import { copyFileSync, existsSync, mkdirSync, readFileSync, renameSync, writeFileSync } from "node:fs";
import { dirname } from "node:path";
import type { AppState } from "./types.js";

function defaultState(): AppState {
  return {
    sessions: [],
    messages: [],
    tasks: [],
    workers: [],
    approvals: [],
    deviceBindings: [],
    events: [],
  };
}

export class FileStore {
  private state: AppState;
  private readonly backupFilePath: string;
  private readonly tempFilePath: string;

  constructor(private readonly filePath: string) {
    this.backupFilePath = `${filePath}.bak`;
    this.tempFilePath = `${filePath}.tmp`;
    this.ensureDirectory();
    this.state = this.load();
  }

  get snapshot(): AppState {
    return structuredClone(this.state);
  }

  mutate<T>(mutator: (state: AppState) => T): T {
    const result = mutator(this.state);
    this.save();
    return result;
  }

  reset(): AppState {
    this.state = defaultState();
    this.save();
    return this.snapshot;
  }

  private ensureDirectory(): void {
    mkdirSync(dirname(this.filePath), { recursive: true });
  }

  private load(): AppState {
    for (const path of [this.filePath, this.backupFilePath]) {
      if (!existsSync(path)) {
        continue;
      }

      try {
        const raw = readFileSync(path, "utf8");
        return { ...defaultState(), ...(JSON.parse(raw) as AppState) };
      } catch {
        // try backup/default
      }
    }

    return defaultState();
  }

  private save(): void {
    const content = `${JSON.stringify(this.state, null, 2)}\n`;
    writeFileSync(this.tempFilePath, content, "utf8");
    if (existsSync(this.filePath)) {
      copyFileSync(this.filePath, this.backupFilePath);
    }
    renameSync(this.tempFilePath, this.filePath);
  }
}