import { z } from "zod";

import { refineHomeworkText } from "@/lib/ai";
import { getServerConfig, resolveModelName } from "@/lib/config";
import { INERT_OLLAMA_AUTH, resolveModelTarget } from "@/lib/providers-server";
import { friendlyErrorMessage, OllamaError } from "@/lib/ollama";
import { rejectCrossOrigin, rejectOversizedBody, requestLocale } from "@/lib/http-guard";
import { translate } from "@/lib/i18n-dict";
import { clientKey, rateLimit, rateLimitResponse } from "@/lib/rate-limit";
import { acquireModelGate } from "@/lib/model-guard";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

/**
 * Homework follow-ups: rewrite one finished piece — shorter, more detail, or
 * a step explained differently. One short model call, plain JSON back.
 */

const requestSchema = z.object({

  model: z.string().min(1).max(200).optional(),
  instruction: z.enum(["shorter", "more", "explain"]),
  text: z.string().min(1).max(20_000),
  /** The assignment, for context (optional). */
  context: z.string().max(8_000).optional(),
  language: z.string().max(60).optional(),
});

export async function POST(request: Request) {
  const locale = requestLocale(request);
  const crossOrigin = rejectCrossOrigin(request);
  if (crossOrigin) return crossOrigin;
  const oversized = rejectOversizedBody(request, 128 * 1024);
  if (oversized) return oversized;

  const config = getServerConfig();
  const limit = rateLimit(`refine:${clientKey(request)}`, config.rateLimits.refine, config.rateLimits.windowMs);
  if (!limit.allowed) return rateLimitResponse(limit, locale);

  // Ollama (server-configured) or a cloud provider the browser sent a key for.
  const resolved = resolveModelTarget(config, request, locale);
  if ("error" in resolved) {
    return Response.json({ error: resolved.error.message, kind: resolved.error.kind }, { status: resolved.error.status });
  }
  const target = resolved.target;
  const provider = target.kind === "provider" ? target.target : undefined;
  const baseAuth = target.kind === "provider" ? INERT_OLLAMA_AUTH : target.auth;

  let payload: unknown;
  try {
    payload = await request.json();
  } catch {
    return Response.json({ error: translate(locale, "server.bodyNotJson") }, { status: 400 });
  }

  const parsed = requestSchema.safeParse(payload);
  if (!parsed.success) {
    return Response.json(
      {
        error: translate(locale, "server.invalidRequest", {
          detail: parsed.error.issues
            .slice(0, 3)
            .map((issue) => `${issue.path.join(".") || "body"} ${issue.message}`)
            .join("; "),
        }),
      },
      { status: 400 },
    );
  }

  // Provider runs carry the model the user picked in Settings → Providers.
  const providerModel = provider ? parsed.data.model : undefined;
  if (provider && !providerModel) {
    return Response.json(
      { error: translate(locale, "server.providerModelNeeded"), kind: "bad_provider" },
      { status: 400 },
    );
  }
  const textModel = provider ? providerModel! : config.textModel;

  const gate = acquireModelGate(request, config, locale);
  if ("response" in gate) return gate.response;
  try {
    const text = await refineHomeworkText({
      model: textModel,
      auth: baseAuth,
      provider,
      instruction: parsed.data.instruction,
      text: parsed.data.text,
      context: parsed.data.context,
    });
    return Response.json(
      { text, model: provider ? textModel : resolveModelName(config.textModel, baseAuth.directCloud) },
      { headers: { "Cache-Control": "no-store" } },
    );
  } catch (error) {
    // Never log the text itself: it may contain the student's homework.
    console.error("[api/homework/refine]", error instanceof OllamaError ? `${error.kind}: ${error.message}` : error);
    return Response.json(
      {
        error: friendlyErrorMessage(error, baseAuth.baseUrl || provider?.baseUrl || '', locale),
        kind: error instanceof OllamaError ? error.kind : "unknown",
      },
      { status: 502 },
    );
  } finally {
    gate.gate.release();
  }
}