import type { ApiErrorBody } from "@/lib/api/types";
import { getPublicApiBaseUrl, getPublicApiTimeoutMs } from "@/lib/env";
import { getUserFriendlyError } from "./errorTypes";
import { markAuthenticationRequired } from "@/lib/auth/session-requirement";

const DEMO_PREVIEW_TOKEN = "docdoe-demo-preview-token";

export function getApiBaseUrl() {
  if (typeof window !== "undefined" && process.env.NODE_ENV === "production") {
    return `${window.location.origin}/api/backend`;
  }
  return getPublicApiBaseUrl();
}

/** Cookie-bearing fetches only work first-party. Chrome blocks credentialed
 *  calls from docdoe.in to the Hugging Face Space, which made login look dead. */
export function getFetchCredentials(): RequestCredentials {
  if (typeof window === "undefined") return "omit";
  try {
    return new URL(getApiBaseUrl()).origin === window.location.origin ? "include" : "omit";
  } catch {
    return "omit";
  }
}

function resolveApiUrl(path: string) {
  return `${getApiBaseUrl()}${path.startsWith("/") ? path : `/${path}`}`;
}

export function resolveMediaUrl(url: string | null | undefined) {
  if (!url) return null;
  if (/^https?:\/\//i.test(url)) {
    try {
      const media = new URL(url);
      if (media.origin === new URL(getPublicApiBaseUrl()).origin && media.pathname.startsWith("/generated/")) {
        return `${getApiBaseUrl()}${media.pathname}${media.search}`;
      }
    } catch { /* Preserve already resolved third-party media URLs. */ }
  }
  if (/^https?:\/\//i.test(url)) return url;
  return `${getApiBaseUrl()}${url.startsWith("/") ? url : `/${url}`}`;
}

export type ApiRequestOptions = RequestInit & {
  timeoutMs?: number;
  /** Keep stored session on 401/403 (used by /auth/session soft-fail). */
  skipAuthClear?: boolean;
};

/** How long the caller should wait before retrying, and whether the wait is a
 *  short recoverable burst ("minute") or a hard daily cap ("daily"). */
export type RateLimitScope = "minute" | "daily";

export class ApiError extends Error {
  status: number | null;
  body: unknown;
  isAuthError: boolean;
  userMessage: string;
  /** Seconds to wait before retrying (from backend `retry_after` or `Retry-After` header). */
  retryAfter: number | null;
  /** "minute" = auto-retry safe; "daily" = come back later, do not loop. */
  rateLimitScope: RateLimitScope | null;
  /** Stable backend error code for feature-specific handling/support. */
  code: string | null;
  /** Correlation ID shared by the backend response, logs, and support report. */
  requestId: string | null;
  /** Whether retrying the same idempotent operation is expected to be safe. */
  retryable: boolean;

  constructor({
    message,
    status,
    body,
    retryAfter = null,
    rateLimitScope = null,
    code = null,
    requestId = null,
    retryable = false,
  }: {
    message: string;
    status: number | null;
    body?: unknown;
    retryAfter?: number | null;
    rateLimitScope?: RateLimitScope | null;
    code?: string | null;
    requestId?: string | null;
    retryable?: boolean;
  }) {
    super(message);
    this.name = "ApiError";
    this.status = status;
    this.body = body;
    this.retryAfter = retryAfter;
    this.rateLimitScope = rateLimitScope;
    this.code = code;
    this.requestId = requestId;
    this.retryable = retryable;
    this.isAuthError = status === 401 || status === 403;
    this.userMessage = normalizeApiError(this);
  }
}

export function isApiError(error: unknown): error is ApiError {
  return error instanceof ApiError;
}

function flattenBackendDetail(detail: unknown): string | null {
  if (typeof detail === "string") return detail;
  if (detail && typeof detail === "object") {
    if ("message" in detail && typeof (detail as { message: unknown }).message === "string") {
      return (detail as { message: string }).message;
    }
    if ("error" in detail && typeof (detail as { error: unknown }).error === "string") {
      return (detail as { error: string }).error;
    }
  }
  if (Array.isArray(detail)) {
    const messages = detail
      .map((item) => {
        if (item && typeof item === "object" && "msg" in item) {
          return String((item as { msg: unknown }).msg);
        }
        return null;
      })
      .filter(Boolean);
    return messages.length > 0 ? messages.join(" ") : null;
  }
  return null;
}

