{-
Copyright (c) 2008 John MacFarlane
All rights reserved.

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modification, are permitted provided that the following conditions
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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-}

module Network.Captcha.ReCaptcha
       ( captchaFields
       , validateCaptcha
       )
where
import Text.XHtml
import Network.Browser
import Network.HTTP
import Network.URI

-- | Returns HTML element to be inserted in the form for which a CAPTCHA is wanted.
captchaFields :: String       -- ^ reCAPTCHA public key
              -> Maybe String -- ^ @Nothing@ or @Just@ an error message returned by previous validate attempt
              -> Html
captchaFields recaptchaPublicKey mbErrorMsg =
  (script ! [src (captchaURL "challenge"), thetype "text/javascript"] << noHtml) +++
  noscript << [ iframe ! [src (captchaURL "noscript"), height "300", width "500", frameborder 0] << noHtml
              , br
              , textarea ! [name "recaptcha_challenge_field", rows "3", cols "40"] << noHtml
              , input ! [thetype "hidden", name "recaptcha_response_field", value "manual_challenge"]
              ]
  where captchaURL s = "https://www.google.com/recaptcha/api/" ++ s ++ "?k=" ++ recaptchaPublicKey ++
          case mbErrorMsg of
               Just e  -> "?error=" ++ e
               Nothing -> ""

-- | Verify a CAPTCHA.
validateCaptcha :: String                 -- ^ reCAPTCHA private key
                -> String                 -- ^ IP address of the user who solved the CAPTCHA
                -> String                 -- ^ value of the recaptcha_challenge_field 
                -> String                 -- ^ value of the recaptcha_response_field
                -> IO (Either String ())  -- ^ @Left@ error message, or @Right ()@ for success
validateCaptcha recaptchaPrivateKey ipaddress challenge response = do
  let verifyURIString = "https://www.google.com/recaptcha/api/verify"
  let verifyURI = case parseURI verifyURIString of
                       Just uri  -> uri
                       Nothing   -> error $ "Could not parse URI: " ++ verifyURIString
  let contents = urlEncodeVars  [("privatekey", recaptchaPrivateKey),
                                 ("remoteip", ipaddress),
                                 ("challenge", challenge),
                                 ("response", response)]
  let req = Request { rqURI = verifyURI,
                      rqMethod = POST,
                      rqHeaders = [ Header HdrContentType "application/x-www-form-urlencoded",
                                    Header HdrContentLength (show $ length contents) ],
                      rqBody = contents }
  (_, resp) <- browse (request req)
  if rspCode resp == (2,0,0)
     then do
       let respLines = lines $ rspBody resp
       if null respLines
          then return $ Left "response-body-empty"
          else if head respLines == "true"
                  then return $ Right ()
                  else if length respLines >= 2
                          then return $ Left $ respLines !! 1
                          else return $ Left "no-error-message"
     else return $ Left "response-code-not-200"