const fs = require('fs');

const DEFAULT_MIN_FREE_BYTES = 256 * 1024 * 1024;

function normalizeMinimumFreeBytes(value) {
  const parsed = Number(value);
  return Number.isSafeInteger(parsed) && parsed >= 0 ? parsed : DEFAULT_MIN_FREE_BYTES;
}

function createHealthService({ db, diskPath, minimumFreeBytes = process.env.HEALTH_MIN_DISK_FREE_BYTES }) {
  const diskThreshold = normalizeMinimumFreeBytes(minimumFreeBytes);

  function checkDatabase() {
    const startedAt = process.hrtime.bigint();
    try {
      const row = db.prepare('SELECT 1 AS ok').get();
      return {
        status: row?.ok === 1 ? 'ok' : 'error',
        latencyMs: Number((Number(process.hrtime.bigint() - startedAt) / 1e6).toFixed(2))
      };
    } catch (error) {
      return { status: 'error', message: error.code || error.name || 'database_error' };
    }
  }

  function checkDisk() {
    try {
      const stats = fs.statfsSync(diskPath);
      const freeBytes = Number(BigInt(stats.bavail) * BigInt(stats.bsize));
      return {
        status: freeBytes >= diskThreshold ? 'ok' : 'low',
        freeBytes,
        minimumFreeBytes: diskThreshold
      };
    } catch (error) {
      return { status: 'error', message: error.code || error.name || 'disk_error' };
    }
  }

  function check() {
    const checks = {
      database: checkDatabase(),
      disk: checkDisk()
    };
    const healthy = checks.database.status === 'ok' && checks.disk.status === 'ok';
    return {
      healthy,
      status: healthy ? 'ok' : 'degraded',
      checks
    };
  }

  return { check };
}

module.exports = {
  createHealthService,
  normalizeMinimumFreeBytes
};