/**
 * Server-only Gemini client. Powers the AI assistant + translation features.
 *
 * SECURITY: GEMINI_API_KEY is read from the server environment and NEVER exposed
 * to the client bundle (no NEXT_PUBLIC_ prefix). All calls go through BFF routes
 * so the key stays on the server. This module must only be imported by route
 * handlers / server code.
 */

const ENDPOINT = "https://generativelanguage.googleapis.com/v1beta/models";

export type GeminiResult =
  | { ok: true; text: string }
  | { ok: false; status: number; error: string; retryable: boolean };

/**
 * Single-shot text generation. Returns a discriminated result so callers can
 * surface a graceful message (e.g. on 429 quota-exhausted) instead of throwing.
 */
export async function geminiGenerate(prompt: string, opts?: { system?: string; temperature?: number }): Promise<GeminiResult> {
  const key = process.env.GEMINI_API_KEY;
  const model = process.env.GEMINI_MODEL || "gemini-2.0-flash";
  if (!key) {
    return { ok: false, status: 0, error: "GEMINI_API_KEY is not configured on the server.", retryable: false };
  }

  const body: Record<string, unknown> = {
    contents: [{ role: "user", parts: [{ text: prompt }] }],
    generationConfig: { temperature: opts?.temperature ?? 0.4 },
  };
  if (opts?.system) {
    body.systemInstruction = { parts: [{ text: opts.system }] };
  }

  let res: Response;
  try {
    res = await fetch(`${ENDPOINT}/${encodeURIComponent(model)}:generateContent?key=${encodeURIComponent(key)}`, {
      method: "POST",
      headers: { "content-type": "application/json" },
      body: JSON.stringify(body),
      cache: "no-store",
    });
  } catch (e) {
    return { ok: false, status: 0, error: `Could not reach Gemini: ${(e as Error).message}`, retryable: true };
  }

  if (!res.ok) {
    const detail = await res.text().catch(() => "");
    const retryable = res.status === 429 || res.status >= 500;
    let msg = `Gemini error ${res.status}`;
    if (res.status === 429) msg = "The AI is rate-limited right now (quota exhausted). Please try again shortly.";
    else if (res.status === 403) msg = "The AI request was rejected (check the API key / permissions).";
    return { ok: false, status: res.status, error: msg, retryable };
  }

  const json = await res.json().catch(() => null);
  const text: string | undefined = json?.candidates?.[0]?.content?.parts?.map((p: any) => p?.text).filter(Boolean).join("\n");
  if (!text) {
    // Blocked (safety) or empty candidate.
    const reason = json?.candidates?.[0]?.finishReason || json?.promptFeedback?.blockReason;
    return { ok: false, status: 200, error: reason ? `The AI returned no text (${reason}).` : "The AI returned an empty response.", retryable: false };
  }
  return { ok: true, text: text.trim() };
}