-- | Minimal XML functionality needed to parse each document's
--   XML_File_ID.
--
module TSN.Xml (
  parse_xmlfid,
  xml_prologue )
where

import Data.Maybe (listToMaybe, mapMaybe)
import Text.Read (readMaybe)
import Text.XML.HXT.Core (
  (>>>),
  (/>),
  getChildren,
  getText,
  hasName,
  runLA,
  xreadDoc )

-- | A tiny parser written in HXT to extract the "XML_File_ID" element
--   from a document.
parse_xmlfid :: String -> Maybe Integer
parse_xmlfid =
  listToMaybe . mapMaybe readMaybe . parse
  where
    parse :: String -> [String]
    parse =
      runLA (xreadDoc
               >>> hasName "message"
               />  hasName "XML_File_ID"
               >>> getChildren
               >>> getText)


-- | The opening "tag" for the XML prologue.
xml_prologue :: String
xml_prologue = "<?xml "