import { mkdir, open, readFile, writeFile } from 'node:fs/promises';
import { dirname } from 'node:path';

export type BridgeState = {
  cursors: Record<string, string>;
  processedMessages: Record<string, { repliedNodeId: string; at: string }>;
};

const EMPTY_STATE: BridgeState = { cursors: {}, processedMessages: {} };

export class StateStore {
  private state: BridgeState = structuredClone(EMPTY_STATE);
  constructor(private readonly path: string) {}

  async load(): Promise<void> {
    await mkdir(dirname(this.path), { recursive: true, mode: 0o700 });
    try {
      const text = await readFile(this.path, 'utf8');
      this.state = { ...structuredClone(EMPTY_STATE), ...JSON.parse(text) };
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== 'ENOENT') throw error;
      await this.save();
    }
  }

  getCursor(key: string): string {
    return this.state.cursors[key] ?? '0';
  }

  async setCursor(key: string, cursor: string): Promise<void> {
    this.state.cursors[key] = cursor;
    await this.save();
  }

  hasProcessed(messageId: string): boolean {
    return Boolean(this.state.processedMessages[messageId]);
  }

  async markProcessed(messageId: string, repliedNodeId: string): Promise<void> {
    this.state.processedMessages[messageId] = { repliedNodeId, at: new Date().toISOString() };
    await this.save();
  }

  private async save(): Promise<void> {
    const handle = await open(this.path, 'w', 0o600);
    try {
      await handle.writeFile(`${JSON.stringify(this.state, null, 2)}\n`, 'utf8');
      await handle.chmod(0o600);
    } finally {
      await handle.close();
    }
  }
}