2010-12-24 07:42:05 +00:00
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-- | This module provides an API for resource providers. Resource providers
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-- allow Hakyll to get content from resources; the type of resource depends on
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-- the concrete instance.
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--
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module Hakyll.Core.ResourceProvider
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( ResourceProvider (..)
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2010-12-31 12:28:31 +00:00
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, resourceExists
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2010-12-26 15:22:05 +00:00
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, resourceDigest
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2010-12-31 11:38:12 +00:00
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, resourceModified
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2010-12-24 07:42:05 +00:00
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) where
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2010-12-26 15:22:05 +00:00
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import Control.Monad ((<=<))
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import Data.Word (Word8)
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2010-12-24 07:42:05 +00:00
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2010-12-26 15:12:24 +00:00
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import qualified Data.ByteString.Lazy as LB
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2010-12-26 15:22:05 +00:00
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import OpenSSL.Digest.ByteString.Lazy (digest)
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import OpenSSL.Digest (MessageDigest (MD5))
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import Hakyll.Core.Identifier
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2010-12-31 11:38:12 +00:00
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import Hakyll.Core.Store
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2010-12-26 15:12:24 +00:00
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2010-12-24 07:42:05 +00:00
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-- | A value responsible for retrieving and listing resources
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--
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data ResourceProvider = ResourceProvider
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{ -- | A list of all resources this provider is able to provide
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resourceList :: [Identifier]
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2010-12-24 07:42:05 +00:00
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, -- | Retrieve a certain resource as string
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2010-12-26 15:12:24 +00:00
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resourceString :: Identifier -> IO String
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, -- | Retrieve a certain resource as lazy bytestring
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resourceLazyByteString :: Identifier -> IO LB.ByteString
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2010-12-24 07:42:05 +00:00
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}
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2010-12-26 15:22:05 +00:00
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2010-12-31 12:28:31 +00:00
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-- | Check if a given resource exists
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--
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resourceExists :: ResourceProvider -> Identifier -> Bool
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resourceExists provider = flip elem $ resourceList provider
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2010-12-26 15:22:05 +00:00
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-- | Retrieve a digest for a given resource
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--
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resourceDigest :: ResourceProvider -> Identifier -> IO [Word8]
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resourceDigest provider = digest MD5 <=< resourceLazyByteString provider
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2010-12-31 11:38:12 +00:00
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-- | Check if a resource was modified
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--
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resourceModified :: ResourceProvider -> Identifier -> Store -> IO Bool
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resourceModified provider identifier store = do
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-- Get the latest seen digest from the store
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lastDigest <- storeGet store itemName identifier
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-- Calculate the digest for the resource
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newDigest <- resourceDigest provider identifier
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-- Check digests
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if Just newDigest == lastDigest
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-- All is fine, not modified
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then return False
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-- Resource modified; store new digest
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else do storeSet store itemName identifier newDigest
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return True
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where
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itemName = "Hakyll.Core.ResourceProvider.resourceModified"
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