{-|
Module      : Portage.EMeta
License     : GPL-3+
Maintainer  : haskell@gentoo.org

Functions to propagate existing ebuild information
(such as its licence, description, switched flags etc.) to
a new ebuild.
-}
module Portage.EMeta
  ( EMeta(..)
  , findExistingMeta
  ) where

import Control.Monad
import Data.Char (isSpace)
import qualified Data.List as L

import System.Directory (doesDirectoryExist, getDirectoryContents)
import System.FilePath ((</>))
import Text.Printf

-- | Extract a value of variable in \'var=\"val\"\' format.
-- There should be exactly one variable assignment in the ebuild.
-- It's a bit of an artificial limitation, but it's common for \'if / else\' blocks.
extract_quoted_string :: FilePath -> String -> String -> Maybe String
extract_quoted_string ebuild_path s_ebuild var_name =
    case filter (L.isPrefixOf var_prefix . ltrim) $ lines s_ebuild of
        []        -> Nothing
        [kw_line] -> up_to_quote $ skip_prefix $ ltrim kw_line
        other     -> bail_out $ printf "strange '%s' assignments:\n%s" var_name (unlines other)

    where ltrim :: String -> String
          ltrim = dropWhile isSpace
          var_prefix = var_name ++ "=\""
          skip_prefix = drop (length var_prefix)
          up_to_quote l = case break (== '"') l of
                              ("", _)  -> Nothing -- empty line
                              (_, "")  -> bail_out $ printf "failed to find closing quote for '%s'" l
                              (val, _) -> Just val
          bail_out :: String -> e
          bail_out msg = error $ printf "%s:extract_quoted_string %s" ebuild_path msg

-- | Extract a value of variable in \'#hackport: var: val\' format.
-- There should be exactly one variable assignment in the ebuild.
extract_hackport_var :: FilePath -> String -> String -> Maybe String
extract_hackport_var ebuild_path s_ebuild var_name =
    case filter (L.isPrefixOf var_prefix) $ lines s_ebuild of
        []         -> Nothing
        [var_line] -> Just $ skip_prefix var_line
        other      -> bail_out $ printf "strange '%s' assignmets:\n%s" var_name (unlines other)

    where var_prefix = "#hackport: " ++ var_name ++ ": "
          skip_prefix = drop (length var_prefix)
          bail_out :: String -> e
          bail_out msg = error $ printf "%s:extract_hackport_var %s" ebuild_path msg

-- | Extract the existing keywords from an ebuild.
extractKeywords :: FilePath -> String -> Maybe [String]
extractKeywords ebuild_path s_ebuild =
    words `fmap ` extract_quoted_string ebuild_path s_ebuild "KEYWORDS"

-- | Extract the existing license from an ebuild.
extractLicense :: FilePath -> String -> Maybe String
extractLicense ebuild_path s_ebuild =
    extract_quoted_string ebuild_path s_ebuild "LICENSE"

-- | Extract the existing Cabal flags from an ebuild.
extractCabalFlags :: FilePath -> String -> Maybe String
extractCabalFlags ebuild_path s_ebuild =
    extract_hackport_var ebuild_path s_ebuild "flags"

-- | Extract the existing description from an ebuild.
extractDescription :: FilePath -> String -> Maybe String
extractDescription ebuild_path s_ebuild =
    extract_quoted_string ebuild_path s_ebuild "DESCRIPTION"

-- | Type representing the aggregated (best inferred) metadata for a
-- new ebuild of a package.
data EMeta = EMeta { keywords :: Maybe [String]
                   , license  :: Maybe String
                   , cabal_flags :: Maybe String
                   , description :: Maybe String
                   }

-- | Find the existing package metadata from the last available ebuild.
findExistingMeta :: FilePath -> IO EMeta
findExistingMeta pkgdir =
    do ebuilds <- filter (L.isSuffixOf ".ebuild") `fmap` do b <- doesDirectoryExist pkgdir
                                                            if b then getDirectoryContents pkgdir
                                                                 else return []
       -- TODO: version sort
       e_metas <- forM ebuilds $ \e ->
                      do let e_path = pkgdir </> e
                         e_conts <- readFile e_path
                         return EMeta { keywords = extractKeywords e e_conts
                                      , license = extractLicense  e e_conts
                                      , cabal_flags = extractCabalFlags e e_conts
                                      , description = extractDescription e e_conts
                                      }
       let get_latest candidates = last (Nothing : filter (/= Nothing) candidates)
           aggregated_meta = EMeta { keywords = get_latest $ map keywords e_metas
                                   , license = get_latest $ map license e_metas
                                   , cabal_flags = get_latest $ map cabal_flags e_metas
                                   , description = get_latest $ map description e_metas
                                   }
       return aggregated_meta