import fs from "node:fs";
import path from "node:path";

export interface StoreIdentity {
  botId: string;
  platform: string;
}

export interface AssistantBinding {
  chatKey: string;
  agentId: string;
  nativeSessionId: string;
  assistantWorkspace: string;
  botFingerprint: string;
  createdAt: number;
  updatedAt: number;
  // Refreshed on every assistant turn; drives the idle reset of long-inactive sessions.
  lastActiveAt?: number;
}

interface StoreData {
  version: 3;
  botId: string;
  platform: string;
  bindings: Record<string, AssistantBinding>;
}

export class DurableSessionStore {
  private data: StoreData;
  private queue: Promise<void> = Promise.resolve();
  private lockFd?: fs.promises.FileHandle;
  private closed = false;

  constructor(readonly file: string, readonly identity: StoreIdentity) {
    this.data = emptyData(identity);
  }

  async open(): Promise<void> {
    const directory = path.dirname(this.file);
    await fs.promises.mkdir(directory, { recursive: true, mode: 0o700 });
    const directoryStat = await fs.promises.lstat(directory);
    if (!directoryStat.isDirectory() || directoryStat.isSymbolicLink()) throw new Error(`Refusing unsafe state directory: ${directory}`);
    const directoryMode = directoryStat.mode & 0o777;
    if (directoryMode !== 0o700) throw new Error(`State directory mode must be 0700, got 0${directoryMode.toString(8)}`);
    if (typeof process.getuid === "function" && directoryStat.uid !== process.getuid()) throw new Error("State directory is not owned by the current user");
    const lockFile = `${this.file}.lock`;
    try {
      this.lockFd = await acquireLock(lockFile);
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== "EEXIST" || !await removeStaleLock(lockFile)) {
        if ((error as NodeJS.ErrnoException).code === "EEXIST") throw new Error(`Session state is locked by another gori-agent instance: ${lockFile}`);
        throw error;
      }
      this.lockFd = await acquireLock(lockFile).catch((retryError) => {
        if ((retryError as NodeJS.ErrnoException).code === "EEXIST") throw new Error(`Session state is locked by another gori-agent instance: ${lockFile}`);
        throw retryError;
      });
    }
    try {
      await this.lockFd.writeFile(`${process.pid}\n`);
      await this.lockFd.sync();
    } catch (error) {
      await this.releaseLock();
      throw error;
    }
    try {
      const raw = await fs.promises.readFile(this.file, "utf8");
      const parsed = parseStoreData(JSON.parse(raw) as unknown);
      if (parsed.botId !== this.identity.botId || parsed.platform !== this.identity.platform) {
        throw new Error(`state identity mismatch: expected bot '${this.identity.botId}' platform '${this.identity.platform}'`);
      }
      this.data = parsed;
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
        await this.releaseLock();
        throw new Error(`Cannot read session state '${this.file}'; original file was preserved: ${error instanceof Error ? error.message : String(error)}`);
      }
    }
  }

  getBinding(chatKey: string): AssistantBinding | undefined {
    const value = this.data.bindings[chatKey];
    return value ? structuredClone(value) : undefined;
  }

  async setBinding(binding: AssistantBinding): Promise<void> {
    this.data.bindings[binding.chatKey] = structuredClone(binding);
    await this.persist();
  }

  async touchBinding(chatKey: string): Promise<void> {
    const binding = this.data.bindings[chatKey];
    if (!binding) return;
    binding.updatedAt = Date.now();
    binding.lastActiveAt = binding.updatedAt;
    await this.persist();
  }

  async deleteBinding(chatKey: string): Promise<AssistantBinding | undefined> {
    const existing = this.data.bindings[chatKey];
    delete this.data.bindings[chatKey];
    if (existing) await this.persist();
    return existing ? structuredClone(existing) : undefined;
  }

  stats(): { bindings: number } {
    return { bindings: Object.keys(this.data.bindings).length };
  }

