import { runAgent } from './plugins.js';
import type { ModelMessage, IAgentRunResult } from './plugins.js';
import type { IChatSessionOptions, IChatCallbacks, IChatUsage } from './smartchat.interfaces.js';

/**
 * ChatSession manages in-memory conversation state and wraps `runAgent()`.
 * Stateless by design — consumers are responsible for persistence.
 */
export class ChatSession {
  private messages: ModelMessage[] = [];
  private usage: IChatUsage = {
    inputTokens: 0,
    outputTokens: 0,
    totalTokens: 0,
    turns: 0,
  };
  private busy = false;

  constructor(
    private options: IChatSessionOptions,
    private callbacks: IChatCallbacks = {},
  ) {}

  /**
   * Send a user message, run the agent, and return the result.
   * Updates internal message history automatically.
   */
  async send(userMessage: string): Promise<IAgentRunResult> {
    if (this.busy) {
      throw new Error('ChatSession is busy — wait for the current turn to complete.');
    }

    this.busy = true;

    try {
      const result = await runAgent({
        model: this.options.model,
        system: this.options.system,
        prompt: userMessage,
        tools: this.options.tools,
        maxSteps: this.options.maxSteps ?? 20,
        messages: this.messages,
        onToken: this.callbacks.onToken,
        onToolCall: this.callbacks.onToolCall,
      });

      // Update conversation history
      this.messages = result.messages;

      // Accumulate usage
      this.usage.inputTokens += result.usage.inputTokens;
      this.usage.outputTokens += result.usage.outputTokens;
      this.usage.totalTokens += result.usage.totalTokens;
      this.usage.turns++;

      this.callbacks.onTurnComplete?.(result);

      return result;
    } catch (error) {
      const err = error instanceof Error ? error : new Error(String(error));
      this.callbacks.onError?.(err);
      throw err;
    } finally {
      this.busy = false;
    }
  }

  /** Whether a turn is currently in progress */
  isBusy(): boolean {
    return this.busy;
  }

  /** Get current conversation history */
  getMessages(): ModelMessage[] {
    return [...this.messages];
  }

  /** Replace messages (e.g. for restoring a saved session) */
  setMessages(messages: ModelMessage[]): void {
    this.messages = [...messages];
  }

  /** Clear conversation history and reset usage */
  clear(): void {
    this.messages = [];
    this.usage = { inputTokens: 0, outputTokens: 0, totalTokens: 0, turns: 0 };
  }

  /** Get accumulated token usage across all turns */
  getUsage(): IChatUsage {
    return { ...this.usage };
  }

  /** Update session options (model, system prompt, tools, etc.) */
  updateOptions(options: Partial<IChatSessionOptions>): void {
    Object.assign(this.options, options);
  }

  /** Update callbacks */
  updateCallbacks(callbacks: Partial<IChatCallbacks>): void {
    Object.assign(this.callbacks, callbacks);
  }
}