From a34b46e1b553623d5dc385fc8e235df808fbadb2 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Sat, 3 Feb 2024 11:58:47 +0100
Subject: Add font compression

---
 lib/Graphics/Fountainhead/Compression.hs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 lib/Graphics/Fountainhead/Compression.hs

(limited to 'lib/Graphics/Fountainhead/Compression.hs')

diff --git a/lib/Graphics/Fountainhead/Compression.hs b/lib/Graphics/Fountainhead/Compression.hs
new file mode 100644
index 0000000..c1a05fc
--- /dev/null
+++ b/lib/Graphics/Fountainhead/Compression.hs
@@ -0,0 +1,27 @@
+-- | Font compression and decompression.
+module Graphics.Fountainhead.Compression
+    ( compress
+    , hDecompress
+    ) where
+
+import qualified Data.ByteString.Lazy as ByteString.Lazy
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as ByteString
+import qualified Codec.Compression.Zlib as Zlib
+import System.IO (Handle, SeekMode(..), hFileSize, hSeek)
+
+-- | Reads the font from a file handle decompressing it if needed.
+hDecompress :: Handle -> IO ByteString
+hDecompress fontHandle = do
+    firstBytes <- ByteString.unpack <$> ByteString.hGet fontHandle 2
+    hSeek fontHandle AbsoluteSeek 0
+    fileSize <- fromIntegral <$> hFileSize fontHandle
+    case firstBytes of
+        0x78 : [secondByte]
+            | secondByte `elem` [0x01, 0x9c, 0x5e, 0xda] ->
+                ByteString.Lazy.toStrict . Zlib.decompress
+                    <$> ByteString.Lazy.hGet fontHandle fileSize
+        _ -> ByteString.hGetContents fontHandle
+
+compress :: ByteString -> ByteString
+compress = ByteString.Lazy.toStrict . Zlib.compress . ByteString.Lazy.fromStrict
-- 
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