import fs from 'fs';
import path from 'path';
import { PluginLogger } from './logger';

export interface PluginSession {
  token: string;
  accountId: string;
  countryCode?: string | null;
  region: string;
  apiBaseUrl: string;
  authFlowUsed?: 'legacy' | 'new';
  // Stable client identity. VeSync binds issued tokens to the terminal id (it appears as a claim in the
  // token JWT), so it is reused across logins and restarts rather than regenerated.
  terminalId?: string;
  appId?: string;
  issuedAt?: number | null;
  expiresAt?: number | null;
  lastValidatedAt?: number | null;
  libraryVersion?: string;
  // Optional: helps ensure session matches configured Homebridge account
  username?: string;
}

export class FileSessionStore {
  private readonly dir: string;
  private readonly file: string;
  private saveInProgress: Promise<void> | null = null;

  constructor(basePath: string, private readonly logger: PluginLogger) {
    this.dir = path.join(basePath, 'tsvesync');
    this.file = path.join(this.dir, 'session.json');
  }

  async load(): Promise<PluginSession | null> {
    try {
      await fs.promises.mkdir(this.dir, { recursive: true });
      const data = await fs.promises.readFile(this.file, 'utf8');
      const session = JSON.parse(data) as PluginSession;
      if (!session || !session.token || !session.accountId) return null;
      try {
        const expSec = session.expiresAt && session.expiresAt > 1e11 ? Math.floor(session.expiresAt / 1000) : session.expiresAt;
        const exp = expSec ? new Date(expSec * 1000).toISOString() : 'unknown';
        this.logger.debug(`Loaded persisted session from ${this.file} (exp: ${exp})`);
      } catch {}
      return session;
    } catch (e: any) {
      if (e?.code === 'ENOENT') {
        this.logger.debug(`No persisted session found at ${this.file}`);
      } else {
        this.logger.debug(`Session load error: ${e?.message || e}`);
      }
      return null;
    }
  }

  async save(session: PluginSession): Promise<void> {
    // Use a mutex to prevent concurrent writes (race condition fix)
    if (this.saveInProgress) {
      await this.saveInProgress;
    }

    this.saveInProgress = (async () => {
      try {
        await fs.promises.mkdir(this.dir, { recursive: true });

        // Load existing session to preserve fields like 'username' that may not be in the new session
        let existingSession: PluginSession | null = null;
        try {
          const data = await fs.promises.readFile(this.file, 'utf8');
          existingSession = JSON.parse(data) as PluginSession;
        } catch {
          // File doesn't exist or is corrupted, that's okay
        }

        // Merge: new session takes precedence, but preserve username if present
        const mergedSession = {
          ...existingSession,
          ...session,
          // Preserve username from existing session if new session doesn't have it
          username: session.username || existingSession?.username,
          // Never lose the client identity: an older library that doesn't report these must not wipe them.
          terminalId: session.terminalId || existingSession?.terminalId,
          appId: session.appId || existingSession?.appId,
        };

        const tmp = this.file + '.tmp';
        await fs.promises.writeFile(tmp, JSON.stringify(mergedSession), { encoding: 'utf8', mode: 0o600 });
        await fs.promises.rename(tmp, this.file);
        try { await fs.promises.chmod(this.file, 0o600); } catch { /* best effort */ }
        try {
          const expSec = session.expiresAt && session.expiresAt > 1e11 ? Math.floor(session.expiresAt / 1000) : session.expiresAt;
          const exp = expSec ? new Date(expSec * 1000).toISOString() : 'unknown';
          this.logger.debug(`Persisted session to ${this.file} (exp: ${exp})`);
        } catch {}
      } catch (e: any) {
        this.logger.error(`Session save error: ${e?.message || e}`);  // Changed to ERROR for visibility
      } finally {
        this.saveInProgress = null;
      }
    })();

    await this.saveInProgress;
  }

  async clear(): Promise<void> {
    try {
      await fs.promises.unlink(this.file);
    } catch (e: any) {
      if (e?.code !== 'ENOENT') {
        this.logger.debug(`Session clear error: ${e?.message || e}`);
      }
    }
  }
}

export function decodeJwtTimestampsLocal(token: string): { iat?: number; exp?: number } | null {
  try {
    const parts = token.split('.');
    if (parts.length !== 3) return null;
    const payload = JSON.parse(Buffer.from(parts[1].replace(/-/g, '+').replace(/_/g, '/'), 'base64').toString('utf8'));
    let iat = typeof payload.iat === 'number' ? payload.iat : undefined;
    let exp = typeof payload.exp === 'number' ? payload.exp : undefined;
    if (iat && iat > 1e11) iat = Math.floor(iat / 1000);
    if (exp && exp > 1e11) exp = Math.floor(exp / 1000);
    return { iat, exp };
  } catch {
    return null;
  }
}