-- Copyright © 2015 Mykola Orliuk <virkony@gmail.com>
-- Distributed under the terms of the GNU General Public License v2

{-# LANGUAGE ViewPatterns, UnicodeSyntax #-}

module Main where

import Control.Applicative
import Control.Monad
import Control.Exception
import Data.Maybe
import Data.ByteString.Lazy.Char8 (unpack)

import System.Environment
import System.IO

import Distribution.Text
import Distribution.Package
import Distribution.License
import Distribution.Version
import Distribution.PackageDescription
import Distribution.PackageDescription.Parse
import Distribution.Verbosity
import Network.HTTP.Client

import qualified Text.Regex.PCRE.Light.Char8 as R

import ExRender

-- |Fetch content by provided URI
simpleFetch ∷ String → IO String
simpleFetch url = do
    let settings = defaultManagerSettings
    req ← parseUrl url
    withManager settings $ liftM (unpack . responseBody) . httpLbs req

licenseHints ∷ [(R.Regex, License)]
licenseHints = [
    (R.compile "http://creativecommons\\.org/publicdomain/zero/1\\.0/" [R.multiline], UnknownLicense "CC0"),
    (R.compile "http://www\\.apache\\.org/licenses/LICENSE-2\\.0" [R.multiline], Apache (Just $ Version [2, 0] [])),
    (R.compile "GNU AFFERO GENERAL PUBLIC LICENSE\\s*Version 3," [R.multiline], UnknownLicense "AGPL-3"),
    (R.compile "Mozilla Public License Version 2\\.0$" [R.multiline], UnknownLicense "MPL-2")
    ]

guessLicense ∷ String → IO License
guessLicense text | isJust foundLicense = return $ fromJust foundLicense where
    foundLicense = listToMaybe $ mapMaybe hint licenseHints
    hint (re, answer) = const answer <$> R.match re text []

guessLicense _ = return OtherLicense

hackageBaseUri ∷ String
hackageBaseUri = "http://hackage.haskell.org/package/"

fixLicense ∷ GenericPackageDescription → IO GenericPackageDescription
fixLicense descr | license pkgDescr == OtherLicense = adjustLicense
                 | otherwise = return descr
    where
        pkgDescr = packageDescription descr
        packageUri = hackageBaseUri ++ display (package pkgDescr)
        adjustLicense = do
            let licensePath = head $ licenseFiles pkgDescr -- TODO: proper handling of multiple licenses
            licenseContent ← simpleFetch (packageUri ++ "/src/" ++ licensePath)
            license' ← guessLicense licenseContent
            case license' of
                OtherLicense → do
                    hPutStrLn stderr licenseContent
                    return descr
                _ → do
                    let pkgDescr' = pkgDescr { license = license' }
                        descr' = descr { packageDescription = pkgDescr' }
                    return descr'

-- |Fetch and parse cabal file for specific 'PackageIdentifier' using URL build
-- in form of http://hackage.haskell.org/package/<pkgid>/<pkgname>.cabal
fetchPackageDescription ∷ PackageIdentifier → IO GenericPackageDescription
fetchPackageDescription pkgid = do
    let cabalFile = display (packageName pkgid) ++ ".cabal"
        packageUri = hackageBaseUri ++ display pkgid
        url = packageUri ++ "/" ++ cabalFile
    ParseOk _ descr ← liftM parsePackageDescription $ simpleFetch url
    fixLicense descr

main ∷ IO ()
main = do
    args ← getArgs
    sources ← case args of
        [] → liftM lines getContents
        _ → return args
    forM_ sources $ \source → do
        descr ← case source of
            ('.':_) → readPackageDescription verbose source >>= fixLicense
            ('/':_) → readPackageDescription verbose source >>= fixLicense
            (simpleParse → Just pkgId) -> fetchPackageDescription pkgId
            _ -> error $ "Specified source " ++ show source
                ++ " neither starts with '.' or '/' (local file)"
                ++ " nor a valid packageIdentifier (to fetch from hackage)"
        let handler ∷ SomeException → IO ()
            handler e = hPutStrLn stderr $ "# Failed fetch/generate for " ++ show source ++ ": " ++ show e
        catch (evaluate (exRender descr) >>= putStrLn) handler