/** Pull `retry_after` (seconds) and `scope` out of a 429 error envelope, falling
 *  back to the `Retry-After` HTTP header. Returns nulls when absent. */
function extractRateLimitMeta(
  body: unknown,
  response: Response,
): { retryAfter: number | null; scope: RateLimitScope | null } {
  let retryAfter: number | null = null;
  let scope: RateLimitScope | null = null;

  const details =
    body && typeof body === "object" && "error" in body
      ? (body as { error?: { details?: unknown } }).error?.details
      : undefined;
  if (details && typeof details === "object") {
    const d = details as { retry_after?: unknown; scope?: unknown };
    if (typeof d.retry_after === "number" && Number.isFinite(d.retry_after)) {
      retryAfter = Math.max(0, Math.round(d.retry_after));
    }
    if (d.scope === "minute" || d.scope === "daily") {
      scope = d.scope;
    }
  }

  if (retryAfter === null) {
    const header = response.headers.get("Retry-After");
    const parsed = header ? Number.parseInt(header, 10) : NaN;
    if (Number.isFinite(parsed)) retryAfter = Math.max(0, parsed);
  }

  return { retryAfter, scope };
}

/** @internal — exported for unit tests only */
export async function readError(response: Response) {
  const fallback = "Could not complete this right now. Please try again.";

  try {
    const body = (await response.json()) as ApiErrorBody;
    const { retryAfter, scope } = extractRateLimitMeta(body, response);
    const requestId =
      response.headers.get("X-Request-ID") ?? body.error?.request_id ?? body.request_id ?? null;
    const detailCode =
      body.detail &&
      typeof body.detail === "object" &&
      "code" in body.detail &&
      typeof (body.detail as { code?: unknown }).code === "string"
        ? (body.detail as { code: string }).code
        : null;
    const code = body.error?.code ?? detailCode;
    const retryable = body.error?.retryable === true;

    // New hardened envelope: { success: false, error: { code, message } }
    if (body.error?.message) {
      return { message: body.error.message, body, retryAfter, scope, requestId, code, retryable };
    }

    // Backward-compat: { detail: { code, message } } or { detail: "string" }
    const detail = flattenBackendDetail(body.detail);
    if (detail) return { message: detail, body, retryAfter, scope, requestId, code, retryable };

    // Legacy: { message: "..." }
    if (typeof body.message === "string") {
      return { message: body.message, body, retryAfter, scope, requestId, code, retryable };
    }
  } catch {
    const { retryAfter, scope } = extractRateLimitMeta(null, response);
    return {
      message: fallback,
      body: null,
      retryAfter,
      scope,
      requestId: response.headers.get("X-Request-ID"),
      code: null,
      retryable: response.status >= 500,
    };
  }

  const { retryAfter, scope } = extractRateLimitMeta(null, response);
  return {
    message: fallback,
    body: null,
    retryAfter,
    scope,
    requestId: response.headers.get("X-Request-ID"),
    code: null,
    retryable: response.status >= 500,
  };
}

function createTimeoutSignal(timeoutMs: number, signal?: AbortSignal) {
  const controller = new AbortController();
  const timeoutId = globalThis.setTimeout(() => controller.abort(), timeoutMs);

  if (signal) {
    if (signal.aborted) {
      controller.abort();
    } else {
      signal.addEventListener("abort", () => controller.abort(), { once: true });
    }
  }

  return { signal: controller.signal, cleanup: () => globalThis.clearTimeout(timeoutId) };
}

function getRequestAuthToken() {
  if (typeof window === "undefined") return null;
  const token = (
    window.localStorage.getItem("exam_success_access_token") ??
    window.sessionStorage.getItem("exam_success_access_token") ??
    window.localStorage.getItem("docdoe_access_token") ??
    window.sessionStorage.getItem("docdoe_access_token") ??
    window.localStorage.getItem("access_token") ??
    window.sessionStorage.getItem("access_token") ??
    window.localStorage.getItem("auth_token") ??
    window.sessionStorage.getItem("auth_token")
  );
  return token === DEMO_PREVIEW_TOKEN ? null : token;
}

function clearInvalidSession(requestToken: string | null) {
  if (typeof window === "undefined") return;
  const token = getRequestAuthToken();
  // A request started before OAuth completed must not revoke the new session.
  if (token !== requestToken) return;
  if (token === "docdoe-demo-preview-token") return;
  for (const storage of [window.localStorage, window.sessionStorage]) {
    storage.removeItem("exam_success_access_token");
    storage.removeItem("exam_success_user");
    storage.removeItem("exam_success_token_expires_at");
  }
  markAuthenticationRequired();
  window.dispatchEvent(new Event("docdoe-auth-session-cleared"));
}

