import {
  REALTIME_EVENT_PROTOCOL,
  type EventTypeId,
  type StreamRegistrationId,
} from "./realtime-streams.ts";

export const REALTIME_EVENT_FIELD_LIMITS = Object.freeze({
  maxOpaqueIdentifierLength: 128,
  maxScopeBindingLength: 256,
  maxResumeCursorLength: 1_024,
  maxSequenceDigits: 20,
  maxTimestampFractionDigits: 9,
});

export const REALTIME_MAX_SEQUENCE = "18446744073709551615";

export type RealtimeEventBase<Payload> = Readonly<{
  protocol: typeof REALTIME_EVENT_PROTOCOL;
  streamId: StreamRegistrationId;
  streamEpoch: string;
  eventType: EventTypeId;
  eventId: string;
  sequence: string;
  occurredAt: string;
  scopeBinding: string;
  payload: Payload;
}>;

export type RealtimeEventEnvelope<Payload = unknown> = Readonly<
  RealtimeEventBase<Payload> &
    (
      | Readonly<{
          recoveryMode: "CURSOR";
          resumeCursor: string;
        }>
      | Readonly<{
          recoveryMode: "SNAPSHOT_ONLY" | "SESSION_REBUILD";
          resumeCursor: null;
        }>
    )
>;

export type SnapshotCheckpoint = Readonly<
  {
    streamEpoch: string;
    lastAppliedSequence: string;
    snapshotRevision: string;
  } & (
    | Readonly<{
        recoveryMode: "CURSOR";
        resumeCursor: string;
      }>
    | Readonly<{
        recoveryMode: "SNAPSHOT_ONLY";
        resumeCursor: null;
      }>
  )
>;

export type RealtimeResumeState = Readonly<
  {
    streamEpoch: string;
    lastAppliedSequence: string;
  } & (
    | Readonly<{
        recoveryMode: "CURSOR";
        resumeCursor: string;
      }>
    | Readonly<{
        recoveryMode: "SNAPSHOT_ONLY" | "SESSION_REBUILD";
        resumeCursor: null;
      }>
  )
>;

const OPAQUE_IDENTIFIER = /^[A-Za-z0-9][A-Za-z0-9._:~+/=-]*$/u;
const HEADER_SAFE_CURSOR = /^[\x21-\x7e]+$/u;
const CANONICAL_SEQUENCE = /^(?:0|[1-9][0-9]{0,19})$/u;
const RFC_3339 =
  /^([0-9]{4})-(0[1-9]|1[0-2])-([0-2][0-9]|3[01])T([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])(?:\.([0-9]{1,9}))?(Z|([+-])([01][0-9]|2[0-3]):([0-5][0-9]))$/u;

export function isRealtimeOpaqueIdentifier(
  value: unknown,
): value is string {
  return (
    typeof value === "string" &&
    value.length >= 1 &&
    value.length <=
      REALTIME_EVENT_FIELD_LIMITS.maxOpaqueIdentifierLength &&
    OPAQUE_IDENTIFIER.test(value)
  );
}

export function isRealtimeScopeBinding(
  value: unknown,
): value is string {
  return (
    typeof value === "string" &&
    value.length >= 1 &&
    value.length <= REALTIME_EVENT_FIELD_LIMITS.maxScopeBindingLength &&
    OPAQUE_IDENTIFIER.test(value)
  );
}

export function isRealtimeResumeCursor(
  value: unknown,
): value is string {
  return (
    typeof value === "string" &&
    value.length >= 1 &&
    value.length <=
      REALTIME_EVENT_FIELD_LIMITS.maxResumeCursorLength &&
    HEADER_SAFE_CURSOR.test(value) &&
    !value.includes("\0") &&
    !value.includes("\r") &&
    !value.includes("\n")
  );
}

export function isCanonicalRealtimeSequence(
  value: unknown,
): value is string {
  if (
    typeof value !== "string" ||
    value.length > REALTIME_EVENT_FIELD_LIMITS.maxSequenceDigits ||
    !CANONICAL_SEQUENCE.test(value)
  ) {
    return false;
  }
  try {
    return BigInt(value) <= BigInt(REALTIME_MAX_SEQUENCE);
  } catch {
    return false;
  }
}

export function compareRealtimeSequences(
  left: string,
  right: string,
): -1 | 0 | 1 {
  if (
    !isCanonicalRealtimeSequence(left) ||
    !isCanonicalRealtimeSequence(right)
  ) {
    throw new TypeError("Realtime sequence is invalid.");
  }
  const leftValue = BigInt(left);
  const rightValue = BigInt(right);
  return leftValue < rightValue ? -1 : leftValue > rightValue ? 1 : 0;
}

export function nextRealtimeSequence(value: string): string | null {
  if (!isCanonicalRealtimeSequence(value)) {
    throw new TypeError("Realtime sequence is invalid.");
  }
  const next = BigInt(value) + 1n;
  return next > BigInt(REALTIME_MAX_SEQUENCE) ? null : next.toString(10);
}

/**
 * A bounded RFC 3339 profile: uppercase T/Z, a required offset, real calendar
 * dates, seconds 00-59 and at most nanosecond fractional precision.
 */
export function isStrictRealtimeTimestamp(
  value: unknown,
): value is string {
  if (typeof value !== "string") return false;
  const match = RFC_3339.exec(value);
  if (!match) return false;
  const year = Number(match[1]);
  const month = Number(match[2]);
  const day = Number(match[3]);
  if (year < 1 || day > daysInMonth(year, month)) return false;
  return Number.isFinite(Date.parse(value));
}

function daysInMonth(year: number, month: number): number {
  if (month === 2) {
    return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0)
      ? 29
      : 28;
  }
  return [4, 6, 9, 11].includes(month) ? 30 : 31;
}