import fs from 'node:fs';
import path from 'node:path';

const DEFAULT_MAX_LOG_BYTES = 2 * 1024 * 1024;

export function resolvePageDataLogDir(workspaceRoot) {
  return path.join(workspaceRoot, '.mindspace', 'page-data-logs');
}

export function resolvePageDataLogPath(workspaceRoot, pageId) {
  const safePageId = String(pageId ?? '').trim();
  if (!safePageId || /[\\/]/.test(safePageId)) {
    throw Object.assign(new Error('pageId 无效'), { code: 'invalid_page_id' });
  }
  return path.join(resolvePageDataLogDir(workspaceRoot), `${safePageId}.jsonl`);
}

export function appendPageDataLog(workspaceRoot, pageId, entry, { maxBytes = DEFAULT_MAX_LOG_BYTES } = {}) {
  const logPath = resolvePageDataLogPath(workspaceRoot, pageId);
  fs.mkdirSync(path.dirname(logPath), { recursive: true });
  const line = `${JSON.stringify({ ...entry, at: entry.at ?? new Date().toISOString() })}\n`;
  fs.appendFileSync(logPath, line, 'utf8');
  if (maxBytes > 0 && fs.existsSync(logPath) && fs.statSync(logPath).size > maxBytes) {
    const raw = fs.readFileSync(logPath, 'utf8').trim().split('\n');
    const trimmed = raw.slice(-Math.max(50, Math.floor(raw.length / 2)));
    fs.writeFileSync(logPath, `${trimmed.join('\n')}\n`, 'utf8');
  }
  return line;
}

export function listPageDataLogs(workspaceRoot, pageId, { limit = 100, offset = 0 } = {}) {
  const logPath = resolvePageDataLogPath(workspaceRoot, pageId);
  if (!fs.existsSync(logPath)) return [];
  const lines = fs.readFileSync(logPath, 'utf8').trim().split('\n').filter(Boolean);
  const parsed = lines
    .map((line) => {
      try {
        return JSON.parse(line);
      } catch {
        return null;
      }
    })
    .filter(Boolean);
  const safeOffset = Math.max(0, Number(offset ?? 0));
  const safeLimit = Math.min(Math.max(1, Number(limit ?? 100)), 500);
  return parsed.slice(safeOffset, safeOffset + safeLimit);
}