import { createHmac, timingSafeEqual } from "node:crypto";
import { eq } from "drizzle-orm";

import { db } from "@tasks/database";
import { objects } from "@tasks/database/schema";
import { transitionConvoy } from "@/server/lib/convoy/convoy-service";
import { rateLimit } from "@/server/lib/rate-limit";

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

const CONVOY_MARKER_RE = /echodo-convoy:\s*([0-9a-f-]{36})/i;
const RATE_LIMIT = { limit: 60, windowMs: 60_000 } as const;

function getClientIp(req: Request): string {
  const fwd = req.headers.get("x-forwarded-for");
  if (fwd) {
    const first = fwd.split(",")[0]?.trim();
    if (first) return first;
  }
  const realIp = req.headers.get("x-real-ip");
  if (realIp?.trim()) return realIp.trim();
  return "unknown";
}

function verifyHmacSignature(rawBody: string, signatureHeader: string | null, secret: string): boolean {
  if (!signatureHeader) return false;
  let sig = signatureHeader.trim();
  if (sig.startsWith("sha256=")) sig = sig.slice(7);
  const computed = createHmac("sha256", secret).update(Buffer.from(rawBody, "utf8")).digest("hex");
  const a = Buffer.from(computed, "utf8");
  const b = Buffer.from(sig, "utf8");
  if (a.length !== b.length) {
    try {
      timingSafeEqual(a, a);
    } catch {
      // ignore
    }
    return false;
  }
  return timingSafeEqual(a, b);
}

function json(status: number, body: unknown): Response {
  return new Response(JSON.stringify(body), {
    status,
    headers: { "Content-Type": "application/json" },
  });
}

export async function POST(req: Request): Promise<Response> {
  const ip = getClientIp(req);
  const rl = rateLimit({
    key: `forge-webhook:${ip}`,
    limit: RATE_LIMIT.limit,
    windowMs: RATE_LIMIT.windowMs,
  });
  if (!rl.allowed) {
    return json(429, { ok: false, error: "rate_limited", retryAfterMs: rl.retryAfterMs });
  }

  const secret = process.env.FORGE_WEBHOOK_SECRET?.trim();
  if (!secret) {
    return json(500, { ok: false, error: "webhook_not_configured" });
  }

  let rawBody: string;
  try {
    rawBody = await req.text();
  } catch {
    return json(400, { ok: false, error: "invalid_body" });
  }

  const hubSig = req.headers.get("x-hub-signature-256") ?? req.headers.get("x-hub-signature");
  const forgejoSig = req.headers.get("x-forgejo-signature");
  const providedSig = hubSig ?? forgejoSig;

  if (!providedSig) {
    return json(401, { ok: false, error: "missing_signature" });
  }

  if (!verifyHmacSignature(rawBody, providedSig, secret)) {
    return json(401, { ok: false, error: "invalid_signature" });
  }

  let payload: Record<string, unknown>;
  try {
    payload = rawBody ? (JSON.parse(rawBody) as Record<string, unknown>) : {};
  } catch {
    return json(200, { ok: true });
  }

  const action = typeof payload.action === "string" ? payload.action : null;
  const prRaw = payload.pull_request as Record<string, unknown> | null | undefined;

  if (action !== "closed" || !prRaw || typeof prRaw !== "object") {
    return json(200, { ok: true });
  }

  const merged = prRaw.merged === true;
  if (!merged) {
    return json(200, { ok: true });
  }

  const bodyText = typeof prRaw.body === "string" ? prRaw.body : "";
  const match = CONVOY_MARKER_RE.exec(bodyText);
  if (!match?.[1]) {
    return json(200, { ok: true });
  }

  const convoyId = match[1].toLowerCase();
  const prNumber = typeof prRaw.number === "number" ? prRaw.number : null;

  const [convoyRow] = await db
    .select({ id: objects.id, workspaceId: objects.workspaceId, status: objects.status, type: objects.type })
    .from(objects)
    .where(eq(objects.id, convoyId))
    .limit(1);

  if (!convoyRow || convoyRow.type !== "project") {
    return json(200, { ok: true });
  }

  if (convoyRow.status !== "pr_review") {
    return json(200, { ok: true });
  }

  const reason = prNumber !== null ? `pr#${prNumber} merged` : "pr merged";

  try {
    await transitionConvoy(db, {
      workspaceId: convoyRow.workspaceId,
      convoyId: convoyRow.id,
      toStatus: "merged",
      actor: "automation",
      reason,
    });
  } catch {
    return json(200, { ok: true });
  }

  return json(200, { ok: true });
}