export function normalizeApiError(error: unknown) {
  // An ApiError carries an authoritative HTTP status — map it FIRST so status
  // wins over fragile message-substring classification (e.g. so a 422 carrying
  // the backend's classification guidance passes through verbatim).
  if (error instanceof ApiError) {
    if (error.status === 401 || error.status === 403) {
      return "Please sign in again to continue.";
    }
    if (error.status === 404) {
      return "DocDoe could not find that item. Refresh and try again.";
    }
    if (error.status === 413) {
      return "This file is too large. Try a smaller file.";
    }
    if (error.status === 402) {
      // Plan/quota limit — backend sends a student-safe specific message.
      return error.message?.trim() || "You've reached your plan limit. Try again later or upgrade.";
    }
    if (error.status === 429) {
      if (error.rateLimitScope === "daily") {
        return "You've reached today's AI study limit. Try again when your allowance resets.";
      }
      if (error.retryAfter && error.retryAfter > 0) {
        return `You're moving fast. I'll be ready in ${error.retryAfter} second${error.retryAfter === 1 ? "" : "s"}.`;
      }
      return "You're moving fast. I'll be ready in a few seconds.";
    }
    // For 5xx errors always return a generic message — never pass raw server
    // messages to students since they may contain internal provider/path details.
    if (error.status && error.status >= 500) {
      const reference = error.requestId ? ` Reference ID: ${error.requestId}` : "";
      return `I couldn't generate this right now. Your request is saved. Try again in a few seconds.${reference}`;
    }
    if (error.status === 422) {
      if (/classify this source first/i.test(error.message)) {
        return error.message.trim();
      }
      // Fall through to the classification system for other 422s.
      const friendly422 = getUserFriendlyError(error);
      if (friendly422 !== "Something failed, but your request is saved. Try again.") {
        return friendly422;
      }
      return "We couldn't create this right now. Please try again.";
    }
  }

  if (error instanceof DOMException && error.name === "AbortError") {
    return "This is taking longer than expected. Your request is saved. Try again.";
  }

  if (error instanceof Error && error.name === "AbortError") {
    return "This is taking longer than expected. Your request is saved. Try again.";
  }

  if (error instanceof TypeError) {
    return "Connection issue. Check your internet and try again.";
  }

  // Non-status errors (local validation strings, generic Errors): use the
  // classification system for a friendly, actionable message.
  const userFriendlyError = getUserFriendlyError(error);
  if (userFriendlyError !== "Something failed, but your request is saved. Try again.") {
    return userFriendlyError;
  }

  if (error instanceof ApiError && error.message.trim()) {
    return error.message;
  }

  if (error instanceof Error && error.message.trim()) {
    return error.message;
  }

  return "Something went wrong. Please try again.";
}

// Calendar hint only: the backend validates the zone and owns all dates.
function getStudentTimezone(): string | null {
  try {
    return Intl.DateTimeFormat().resolvedOptions().timeZone || null;
  } catch {
    if (process.env.NODE_ENV !== "production" && process.env.LOG_LEVEL === "debug") {
      console.debug("[FIX:student-calendar] Timezone unavailable; using server fallback");
    }
    return null;
  }
}

export async function apiFetch<TResponse>(
  path: string,
  init: ApiRequestOptions = {},
): Promise<TResponse> {
  const authToken = getRequestAuthToken();
  const studentTimezone = getStudentTimezone();
  const { timeoutMs = getPublicApiTimeoutMs(), signal, headers, skipAuthClear = false, ...requestInit } = init;
  const timeout = createTimeoutSignal(timeoutMs, signal ?? undefined);

  let response: Response;
  try {
    response = await fetch(resolveApiUrl(path), {
      ...requestInit,
      credentials: getFetchCredentials(),
      signal: timeout.signal,
      headers: {
        Accept: "application/json",
        ...(authToken ? { Authorization: `Bearer ${authToken}` } : {}),
        ...(studentTimezone ? { "X-Student-Timezone": studentTimezone } : {}),
        ...(requestInit.body instanceof FormData ? {} : { "Content-Type": "application/json" }),
        ...headers,
      },
    });
  } catch (error) {
    throw new ApiError({
      message: normalizeApiError(error),
      status: null,
      body: error,
    });
  } finally {
    timeout.cleanup();
  }

  if (!response.ok) {
    const errorData = await readError(response);
    const apiError = new ApiError({
      message: errorData.message,
      status: response.status,
      body: errorData.body,
      retryAfter: errorData.retryAfter,
      rateLimitScope: errorData.scope,
      code: errorData.code,
      requestId: errorData.requestId,
      retryable: errorData.retryable,
    });
    if (apiError.isAuthError) {
      if (!skipAuthClear) clearInvalidSession(authToken);
    }
    throw apiError;
  }

