surf: Open Diff to custom construction

Put the Diff type in lines with its associated types by opening it up to
construction by crate consumers.  The existing associated types have all
their fields public.

Open construction up by making the `Diff::insert_*` methods public and
updating the Diff's stats manually.  `Diff::stat` correctness is covered
by existing tests.

radicle-surf/src/diff.rs

@@ -97,17 +97,40 @@ impl Diff {
         &self.stats
     }
 
-    fn insert_modified(&mut self, path: PathBuf, diff: DiffContent, old: DiffFile, new: DiffFile) {
+    fn update_stats(&mut self, diff: &DiffContent) {
+        self.stats.files_changed += 1;
+        if let DiffContent::Plain { hunks, .. } = diff {
+            for h in hunks.iter() {
+                for l in &h.lines {
+                    match l {
+                        Modification::Addition(_) => self.stats.insertions += 1,
+                        Modification::Deletion(_) => self.stats.deletions += 1,
+                        _ => (),
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn insert_modified(
+        &mut self,
+        path: PathBuf,
+        diff: DiffContent,
+        old: DiffFile,
+        new: DiffFile,
+    ) {
+        self.update_stats(&diff);
         let diff = FileDiff::Modified(Modified {
             path,
             diff,
             old,
             new,
         });
-        self.files.push(diff)
+        self.files.push(diff);
     }
 
-    fn insert_moved(&mut self, old_path: PathBuf, new_path: PathBuf) {
+    pub fn insert_moved(&mut self, old_path: PathBuf, new_path: PathBuf) {
+        self.update_stats(&DiffContent::Empty);
         let diff = FileDiff::Moved(Moved {
             old_path,
             new_path,
@@ -116,7 +139,8 @@ impl Diff {
         self.files.push(diff);
     }
 
-    fn insert_copied(&mut self, old_path: PathBuf, new_path: PathBuf) {
+    pub fn insert_copied(&mut self, old_path: PathBuf, new_path: PathBuf) {
+        self.update_stats(&DiffContent::Empty);
         let diff = FileDiff::Copied(Copied {
             old_path,
             new_path,
@@ -125,12 +149,14 @@ impl Diff {
         self.files.push(diff);
     }
 
-    fn insert_added(&mut self, path: PathBuf, diff: DiffContent, new: DiffFile) {
+    pub fn insert_added(&mut self, path: PathBuf, diff: DiffContent, new: DiffFile) {
+        self.update_stats(&diff);
         let diff = FileDiff::Added(Added { path, diff, new });
         self.files.push(diff);
     }
 
-    fn insert_deleted(&mut self, path: PathBuf, diff: DiffContent, old: DiffFile) {
+    pub fn insert_deleted(&mut self, path: PathBuf, diff: DiffContent, old: DiffFile) {
+        self.update_stats(&diff);
         let diff = FileDiff::Deleted(Deleted { path, diff, old });
         self.files.push(diff);
     }

radicle-surf/src/diff/git.rs

@@ -229,7 +229,6 @@ impl<'a> TryFrom<git2::Diff<'a>> for Diff {
         use git2::Delta;
 
         let mut diff = Diff::new();
-        diff.stats = git_diff.stats()?.into();
 
         for (idx, delta) in git_diff.deltas().enumerate() {
             match delta.status() {