From cfb9ed248fd7afa9029695cb5cc759b43276d79b Mon Sep 17 00:00:00 2001
From: Andrei Dziahel <develop7@develop7.info>
Date: Wed, 20 Dec 2017 01:16:44 +0300
Subject: [PATCH] Introduces highlighting package version differences

---
 src/Stackage/Snapshot/Diff.hs  | 16 ++++++++++++++++
 templates/package-list.lucius  |  9 +++++++++
 templates/stackage-diff.hamlet | 24 +++++++++++++++++-------
 3 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/src/Stackage/Snapshot/Diff.hs b/src/Stackage/Snapshot/Diff.hs
index 5900e05..f3335be 100644
--- a/src/Stackage/Snapshot/Diff.hs
+++ b/src/Stackage/Snapshot/Diff.hs
@@ -4,10 +4,12 @@ module Stackage.Snapshot.Diff
   , snapshotDiff
   , SnapshotDiff()
   , toDiffList
+  , toVersionedDiffList
   , VersionChange(..)
   , WithSnapshotNames(..)
   ) where
 
+import qualified Data.Text as T(commonPrefixes)
 import           Data.Align
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HashMap
@@ -36,6 +38,20 @@ instance ToJSON (WithSnapshotNames SnapshotDiff) where
 toDiffList :: SnapshotDiff -> [(PackageName, VersionChange)]
 toDiffList = sortOn (toCaseFold . unPackageName . fst) . HashMap.toList . unSnapshotDiff
 
+versionPrefix :: VersionChange -> Maybe (Text,Text,Text)
+versionPrefix vc = case unVersionChange vc of
+        These (Version a) (Version b) -> T.commonPrefixes a b
+        _ -> Nothing
+
+versionedDiffList :: [(PackageName, VersionChange)] -> [(PackageName, VersionChange, Maybe (Text,Text,Text))]
+versionedDiffList = map withPrefixedVersion
+  where
+    withPrefixedVersion (packageName, versionChange) = (packageName, versionChange, versionPrefix versionChange)
+
+
+toVersionedDiffList :: SnapshotDiff -> [(PackageName, VersionChange, Maybe (Text, Text, Text))]
+toVersionedDiffList = versionedDiffList . toDiffList
+
 -- | Versions of a package as it occurs in the listings provided to `snapshotDiff`.
 --
 --   Would be represented with `These v1 v2` if the package is present in both listings,
diff --git a/templates/package-list.lucius b/templates/package-list.lucius
index 54a842d..556bcb9 100644
--- a/templates/package-list.lucius
+++ b/templates/package-list.lucius
@@ -2,4 +2,13 @@
   .table th, .table td {
     padding-left: 0;
   }
+
+  .table span.version-removed {
+    background-color: red;
+    text-decoration: line-through;
+  }
+
+  .table span.version-added {
+    background-color: green;
+  }
 }
diff --git a/templates/stackage-diff.hamlet b/templates/stackage-diff.hamlet
index 4b414d3..4cae29d 100644
--- a/templates/stackage-diff.hamlet
+++ b/templates/stackage-diff.hamlet
@@ -33,7 +33,7 @@
                 $else
                   <option value=@{StackageDiffR name1 name2'}>#{toPathPiece name2'}
       <tbody>
-        $forall (pkgname, VersionChange verChange) <- toDiffList snapDiff
+        $forall (pkgname, VersionChange verChange, versionDiff) <- toVersionedDiffList snapDiff
           <tr>
             $case verChange
               $of This oldVersion
@@ -47,9 +47,19 @@
                   <a href=@{packageUrl name2 pkgname newVersion}#changes>
                     #{pkgname}-#{newVersion}
               $of These oldVersion newVersion
-                <td>
-                  <a href=@{packageUrl name1 pkgname oldVersion}#changes>
-                    #{pkgname}-#{oldVersion}
-                <td>
-                  <a href=@{packageUrl name2 pkgname newVersion}#changes>
-                    #{pkgname}-#{newVersion}
+                $maybe (common, old, new) <- versionDiff
+                  <td>
+                    <a href=@{packageUrl name1 pkgname oldVersion}#changes>
+                      #{pkgname}-#{common}#
+                      <span .version-removed>#{old}
+                  <td>
+                    <a href=@{packageUrl name2 pkgname newVersion}#changes>
+                      #{pkgname}-#{common}#
+                      <span .version-added>#{new}
+                $nothing
+                  <td>
+                    <a href=@{packageUrl name1 pkgname oldVersion}#changes>
+                      #{pkgname}-#{oldVersion}
+                  <td>
+                    <a href=@{packageUrl name2 pkgname newVersion}#changes>
+                      #{pkgname}-#{newVersion}