44 lines
1.3 KiB
Haskell
44 lines
1.3 KiB
Haskell
module Util.Hakyll.Context (
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updateFieldWith,
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defaultConstField,
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ifField,
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) where
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import Hakyll
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import Data.Maybe (fromMaybe)
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import Control.Applicative (empty)
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{- |
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Shortcut function for getting an Items Metadata
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This is used as a helper function in a lot of places.
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-}
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getItemMetadata :: Item a -> Compiler Metadata
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getItemMetadata = getMetadata . itemIdentifier
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{- |
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-}
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updateFieldWith :: String -> String -> (String -> String) -> Item a -> Compiler String
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updateFieldWith field defaultPreviousValue f =
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fmap updateField . getMetadata . itemIdentifier
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where
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updateField :: Metadata -> String
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updateField = f . fromMaybe defaultPreviousValue . lookupString field
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{- |
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This function takes a field name, and a default String value.
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If the field is found, it will leave it be, else inject the default value.
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Similar to the behaviour of (fromMaybe)
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-}
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defaultConstField :: String -> String -> Context String
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defaultConstField fieldString defaultValue =
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field fieldString (fmap f . getItemMetadata)
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where
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f :: Metadata -> String
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f = fromMaybe defaultValue . lookupString fieldString
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{-
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-}
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ifField :: String -> (Item a -> Compiler ContextField) -> Context a
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ifField key value = Context $ \k _ i -> if k == key then value i else empty
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