#!/usr/bin/env node

/**
 * Coverage Trend Script
 *
 * Reads Vitest coverage summary and appends to a JSON trend file.
 * Usage: node scripts/coverage-trend.mjs [coverage-summary.json] [trend-output.json]
 */

import { readFileSync, writeFileSync, existsSync } from 'fs';

const summaryPath = process.argv[2] || 'apps/web/coverage/coverage-summary.json';
const trendPath = process.argv[3] || 'coverage-trend.json';

function readTrend() {
  if (existsSync(trendPath)) {
    return JSON.parse(readFileSync(trendPath, 'utf8'));
  }
  return { entries: [] };
}

function extractCoverage(summaryPath) {
  if (!existsSync(summaryPath)) {
    console.error(`Coverage summary not found: ${summaryPath}`);
    return null;
  }

  const summary = JSON.parse(readFileSync(summaryPath, 'utf8'));
  const total = summary.total || {};

  return {
    date: new Date().toISOString().split('T')[0],
    commit: process.env.GITHUB_SHA?.slice(0, 7) || 'local',
    lines: total.lines?.pct ?? 0,
    branches: total.branches?.pct ?? 0,
    functions: total.functions?.pct ?? 0,
    statements: total.statements?.pct ?? 0,
  };
}

const coverage = extractCoverage(summaryPath);
if (coverage) {
  const trend = readTrend();

  // Keep last 100 entries
  trend.entries.push(coverage);
  if (trend.entries.length > 100) {
    trend.entries = trend.entries.slice(-100);
  }

  writeFileSync(trendPath, JSON.stringify(trend, null, 2));
  console.log(`Coverage trend updated: lines=${coverage.lines}%, branches=${coverage.branches}%`);

  // Check for regression (> 2% drop from last entry)
  if (trend.entries.length >= 2) {
    const prev = trend.entries[trend.entries.length - 2];
    const linesDrop = prev.lines - coverage.lines;
    if (linesDrop > 2) {
      console.warn(`WARNING: Line coverage dropped ${linesDrop.toFixed(1)}% (${prev.lines}% -> ${coverage.lines}%)`);
    }
  }
}