import { ServiceAccountCredential } from "../credential";
import { ErrorInfo } from "../error";
import { ALGORITHMS } from "./consts";
import {
  arrayBufferToBase64,
  pemToArrayBuffer,
  stringToArrayBuffer,
} from "./utils";

const ALGORITHM_RS256 = "RS256" as const;

export interface CryptoSigner {
  readonly algorithm: "RS256" | "none";

  sign(token: string): Promise<string>;
  getAccountId(): Promise<string>;
}

export class ServiceAccountSigner implements CryptoSigner {
  algorithm = ALGORITHM_RS256;

  constructor(private readonly credential: ServiceAccountCredential) {
    if (!credential) {
      throw new CryptoSignerError({
        code: CryptoSignerErrorCode.INVALID_CREDENTIAL,
        message:
          "INTERNAL ASSERT: Must provide a service account credential to initialize ServiceAccountSigner.",
      });
    }
  }

  public async sign(token: string): Promise<string> {
    const tokenBuffer = stringToArrayBuffer(token);
    const keyData = pemToArrayBuffer(this.credential.privateKey);
    const key = await crypto.subtle.importKey(
      "pkcs8",
      keyData,
      ALGORITHMS[ALGORITHM_RS256],
      false,
      ["sign"]
    );

    const signed = await crypto.subtle.sign(
      ALGORITHMS[ALGORITHM_RS256],
      key,
      tokenBuffer
    );
    return arrayBufferToBase64(signed);
  }

  /**
   * @inheritDoc
   */
  public getAccountId(): Promise<string> {
    return Promise.resolve(this.credential.clientEmail);
  }
}

export interface ExtendedErrorInfo extends ErrorInfo {
  cause?: Error;
}

export class CryptoSignerError extends Error {
  constructor(private errorInfo: ExtendedErrorInfo) {
    super(errorInfo.message);

    Object.setPrototypeOf(this, CryptoSignerError.prototype);
  }

  public get code(): string {
    return this.errorInfo.code;
  }

  public get message(): string {
    return this.errorInfo.message;
  }

  public get cause(): Error | undefined {
    return this.errorInfo.cause;
  }
}

export class CryptoSignerErrorCode {
  public static INVALID_ARGUMENT = "invalid-argument";
  public static INTERNAL_ERROR = "internal-error";
  public static INVALID_CREDENTIAL = "invalid-credential";
  public static SERVER_ERROR = "server-error";
}