#!/usr/bin/runghc

\begin{code}
import Distribution.PackageDescription
import Distribution.Setup
import Distribution.Simple
import Distribution.Simple.LocalBuildInfo
import Distribution.Simple.Utils(rawSystemVerbose)
import System.Info
import System.Exit
import System.Directory
import System.Process(runInteractiveProcess, waitForProcess)
import System.IO(hClose, hGetContents, hPutStr, stderr)
import Control.Monad(when)
import Control.Exception(try)

main = defaultMainWithHooks defaultUserHooks{preConf=preConf, postConf=postConf}
  where
    preConf ::  [String] -> ConfigFlags -> IO HookedBuildInfo
    preConf args flags = do
      try (removeFile "SQLite3.buildinfo")
      return emptyHookedBuildInfo
    postConf :: [String] -> ConfigFlags -> PackageDescription -> LocalBuildInfo -> IO ExitCode
    postConf args flags _ localbuildinfo = do
      mb_bi <- pkgConfigBuildInfo (configVerbose flags) "sqlite3"
      let bi = case mb_bi of
                 Just bi -> bi
                 Nothing -> emptyBuildInfo{extraLibs=["sqlite3"]}
      writeHookedBuildInfo "SQLite3.buildinfo" (Just bi,[])
      return ExitSuccess
\end{code}

The following code is derived from Distribution.Simple.Configure
\begin{code}
findProgram
    :: String              -- ^ program name
    -> Maybe FilePath      -- ^ optional explicit path
    -> IO (Maybe FilePath)
findProgram name Nothing = do
  mb_path <- findExecutable name
  case mb_path of
    Nothing   -> message ("No " ++ name ++ " found")
    Just path -> message ("Using " ++ name ++ ": " ++ path)
  return mb_path
findProgram name (Just path) = do
  message ("Using " ++ name ++ ": " ++ path)
  return (Just path)

rawSystemGrabOutput :: Int -> FilePath -> [String] -> IO String
rawSystemGrabOutput verbose path args = do
  when (verbose > 0) $
        putStrLn (path ++ concatMap (' ':) args)
  (inp,out,err,pid) <- runInteractiveProcess path args Nothing Nothing
  exitCode <- waitForProcess pid
  if exitCode /= ExitSuccess
    then do errMsg <- hGetContents err
            hPutStr stderr errMsg
            exitWith exitCode
    else return ()
  hClose inp
  hClose err
  hGetContents out

message :: String -> IO ()
message s = putStrLn $ "configure: " ++ s
\end{code}

Populate BuildInfo using pkg-config tool.
\begin{code}
pkgConfigBuildInfo :: Int -> String -> IO (Maybe BuildInfo)
pkgConfigBuildInfo verbose pkgName = do
  mb_pkg_config_path <- findProgram "pkg-config" Nothing
  case mb_pkg_config_path of
    Just pkg_config_path -> do
       message ("configuring "++pkgName++" package using pkg-config") 
       res <- rawSystemGrabOutput verbose pkg_config_path [pkgName, "--libs-only-l"]
       let libs = map (tail.tail) (words res)
       res <- rawSystemGrabOutput verbose pkg_config_path [pkgName, "--libs-only-L"]
       let lib_dirs = map (tail.tail) (words res)
       res <- rawSystemGrabOutput verbose pkg_config_path [pkgName, "--libs-only-other"]
       let ld_opts = words res
       res <- rawSystemGrabOutput verbose pkg_config_path [pkgName, "--cflags-only-I"]
       let inc_dirs = map (tail.tail) (words res)
       res <- rawSystemGrabOutput verbose pkg_config_path [pkgName, "--cflags-only-other"]
       let cc_opts = words res
       let bi = emptyBuildInfo{extraLibs=libs, extraLibDirs=lib_dirs, ldOptions=ld_opts, includeDirs=inc_dirs, ccOptions=cc_opts}
       return (Just bi)
    Nothing -> do
       message ("The package will be built using default settings for "++pkgName)
       return Nothing
\end{code}