export const MAX_CLIENT_WS_PAYLOAD_BYTES = 10 * 1024 * 1024;

export class WsPayloadTooLargeError extends Error {
  constructor(byteLength: number) {
    super(`WebSocket message too large: ${byteLength} bytes`);
    this.name = "WsPayloadTooLargeError";
  }
}

export interface JsonWsMessage {
  type: string;
  payload?: unknown;
  [key: string]: unknown;
}

function assertPayloadSize(byteLength: number): void {
  if (byteLength > MAX_CLIENT_WS_PAYLOAD_BYTES) {
    throw new WsPayloadTooLargeError(byteLength);
  }
}

function decodeWsText(data: unknown): string {
  if (typeof data === "string") {
    assertPayloadSize(Buffer.byteLength(data, "utf8"));
    return data;
  }

  if (data instanceof ArrayBuffer) {
    assertPayloadSize(data.byteLength);
    return new TextDecoder().decode(new Uint8Array(data));
  }

  if (ArrayBuffer.isView(data)) {
    assertPayloadSize(data.byteLength);
    return new TextDecoder().decode(
      new Uint8Array(data.buffer, data.byteOffset, data.byteLength),
    );
  }

  if (Array.isArray(data) && data.every(Buffer.isBuffer)) {
    const byteLength = data.reduce((total, chunk) => total + chunk.byteLength, 0);
    assertPayloadSize(byteLength);
    return Buffer.concat(data, byteLength).toString("utf8");
  }

  throw new Error("Unsupported WebSocket message payload");
}

export function decodeJsonWsMessage(data: unknown): JsonWsMessage {
  const parsed = JSON.parse(decodeWsText(data)) as unknown;
  if (
    typeof parsed !== "object" ||
    parsed === null ||
    !("type" in parsed) ||
    typeof parsed.type !== "string"
  ) {
    throw new Error("Invalid WebSocket message payload");
  }
  return parsed as JsonWsMessage;
}