  async flush(): Promise<void> { await this.queue; }

  async close(): Promise<void> {
    if (this.closed) return;
    this.closed = true;
    try { await this.flush(); } finally { await this.releaseLock(); }
  }

  private persist(): Promise<void> {
    if (this.closed) return Promise.reject(new Error("Session store is closed"));
    const snapshot = JSON.stringify(this.data, null, 2) + "\n";
    const operation = this.queue.then(() => atomicWrite(this.file, snapshot));
    this.queue = operation.catch(() => undefined);
    return operation;
  }

  private async releaseLock(): Promise<void> {
    if (!this.lockFd) return;
    await this.lockFd.close();
    this.lockFd = undefined;
    await fs.promises.unlink(`${this.file}.lock`).catch((error: NodeJS.ErrnoException) => {
      if (error.code !== "ENOENT") throw error;
    });
  }
}

export function chatKeyFor(platform: string, chatId: string): string { return `${platform}:${chatId}`; }

function emptyData(identity: StoreIdentity): StoreData {
  return { version: 3, botId: identity.botId, platform: identity.platform, bindings: {} };
}

function parseStoreData(value: unknown): StoreData {
  if (!isRecord(value) || value.version !== 3 || typeof value.botId !== "string" || typeof value.platform !== "string" || !isRecord(value.bindings)) {
    throw new Error("unsupported state version; Config v3 requires state v3 in a new GORI_AGENT_HOME");
  }
  for (const [chatKey, binding] of Object.entries(value.bindings)) {
    if (!isRecord(binding)
      || binding.chatKey !== chatKey
      || typeof binding.agentId !== "string"
      || typeof binding.nativeSessionId !== "string"
      || typeof binding.assistantWorkspace !== "string"
      || typeof binding.botFingerprint !== "string"
      || typeof binding.createdAt !== "number"
      || typeof binding.updatedAt !== "number"
      || (binding.lastActiveAt !== undefined && typeof binding.lastActiveAt !== "number")) {
      throw new Error(`invalid state v3 binding '${chatKey}'`);
    }
  }
  return value as unknown as StoreData;
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

async function acquireLock(lockFile: string): Promise<fs.promises.FileHandle> {
  return fs.promises.open(lockFile, "wx", 0o600);
}

async function removeStaleLock(lockFile: string): Promise<boolean> {
  let handle: fs.promises.FileHandle | undefined;
  try {
    handle = await fs.promises.open(lockFile, "r");
    const pid = Number((await handle.readFile("utf8")).trim());
    if (!Number.isSafeInteger(pid) || pid <= 1 || processExists(pid)) return false;
    const opened = await handle.stat();
    const current = await fs.promises.lstat(lockFile);
    if (opened.dev !== current.dev || opened.ino !== current.ino) return false;
    await fs.promises.unlink(lockFile);
    return true;
  } catch { return false; }
  finally { await handle?.close().catch(() => undefined); }
}

function processExists(pid: number): boolean {
  try { process.kill(pid, 0); return true; }
  catch (error) { return (error as NodeJS.ErrnoException).code === "EPERM"; }
}

async function atomicWrite(file: string, content: string): Promise<void> {
  const temp = `${file}.${process.pid}.${Date.now()}.tmp`;
  let handle: fs.promises.FileHandle | undefined;
  try {
    handle = await fs.promises.open(temp, "wx", 0o600);
    await handle.writeFile(content, "utf8");
    await handle.sync();
    await handle.close();
    handle = undefined;
    await fs.promises.rename(temp, file);
    await fs.promises.chmod(file, 0o600);
    const dir = await fs.promises.open(path.dirname(file), "r");
    try { await dir.sync(); } finally { await dir.close(); }
  } catch (error) {
    if (handle) await handle.close().catch(() => undefined);
    await fs.promises.unlink(temp).catch(() => undefined);
    throw error;
  }
}