import { existsSync, readFileSync } from 'node:fs';
import { join } from 'node:path';
import type { LLMProvider, ModelMessage } from '../provider/index.ts';

const HEARTBEAT_TOOL = [
  {
    type: 'function' as const,
    function: {
      name: 'heartbeat_decision',
      description: 'Decide whether to act on this heartbeat tick.',
      parameters: {
        type: 'object',
        properties: {
          action: {
            type: 'string',
            enum: ['skip', 'run'],
            description: '"skip" to do nothing, "run" to execute the tasks.',
          },
          tasks: {
            type: 'array',
            items: { type: 'string' },
            description: 'List of tasks to perform (only when action is "run").',
          },
          reason: { type: 'string', description: 'Brief reason for the decision.' },
        },
        required: ['action'],
      },
    },
  },
];

export type HeartbeatExecuteCallback = (tasks: string[]) => Promise<string>;
export type HeartbeatNotifyCallback = (content: string) => Promise<void>;

export class HeartbeatService {
  private _workspace: string;
  private _provider: LLMProvider;
  private _model: string;
  private _intervalMs: number;
  private _onExecute: HeartbeatExecuteCallback;
  private _onNotify: HeartbeatNotifyCallback;
  private _timer: ReturnType<typeof setTimeout> | null = null;
  private _running = false;

  constructor(opts: {
    workspace: string;
    provider: LLMProvider;
    model: string;
    intervalMinutes: number;
    onExecute: HeartbeatExecuteCallback;
    onNotify: HeartbeatNotifyCallback;
  }) {
    this._workspace = opts.workspace;
    this._provider = opts.provider;
    this._model = opts.model;
    this._intervalMs = opts.intervalMinutes * 60 * 1000;
    this._onExecute = opts.onExecute;
    this._onNotify = opts.onNotify;
  }

  start(): void {
    if (this._running) return;
    this._running = true;
    this._schedule();
    console.info(`[heartbeat] Started (interval: ${this._intervalMs / 60000}min)`);
  }

  stop(): void {
    this._running = false;
    if (this._timer) {
      clearTimeout(this._timer);
      this._timer = null;
    }
  }

  async triggerNow(): Promise<void> {
    await this._tick();
  }

  private _schedule(): void {
    if (!this._running) return;
    this._timer = setTimeout(() => {
      void this._tick().finally(() => this._schedule());
    }, this._intervalMs);
  }

  private async _tick(): Promise<void> {
    const heartbeatContent = this._loadHeartbeatMd();
    if (!heartbeatContent) {
      console.debug('[heartbeat] No HEARTBEAT.md found, skipping tick.');
      return;
    }

    const now = new Date().toISOString();
    const messages: ModelMessage[] = [
      {
        role: 'system',
        content:
          'You are a heartbeat agent. Read the HEARTBEAT.md instructions and decide whether to act on this tick. Call heartbeat_decision with action="skip" or action="run".',
      },
      {
        role: 'user',
        content: `Current time: ${now}\n\n## HEARTBEAT.md\n\n${heartbeatContent}`,
      },
    ];

    const { response } = await this._provider.chatWithRetry({
      messages,
      tools: HEARTBEAT_TOOL,
      model: this._model,
      toolChoice: 'required',
    });

    const decision = response.toolCalls[0];
    if (!decision) {
      console.debug('[heartbeat] No decision tool call returned, skipping.');
      return;
    }

    const action = typeof decision.arguments['action'] === 'string' ? decision.arguments['action'] : 'skip';
    if (action !== 'run') {
      const reason = typeof decision.arguments['reason'] === 'string' ? decision.arguments['reason'] : '';
      console.debug(`[heartbeat] Decision: skip (${reason})`);
      return;
    }

    const tasks = Array.isArray(decision.arguments['tasks'])
      ? (decision.arguments['tasks'] as string[])
      : [];

    console.info(`[heartbeat] Decision: run (${tasks.length} tasks)`);

    try {
      const result = await this._onExecute(tasks);
      await this._onNotify(result);
    } catch (err) {
      console.error(`[heartbeat] Execution failed: ${String(err)}`);
    }
  }

  private _loadHeartbeatMd(): string | null {
    const path = join(this._workspace, 'HEARTBEAT.md');
    if (!existsSync(path)) return null;
    return readFileSync(path, 'utf8');
  }
}