import * as Crypto from 'expo-crypto';

/**
 * Cryptographic utilities for BLE communication
 * Provides proper MD5 hashing to match Android implementation
 */
export class CryptoUtils {
  /**
   * Calculate MD5 hash of data
   * @param data - ArrayBuffer or string to hash
   * @returns Promise<string> - MD5 hash as hexadecimal string
   */
  public static async calculateMD5(data: ArrayBuffer | string): Promise<string> {
    let dataString: string;
    
    if (data instanceof ArrayBuffer) {
      // Convert ArrayBuffer to string
      const uint8Array = new Uint8Array(data);
      dataString = Array.from(uint8Array)
        .map(byte => String.fromCharCode(byte))
        .join('');
    } else {
      dataString = data;
    }
    
    const hash = await Crypto.digestStringAsync(
      Crypto.CryptoDigestAlgorithm.MD5,
      dataString
    );
    return hash.toUpperCase();
  }

  /**
   * Calculate MD5 hash of a file
   * @param file - File object to hash
   * @returns Promise<string> - MD5 hash as hexadecimal string
   */
  public static async calculateFileMD5(file: File): Promise<string> {
    return new Promise((resolve, reject) => {
      const reader = new FileReader();
      
      reader.onload = async (event) => {
        try {
          const arrayBuffer = event.target?.result as ArrayBuffer;
          const hash = await this.calculateMD5(arrayBuffer);
          resolve(hash);
        } catch (error) {
          reject(error);
        }
      };
      
      reader.onerror = () => {
        reject(new Error('Failed to read file for MD5 calculation'));
      };
      
      reader.readAsArrayBuffer(file);
    });
  }

  /**
   * Get partial MD5 hash (substring) to match Android implementation
   * Android uses substring(8, 24) for file transfers
   * @param data - Data to hash
   * @returns Promise<string> - Partial MD5 hash
   */
  public static async calculatePartialMD5(data: ArrayBuffer | string): Promise<string> {
    const fullHash = await this.calculateMD5(data);
    return fullHash.substring(8, 24); // Match Android implementation
  }

  /**
   * Get partial file MD5 hash
   * @param file - File to hash
   * @returns Promise<string> - Partial MD5 hash
   */
  public static async calculatePartialFileMD5(file: File): Promise<string> {
    const fullHash = await this.calculateFileMD5(file);
    return fullHash.substring(8, 24); // Match Android implementation
  }
}