add twitter [etc] card previews

make-pages/Info.hs

@@ -5,6 +5,7 @@ module Info
    GalleryInfo (..), GalleryFilters (..), ArtistFilter (..), NsfwFilter (..),
    IndexInfo (..),
    readArtistFilter, matchArtist, readNsfwFilter, matchNsfw, matchFilters,
+   NoThumb (..), getThumb, thumbFile, pageFile,
    -- ** Reexports
    Day (..), Text)
 where
@@ -13,6 +14,7 @@ import Records
 
 import Control.Applicative
 import Control.Monad
+import Control.Exception
 import Data.Foldable (find)
 import Data.Hashable (Hashable)
 import Data.HashSet (HashSet)
@@ -26,7 +28,7 @@ import qualified Data.Text as Text
 import Data.Time.Calendar (Day (..), toGregorian)
 import Data.YAML (FromYAML (..), (.:), (.:?), (.!=))
 import qualified Data.YAML as YAML
-import System.FilePath (takeBaseName)
+import System.FilePath ((</>), takeBaseName, takeExtension, splitExtension)
 import Text.Read (readMaybe)
 
 
@@ -117,6 +119,28 @@ instance Ord Info where
   compare = comparing \Info {date, title} -> (date, title)
 
 
+newtype NoThumb = NoThumb FilePath
+  deriving stock Eq deriving anyclass Exception
+instance Show NoThumb where show (NoThumb dir) = "no thumbnail for " ++ dir
+
+getThumb :: FilePath -> Info -> FilePath
+getThumb dir =
+  maybe (throw $ NoThumb dir) (\t -> dir </> thumbFile t) . #thumb
+
+thumbFile :: FilePath -> FilePath
+thumbFile = addSuffix "_small"
+
+pageFile :: FilePath -> FilePath
+pageFile f
+  | takeExtension f == ".gif" = f
+  | otherwise                 = addSuffix "_med" f
+
+addSuffix :: String -> FilePath -> FilePath
+addSuffix suf path =
+  let (pre, ext) = splitExtension path in
+  pre ++ suf ++ ext
+
+
 instance FromYAML Info where
   parseYAML = YAML.withMap "info" \m ->
     Info <$>  m .:  "date"
@@ -259,6 +283,7 @@ instance FromYAML ArtistFilter where
 data IndexInfo =
   IndexInfo {
     title     :: !Text,
+    desc      :: !Text,
     galleries :: ![GalleryInfo],
     links     :: ![Link],
     footer    :: !(Maybe Text)
@@ -268,6 +293,7 @@ data IndexInfo =
 instance FromYAML IndexInfo where
   parseYAML = YAML.withMap "index info" \m ->
     IndexInfo <$> m .:  "title"
+              <*> m .:  "desc"
               <*> m .:? "galleries" .!= []
               <*> m .:? "links"     .!= []
               <*> m .:? "footer"