# This action requires the following secrets to be set on the repository:
#   GH_USER_TOKEN: GitHub user token, to be used by ncu and to push changes
name: Comment on PR on Nix changes

on:
  workflow_run:
    workflows: [Nix files edited]
    types: [completed]

permissions: {}

jobs:
  aggregate-results:
    if: ${{ github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.event == 'pull_request' }}
    name: Aggregate results
    runs-on: ubuntu-slim
    permissions:
      pull-requests: write
    steps:
      - name: Download artefacts
        uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333  # v8.0.2
        with:
          run-id: ${{ github.event.workflow_run.id }}
          # Using privileged token to be able to download file from a different workflow
          github-token: ${{ secrets.GH_USER_TOKEN }}

      - name: Fetch PR data
        id: pr-data
        run: |
          mv requisites-*/* .
          ls
          if grep -nvHE '^/nix/store/[0-9a-df-np-sv-z]{32}-[A-Za-z0-9?=._+-]+$' requisites-*.list; then
            echo 'Unexpected line format in requisites list; refusing to process.' >&2
            exit 1
          fi
          echo "NUMBER=$(grep -E '^[0-9]+$' pr_number.txt || true)" >> "$GITHUB_OUTPUT"

      - name: Aggregate results
        if: ${{ steps.pr-data.outputs.NUMBER }}
        run: |
          set -x
          > requisites-before.list
          > requisites-after.list
          TABLE=$(
            echo '| Platform | Number of requisites | Proportion of new derivations |'
            echo '| :-: | -: | -: |'
            TOTAL_BEFORE=0
            TOTAL_AFTER=0
            TOTAL_CHANGED=0
            QUOTE='`'
            for PLATFORM in x86_64-linux aarch64-linux x86_64-darwin aarch64-darwin; do
              BEFORE=$(wc -l < "requisites-${PLATFORM}-before.list")
              TOTAL_BEFORE=$(($TOTAL_BEFORE + $BEFORE))
              AFTER=$(wc -l < "requisites-${PLATFORM}-after.list")
              TOTAL_AFTER=$(($TOTAL_AFTER + $AFTER))
              DIFF="_no changes_"
              [ "$BEFORE" = "$AFTER" ] || DIFF="**$([ "$AFTER" -lt "$BEFORE" ] || echo '+')$(($AFTER - $BEFORE))**"
              CHANGED=$(git diff --no-index "requisites-${PLATFORM}-before.list" "requisites-${PLATFORM}-after.list" | grep -c '^+[^+]')
              TOTAL_CHANGED=$(($TOTAL_CHANGED + $CHANGED))
              PERCENT=100
              [ "$CHANGED" = "$AFTER" ] || {
                PERMILLE=$((1000 * $CHANGED / $AFTER))
                PERCENT="$((PERMILLE / 10)).$((PERMILLE % 10))"
              }
              echo "| ${QUOTE}${PLATFORM}${QUOTE} | $BEFORE -> $AFTER => $DIFF | $CHANGED / $AFTER = $PERCENT% |"
              awk '{ print $0 " ('"$PLATFORM"')" }' "requisites-${PLATFORM}-before.list" >> requisites-before.list
              awk '{ print $0 " ('"$PLATFORM"')" }' "requisites-${PLATFORM}-after.list" >> requisites-after.list
            done

            DIFF="_no changes_"
            [ "$TOTAL_BEFORE" = "$TOTAL_AFTER" ] || DIFF="**$([ "$TOTAL_AFTER" -lt "$TOTAL_BEFORE" ] || echo '+')$(($TOTAL_AFTER - $TOTAL_BEFORE))**"
            PERCENT=100
            [ "$TOTAL_CHANGED" = "$TOTAL_AFTER" ] || {
              PERMILLE=$((1000 * $TOTAL_CHANGED / $TOTAL_AFTER))
              PERCENT="$((PERMILLE / 10)).$((PERMILLE % 10))"
            }
            echo "| **Total** | $TOTAL_BEFORE -> $TOTAL_AFTER => $DIFF | $TOTAL_CHANGED / $TOTAL_AFTER = $PERCENT% |"
          )
          sort -k1.45 requisites-before.list > requisites-before.sort
          sort -k1.45 requisites-after.list > requisites-after.sort
          if git diff -U0 --no-color --no-index requisites-before.sort requisites-after.sort > requisites.diff; then
            echo 'No changes detected.'
          else
          {
            echo "$TABLE"
            echo
            echo '<details><summary>Changelog</summary>'
            echo
            echo '```diff'
            tail -n +5 requisites.diff
            echo '```'
            echo
            echo '</details>'
          } | gh pr comment -R "$GITHUB_REPOSITORY" "$PR_NUMBER" -F -
          fi
        env:
          GH_TOKEN: ${{ github.token }}
          PR_NUMBER: ${{ steps.pr-data.outputs.NUMBER }}