{-# OPTIONS_GHC -XEmptyDataDecls #-}
--
-- Simple experimentation with System.Xml.Linq functionality
-- 
-- Example invocations:
--   runQuery "@examples\\xml\\books.xml" "book"
--   runQuery "<root><a><c>b</c></a><c>d</c></root>" "c"
module LINQ where

import NET

data XDocument_ a
type XDocument a = Object (XDocument_ a)

data XContainer_ a
type XContainer a = Object (XContainer_ a)

data XObject_ a
type XObject a = Object (XContainer_ a)

parseDocument :: String -> IO (XDocument ())
parseDocument s = invokeStatic "System.Xml.Linq.XDocument" "Parse" s

enumMethod :: String -> String
enumMethod s = "System.Collections.Generic.IEnumerable<System.Xml.Linq.XElement>." ++ s

enumaMethod :: String -> String
enumaMethod s = "System.Collections.Generic.IEnumerator<System.Xml.Linq.XElement>." ++ s

loadDocument :: String -> IO (XDocument ())
loadDocument s = invokeStatic "System.Xml.Linq.XDocument" "Load" s
   
descendants :: String -> XDocument a -> IO (XContainer ())
descendants str d = do
    -- too funky, no XName constructor just an implicit from-string operator (which is accessed as below..)
  nm <- invokeStatic "System.Xml.Linq.XName" "op_Implicit" str
  obj <- d # invoke "Descendants" (nm :: Object ())
  ie <- obj # invoke (enumMethod "GetEnumerator") () -- nm :: Object ())
  ie # invoke_ "MoveNext" ()
  return ie

enumObjs :: XContainer () -> IO [XObject ()]
enumObjs obj =  go []
 where
  go acc = do
    v <- obj # qCurrent
    b <- obj # invoke "MoveNext" () 
    if not b
     then return (reverse (v:acc))
     else go (v:acc)

qCurrent :: XContainer a -> IO (XObject b)
qCurrent c = c # invoke (enumaMethod "get_Current") ()

runQuery :: String -> String -> IO ()
runQuery s chNode = do
  d  <- case s of { '@':xs -> loadDocument xs ; _ -> parseDocument s}
  ds <- d # descendants chNode
  ls <- ds # enumObjs
  putStrLn (filter (/='\r') $ show ls)