import {
  BinaryLike,
  randomBytes,
  scrypt,
  ScryptOptions,
  timingSafeEqual,
} from "node:crypto";
import { promisify } from "node:util";
import { Injectable } from "@nestjs/common";
import { ConfigService } from "@nestjs/config";
import { KEY_LENGTH, SCRYPT_PARAMS } from "../constants/hash.constants";

const scryptAsync = promisify<
  BinaryLike,
  BinaryLike,
  number,
  ScryptOptions,
  Buffer
>(scrypt);

@Injectable()
export class HashService {
  private readonly pepper: string;

  constructor(private readonly configService: ConfigService) {
    this.pepper = this.configService.get<string>("HASH_PEPPER");
  }

  private applyPepper(input: string): string {
    return this.pepper ? `${input}${this.pepper}` : input;
  }

  private generateSalt(bytes: number = 16): string {
    return randomBytes(bytes).toString("hex");
  }

  private async scrypt(password: string): Promise<[string, string]> {
    const salt = this.generateSalt();
    const pepperedInput = this.applyPepper(password);
    const hashedPassword = await scryptAsync(
      pepperedInput,
      salt,
      KEY_LENGTH,
      SCRYPT_PARAMS,
    );

    return [salt, hashedPassword.toString("hex")];
  }

  private async verifyScrypt(
    password: string,
    salt: string,
    hashedPassword: string,
  ): Promise<boolean> {
    const pepperedInput = this.applyPepper(password);
    const derived = await scryptAsync(
      pepperedInput,
      salt,
      KEY_LENGTH,
      SCRYPT_PARAMS,
    );
    const storedBuffer = Buffer.from(hashedPassword, "hex");

    if (derived.length !== storedBuffer.length) return false;

    return timingSafeEqual(derived, storedBuffer);
  }
}