src/summary-builder.ts

import type { TransitionEvent } from "story-engine";

export interface SummaryBuilderOptions {
  apiKey: string;
  model?: string;          // defaults to gpt-4o-mini
  baseUrl?: string;        // defaults to /openai/v1/chat/completions
}

export class SummaryBuilder {
  private apiKey: string;
  private model: string;
  private baseUrl: string;

  constructor(opts: SummaryBuilderOptions) {
    this.apiKey = opts.apiKey;
    this.model = opts.model ?? "gpt-4o-mini";
    this.baseUrl = opts.baseUrl ?? "/openai/v1/chat/completions";
  }

  async summarize(events: TransitionEvent[]): Promise<string> {
    if (events.length === 0) return "(The story is just beginning.)";
    const log = events
      .map((e) => {
        switch (e.type) {
          case "storyEntered": return `Story "${e.storyId}" began.`;
          case "storyExited": return `User exited the story.`;
          case "sceneChanged": return `Scene changed: ${e.from ?? "?"} → ${e.to}.`;
          case "speakerChanged": return `Now speaking: ${e.to} (was ${e.from ?? "narrator"}).`;
          case "flagSet": return `Flag set: ${e.name} = ${e.value}.`;
          case "blocked": return `Blocked: ${e.reason}.`;
        }
      })
      .join("\n");

    const prompt = `Given these recent story events, write a 2-3 sentence summary suitable for handing off to a new character voice. Capture what just happened and what the user was doing. Plain spoken English, no markdown.\n\nEvents:\n${log}`;

    const res = await fetch(this.baseUrl, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${this.apiKey}`,
      },
      body: JSON.stringify({
        model: this.model,
        messages: [{ role: "user", content: prompt }],
        max_tokens: 200,
        temperature: 0.4,
      }),
    });
    if (!res.ok) {
      throw new Error(`Summary API ${res.status}: ${await res.text()}`);
    }
    const data = await res.json();
    return data.choices[0]?.message?.content?.trim() ?? "(No summary available.)";
  }
}