import { UnauthorizedError } from "@modelcontextprotocol/client";
import type { CallbackParams } from "./types.js";
import { ZodError } from "zod";

type ZodIssueLike = {
  path?: unknown[];
  message?: string;
  code?: string;
};

function isZodIssueArray(value: unknown): value is ZodIssueLike[] {
  return (
    Array.isArray(value) &&
    value.length > 0 &&
    typeof value[0] === "object" &&
    value[0] !== null &&
    "code" in value[0]
  );
}

function formatZodIssues(issues: ZodIssueLike[]): string {
  const tokenResponseIssue = issues.some(
    (issue) =>
      Array.isArray(issue.path) &&
      (issue.path.includes("access_token") ||
        issue.path.includes("token_type")),
  );
  if (tokenResponseIssue) {
    return "The authorization server did not return valid tokens. Check your OAuth client ID and secret, then try again.";
  }
  return issues
    .map((issue) => {
      const path =
        Array.isArray(issue.path) && issue.path.length
          ? issue.path.join(".")
          : "input";
      return `${path}: ${issue.message ?? "invalid"}`;
    })
    .join(" ");
}

/**
 * Human-readable detail for OAuth failure toasts/banners (never raw Zod JSON).
 */
export function formatOAuthFailureDetail(detail: unknown): string {
  if (detail instanceof ZodError) {
    return formatZodIssues(detail.issues);
  }
  const raw =
    detail instanceof Error
      ? detail.message
      : typeof detail === "string"
        ? detail
        : String(detail);
  const trimmed = raw.trim();
  if (trimmed.startsWith("[")) {
    try {
      const parsed: unknown = JSON.parse(trimmed);
      if (isZodIssueArray(parsed)) {
        return formatZodIssues(parsed);
      }
    } catch {
      // fall through
    }
  }
  return raw;
}

/**
 * Parse a string as an absolute URL. On failure, throws with `label` and the
 * offending value so callers (and UI toasts) can show what to fix.
 */
export function parseHttpUrl(value: string, label: string): URL {
  const trimmed = value.trim();
  try {
    return new URL(trimmed);
  } catch (err) {
    const detail = err instanceof Error ? err.message : String(err);
    throw new Error(`Invalid ${label}: "${trimmed}" (${detail})`, {
      cause: err,
    });
  }
}

/**
 * Parses OAuth 2.1 callback parameters from a URL search string
 * @param location The URL search string (e.g., "?code=abc123" or "?error=access_denied")
 * @returns Parsed callback parameters with success/error information
 */
export const parseOAuthCallbackParams = (location: string): CallbackParams => {
  const params = new URLSearchParams(location);

  const code = params.get("code");
  if (code) {
    const iss = params.get("iss");
    return iss === null
      ? { successful: true, code }
      : { successful: true, code, iss };
  }

  const error = params.get("error");
  const error_description = params.get("error_description");
  const error_uri = params.get("error_uri");

  if (error) {
    return { successful: false, error, error_description, error_uri };
  }

  return {
    successful: false,
    error: "invalid_request",
    error_description: "Missing code or error in response",
    error_uri: null,
  };
};

/**
 * Generate a random state for the OAuth 2.0 flow.
 * Works in both browser and Node.js environments.
 *
 * @returns A random state for the OAuth 2.0 flow.
 */
export const generateOAuthState = (): string => {
  // OAuth state is a CSRF token — it MUST be unpredictable. crypto.getRandomValues
  // is available in every supported runtime (browsers, Node ≥15); if it's somehow
  // missing, fail loudly rather than silently degrading to Math.random (whose
  // output is predictable from a small amount of observed state).
  if (typeof crypto === "undefined" || !crypto.getRandomValues) {
    throw new Error(
      "crypto.getRandomValues is not available; refusing to generate an OAuth state with a non-cryptographic RNG.",
    );
  }
  const array = new Uint8Array(32);
  crypto.getRandomValues(array);
  return Array.from(array, (byte) => byte.toString(16).padStart(2, "0")).join(
    "",
  );
};

/**
 * Parse OAuth `state` to extract the auth session id (CSRF token).
 * Must be the 64-char hex value from {@link generateOAuthState}.
 */
export const parseOAuthState = (state: string): { authId: string } | null => {
  if (!state || typeof state !== "string") return null;
  if (/^[a-f0-9]{64}$/i.test(state)) {
    return { authId: state };
  }
  return null;
};

/**
 * Generates a human-readable error description from OAuth callback error parameters
 * @param params OAuth error callback parameters containing error details
 * @returns Formatted multiline error message with error code, description, and optional URI
 */
export const generateOAuthErrorDescription = (
  params: Extract<CallbackParams, { successful: false }>,
): string => {
  const error = params.error;
  const errorDescription = params.error_description;
  const errorUri = params.error_uri;

  return [
    `Error: ${error}.`,
    errorDescription ? `Details: ${errorDescription}.` : "",
    errorUri ? `More info: ${errorUri}.` : "",
  ]
    .filter(Boolean)
    .join("\n");
};

/**
 * True when a thrown connect error represents an upstream 401. The remote
 * transport preserves the status on the error object; as a fallback, match
 * transport wording `"failed …(401)"` so unrelated `(401)` in messages does
 * not trigger OAuth.
 *
 * Under `protocolEra: auto|modern`, a negotiation-probe 401 can surface as
 * `SdkError(EraNegotiationFailed)` with the real {@link UnauthorizedError} at
 * `error.data.cause` (and sometimes native `error.cause`). Walk that chain so
 * OAuth recovery still starts.
 */
export function isUnauthorizedError(err: unknown): boolean {
  return isUnauthorizedErrorDeep(err, new Set());
}

function isUnauthorizedErrorDeep(err: unknown, seen: Set<unknown>): boolean {
  if (err == null) return false;
  if (typeof err !== "object") {
    return /\bfailed\b[^\n]*\(401\)/i.test(String(err));
  }
  if (seen.has(err)) return false;
  seen.add(err);

  if (UnauthorizedError.isInstance(err)) return true;

  const status = (err as { status?: number }).status;
  const code = (err as { code?: unknown }).code;
  if (status === 401 || code === 401) return true;

  if (err instanceof Error && /\bfailed\b[^\n]*\(401\)/i.test(err.message)) {
    return true;
  }

  if (
    "cause" in err &&
    isUnauthorizedErrorDeep((err as { cause: unknown }).cause, seen)
  ) {
    return true;
  }

  const data = (err as { data?: unknown }).data;
  if (
    data !== null &&
    typeof data === "object" &&
    "cause" in data &&
    isUnauthorizedErrorDeep((data as { cause: unknown }).cause, seen)
  ) {
    return true;
  }

  return false;
}