name: Query Counts — Label

# Manages the "query-count changed" label and a diff comment on PRs that
# alter per-route DB query counts. When a PR's snapshot files differ from
# base, the label and a comparison comment are added; when they match base
# again (e.g. the delta was reverted, or base caught up via a merge), both
# are removed.
#
# Deliberately NOT path-filtered. A `paths:` filter would create a catch-22:
# the workflow could never run to clear a stale label/comment once a
# previously-changed snapshot matched base again, because at that point the
# PR diff no longer touches the snapshot files. The script below is cheap
# (a couple of API reads) and decides what to do from the actual base/head
# diff on every run.
on:
  pull_request_target:
    branches: [main]
    types: [opened, synchronize, reopened, edited]

permissions:
  pull-requests: write

jobs:
  label:
    runs-on: ubuntu-latest
    timeout-minutes: 5
    steps:
      - name: Sync query-count label and diff comment
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
        with:
          script: |
            const { owner, repo } = context.repo;
            const pr = context.payload.pull_request;
            const baseRef = pr.base.sha;
            const headRef = pr.head.sha;
            const label = 'query-count changed';

            // Fetch a JSON file at a given ref. Returns {} if the file
            // doesn't exist on that ref (e.g. snapshot added in this PR).
            async function loadSnapshot(ref, path) {
              try {
                const { data } = await github.rest.repos.getContent({
                  owner,
                  repo,
                  ref,
                  path,
                });
                if (Array.isArray(data) || data.type !== 'file' || !data.content) {
                  return {};
                }
                const raw = Buffer.from(data.content, 'base64').toString('utf8');
                return JSON.parse(raw);
              } catch (err) {
                if (err.status === 404) return {};
                throw err;
              }
            }

            function diffRows(before, after) {
              const keys = new Set([...Object.keys(before), ...Object.keys(after)]);
              const rows = [];
              for (const key of [...keys].sort()) {
                const b = before[key];
                const a = after[key];
                if (b === a) continue;
                const bCell = b === undefined ? '—' : String(b);
                const aCell = a === undefined ? '—' : String(a);
                const delta = (a ?? 0) - (b ?? 0);
                const deltaCell =
                  a === undefined
                    ? 'removed'
                    : b === undefined
                      ? 'added'
                      : delta > 0
                        ? `+${delta}`
                        : String(delta);
                rows.push(`| \`${key}\` | ${bCell} | ${aCell} | ${deltaCell} |`);
              }
              return rows;
            }

            const dialects = [
              ['SQLite', 'scripts/query-counts.snapshot.sqlite.json'],
              ['D1', 'scripts/query-counts.snapshot.d1.json'],
            ];

            const sections = [];
            let totalDelta = 0;
            let totalChanged = 0;

            for (const [name, path] of dialects) {
              const [before, after] = await Promise.all([
                loadSnapshot(baseRef, path),
                loadSnapshot(headRef, path),
              ]);
              const rows = diffRows(before, after);
              if (rows.length === 0) continue;
              totalChanged += rows.length;
              for (const key of new Set([...Object.keys(before), ...Object.keys(after)])) {
                const b = before[key] ?? 0;
                const a = after[key] ?? 0;
                if (a !== b) totalDelta += a - b;
              }
              sections.push(
                [
                  `### ${name}`,
                  '',
                  '| Route | Before | After | Δ |',
                  '| --- | ---: | ---: | --- |',
                  ...rows,
                ].join('\n'),
              );
            }

            const hasChange = sections.length > 0;

            // Label: present iff the snapshots differ from base on this run.
            if (hasChange) {
              try {
                await github.rest.issues.createLabel({
                  owner,
                  repo,
                  name: label,
                  color: 'fbca04',
                  description: 'PR diff modifies query-count snapshot files',
                });
              } catch (err) {
                if (err.status !== 422) throw err; // 422 = already exists
              }
              await github.rest.issues.addLabels({
                owner,
                repo,
                issue_number: pr.number,
                labels: [label],
              });
            } else {
              try {
                await github.rest.issues.removeLabel({
                  owner,
                  repo,
                  issue_number: pr.number,
                  name: label,
                });
              } catch (err) {
                if (err.status !== 404) throw err; // 404 = label not applied
              }
            }

            // Comment: upsert when changed, delete when not.
            const marker = '<!-- query-count-diff -->';
            const comments = await github.paginate(github.rest.issues.listComments, {
              owner,
              repo,
              issue_number: pr.number,
              per_page: 100,
            });
            const prior = comments.find(
              (c) => typeof c.body === 'string' && c.body.includes(marker),
            );

            if (!hasChange) {
              // Snapshots match base on this run; remove any stale comment
              // (e.g. an earlier push had a delta that base has since caught
              // up to, or it was reverted).
              if (prior) {
                await github.rest.issues.deleteComment({
                  owner,
                  repo,
                  comment_id: prior.id,
                });
              }
              return;
            }

            const sign = totalDelta > 0 ? '+' : '';
            const summary = `**${totalChanged}** route${totalChanged === 1 ? '' : 's'} changed, total Δ ${sign}${totalDelta} quer${Math.abs(totalDelta) === 1 ? 'y' : 'ies'}.`;

            const body = [
              marker,
              '## Query-count snapshot changes',
              '',
              summary,
              '',
              ...sections,
              '',
              '<sub>Comparing snapshot files between base and head. Updated automatically on each push.</sub>',
            ].join('\n');

            if (prior) {
              await github.rest.issues.updateComment({
                owner,
                repo,
                comment_id: prior.id,
                body,
              });
            } else {
              await github.rest.issues.createComment({
                owner,
                repo,
                issue_number: pr.number,
                body,
              });
            }