Add tx-cost-diff executable (#1718)

<!-- Describe your change here -->

---

<!-- Consider each and tick it off one way or the other -->
* [ ] CHANGELOG updated or not needed
* [ ] Documentation updated or not needed
* [ ] Haddocks updated or not needed
* [ ] No new TODOs introduced or explained herafter

.github/workflows/ci-nix.yaml

@@ -371,15 +371,6 @@ jobs:
     steps:
     - name: "Checkout the PR as the 'new' source"
       uses: actions/checkout@v4
-      with:
-        path: ./new
-        ref: ${{ github.event.pull_request.head.sha }}
-
-    - name: "Checkout `master` as the 'old' source"
-      uses: actions/checkout@v4
-      with:
-        path: ./old
-        ref: master
 
     - name: ❄ Prepare nix
       uses: cachix/install-nix-action@v30
@@ -397,33 +388,11 @@ jobs:
     - name: Set up and use the "ci" devShell
       uses: nicknovitski/nix-develop@v1
       with:
-        arguments: "./new#costDifferences"
-
-    - name: "Compute costs on both old and new"
-      run: |
-        SEED=$RANDOM
-        echo "Using random seed $SEED"
-        nix run ./new/#tx-cost -- --seed $SEED >new.md
-        nix run ./old/#tx-cost -- --seed $SEED >old.md
+        arguments: ".#costDifferences"
 
     - name: "Compute the difference markdown"
       run: |
-        # Convert to HTML, as that's the easiest way to read the markdown
-        # tables via pandas (!!!)
-        pandoc -i new.md -o new.html
-        pandoc -i old.md -o old.html
-
-        cat new.md | grep '##' >new-headers.txt
-        cat old.md | grep '##' >old-headers.txt
-
-        # Stop if the heading columns aren't the same.
-        cmp old-headers.txt new-headers.txt
-
-        # Run the diff script; note that it's located in the "new" folder.
-        ./new/.github/workflows/cost-differences/diff.py \
-          old-headers.txt \
-          old.html \
-          new.html >diff.md
+        nix run ".#tx-cost-diff"
 
     - name: 🔎 Find Comment
       uses: peter-evans/find-comment@v3

flake.nix

@@ -127,6 +127,19 @@
                     value = addWerror v;
                   })
                   x.components."${y}") [ "benchmarks" "exes" "sublibs" "tests" ]);
+
+          tx-cost-diff =
+            let
+              pyEnv = (pkgs.python3.withPackages (ps: with ps; [ pandas html5lib beautifulsoup4 tabulate ]));
+            in
+            pkgs.writers.writeHaskellBin
+              "tx-cost-diff"
+              {
+                libraries =
+                  with pkgs.haskellPackages;
+                  [ aeson text bytestring lens lens-aeson shh ];
+              } ''${builtins.readFile scripts/tx-cost-diff.hs}'';
+
         in
         {
           legacyPackages = pkgs // hsPkgs;
@@ -135,6 +148,7 @@
             hydraPackages //
             (if pkgs.stdenv.isLinux then (prefixAttrs "docker-" hydraImages) else { }) // {
               spec = inputs.hydra-spec.packages.${system}.default;
+              inherit tx-cost-diff;
             };
           process-compose."demo" = import ./nix/hydra/demo.nix {
             inherit system pkgs inputs self;

scripts/tx-cost-diff.hs

@@ -0,0 +1,80 @@
+{-# LANGUAGE ExtendedDefaultRules #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+import Control.Lens (asIndex, to, (&), (^.), (^?))
+import Data.Aeson
+import qualified Data.Aeson.Key as Key
+import Data.Aeson.Lens
+import Data.ByteString.Lazy (ByteString)
+import qualified Data.ByteString.Lazy as LBS
+import Data.Maybe (fromJust)
+import Data.String
+import Data.Text (Text)
+import qualified Data.Text.Lazy as Text
+import Data.Text.Lazy.Encoding (decodeLatin1)
+import Shh
+import System.Environment
+
+runRemoteTxCost :: ByteString -> Integer -> IO ByteString
+runRemoteTxCost revision seed = do
+  exe
+    "nix"
+    "run"
+    ("git+https://github.com/cardano-scaling/hydra?" <> revision <> "#tx-cost")
+    "--"
+    "--seed"
+    seed
+    |> capture
+
+runLocalTxCost :: Integer -> IO ByteString
+runLocalTxCost seed = do
+  exe
+    "nix"
+    "run"
+    ".#tx-cost"
+    "--"
+    "--seed"
+    seed
+    |> capture
+
+runPandoc :: FilePath -> FilePath -> IO ByteString
+runPandoc i o = do
+  exe
+    "pandoc"
+    "-i"
+    i
+    "-o"
+    o
+    |> capture
+
+extractHeaders :: ByteString -> IO ByteString
+extractHeaders md = do
+  exe "echo" md |> exe "grep" "##" |> capture
+
+runPandasDiff :: FilePath -> FilePath -> FilePath -> IO ByteString
+runPandasDiff headers old new = do
+  exe
+    "./scripts/diff.py"
+    headers
+    old
+    new
+    |> capture
+
+main :: IO ()
+main = do
+  args <- getArgs
+  let revision =
+        case args of
+          [x] -> "rev=" <> x
+          _ -> "ref=master"
+  a <- runLocalTxCost 0
+  b <- runRemoteTxCost (fromString revision) 0
+  LBS.writeFile "new.md" a
+  LBS.writeFile "old.md" b
+  runPandoc "new.md" "new.html"
+  runPandoc "old.md" "old.html"
+  x <- extractHeaders a
+  y <- extractHeaders b
+  LBS.writeFile "new-headers.txt" x
+  k <- runPandasDiff "new-headers.txt" "old.html" "new.html"
+  LBS.writeFile "diff.md" k