const DEFAULT_GANTT_API_BASE_URL = "http://localhost:3000/api";
const DEFAULT_REVALIDATE_SECONDS = 15;
let hasWarnedDefaultBaseUrl = false;

type CacheEntry = {
  expiresAt: number;
  value: unknown;
  promise?: Promise<unknown>;
};

const responseCache = new Map<string, CacheEntry>();

function normalizeBaseUrl(url: string): string {
  return url.replace(/\/+$/, "");
}

function deriveApiBaseUrlFromGanttBoardUrl(): string | null {
  const ganttBoardUrl = process.env.NEXT_PUBLIC_GANTT_BOARD_URL;
  if (!ganttBoardUrl) return null;

  try {
    const parsed = new URL(ganttBoardUrl);
    const pathname = parsed.pathname.replace(/\/+$/, "");
    parsed.pathname = `${pathname}/api`;
    parsed.search = "";
    parsed.hash = "";
    return normalizeBaseUrl(parsed.toString());
  } catch {
    return null;
  }
}

export function getGanttApiBaseUrl(): string {
  const derivedFromGanttBoardUrl = deriveApiBaseUrlFromGanttBoardUrl();
  const configured =
    process.env.GANTT_API_BASE_URL ||
    process.env.NEXT_PUBLIC_GANTT_API_BASE_URL ||
    derivedFromGanttBoardUrl ||
    DEFAULT_GANTT_API_BASE_URL;

  if (
    configured === DEFAULT_GANTT_API_BASE_URL &&
    process.env.NODE_ENV === "production" &&
    !hasWarnedDefaultBaseUrl
  ) {
    hasWarnedDefaultBaseUrl = true;
    console.warn(
      "[gantt-api] Using default base URL http://localhost:3000/api. Set GANTT_API_BASE_URL or NEXT_PUBLIC_GANTT_API_BASE_URL for deployed environments.",
    );
  }

  return normalizeBaseUrl(configured);
}

function getRevalidateSeconds(): number {
  const raw = Number(process.env.GANTT_API_REVALIDATE_SECONDS || String(DEFAULT_REVALIDATE_SECONDS));
  return Number.isFinite(raw) && raw > 0 ? raw : DEFAULT_REVALIDATE_SECONDS;
}

function buildAuthHeaders(): HeadersInit {
  const headers: Record<string, string> = {};

  if (process.env.GANTT_API_BEARER_TOKEN) {
    headers.Authorization = `Bearer ${process.env.GANTT_API_BEARER_TOKEN}`;
  }

  if (process.env.GANTT_API_COOKIE) {
    headers.Cookie = process.env.GANTT_API_COOKIE;
  }

  return headers;
}

export async function fetchGanttApi<T>(endpoint: string): Promise<T> {
  const baseUrl = getGanttApiBaseUrl();
  const revalidateSeconds = getRevalidateSeconds();
  const cacheKey = `${baseUrl}${endpoint}`;
  const now = Date.now();
  const cached = responseCache.get(cacheKey);

  if (cached && cached.expiresAt > now) {
    if (cached.promise) {
      return (await cached.promise) as T;
    }
    return cached.value as T;
  }

  const requestPromise = (async () => {
    const response = await fetch(cacheKey, {
      method: "GET",
      cache: "no-store",
      headers: {
        Accept: "application/json",
        ...buildAuthHeaders(),
      },
    });

    const contentType = response.headers.get("content-type") || "";
    const isJson = contentType.includes("application/json");
    const payload = (isJson ? await response.json().catch(() => null) : null) as
      | { error?: string; message?: string }
      | null;
    const nonJsonBody = !isJson ? await response.text().catch(() => "") : "";

    if (!response.ok) {
      const details =
        payload?.error ||
        payload?.message ||
        (nonJsonBody ? nonJsonBody.replace(/\s+/g, " ").slice(0, 200) : response.statusText);
      throw new Error(`gantt-board API request failed (${response.status} ${endpoint}): ${details}`);
    }

    if (!isJson) {
      throw new Error(`gantt-board API request failed (${response.status} ${endpoint}): expected JSON response`);
    }

    return payload as T;
  })();

  responseCache.set(cacheKey, {
    expiresAt: now + revalidateSeconds * 1000,
    value: null,
    promise: requestPromise as Promise<unknown>,
  });

  try {
    const result = await requestPromise;
    responseCache.set(cacheKey, {
      expiresAt: Date.now() + revalidateSeconds * 1000,
      value: result as unknown,
    });
    return result;
  } catch (error) {
    responseCache.delete(cacheKey);
    throw error;
  }
}