{- |
Copyright:  (c) 2018-2020 Kowainik
SPDX-License-Identifier: MPL-2.0
Maintainer: Kowainik <xrom.xkov@gmail.com>
Stability:  experimental

__NOTE:__ This functionality is not to be considered stable
or ready for production use. While we enourage you
to try it out and report bugs, we cannot assure you
that everything will work as advertised :)
-}

module Colog.Rotation
       ( Limit(..)
       , withLogRotation
       ) where

import Control.Monad (when, (>=>))
import Control.Monad.IO.Class (MonadIO (..))
import Data.IORef (IORef, newIORef, readIORef, writeIORef)
import Data.List (isPrefixOf)
import Data.List.NonEmpty (nonEmpty)
import Data.Maybe (fromMaybe, mapMaybe)
import Numeric.Natural (Natural)
import System.FilePath.Posix ((<.>))
import System.IO (Handle, IOMode (AppendMode), hClose, hFileSize, openFile)
import Text.Read (readMaybe)

import Colog.Core.Action (LogAction (..), (<&))

import qualified Data.List.NonEmpty as NE
import qualified System.Directory as D
import qualified System.FilePath.Posix as POS


{- | Limit for the logger rotation. Used for two purposes:

1. Limit the number of kept files.
2. Limit the size of the files.
-}
data Limit
    = LimitTo Natural
    | Unlimited
    deriving stock (Eq, Ord, Show)

{- | Logger rotation action. Takes name of the logging file @file.foo@. Always
writes new logs to file named @file.foo@ (given file name, also called as /hot log/).

* If the size of the file exceeds given limit for file sizes then this action
  renames @file.foo@ to @file.foo.(n + 1)@ (where @n@ is the number of latest
  renamed file).
* If the number of files on the filesystem is bigger than the files number limit
  then the given @FilePath -> IO ()@ action is called on the oldest file. As
  simple solution, you can pass @removeFile@ function to delete old files but
  you can also pass some archiving function if you don't want to lose old logs.
-}
withLogRotation
    :: forall r msg m .
       MonadIO m
    => Limit
    -- ^ Max allowed file size in bytes
    -> Limit
    -- ^ Max allowed number of files to have
    -> FilePath
    -- ^ File path to log
    -> (FilePath -> IO ())
    -- ^ What to do with old files; pass @removeFile@ here for deletion
    -> (Handle -> LogAction m msg)
    -- ^ Action that writes to file handle
    -> (LogAction m msg -> IO r)
    -- ^ Continuation action
    -> IO r
withLogRotation sizeLimit filesLimit path cleanup mkAction cont = do
    -- TODO: figure out how to use bracket to safely manage
    -- possible exceptions
    handle <- openFile path AppendMode
    handleRef <- newIORef handle
    cont $ rotationAction handleRef
  where
    rotationAction :: IORef Handle -> LogAction m msg
    rotationAction refHandle = LogAction $ \msg -> do
        handle <- liftIO $ readIORef refHandle
        mkAction handle <& msg

        isLimitReached <- isFileSizeLimitReached sizeLimit handle
        when isLimitReached $ cleanupAndRotate refHandle

    cleanupAndRotate :: IORef Handle -> m ()
    cleanupAndRotate refHandle = liftIO $ do
      readIORef refHandle >>= hClose
      maxN <- maxFileIndex path
      renameFileToNumber (maxN + 1) path
      oldFiles <- getOldFiles filesLimit path
      mapM_ cleanup oldFiles
      newHandle <- openFile path AppendMode
      writeIORef refHandle newHandle

-- Checks whether an input is strictly larger than the limit
isLimitedBy :: Integer -> Limit -> Bool
isLimitedBy _ Unlimited = False
isLimitedBy size (LimitTo limit)
  | size <= 0 = False
  | otherwise = size > toInteger limit

isFileSizeLimitReached :: forall m . MonadIO m => Limit -> Handle -> m Bool
isFileSizeLimitReached limit handle = liftIO $ do
  fileSize <- hFileSize handle
  pure $ isLimitedBy fileSize limit

-- if you have files node.log.0, node.log.1 and node.log.2 then this function
-- will return `2` if you give it `node.log`
maxFileIndex :: FilePath -> IO Natural
maxFileIndex path = do
  files <- D.listDirectory (POS.takeDirectory path)
  let logFiles = getLogFiles path files
  let maxFile = maximum <$> nonEmpty (mapMaybe logFileIndex logFiles)
  pure $ fromMaybe 0 maxFile

getLogFiles :: FilePath -> [FilePath] -> [FilePath]
getLogFiles logPath = filter (\p -> POS.takeFileName logPath `isPrefixOf` POS.takeFileName p)

-- given number 4 and path `node.log` renames file `node.log` to `node.log.4`
renameFileToNumber :: Natural -> FilePath -> IO ()
renameFileToNumber n path = D.renameFile path (path <.> show n)

-- if you give it name like `node.log.4` then it returns `Just 4`
logFileIndex :: FilePath -> Maybe Natural
logFileIndex path = fmap NE.tail (nonEmpty (POS.takeExtension path)) >>= readMaybe

-- creates list of files with indices who are older on given Limit than the latest one
getOldFiles :: Limit -> FilePath -> IO [FilePath]
getOldFiles limit path = do
    currentMaxN <- maxFileIndex path
    files <- D.listDirectory (POS.takeDirectory path)
    let logFiles = getLogFiles path files
    pure $ mapMaybe (takeFileIndex >=> guardFileIndex currentMaxN) logFiles
  where
    takeFileIndex  :: FilePath -> Maybe (FilePath, Natural)
    takeFileIndex p = fmap (p,) (logFileIndex p)

    guardFileIndex :: Natural -> (FilePath, Natural) -> Maybe FilePath
    guardFileIndex maxN (p, n)
      | isOldFile maxN n = Just p
      | otherwise       = Nothing

    isOldFile :: Natural -> Natural -> Bool
    isOldFile maxN n = case limit of
                         Unlimited -> False
                         LimitTo l -> n + l < maxN