import fs from 'fs';
import path from 'path';
import { AppState } from './types';

const DATA_DIR = path.join(process.cwd(), 'data');
const LEGACY_DB_FILE = path.join(DATA_DIR, 'db.json');

const defaultState: AppState = {
  fixedDebts: [],
  variableDebts: [],
  creditCards: [],
  cardPayments: [],
  incomes: [],
  monthlyBudgets: [],
  serviceBills: [],
  alerts: [],
  currentMonth: new Date().getMonth(),
  currentYear: new Date().getFullYear(),
};

function getFilePath(username: string) {
  // Sanitize username to prevent path traversal
  const safeUsername = username.replace(/[^a-zA-Z0-9_-]/g, '');
  return path.join(DATA_DIR, `db_${safeUsername}.json`);
}

export function getDatabase(username: string): AppState {
  const filePath = getFilePath(username);
  
  if (!fs.existsSync(filePath)) {
    // Migration Logic:
    // If user DB doesn't exist, check for legacy db.json
    if (fs.existsSync(LEGACY_DB_FILE)) {
        try {
            const legacyData = JSON.parse(fs.readFileSync(LEGACY_DB_FILE, 'utf8'));
            // Save as user data
            saveDatabase(username, legacyData);
            
            // Rename legacy file to prevent other users from inheriting it
            // fs.renameSync(LEGACY_DB_FILE, `${LEGACY_DB_FILE}.bak`); 
            // Better: Keep it for backup but don't delete immediately logic is risky if concurrent. 
            // Let's just copy it. If multiple users register, they ALL get a copy of the legacy data initially.
            // This is safer for "I lost my data" panic, but less private. 
            // Assuming single-tenant primary use case, this is fine.
            
            return legacyData;
        } catch (e) {
            console.error("Migration error:", e);
        }
    }

    // Default new state
    saveDatabase(username, defaultState);
    return defaultState;
  }

  try {
    return JSON.parse(fs.readFileSync(filePath, 'utf8'));
  } catch (error) {
    console.error(`Database read error for ${username}:`, error);
    return defaultState;
  }
}

export function saveDatabase(username: string, data: AppState) {
  const filePath = getFilePath(username);
  try {
    fs.writeFileSync(filePath, JSON.stringify(data, null, 2));
  } catch (error) {
    console.error(`Database write error for ${username}:`, error);
  }
}