name: Backfill PR Labels

on:
  workflow_dispatch:
    inputs:
      state:
        description: Pull request state to scan
        required: true
        default: all
        type: choice
        options:
          - open
          - closed
          - all
      limit:
        description: Maximum number of pull requests to inspect
        required: true
        default: "100"
        type: string

permissions:
  contents: read
  pull-requests: write

jobs:
  backfill:
    name: Backfill missing PR labels
    runs-on: ubuntu-latest
    steps:
      - name: Backfill PR labels
        uses: actions/github-script@v9
        with:
          script: |
            const owner = context.repo.owner;
            const repo = context.repo.repo;
            const inputs = context.payload.inputs || {};
            const requestedState = inputs.state || 'all';
            const limit = Number.parseInt(inputs.limit || '100', 10);
            const sizeLabels = ['size: XS', 'size: S', 'size: M', 'size: L', 'size: XL', 'size: XXL'];
            const areaRules = [
              { label: 'area: db', include: ['src/server/db/', 'drizzle/'] },
              { label: 'area: server', include: ['src/server/'], exclude: ['src/server/db/'] },
              { label: 'area: web', include: ['src/web/'] },
              { label: 'area: desktop', include: ['src/desktop/', 'electron-builder.yml', 'tsconfig.desktop.json'] },
              { label: 'area: docs', include: ['docs/', 'README.md', 'README_EN.md'] },
              { label: 'area: scripts', include: ['scripts/'] },
              { label: 'area: ci', include: ['.github/', 'docker/', 'render.yaml', 'zeabur-template.yaml'] },
            ];

            if (!Number.isFinite(limit) || limit <= 0) {
              core.setFailed('The limit input must be a positive integer.');
              return;
            }

            function matchesRule(filename, rule) {
              const included = rule.include.some((prefix) => filename === prefix || filename.startsWith(prefix));
              if (!included) return false;
              if (!rule.exclude) return true;
              return !rule.exclude.some((prefix) => filename === prefix || filename.startsWith(prefix));
            }

            function computeAreaLabels(files) {
              return areaRules
                .filter((rule) => files.some((file) => matchesRule(file.filename, rule)))
                .map((rule) => rule.label);
            }

            function computeSizeLabel(totalChanges) {
              if (totalChanges < 50) return 'size: XS';
              if (totalChanges < 200) return 'size: S';
              if (totalChanges < 500) return 'size: M';
              if (totalChanges < 1000) return 'size: L';
              if (totalChanges < 2000) return 'size: XL';
              return 'size: XXL';
            }

            const state = requestedState === 'all' ? 'all' : requestedState;
            const pulls = await github.paginate(github.rest.pulls.list, {
              owner,
              repo,
              state,
              per_page: 100,
            });

            let inspected = 0;
            let updated = 0;
            let skipped = 0;
            let warned = 0;

            for (const pull of pulls) {
              if (inspected >= limit) {
                break;
              }

              inspected += 1;

              const { data: fullPull } = await github.rest.pulls.get({
                owner,
                repo,
                pull_number: pull.number,
              });

              const files = await github.paginate(github.rest.pulls.listFiles, {
                owner,
                repo,
                pull_number: pull.number,
                per_page: 100,
              });

              const desiredAreaLabels = computeAreaLabels(files);
              const totalChanges = fullPull.additions + fullPull.deletions;
              const hasValidSizeData = Number.isFinite(totalChanges) && totalChanges >= 0;
              const currentLabels = pull.labels.map((label) => label.name);
              const missingAreaLabels = desiredAreaLabels.filter((label) => !currentLabels.includes(label));
              const currentSizeLabels = currentLabels.filter((label) => sizeLabels.includes(label));
              const desiredSizeLabel = hasValidSizeData ? computeSizeLabel(totalChanges) : null;
              const sizeMatches =
                hasValidSizeData &&
                currentSizeLabels.length === 1 &&
                currentSizeLabels[0] === desiredSizeLabel;

              if (!hasValidSizeData) {
                warned += 1;
                core.warning(`Skipping size label for PR #${pull.number}: invalid additions/deletions values.`);
              }

              if (missingAreaLabels.length === 0 && (hasValidSizeData ? sizeMatches : currentSizeLabels.length === 0)) {
                skipped += 1;
                continue;
              }

              if (hasValidSizeData) {
                for (const label of currentSizeLabels) {
                  if (label === desiredSizeLabel) {
                    continue;
                  }

                  try {
                    await github.rest.issues.removeLabel({
                      owner,
                      repo,
                      issue_number: pull.number,
                      name: label,
                    });
                  } catch (error) {
                    if (error.status !== 404) {
                      throw error;
                    }
                  }
                }
              }

              const labelsToAdd = [...missingAreaLabels];
              if (hasValidSizeData && !sizeMatches) {
                labelsToAdd.push(desiredSizeLabel);
              }

              if (labelsToAdd.length > 0) {
                await github.rest.issues.addLabels({
                  owner,
                  repo,
                  issue_number: pull.number,
                  labels: labelsToAdd,
                });
              }

              updated += 1;
            }

            core.summary
              .addHeading('Backfill summary')
              .addRaw(`Inspected PRs: ${inspected}\n`)
              .addRaw(`Updated PRs: ${updated}\n`)
              .addRaw(`Skipped PRs: ${skipped}\n`)
              .addRaw(`Warnings: ${warned}\n`)
              .write();