Add review checking script

.github/workflows/check-required-reviews.yml

@@ -20,19 +20,50 @@ jobs:
 
       - name: Check reviews
         env:
-          PR_REF: github.ref
+          REF: ${{ github.ref }}
+          REPO: ${{ github.repository }}
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         shell: python
         run: |
+          import json
           import os
+          import re
+          import subprocess
           import sys
 
-          ref = os.getenv("PR_REF")
-          print(f"Ref: {ref}")
+          REQUIRED_REVIEWS = 3
+          ref = os.getenv("REF")
+          repo = os.getenv("REPO")
 
-          # Get info with gh pr -R MetOffice/CSET view $PR_NUMBER --json
-          # labels,reviews If full_review label exists parse with program to see
-          # if enough reviews. Newer reviews by the same person should
-          # invalidate older reviews.
+          # Get PR number from ref. Will crash if doesn't match -> failed exit code.
+          pr_number = re.fullmatch(r"refs/pulls/([0-9]+)/merge", ref).group(1)
 
-          sys.exit(0)
+          # Get info on PR labels and reviews.
+          pr_info = json.loads(
+              subprocess.run(
+                  ("gh", "pr", "--json", "labels,reviews", "--repo", repo, "view", pr_number),
+                  check=True,
+                  capture_output=True,
+                  timeout=60,
+                  text=True,
+              ).stdout
+          )
+
+          # Exit early if PR not labeled with full_review.
+          if not any(label["name"] == "full_review" for label in pr_info["labels"]):
+              print('Skipping PR without "full_review" label.')
+              sys.exit(0)
+
+          # Check for enough reviews. Newer reviews invalidate older ones.
+          approving_reviewers = set()
+          for review in sorted(pr_info["reviews"], key=lambda r: r["submittedAt"]):
+              if review["state"] == "APPROVED":
+                  approving_reviewers.add(review["author"]["login"])
+              elif review["state"] == "CHANGES_REQUESTED":
+                  approving_reviewers.discard(review["author"]["login"])
+
+          if len(approving_reviewers) < REQUIRED_REVIEWS:
+              print(f"Not enough reviews: {len(approving_reviewers)}/{REQUIRED_REVIEWS}")
+              sys.exit(1)
+          else:
+              print(f"Sufficient reviews: {len(approving_reviewers)}/{REQUIRED_REVIEWS}")