export interface AdmissionMessages {
  registrationMessage: string;
  groupAccessDeniedMessage: string;
  vpnDeniedMessage: string;
  scheduledAccessDeniedMessage: string;
}

export type AdmissionDenialReason =
  | "not_registered"
  | "group_access_disabled"
  | "schedule_disallowed"
  | "anonymized_network_disallowed";

export const DEFAULT_ADMISSION_MESSAGES: AdmissionMessages = {
  registrationMessage: "Please register your Minecraft account before joining.",
  groupAccessDeniedMessage: "Your account group does not currently have server access. Contact a host if you believe this is a mistake.",
  vpnDeniedMessage: "VPN, proxy, and Tor connections are not allowed. Contact a host to request an exception.",
  scheduledAccessDeniedMessage: "Your group is only allowed access from {next_start} to {next_end}.",
} as const;

export function admissionDenialMessage(reason: AdmissionDenialReason, messages: AdmissionMessages) {
  if (reason === "not_registered") return messages.registrationMessage;
  if (reason === "group_access_disabled") return messages.groupAccessDeniedMessage;
  if (reason === "schedule_disallowed") return messages.scheduledAccessDeniedMessage;
  return messages.vpnDeniedMessage;
}

const CONTROL_CHARACTERS = /[\u0000-\u001f\u007f]/;
const TEMPLATE_VARIABLE = /\{([a-z_]+)\}/g;
const COMMON_VARIABLES = new Set(["player", "group"]);
const SCHEDULE_VARIABLES = new Set(["player", "group", "next_start", "next_end"]);

type MessageName = keyof AdmissionMessages;

function messageValue(formData: FormData, name: MessageName, allowedVariables: Set<string>) {
  const value = String(formData.get(name) ?? "").trim();
  if (value.length < 10 || value.length > 500 || CONTROL_CHARACTERS.test(value)) return null;
  const withoutVariables = value.replace(TEMPLATE_VARIABLE, (match, variable: string) =>
    allowedVariables.has(variable) ? "" : match);
  return /[{}]/.test(withoutVariables) ? null : value;
}

export function parseAdmissionMessages(formData: FormData) {
  const registrationMessage = messageValue(formData, "registrationMessage", COMMON_VARIABLES);
  const groupAccessDeniedMessage = messageValue(formData, "groupAccessDeniedMessage", COMMON_VARIABLES);
  const vpnDeniedMessage = messageValue(formData, "vpnDeniedMessage", COMMON_VARIABLES);
  const scheduledAccessDeniedMessage = messageValue(formData, "scheduledAccessDeniedMessage", SCHEDULE_VARIABLES);
  if (!registrationMessage || !groupAccessDeniedMessage || !vpnDeniedMessage || !scheduledAccessDeniedMessage) return null;
  return { registrationMessage, groupAccessDeniedMessage, vpnDeniedMessage, scheduledAccessDeniedMessage };
}

export function renderAdmissionMessage(template: string, variables: Record<string, string>) {
  return template.replace(TEMPLATE_VARIABLE, (match, variable: string) => variables[variable] ?? match);
}