  if (response.status === 204) {
    return undefined as TResponse;
  }

  return (await response.json()) as TResponse;
}

export function apiGet<TResponse>(path: string, init?: ApiRequestOptions) {
  return apiFetch<TResponse>(path, {
    ...init,
    method: "GET",
  });
}

export async function apiJson<TResponse, TBody extends object>(
  path: string,
  body: TBody,
  init?: ApiRequestOptions,
): Promise<TResponse> {
  return apiFetch<TResponse>(path, {
    ...init,
    method: "POST",
    body: JSON.stringify(body),
  });
}

export function apiPost<TResponse, TBody extends object>(
  path: string,
  body: TBody,
  init?: ApiRequestOptions,
) {
  return apiJson<TResponse, TBody>(path, body, init);
}

export function apiPatch<TResponse, TBody extends object>(
  path: string,
  body: TBody,
  init?: ApiRequestOptions,
) {
  return apiFetch<TResponse>(path, {
    ...init,
    method: "PATCH",
    body: JSON.stringify(body),
  });
}

export function apiDelete<TResponse = void>(path: string, init?: ApiRequestOptions) {
  return apiFetch<TResponse>(path, {
    ...init,
    method: "DELETE",
  });
}

export async function apiForm<TResponse>(
  path: string,
  body: FormData,
  init?: ApiRequestOptions,
): Promise<TResponse> {
  return apiFetch<TResponse>(path, {
    ...init,
    method: "POST",
    body,
  });
}

export const apiUpload = apiForm;

export function buildQuery(params: Record<string, string | number | boolean | null | undefined>) {
  const query = new URLSearchParams();
  Object.entries(params).forEach(([key, value]) => {
    if (value === null || value === undefined || value === "") return;
    query.set(key, String(value));
  });
  const text = query.toString();
  return text ? `?${text}` : "";
}

export async function isBackendAvailable() {
  try {
    await apiFetch<unknown>("/health", { timeoutMs: 4000 });
    return true;
  } catch {
    return false;
  }
}

/**
 * Basic SSE streaming helper (for /ask/stream or /chat/stream etc).
 * Uses native ReadableStream. Callers provide onDelta etc.
 * (enh1: added to base client for /ask or chat streaming clients)
 */
type SseEventPayload = Record<string, unknown> & {
  delta?: unknown;
  done?: unknown;
  error?: unknown;
};

export async function streamSSE(
  path: string,
  body: unknown,
  callbacks: {
    onDelta?: (text: string) => void;
    onEvent?: (evt: SseEventPayload) => void;
    onDone?: (meta?: SseEventPayload) => void;
    onError?: (msg: string) => void;
  },
  signal?: AbortSignal,
): Promise<void> {
  const authToken = getRequestAuthToken();
  const studentTimezone = getStudentTimezone();
  let response: Response;
  try {
    response = await fetch(resolveApiUrl(path), {
      method: "POST",
      credentials: getFetchCredentials(),
      signal,
      headers: {
        "Content-Type": "application/json",
        Accept: "text/event-stream",
        ...(studentTimezone ? { "X-Student-Timezone": studentTimezone } : {}),
        ...(authToken ? { Authorization: `Bearer ${authToken}` } : {}),
      },
      body: JSON.stringify(body),
    });
  } catch (err: unknown) {
    if (err instanceof Error && err.name === "AbortError") return;
    callbacks.onError?.("Stream request failed to start.");
    return;
  }
  if (!response.ok || !response.body) {
    callbacks.onError?.("Streaming endpoint unavailable.");
    return;
  }
  const reader = response.body.getReader();
  const decoder = new TextDecoder();
  let buf = "";
  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      buf += decoder.decode(value, { stream: true });
      let idx;
      while ((idx = buf.indexOf("\n\n")) >= 0) {
        const line = buf.slice(0, idx).trim();
        buf = buf.slice(idx + 2);
        if (line.startsWith("data: ")) {
          const payload = line.slice(6);
          try {
            const evt = JSON.parse(payload) as SseEventPayload;
            callbacks.onEvent?.(evt);
            if (evt.delta) callbacks.onDelta?.(String(evt.delta));
            if (evt.done || evt.error) {
              callbacks.onDone?.(evt);
              return;
            }
          } catch {
            // plain text delta fallback
            callbacks.onDelta?.(payload);
          }
        }
      }
    }
    callbacks.onDone?.();
  } catch (e: unknown) {
    if (e instanceof Error && e.name !== "AbortError") {
      callbacks.onError?.(e.message || "Stream read error.");
    }
  } finally {
    try { reader.releaseLock(); } catch {}
  }
}