LowLevelAPI.hs

module GEOSTest.LowLevelAPI (demo) where

import Control.Exception
import Data.Geolocation.GEOS.Imports
import Foreign.C

-- Demonstrates direct use of imports
-- Lifetimes of various GEOS objects, including readers, writers and
-- geometries, must be managed explicitly by clients using explicit calls to
-- various destroy/free functions
demo :: IO ()
demo = do
    wkt0 <- newCString "POLYGON (( 10 10, 10 20, 20 20, 20 10, 10 10 ))"
    wkt1 <- newCString "POLYGON (( 11 11, 11 12, 12 12, 12 11, 11 11 ))"

    withGEOS $ \ctx -> do
        withWKTReader ctx $ \reader -> do
            withGeometry ctx reader wkt0 $ \g0 -> do
                withGeometry ctx reader wkt1 $ \g1 -> do
                    bracket (c_GEOSIntersection_r ctx g0 g1) (c_GEOSGeom_destroy_r ctx) $ \g2 -> do
                        withWKTWriter ctx $ \writer -> do
                            str <- bracket
                                (c_GEOSWKTWriter_write_r ctx writer g2)
                                (c_GEOSFree_r_CString ctx)
                                peekCString
                            putStrLn str
                            putStrLn "LowLevelAPI.demo done"
    where
        withGEOS :: (GEOSContextHandle_t -> IO a) -> IO a
        withGEOS = bracket c_initializeGEOSWithHandlers c_finishGEOS_r
        withWKTReader :: GEOSContextHandle_t -> (GEOSWKTReaderPtr -> IO a) -> IO a
        withWKTReader ctx = bracket (c_GEOSWKTReader_create_r ctx) (c_GEOSWKTReader_destroy_r ctx)
        withWKTWriter :: GEOSContextHandle_t -> (GEOSWKTWriterPtr -> IO a) -> IO a
        withWKTWriter ctx = bracket (c_GEOSWKTWriter_create_r ctx) (c_GEOSWKTWriter_destroy_r ctx)
        withGeometry :: GEOSContextHandle_t -> GEOSWKTReaderPtr -> CString -> (GEOSGeometryPtr -> IO a) -> IO a
        withGeometry ctx reader wkt =
            bracket
                (c_GEOSWKTReader_read_r ctx reader wkt)
                (c_GEOSGeom_destroy_r ctx)