UrlTable.hs

module Breve.UrlTable
( UrlTable
, load
, insert
, extract
) where

import Breve.Generator

import Control.Monad       (forever)
import Control.Concurrent  (forkIO, threadDelay)
import Text.Read           (readMaybe)
import qualified Data.HashTable.IO as H

type UrlTable = H.CuckooHashTable Word Url

-- Periodically write a url table to a file
sync :: UrlTable -> FilePath -> IO ()
sync table file = forever $ do
  threadDelay (round 3.0e8)
  content <- fmap show (H.toList table)
  writeFile file content

-- Load a url table from a file
load :: FilePath -> IO UrlTable
load file = do
  content <- readFile file
  table <- case readMaybe content of
    Just list -> H.fromList list
    Nothing   -> H.new
  forkIO (sync table file)
  return table

-- Insert the url in a table and return the word
insert :: UrlTable -> Url -> IO Word
insert table url = H.insert table new url >> return new
  where new = wordID url

-- Lookup a table for the associated url
extract :: UrlTable -> Word -> IO (Maybe Url)
extract = H.lookup