Provide a link to snapshot's changes

Handler/StackageHome.hs

@@ -11,13 +11,13 @@ import qualified Data.HashMap.Strict as HashMap
 import Data.These
 import Data.Time (FormatTime)
 import Stackage.Database
-import Stackage.Database.Types (sortNicely)
+import Stackage.Database.Types (sortNicely, previousSnapName)
 import Stackage.Snapshot.Diff
 
 getStackageHomeR :: SnapName -> Handler Html
 getStackageHomeR name = do
     Entity sid snapshot <- lookupSnapshot name >>= maybe notFound return
-
+    snapNames <- map snapshotName . snd <$> getSnapshots 0 0
     let hoogleForm =
             let queryText = "" :: Text
                 exact = False

Stackage/Database/Types.hs

@@ -1,6 +1,7 @@
 module Stackage.Database.Types
     ( SnapName (..)
     , sortNicely
+    , previousSnapName
     ) where
 
 import ClassyPrelude.Conduit
@@ -26,6 +27,10 @@ sortNicely :: [SnapName] -> [SnapName]
 sortNicely ns = reverse (sort lts) ++ reverse (sort nightly)
   where (lts, nightly) = partition isLTS ns
 
+previousSnapName :: [SnapName] -> SnapName -> SnapName
+previousSnapName ns n =
+  fromMaybe n $ maximumMay $ filter (< n) $ filter ((isLTS n ==) . isLTS) ns
+
 instance PersistField SnapName where
     toPersistValue = toPersistValue . toPathPiece
     fromPersistValue v = do

templates/stackage-home.hamlet

@@ -5,6 +5,9 @@ $newline never
     <p>
         Published on #{yearMonthDay (snapshotCreated snapshot)}
         <span .separator>
+        <span>
+            <a href=@{StackageDiffR (previousSnapName snapNames name) name}>View changes
+        <span .separator>
         <span>
             stack #
             <code>resolver: #{toPathPiece name}