import { DEFAULT_SYSTEM_PROMPT, RECENCY_HINT } from "./constants";
import type { ApiMessage, ChatTurn } from "./types";

/**
 * Turns stored turns into the message array sent to the model.
 *
 * Only completed question/answer pairs are replayed. The intermediate tool
 * messages from a previous turn are intentionally dropped: they are noise once
 * the answer is written, and replaying them would re-send large page contents
 * on every subsequent request.
 */
export function buildMessages(systemPrompt: string, turns: ChatTurn[], prompt: string): ApiMessage[] {
  const messages: ApiMessage[] = [{ role: "system", content: systemPrompt }];

  for (const turn of turns) {
    if (!turn.response) continue;
    messages.push({ role: "user", content: turn.prompt });
    messages.push({ role: "assistant", content: turn.response });
  }

  messages.push({ role: "user", content: prompt });
  return messages;
}

/** Uses the user's prompt if they set one, otherwise Lam's default. */
export function composeSystemPrompt(customPrompt: string, webEnabled: boolean): string {
  const parts = [customPrompt.trim() || DEFAULT_SYSTEM_PROMPT];
  if (webEnabled) parts.push(RECENCY_HINT);
  return parts.join("\n\n");
}