocResult resp) =
  printf "%s\nURL: %s\n%s" (self resp) (location resp) (docs resp)

-- | Render a Hoogle result to HTML.
renderHtml :: HoogleResult -> String
renderHtml (NoResult resp) =
  printf "<span class='err-msg'>No result: %s</span>" resp

renderHtml (DocResult resp) =
  renderSelf (self resp) (location resp)
  ++
  renderDocs (docs resp)

renderHtml (SearchResult resp) =
  renderSelf (self resp) (location resp)
  ++
  renderDocs (docs resp)

renderSelf :: String -> String -> String
renderSelf string loc
  | startswith "package" string =
      pkg ++ " " ++ span "hoogle-package" (link loc $ extractPackage string)

  | startswith "module" string =
      let package = extractPackageName loc
      in mod ++ " " ++
                span "hoogle-module" (link loc $ extractModule string) ++
                packageSub package

  | startswith "class" string =
      let package = extractPackageName loc
      in cls ++ " " ++
                span "hoogle-class" (link loc $ extractClass string) ++
                packageSub package

  | startswith "data" string =
      let package = extractPackageName loc
      in dat ++ " " ++
                span "hoogle-class" (link loc $ extractData string) ++
                packageSub package

  | otherwise =
      let [name, args] = split "::" string
          package = extractPackageName loc
          modname = extractModuleName loc
      in span "hoogle-name"
           (unicodeReplace $
              link loc (strip name) ++
              " :: " ++
              strip args)
         ++ packageAndModuleSub package modname
  where
    extractPackage = strip . replace "package" ""
    extractModule = strip . replace "module" ""
    extractClass = strip . replace "class" ""
    extractData = strip . replace "data" ""
    pkg = span "hoogle-head" "package"
    mod = span "hoogle-head" "module"
    cls = span "hoogle-head" "class"
    dat = span "hoogle-head" "data"

    unicodeReplace :: String -> String
    unicodeReplace =
      replace "forall" "&#x2200;" .
      replace "=>" "&#x21D2;" .
      replace "->" "&#x2192;" .
      replace "::" "&#x2237;"

    packageSub Nothing = ""
    packageSub (Just package) =
      span "hoogle-sub" $
        "(" ++ pkg ++ " " ++ span "hoogle-package" package ++ ")"

    packageAndModuleSub Nothing _ = ""
    packageAndModuleSub (Just package) Nothing = packageSub (Just package)
    packageAndModuleSub (Just package) (Just modname) =
      span "hoogle-sub" $
        "(" ++ pkg ++ " " ++ span "hoogle-package" package ++
                             ", " ++ mod ++ " " ++ span "hoogle-module" modname ++ ")"

renderDocs :: String -> String
renderDocs doc =
  let groups = groupBy bothAreCode $ lines doc
      nonull = filter (not . null . strip)
      bothAreCode s1 s2 =
                           startswith ">" (strip s1) &&
                           startswith ">" (strip s2)
      isCode (s:_) = startswith ">" $ strip s
      makeBlock lines =
                         if isCode lines
                           then div "hoogle-code" $ unlines $ nonull lines
                           else div "hoogle-text" $ unlines $ nonull lines
  in div "hoogle-doc" $ unlines $ map makeBlock groups

extractPackageName :: String -> Maybe String
extractPackageName link = do
  let pieces = split "/" link
  archiveLoc <- elemIndex "archive" pieces
  latestLoc <- elemIndex "latest" pieces
  guard $ latestLoc - archiveLoc == 2
  return $ pieces !! (latestLoc - 1)

extractModuleName :: String -> Maybe String
extractModuleName link = do
  let pieces = split "/" link
  guard $ not $ null pieces
  let html = last pieces
      mod = replace "-" "." $ takeWhile (/= '.') html
  return mod

div :: String -> String -> String
div = printf "<div class='%s'>%s</div>"

span :: String -> String -> String
span = printf "<span class='%s'>%s</span>"

link :: String -> String -> String
link = printf "<a target='_blank' href='%s'>%s</a>"