difficulty.yml

name: PR Difficulty Labeler

on:
  pull_request_target:
    types: [opened, synchronize, reopened, ready_for_review, edited]

permissions:
  issues: write
  pull-requests: write

jobs:
  detect-difficulty:
    name: Assign difficulty label
    runs-on: ubuntu-latest

    steps:
      - name: Analyze PR and assign difficulty label
        uses: actions/github-script@v7
        with:
          script: |
            const pr      = context.payload.pull_request;
            const prNum   = pr.number;
            const repo    = { owner: context.repo.owner, repo: context.repo.repo };

            // ── Label catalogue ────────────────────────────────────────────
            const DIFFICULTY_LABELS = ['level:beginner', 'level:intermediate', 'level:advanced', 'level:critical'];

            const LABEL_META = {
              'level:beginner':     { color: '0E8A16', description: 'Small, low-risk change (≤3 files, ≤50 lines)' },
              'level:intermediate': { color: 'FBCA04', description: 'Medium-sized feature or fix (≤10 files, ≤250 lines)' },
              'level:advanced':     { color: 'D93F0B', description: 'Large feature or broad change (≤25 files, ≤800 lines)' },
              'level:critical':     { color: 'B60205', description: 'Major / core-repository change' },
            };

            const CORE_PATTERNS = [
              /^\.github\/workflows\//,
              /package(-lock)?\.json$/,
              /^src\/App\.(js|jsx|ts|tsx)$/,
              /^src\/main\.(js|jsx|ts|tsx)$/,
              /^src\/config\//,
              /^server\/server\.js$/,
              /^server\/routes\//,
              /^server\/middleware\//,
            ];

            const ALWAYS_CRITICAL_PATTERNS = [
              /^src\/main\.(js|jsx|ts|tsx)$/,
              /^server\/server\.js$/,
              /^server\/routes\//,
            ];

            // ── Helpers ────────────────────────────────────────────────────
            async function ensureLabels() {
              await Promise.all(
                Object.entries(LABEL_META).map(async ([name, { color, description }]) => {
                  try {
                     await github.rest.issues.getLabel({ ...repo, name });
                  } catch (err) {
                    if (err.status !== 404) throw err;
                    await github.rest.issues.createLabel({ ...repo, name, color, description });
                    console.log(`✅ Created label: ${name}`);
                  }
                })
              );
            }

            async function getFiles() {
              return github.paginate(github.rest.pulls.listFiles, {
                ...repo,
                pull_number: prNum,
                per_page: 100,
              });
            }

            async function getCurrentLabels() {
              const { data } = await github.rest.issues.get({ ...repo, issue_number: prNum });
              return data.labels.map(l => (typeof l === 'string' ? l : l.name));
            }

            function classify({ filesChanged, linesChanged, hasCoreChanges, hasAlwaysCritical }) {
              if (hasAlwaysCritical)                              return 'level:critical';
              if (filesChanged > 25 || linesChanged > 800)       return 'level:critical';
              if (hasCoreChanges && (filesChanged > 10 || linesChanged > 300))
                                                                  return 'level:critical';
              if (filesChanged <=  3 && linesChanged <=  50)    return 'level:beginner';
              if (filesChanged <= 10 && linesChanged <= 250)    return 'level:intermediate';
              return 'level:advanced';
            }

            async function applyLabel(targetLabel) {
              const current = await getCurrentLabels();
              const existingDifficulty = current.filter(l => DIFFICULTY_LABELS.includes(l));

              // Append-only mode: never remove existing difficulty labels.
              // If any difficulty label already exists, preserve mentor/manual choice.
              if (existingDifficulty.length > 0) {
                if (current.includes(targetLabel)) {
                  console.log(`✔ Difficulty label already present: ${targetLabel} — skipping.`);
                } else {
                  console.log(`Existing difficulty label(s) detected (${existingDifficulty.join(', ')}) — skipping auto-overwrite.`);
                }
                return;
              }

              await github.rest.issues.addLabels({ ...repo, issue_number: prNum, labels: [targetLabel] });
              console.log(`🏷 Applied difficulty label: ${targetLabel}`);
            }

            // ── Main ───────────────────────────────────────────────────────
            const files = await getFiles();

            const additions    = files.reduce((s, f) => s + f.additions, 0);
            const deletions    = files.reduce((s, f) => s + f.deletions, 0);
            const linesChanged = additions + deletions;
            const filesChanged = files.length;
            const hasCoreChanges     = files.some(f => CORE_PATTERNS.some(p => p.test(f.filename)));
            const hasAlwaysCritical  = files.some(f => ALWAYS_CRITICAL_PATTERNS.some(p => p.test(f.filename)));

            const targetLabel = classify({ filesChanged, linesChanged, hasCoreChanges, hasAlwaysCritical });

            console.log(`PR #${prNum} — "${pr.title}"`);
            console.log(`  Files : ${filesChanged}  |  Lines: +${additions} -${deletions} = ${linesChanged}`);
            console.log(`  Core changes: ${hasCoreChanges}  |  Always-critical paths: ${hasAlwaysCritical}`);
            console.log(`  → Difficulty: ${targetLabel}`);

            await ensureLabels();
            await applyLabel(targetLabel);