import { execSync } from 'node:child_process';
import path from 'node:path';
import { fileURLToPath } from 'node:url';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const repoRoot = path.resolve(__dirname, '../../../../');

try {
  // 1. Fetch recent PR numbers and reviews from GitHub (so we have reviewer names/logins)
  const query = `
  query($owner: String!, $repo: String!) {
    repository(owner: $owner, name: $repo) {
      pullRequests(last: 100, states: MERGED) {
        nodes {
          number
          reviews(first: 20) {
            nodes {
              authorAssociation
              author { login, ... on User { name } }
            }
          }
        }
      }
    }
  }
  `;
  const output = execSync(`gh api graphql -F owner=google-gemini -F repo=gemini-cli -f query='${query}'`, { encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] });
  const data = JSON.parse(output).data.repository;

  // 2. Map PR numbers to local commits using git log
  const logOutput = execSync('git log -n 5000 --format="%H|%s"', { cwd: repoRoot, encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] });
  const prCommits = new Map();
  for (const line of logOutput.split('\n')) {
    if (!line) continue;
    const [hash, subject] = line.split('|');
    const match = subject.match(/\(#(\d+)\)$/);
    if (match) {
      prCommits.set(parseInt(match[1], 10), hash);
    }
  }

  let totalMaintainerReviews = 0;
  let maintainerReviewsWithExpertise = 0;

  for (const pr of data.pullRequests.nodes) {
    if (!pr.reviews?.nodes || pr.reviews.nodes.length === 0) continue;
    
    const commitHash = prCommits.get(pr.number);
    if (!commitHash) continue; // Skip if we don't have the commit locally

    // 3. Get exact files changed using local git diff-tree, bypassing GraphQL limits
    const diffTreeOutput = execSync(`git diff-tree --no-commit-id --name-only -r ${commitHash}`, { cwd: repoRoot, encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] });
    const files = diffTreeOutput.split('\n').filter(Boolean);
    if (files.length === 0) continue;

    // Cache git log authors per path to avoid redundant child_process calls
    const authorCache = new Map();
    const getAuthors = (targetPath) => {
      if (authorCache.has(targetPath)) return authorCache.get(targetPath);
      try {
        const authors = execSync(`git log --format="%an|%ae" -- "${targetPath}"`, { cwd: repoRoot, encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] }).toLowerCase();
        authorCache.set(targetPath, authors);
        return authors;
      } catch (e) {
        authorCache.set(targetPath, "");
        return "";
      }
    };

    const reviewersOnPR = new Map();
    for (const review of pr.reviews.nodes) {
      if (['MEMBER', 'OWNER'].includes(review.authorAssociation) && review.author?.login) {
        const login = review.author.login.toLowerCase();
        if (login.endsWith('[bot]') || login.includes('bot')) continue;
        reviewersOnPR.set(login, review.author);
      }
    }

    for (const [login, authorInfo] of reviewersOnPR.entries()) {
      totalMaintainerReviews++;
      let hasExpertise = false;
      const name = authorInfo.name ? authorInfo.name.toLowerCase() : "";

      for (const file of files) {
        // Precise check: immediate file
        let authorsStr = getAuthors(file);
        if (authorsStr.includes(login) || (name && authorsStr.includes(name))) {
          hasExpertise = true;
          break;
        }

        // Fallback: file's directory
        const dir = path.dirname(file);
        authorsStr = getAuthors(dir);
        if (authorsStr.includes(login) || (name && authorsStr.includes(name))) {
          hasExpertise = true;
          break;
        }
      }
      
      if (hasExpertise) {
        maintainerReviewsWithExpertise++;
      }
    }
  }

  const ratio = totalMaintainerReviews > 0 ? maintainerReviewsWithExpertise / totalMaintainerReviews : 0;
  const timestamp = new Date().toISOString();

  process.stdout.write(JSON.stringify({
    metric: 'domain_expertise',
    value: Math.round(ratio * 100) / 100,
    timestamp,
    details: {
      totalMaintainerReviews,
      maintainerReviewsWithExpertise
    }
  }) + '\n');

} catch (err) {
  process.stderr.write(err instanceof Error ? err.message : String(err));
  process.exit(1);
}