From 865b972ea417633b7b53c19038faab8bd57d8711 Mon Sep 17 00:00:00 2001
From: Ben Sima <ben@bsima.me>
Date: Sat, 20 Mar 2021 05:48:25 -0400
Subject: Calculate hotspotMap in Analysis

---
 Biz/Devalloc.hs | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/Biz/Devalloc.hs b/Biz/Devalloc.hs
index cafe9fa..2131983 100644
--- a/Biz/Devalloc.hs
+++ b/Biz/Devalloc.hs
@@ -13,6 +13,7 @@
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE Strict #-}
 {-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TupleSections #-}
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
@@ -83,6 +84,7 @@ import Data.Data (Data, Typeable)
 import Data.IxSet (Indexable (..), IxSet, ixFun, ixSet, (&&&), (@=))
 import qualified Data.IxSet as IxSet
 import qualified Data.List as List
+import qualified Data.Map as Map
 import Data.SafeCopy (base, deriveSafeCopy, extension)
 import qualified Data.SafeCopy as SafeCopy
 import qualified Data.Set as Set
@@ -271,6 +273,7 @@ data Analysis0 = Analysis0
   { analysisId :: Id.Id Analysis0,
     url :: URL,
     bareRepo :: FilePath,
+    repoVisibility :: Visibility,
     blackholes :: [Text],
     liabilities :: [Text],
     stale :: [(FilePath, Int)],
@@ -299,6 +302,9 @@ data Analysis = Analysis
     blackholes :: [Text],
     -- | A path with < 3 active contributors
     liabilities :: [Text],
+    -- | Map of path to number of commits, for detecting paths that continually
+    -- get rewritten.
+    hotspotMap :: Map FilePath Int,
     -- | Files that have not been touched in 6 months
     stale :: [(FilePath, Int)],
     -- | Total score for the repo
@@ -319,7 +325,7 @@ instance SafeCopy.Migrate Analysis where
   migrate Analysis0 {..} =
     Analysis
       { analysisId = Id.mk (Proxy :: Proxy Analysis) <| Id.untag analysisId,
-        repoVisibility = Public,
+        hotspotMap = mempty,
         ..
       }
 
@@ -1461,6 +1467,8 @@ analyze keep askedBy activeAuthors url bareRepo repoPrivate = do
       let numBlackholes = realToFrac <| length blackholes
       let numLiabilities = realToFrac <| length liabilities
       let numTotal = realToFrac <| length tree
+      hotspotMap <-
+        Map.fromList </ Async.mapConcurrently getChangeCount tree
       Analysis
         { analysisId = mempty,
           stale =
@@ -1479,6 +1487,13 @@ analyze keep askedBy activeAuthors url bareRepo repoPrivate = do
     third :: (a, b, c) -> c
     third (_, _, a) = a
     git args = Process.readProcess "git" (["--git-dir", bareRepo] ++ args) ""
+    getChangeCount :: FilePath -> IO (FilePath, Int)
+    getChangeCount path =
+      git ["rev-list", "--count", "HEAD", "--", path]
+        /> filter (/= '\n')
+        /> readMaybe
+        /> fromMaybe 0
+        /> (path,)
 
 -- | Does the aggregate score calculation given number of files found to be
 -- blackholes, liabilities, etc.
@@ -1529,7 +1544,7 @@ lastTouched bareRepo path = do
   where
     calculateAge now n = round <| Time.diffUTCTime now n / Time.nominalDay
 
--- | Given a git dir and a path inside the git repo, pure a list of tuples
+-- | Given a git dir and a path inside the git repo, return a list of tuples
 -- with number of commits and author.
 authorsFor ::
   FilePath ->
-- 
cgit v1.2.3